POLDERS OFTH E WORLD

FINAL REPORT

INTERNATIONAL SYMPOSIUM THE 1983 THE SYMPOSIUM ORGANIZATION - Department of Civil Engineering- Delf t"Universit yo fTechnolog y - IJsselmeerpoldersDevelopmen t Authority -Ministr y ofTranspor t and PublicWork s - Committee forHydrologica l ResearchTN O -Associatio n forWate rManagemen tan dLan d UsePlannin g

CO-SPONSORS OFTH E SYMPOSIUM INTERNATIONAL ORGANIZATIONS - ^ood andAgricultur e Organization of theUnite d Nations (FAO) -Unite d NationsEducationa l Scientific and Cultural Organization (UNESCO) - Commission Internationale duGéni eRura l (CIGR) - International Association forHydrauli c Research (IAHR) - InternationalAssociatio n ofHydrologica l Sciences (IAHS) - International Association ofHydrogeologist s (IAH) - International Commission on Irrigation andDrainag e (ICID) - International Society of Soil Science (ISSS) - International Water ResourcesAssociatio n (IWRA)

ORGANIZATIONS INTH ENETHERLAND S -Agricultura l University Wageningen - DelftHydraulic s Laboratory - International Institute forLan d Reclamation and Improvement (ILRI) - International Institute forHydrauli c andEnvironmenta l Engineering (IHE) - Joint CivilEngineerin g Organizations -Ministr y ofAgricultur e andFisheries : ForeignMarketin g andEconomi c CoooerationServic e Government Service forLan d andWate rUs e -Ministr y ofEconomi cAffairs : TheNetherland sForeig n TradeAgenc y -Ministr y ofEducatio n andScience : Directorate-General forScienc ePolic y -Ministr y ofTranspor t and PublicWork s Exposition CentreNe wLan d Information Division Rijkswaterstaat,Directorat e ofWate rManagemen tan d Hydraulic Research Rijkswaterstaat,Zuyde r ZeeProjec t Authority " Netherlands Engineering Consultants (NEDECO) - Research Institute forNatur eManagemen t (RIN) - Royal Institute ofEngineer s inTh eNetherland s (KIVI) - RoyalNetherland s Society forAgricultura l Science - Union ofWate r Boards

EXECUTIVE COMMITTEE 'POLDERSO FTH EWORLD ' Prof. Ir.W .A . Segeren,chairma n Ir.E .Schultz ,secretar y Mrs.W.J.M . vanGiersberge n Mrs. Ir.J ,M . Leemhuis-Stout Ir.J . Luijendijk Ir.W .Wolter s

SCIENTIFIC COMMITTEE 'POLDERSO FTH EWORLD '

Prof.Dr .Ir .J . C.va nDam ,chairma n Ir.H .J . Colenbrander,secretar y Ir.E .R .Dahmen ,secretar y Ir.W .Wolters ,scientifi c officer Ir.E .Allersm a Ir.K .P . Blumenthal Prof.Dr .A .K .Constands e Ir.J .va n Duivendijk Dr. Ir.J .W .va nHoor n Dr.J . deJon g Prof.Dr .N .A .d eRidde r Prof. Ir.W .A . Segeren Prof. Ir.A .Volke r Prof.Dr .A .J . Wiggers PREFACE

The International Symposium and Exhibition 'POLDERS0 ^TH EWORLD ' washel d inLelystad ,Th eNetherlands ,fro m 4t o 10October ,1982 . Theai mo f the Symposiumwa s toprovid e acomprehensiv evie wo fth e various aspects ofpolde r development and togiv escientists , engineers,decision-makers ,an dmanager s a forum fora discussio no f theseaspect s and their related problems.

The Symposiumwa s arranged under the themeso f land andwate r management,construction ,agriculture ,socio-econom y and physical planning,an d theenvironment . Thesewer e treated inplenar y sessionswher ekeynote swer epresente d and inworkshop swher epaper s werediscussed . Because of the overwhelming number ofpapers , general reporters summarized them,

Presented inthi sFINA LREPOR To nPolder s of theWorld ,ar eth e keynotes,th eGenera l Reports,an d theConclusions ,a swel l asa list ofauthor s and the titleso f theirpapers . Theactua l papers havebee npublishe d by ILRI,Wageningen ,i na seto f threevolumes .

Ihop e that thisboo kwil l provide itsreader swit h anoveral lvie w onpolders ,polde r development,an d onwha t could be concluded because of this first-ever Symposium on 'Polderso f theWorld' . Toge t thisboo k intoprin t asquickl y aspossible ,w ehav edecide d toforg o the time-consuming tasko fcorrectin g and editing the English language.W ehop e our readerswil l forgive theimperfections .

Delft,Jun e 16,198 3 W.A . Segeren Chairman 'holderso f theWorld ' CONTENTS

PREFACE V

THE SYMPOSIUMAN D EXHIBITION

W,A. Segeren 11

KEYNOTES 15

INTRODUCTION W. A. Segeren. Introduction toPolder so f theWorl d 15

LANDAN DWATE RMANAGEMEN T 26 E. Schultz. Fromnatura l toreclaime d land. Land andwate r management inth epolder so fTh eNetherland s. 26 K. Pranioh. Land andwate rmanagemen t inpolder s 52

CONSTRUCTIONASPECT S 64 P. C. Masure. Thedevelopmen t of theDutc hpolde r dikes 64 R. Segers. Fromwindmil l towind-generator . Development in construction 82 M. A. Meyer. Construction aspects ofpolder s inth eworl d 98

AGRICULTURAL ASPECTS 126 J. Van der Veen. Agriculturalaspect s inpolde r areas inTh e Netherlands. 126 - H. Brommer. Agriculture and food production inpolde r areas 141

SOCIO-ECONOMIC ANDPHYSICA L PLANNINGASPECT S 166 - A. K. Constandse. From spontaneous settlement to integrated planning and development 166 - J.H.M. Kierihuis. Themanagemen t ofpolder s inTh eNetherland s 176 - A. S-feir Younis. Economic aspects of soil conservation progress inLDC' s 187

ENVIRONMENTAL ASPECTS 221 - J. de Jong and A, J. Wiggers. and theirenvironmen t in TheNetherland s 221 - M. Vannuooi. Ecological values ofpotentia l polder areas 242

SPECIALKEYNOTE S 251 - A, Volker. Lessons from thehistor y of impoldering inth eworl d 251 - B. Verhoeven. Polders of the future 268

GENERAL REPORTSAN D CONCLUSIONS PERTHEM E 279 THEMEA :POLDE R PROJECTS 280 - D, S. Heslam. Various aspects ofpolder s ina certai n area 280 - E. Allersma. Various aspects ofpolder s ina certai nare a (continued) 293 - D. W.Ryaroft. General description ofpolde rproject s 304 - J. Mihnea. Workshop conclusions 314

THEMEB 1:LAN DAN DWATE RMANAGEMEN T 316 - M. J. Hall. Watermanagemen t systemsan d designcriteri a 316 - J.J.A. Feijen. Watermanagemen t systems and design criteria (continued) 326 - J. Wesseling. Water quality,geohydrolog y and soils 339 - E. Romijn. Water quality,geohydrolog y and soils (continued) 349 - D. Kirkham. Workshop conclusions 355

THEME B2:CONSTRUCTIO NASPECT S 358 - J. Van Duivendi.jk. Dikesan d embankments 358 T. G. Hammond. Miscellaneous construction aspects 370 H. S. Adhin. Workshop conclusions 377

THEME B3: AGRICULTURAL ASPECTS 378 J. W.van Hoorn. Agricultural aspects 378 R.J.A. Dudal. Workshop conclusions 383

THEME B4:SOCIO-ECONOMI CAN DPHYSICA L PLANNING ASPECTS 385 H. J. Groenewegen. Physical planning 385 D.B.W.M. van Düsseldorf and P.11.G. van Steekelenburg. Socio­ economic aspects. 398 A. K. Constandse. Workshop conclusions 410

THEME B5:ENVIRONMENTA L ASPECTS 411 A. van der Beken. Environmental aspects 411 M. Vannuoai, Workshop conclusions 421

CONCLUSIONS 423 J. C, van . Final conclusions 423

LISTO FAUTHOR SAN DPAPER S 431

PUBLICATIONS 441 Listo fpublication s withinth eframewor ko fth eSymposium , including information where toobtai n them 441 THE SYMPOSIUM AND EXHIBITION

'Polderso f theWorld 'wa shel d fromMonda y October 4throug h Sunday October 10,198 2i nLelystad ,th ecapita l cityo f theIJsselmeerpolders . TheSymposiu mwa shos t to42 6participant s from 52countrie s allove r theworld ,developin g countries aswel l asdevelope d countries. The first threeday swer emainl y devoted to thescientifi c parto f Polderso f theWorld . Inth eplenar ymornin g sessions twelvekeynote s were delivered.Th efirs tmornin gwa suse d foropenin g addresses and introduction speeches,statin g generalview s onpolde r development now and inth efuture .Th eothe rmornin g tenkeynote swer epresented ,deal ­ ing thefiv e themeschose n to treat thesubject : - Land andwate rmanagement ; - Constructionaspects ; - Socio-economic andphysica lplannin gaspects ; - Environmentalaspects . The Symposiumwa shonoure d by thesponsorshi p of agrea tman y interna­ tionalorganizations ,a se.g . theWorldbank ,FAO ,Unesco .Thes eorgani ­ zationswer erepresente d bydirector s and other staff,presentin g key­ notes on thejus tmentione d themes.Als omany ,mor edisciplin e orien­ tated,internationa l organizations granted their support assponsor . Inth eafternoo no f thefirs t threeday sworkshop swer ededicate d toth e exchangeo fview so nproblems ,idea san d solutions inpolder-development . Thebasi s for thisha dbee nprovide d by thepaper swritte nb yman yo f theparticipants . Theoverwhelmin g amounto fpaper s (some 140)di d notallo w everypape r tob epresente d infull .Genera lreport shav e summarized thepaper so f

11 their sessions and risenquestion s or topics for discussion.Th ework ­ shops,mostl ywit hmor e thanon ereporter ,wer e concluded by thechair ­ men,wh opresente d theirfinding s and conclusions onWednesda y after­ noon, thelas tplenar y session. Finally thechairma no f theScientifi c Committeepresente d theoveral l conclusionso f theSymposium . Twowel lknow n 'polder'professor s -A .Volke r and B.Verhoeve n- wer e honoured for theirman y contributions topolde r development inth e world,o n theirpresentin g keynoteswit ha 'lessons tob e learned' character. The first threeday so f theSymposiu mwer e followed by threeday so f fieldtrips to:th eIJsselmee r polders,th eolde rpolder s in themi dan d west ofTh eNetherland s and the 'DeltaWorks' ,th e large engineering works inprogres s at thismoment ,fo r theprotectio no f the south-west regiono fTh eNetherlands .Th eparticipant s visited anope nai rdemon ­ stration and exhibition of 'polderequipmen t andmachinery 'o n thefirs t fieldtrip. Parallel to thementione d activitiesa nExhibitio nwa shel d (October 4 through 10)i nwhich ,nex t toa n introductory partwit h informationo n polders allove r theworld ,governmen t services,researc h institutesan d companies could showthei rabilit y andknow-ho wwit h respect topolders . Thenumbe r ofvisitor so f thisExhibitio n exceeded expectations and requestshav ebee nmad e for showing thiscollectio n of informationo n polders invariou s othercountries .

Followu p

On theoccasio no f 'Polderso f theWorld 'man y data and largeamoun to f knowledgean d experiencehav ebee ncollected .Durin g theSymposiu m I promised theparticipant s toshap ean dpublis h thismaterial .Contact s havebee nestablishe d betweenFAO ,Worl d Food Programan d the Committee Polders of theWorld , todeliberat eupo na studyprogra m towardsen ­ larging theinsigh t inth erol eo fpolder s insolvin g theworldwid e problem ofa growin g fooddemand . During theSymposiu m Ialread y extendedm yview so na repetitio n ofa n eventalike ,a swa spropose d byman yparticipants .Worldbank ,FAO ,

12 Unesco andals omor edisciplin eorientate d organizations ase.g .CGI R and ICIDshoul d bemor e involved in the second Symposium of thisnature . Let theconclusio no f this Symposiumb ea nincentiv e tog oo nwit h this initiative to,i nth eend , thebenefi t ofal lcountrie swher e polders cancontribut e toprosperit y andwell-being .

W.A. Segeren Chairman 'Polders of theWorld '

13 KEYNOTES

INTRODUCTION

Prof.ir.W.A . Segeren Professor inPolde rDevelopment , Delft University ofTechnology , Department of Civil Engineering, Deputy-Director of the Government Service forLan d and WaterUse .

The lesson tob e learned is thatw e should design,buil d andmaintai n polders insuc ha wa y that it issaf e to live in.Fo r thisreaso n government,administrators ,lan d users,consultant s and contractors should allwor k together.Thes e groups areal l together here in Lelystad todiscuss ,fo r the first time inhistory ,polde r development. Whenw e speak of apolder ,wha t exactly dow emean ? As Idefin e it,a polde r isa level areawhic h was originally subject toa hig hwater-level ,eithe r permanently or seasonally and due to either or surfacewater .I tbecome s apolde rwhe n iti s separated from the surrounding hydrological regime sotha t itswater - level canb econtrolle d independently of the surroundingregime . This definition ofa polde r still leaves room forvariou s inter­ pretations. Itallow s for instance tocal l apaddy-fiel d apolder .O r we could refer toa floodplai n of alarg e river protected froma n upstreamda m as apolder .Bu t ingeneral ,neithe r of these areas is ever called apolder . For this Symposium, arathe rbroa d definition isdeliberatel y accepted toinclud e allperiodicall y waterlogged or flooded low-lyingplains , which need somekin d of impoldering toimprov e theirland-use .

Within theframewor k of theSymposium , agloba l inventory hasbee n madeo f thearea swhic h could bemad emor e productive,especiall y to agriculture,b ymean s of impolderingo r impoldering-techniques. From theFAO-Unesco-world-soil-map ,th e International SoilMuseu mha s estimated that for some 900millio nhectare s in theworld ,food -

15 production isseverel y hampered byhig h groundwater levels and regular flooding. If these areas could be impoldered,a considerabl e contribu­ tion could be achieved. Letm e recall somewell-know n data toclarif y thispoint . Theworl d population today isestimate d at4. 2 billion people.I ti s expected by theyea r 2000 tohav e increased to6. 6 billion. Thismean s thatwithi n aperio d of 20year s extra foodmus tb eproduce d for this extra 2.2 billion ofpeople .Thi s assessment assumes that the presentworl d foodproduction issufficien t tomee t theneed s ofth e presentworl d population,i f the imbalances of thefoo d distribution arecorrected . Studies into theworl d food supply in the coming decenniab y theFA Ohav e already beenmentione d byMr .Dudal .Othe r studies inthi s field have amongother sbee n undertakenb y theWorld - bank andWorl d Food Study Centre in theNetherlands .Mos t of theextr a food- about 72%o f the total- should comefro m thepresen t 1500 millionh a cropland of theworld .A n overallyiel d increase of some 40%, evenu p to 100%i n thedevelopin g countries,i n thecomin g 20year s aredeeme d tob enecessary .Th e implicationswit h respect toim - polderingwil lb e discussed ina moment .Th e remaining 28%o f theextr a foodneede d by theyea r 2000shoul d growo nnewl y reclaimed cropland according to these studies.Th eFA O estimates this latter areaa t 200millio nha .I tmus t alsob e recognized that every year about 13millio nh a of cropland are lostbecaus e of ,desertification , salinization andurbanization . Anestimate d 1700millio nh a of land in theworl d isavailabl e for reclamation.Th e choice is,a si sexplaine d by ourkeynot e speaker, Mr. Pranich: 'Doyo ug ou p toth ehil l ordow n to the sea?' This canb e translated as:ar ew e going to increase ourworl d cropland areab y reclaiming thedrier ,highe r lands orb y reclaiming thelow - lyingwetlands . Very general,on e can say that thereclamatio n of thewe t areas,th e potential polder-areas,i s tob epreferre d froma neconomi c and tech­ nicalviewpoint .However ,ecologically , the reclamation of thehighe r anddrie r soilsma y oftenb epreferable .I fw e assume thatbot h these alternatives will contribute inproportio n to their availability, then wehav e calculated thatb y 2000som e 80millio n hao fpolderlan d has tob e reclaimed.

16 1.Nee d for additional polder land by theyea r 2000. rise infoo d supply because loss ofproductiv e landdu e of increase ofworl d to land degradation and population non-agriculture land

rise inproductio n onexistin g reclamationo f reclamationo f agriculture land new land new land

on450.1 0 ha 40.10 polder 40.10°polde r polder area areaha s tob e areaha s tob e productionha s reclaimed by reclaimed by tob eraise d 2000 2000 by 2000

17 The distribution of these areas over theworl d isdepicte d in thetable . Hereb y again,th eavailabilit y indifferen t parts of theworl d istake n intoaccount .

Potential polders Reclaimed by 2000 6 106 ha % .o ha

SouthAmeric a 119,3 28,6 22: ,9

Africa 138,4 33,3 26; ,6 Asia 85,3 20,5 16., 4 NorthAmeric a 35,9 8,6 6:, 9 Europe 36,8 8,8 7,, 0

With regard to thepolderdevelopmen t in the future,w e candistinguis h threedifferen t types ofpotentia lpolders .

1.Th e first type ispolde r development inalread y densely populated areas,mostl y small farmers,workin g under bad conditions ofwater - management,soil s and infrastructure. 2.Th e second type concerns thedevelopmen t of the sparsely populated level and wet areas,situate d ina densel y populated region. 3.Th e third typeconcern s polder development insparsel y populated, levelwe t areas,i na sparsel y populated region. Each of these three types ofpolder s has itsow nproblem s and requires itsow napproach .

Type 1.

The densely populated potential polder areas aremainl y situated in Asia and inEurope .A good example of this type isBanglades h as described by Brammer inhi skeynote . Inm y view aris e infood-productio n by the local farmers can onlyb e achieved by integrated ruraldevelopment . Development isno tjus t amatte r of improving land-an dwatermanagement . Attention should alsob epai d toeducation ,extensio n services,credi t andmarketin g facilities,agro-processin g industries and soon .Onl y by acautiou s pace andwit h astron g participation of the local population this sorto f rural development will have achanc e tosucceed .

18 Letm e now comebac k to the calculations of theFA Owhic h indicated that agricultural production in the lessdevelope d countries by the year 2000ha s tob e increased by 100%. This isobviousl y aver y difficult task, ifno t impossible,considerin g that theactua l growth of the last 15year swa s hardly half of this. Improved land-an dwate rmanagemen twil l alwaysb e afirs t requirement. Thismean s that the 360millio nh a ofexistin gwe t landha s tob e improved substantially inth enex t twentyyears . The taskw e are confronted with leadsm e to the conclusion that Ica n not share theview s of somekeynot e speakers and some authorso f papers:The y claim thatwit h relatively simplemean s and onlyb y increasing production onexistin g landw e cancop ewit h thegrowin g demand forfoo d in the coming years.

Type2 .

Thepotentia l polders,concernin g thesparsel y populated areasi n densely populated regions.The y aremainl y found inSout hAsi a and some areas inNorth ,Centra l and SouthAmerica .Som e of thepaper s dealing withne w reclamations inIndonesi a are good examples of these typeo f polders.A mai n characteristic of these areas is their inaccessibility. Thereclamatio no f these areas isgenerall y undertaken toreliev eover ­ population inth esurroundin g region aswel l as for theproductio no f food,mainl y for the regionitself . Large scale engineeringwork s areofte nnecessary ,a swel l asextensiv e on-farmdevelopment s toprepar e thereclaime d land for theman y small farmers. Ingeneral ,thes e engineering and land-development projects require large investments and although these investments as such are generally quite feasible,findin g thenecessar y funds isofte ndifficult . Often achoic eha s tob emad eho w toallocat e the limited funds,where ­ by the following two criteria should havehig hpriority . Firstly the investment in largeengineerin g and land development pro­ jects has tob e such that later on,whe n additional funds areavailable , further development canbuil d onwha t has already been constructed without thenecessit y tod o things twice.Fo r this,on e needs tohav e a clear conception of the finalstage .

19 Secondly the and the on-farmdevelopmen t shouldb e adequate for the farmer togro whi s first cropwithou t toogrea trisks . Thiswil l often call for strong government assistance or involvement in the initial development stages,o f course the integrated approach for rural areas asmentione d under type 1als o applies to thiscase . This type of potential polders involves 158millio nha .

Type 3.

The potential polders in thesparsel y populated areas in sparselypopu ­ lated surroundings.The y aremainl y found inCentra l and SouthAmerica , parts ofAfric a andAustralia .Thes e areas should produce mainly for theworl d market.Th e cost of reclamation and productionha s tob e made good by theprice s of agricultural products on theworl dmarket . Ingenerall y this implies that recalamation-an d production-costs have tob e low.Th emai n aim is food productionwit hminimu m costs,this in contrast totyp e (1)an d (2),wher e social consideration often play an importantrole . These low costs arepossibl e-becaus e in these areas high degreeso f mechanization canb e applied both for thereclamatio n activitiesa s well as for the agricultural production itself. This type ofpotentia l polders involves 258millio nha .

Theprojection s Ihav ementione d weremad e on agloba lscale . For acountr y and certainly for project-planning muchmor e detailed datamus tb eavailable . Not only datao n soil or technical aspects;economi c factors areimpor ­ tant tooa s thebenefit-cost-ratio' swil l alwaysb e an importantde - cission.Onc e thedecissio n to impolderha sbee nmade ,socia l factors will influence thedesign ,constructio n andmanagement .Th e distinction into three types of polder development shows this clearly.

Political influence ob e decisive.Th e calculation and estimates ofworl d food problemwer emad e almost exclusively ona technicalbasis . However, it is clear that theproductio n of food and its distribution between theurba n and rural areas of acountr y aswel l asbetwee n the countries and even theworl d regions canb epowerfu l politicalweapon s

20 and canhav e farreaching political consequences. Themos t important decision factor frommos t of therecen t polder recla­ mations has emerged only recently. Thepotentia l polderareas arever y dynamic and productive ecosystems.The y are often intensely and closely related with each other so that reclamationwork s inon eare a canhav e consequences inothers ,eve n those faraway . None wpolde r project should be undertakenwithou t acarefu l assessment of these consequences.Als o in thedesig n and layout ofne wpolderpro - jects oneha s toconside r possible impacts on thenatura l environment. Inkeynote s andpapers ,attentio n isgive n tothes e aspects.Studie s in The Netherlands aboutMarkerwaard ,Waddense a andLanddevelopmentproject s have givenmuc hmor e insight into thisproblem .Althoug h theinterpre ­ tation of theresult s of ecological studies leadst owidel y conflicting opinions.

Whenw e review the three types of potential polders identified iti s clear that the first two types haveman y common characteristics. Besides thecontributio n to the food supply, thecontributio n toth e well-being andwell-far e of the local farmers isanothe r important aspect. In this respect,I full y agreewit h thepolic y of for instance theDutc hMiniste r ofDevelopmen t Aid,whic h emphasizes the economic and social development of therura l populations.Polde r projects of the type (1)an d (2)fi twel l into thispolicy .

Food,however ,als oha s tob eproduce d for areasno t capable ofpro ­ ducing for their increasing need as Iexplaine d before.Thi s isfo r instance thecas ewit hman y rapidly growing cities.Her e the third type ofpolde r development canmak e acontribution ,becomin g themoder n graneries of theworld . I amperfectl y aware of theman y political problems,involve d inthi s policy. But Ials ohop e that theseproblem s canb e reconciled inth e faceo f thestrongl y emergingworld-food-crisis .

As theDutc hMiniste r ofTranspor t and PublicWork sha s just said,i n TheNetherland s thevariou s Government Services,consultin g engineers and contractors have a loto f experiencewit h theoveral l development ofpolde r areas.Thi s experience andknowledg e isrelevan t toeac ho f

21 '-F'; 'HY ,• :; TVCQ « riATUURBEBSEfi r . .: . .^'-'-tRWFf i fi7 the threedifferen t types ofpotentia lpolde rareas . The development of the first two types isofte nb e initiated and imple­ mented by thegovernmen t of thecountrie s inwhic h the areasar e situated. Theprogramme s ofWorldban k andFA O aswel l asman y bilateral aid pro­ grammes attend to thedevelopmen t of these two types ofpotentia l polders. For thedevelopmen t of the third type,th e large scale graneries,a moredirec t approach canofte nb e followed,whereb y design,construc ­ tionan d finance areal l in thehan d of one organisation. Ica ncon ­ ceive of adevelopin g country,whic h isprepare d tohan d over theentir e reclamation and development of sucha polder-are a tosuc ha norganisa ­ tionprovided , that there is an assurance that- afte r say 15o r 20 years- thereclaime d land,includin g all infrastructure,wil lb e handed over to theGovernmen t or tofarmers . And also if there is theassuranc e ofa nefficientl y functioning extensionprogramme . I canals o conceive ofdevelope d countriesprepare d tomak e expertise and funds available todevelo p polders thatwil l pay aprofi t overa 15t o 20year speriod . In this respect aple a ismad e for theDutc h Government,consultants ,contractors ,farmer s organisations andbank s tocooperat e togiv e theworl d the food itneed s and topromot e the export ofDutc h polderknow-how .

Objectives

Thenee d for thefurthe r development of polder areas is themai n reason for this symposium and exhibition.Tha t it isbein g held inTh eNether ­ lands and specifically inLelysta d youwil l understand from the speeches by theMiniste r and theMayor .Tha t it isbein ghel d in 1982 isbecaus e of theman y celebrations wehav e in this country thisyear . Youwil lhav e read about these celebrations in theearlie r circulars thatw e sent toyou . The Symposium andExhibitio n arebein ghel d together topersu e three objectives:

1 The first isa n international exchange ofknowledg e and experience

22 onpolder sby ,an d for,policy-maker s and engineers,scientists , managers,contractor s andpolitician s alike. Part of this objective has already been fulfilled.Fro m allove r the worldw e received 150paper s and thesehav e since beenprinted . I think that all the information gathered justifiesm y feeling that thebasi s for agoo d symposium exists,especiall y whenon e considers that thepaper shav e come from soman y countries of theworld . In the light of thepreviou s considerations on theproble m of the worldfoodproduction Iwan t tomak e one general remark about thepaper s received. Iti s remarkable thatmos tpaper s on the theme environment question impoldering as such.The y all conclude that thenee d for food hast o be realized by increase ofproductio n onexistin g land. Contrary to this, somekeynot e speakers andman y authors ofpapers , taking atechnica l and economic point of view,d ono t conclude that impoldering isneeded .The y discuss details,ver y importantaspects , but still details.I think that this lastgrou pha s torealiz e thata serious debate isgoin g onabou t thenecessit y of impoldering in general. My opinion shouldb e clear;w emus t increase production onexistin g cropland asmuc h aspossible ,bu t thiswil l notb e enough.Fo r this, new impolderingwil lb enecessary .Thi sha s tob edon ewit hcare . To arrive atgoo d solutions,environmentalists ,technician s and economistshav et ocom e toseriou s discussions once again tosolv e the realproble m of foodproduction.

2.A second objective is tooffe r participants of the Symposium the opportunity tobecom e acquainted with theexperienc e that theDutc h Government andDutc h industry have acquired inth eman y aspectso f impoldering.Thi s statement needs further clarification. Impoldering isno tmerel y amatte r of solving technical,socio ­ economic and ecological problems.Apar t from thesemore-or-les s technicalmatters ,i t iso f theutmos t importance that anorganise d administrative infrastructure iscreate d not only for theplannin g and implementation of thepolde r but also for itsmanagemen t after thework s havebee n completed. Insevera l centuries ofexperienc e inpolde r development specific

23 know-howha sbee nbuil tup ,bot hwithi n Government institutes and services andwithi n theprivat e sector (consultants and contractors), and ital l rests on thebas e of awell-organise d administration. Togiv e an insight into the integralDutc h approach topolde r develop­ ment,a nexhibitio n hasbee n setup . Represented at theexhibitio n are some fifty Government institutes, services and private firms,whic hwil l allb e pleased topas s on their accumulated know-how.

Serving as aframewor k for theExhibitio n there isa separat e exposition showing how thevariou s aspects of planning and constructing apolde r areapplie d indifferen t countries.Eac h takes into account thepeopl e of that country, theirprosperity-level ,th e soils that occur,th e prevailing ,an d soon . This exposition isarrange d in linewit h the themes of the Symposium. Itha s beenbuil t insuc h awa y that itca nb e shipped abroad to serve,partiall y orwholly ,a sa nexpositio n inan y country thatma y requestit . So, after the close of theSymposiu m andExhibition ,w e are still offering other countries the chance toge t acquainted withDutc hknow ­ ledge andexperience .

3.A third objective isa mor ephilosophica lone . Its aim is toprovid e understanding of theworkin g and living conditions of people invariou scountries . Iti sm y personal experience thatb y seeingho wpeopl e indifferen t countries livean dwor k -eac hwit h their own culturalback-groun d and eachwit h theirow norganizationa l infrastructure- I fin d thatw e have adeepe r understanding,no t onlyo f theirwa y of life,bu t alsoo f ourow nDutc hwa y of life.B y showing theDutc h people how thepeopl e of other countries live andwor k and how they solve their sometimes localproblems ,w ehop e tocontribut e toa greate r understanding betweenpeople . That iswh yman y activities,o f interest to theDutc h public,hav e beenorganise d around theSymposium .An d this isals owh y theMinistr y ofTranspor t and PublicWork sha s issued abrochur e entitled "Polderso fth eWorld" .

24 In thisbrochur e theyhav e reproduced many of theSymposiu m datat o make that information available toa wide rpublic . Many Dutch andForeig n technical journals,newspaper s and othermedi a are focusing attention on the Symposium. Spontaneously,exhibition so f paintings and ceramics,thei r subjects inspired by polders,wil lb e held.

Ladies andGentlemen ,I wis hyou ,participants ,a n interesting and fruitful Symposium andyou ,participant s in theExhibition ,a successfulweek .

25 LANDAN DWATE RMANAGEMEN T

FROM NATURAL TORECLAIME DLAN D Land- andwate rmanagemen t inth e polders of theNetherlands . E. Schultz IJsselmeerpolders Development Authority, Scientific Division Lelystad,Th eNetherlands .

Abstract

This article dealswit h land andwate rmanagemen t in thepolder so f theNetherlands .I tstart swit h abrie f overview,o f thehistor y of impoldering. Informationconcernin g meteorological,hydrologica l and geohydrological data isgiven .Th e structure of thewate rmanagemen t system isdescribed . Someattentio n ispai d to soilmanagement ,wa ­ terqualit y aspects and themai n structureo f thewate rmanagemen t in theNetherlands .Finall y some ideas aregive n for thefutur eo flan d andwate rmanagemen t inth epolder s of theNetherlands .

Introduction

TheNetherland s isa lo w lying,densel y populated countryborderin g theNort h Sea.Th emajo r parto f thecountr y consists of lagoonan d delta typeareas .Th eDutc hhav emad e thisare a inhabitableb yrecla ­ mation and protection against thewater .Bu t for this creationo f their country theDutc hha d tofigh t during centuries against the water,comin g from theNort h Sea,fro m therivers ,fro mrainfall ,o r water fromlake s andblow nove r theadjacen t landsdurin ggales .

This articlewil l dealwit h thedifferen t aspectso f land and andwa ­ termanagemen t in thepolder s of theNetherlands .Firs t somedat a about theNetherlands ,togethe rwit h somegenera l informationabou t the polderswil l begiven .

26 Startingwit h thepas t and abrie f description of thevariou swork s andproject sb ywhic h theNetherland s was developed, some of theas ­ pects thatgover n thepossibilitie s tomak epolders ,suc h as themete ­ orological,hydrological ,geologica l and geohydrological conditions, willb ediscussed . Based upon these conditions adrainag e systeman d agoo d soilmanagemen thav e tob eestablishe d ina polder .Aspect s of system, lay-out,desig nnorm s andmean swil lb ediscussed . Some attentionwil lb e paid towate rqualit y aspects and toth emai n structure of thewate rmanagemen t inth eNetherlands .

Onbasi s of theexperienc e gained during centuries of impoldering and recentdevelopment s in techniques andwa y of thinking,som e ideaswil l be given for the future of land andwate rmanagemen t in theNetherlands .

1 TheNetherlands .

The land areao f theNetherland s is 3,400,000 ha.A s aresul t of land- reclamation and subsidence about one third is situated belowmea nse a level (figure 1).Th eNetherland s is aver y densely populated country, 2 varying from 190inhabitant s perk m in thenorther npar t to91 5inha - bitantspe rk m in the low lyingwester npart .Th e cities andindus ­ trialarea s-8 %o f the area-ar emainl y located in thewester npart . The agricultural lands- 71%o f theare a- aresprea d allove rth e country.Th e forests andnatur e reserves -9 %o f theare a- ar eloca ­ tedpredominantl y on therelativel ywe t soils in thewester n and northernpar t and on thesand y soils in thedune s and in theeaster n part. (CBS,1981) .

3 Polders,genera laspects .

Originally themajo rpar t of theNetherland s -som e 2,000,000 ha.- , consists of lagoon and delta type areas originating from thedelta' s

27 Figure 1.Th e ground level in theNetherlands .

28 of the rivers ,Meus e and Scheldt.Owin g to the transgressions and regressions of these aan d thedifferen t climatologicalconditions , the land areareduce d orextende d atregula r intervals.Regula rfloo ­ ding of theare aoccurre d owing tohig hwate r levels of theNort h Sea during gales and orowin g tohig h river .Th epeople ,mainl y fishermen andhunters ,live d on therive rbank s unprotected against extremesituations .

As fara s isknown,th emakin go fprotectio nwork sagains tth ewate rstarte d approximately inth e third centurybefor eChris twhe npeopl e inth e northernpar to f theNetherland s built artificialmound s toliv eon . In the first century therewas ,unde r theinfluenc e of the technical power of theRomans ,abeginnin g of the construction of smalldam s along therivers .Late r also damswer e constructed toconnec t thesevera l mounds.Thes e could resist theregula r floods and protected the landsmor e or less against thewater ,bu t theywer eprobabl y too lowt o safeguard the land under extreme conditions.Late r on the system ofdam s gradually improved anddischarg e structures (sluices)wer emad e inth e dams.Larg e activities indik e construction during the seventh and eighth centurymak ei treasonabl et osuppos etha ti nth eeieht h centurv the firstpolder swer emade .Durin g the following centuries theprotec ­ tion against these aan d theriver s improved regularly.

Gradually four aspects inrelatio n toth e land- andwate rmanagemen t became of importance,namely : - bydammin g off thevariou s connectionswit h thesea ,system so f canals and reservoirs for superfluous polderwate r -o rbriefl y systems -graduall y developed These systemshav ea relativelyhig hwate r level (+0.4 0 m.belo wmea n sea level).Th e polders andhighe r lands drain theirwate rint o thesesystems , throughwhic h thewate ri s then,transported toth ese aan d dis­ charged during lowtid e (figure2) ; - owing tosubsidenc e of thereclaime d soils,larg e areasbecam e gradually belowmea n sealevel ; - therewer e alo to f .Th e top soil inth e adjacent areasmain ­ ly consists ofpeat .Durin g gales thewate r of the lakes destroyed thebank s asa resul to fwhic h the lakesextended .

29 There are largepea t areas.Th epea tha sbee nuse d for fuel during centuries.B y digging thepeat , swer e created.

Veluwe

40

dunes 30

20 10 pumping y IJssel old polders station new polder Schermer f MSL i Markermeer

-10 / S * 20 / •3o y

40I

Figure 2.Schem eo f therelativ e levels inth epolders ,th esyste mo f canals and reservoirs forsuperfluou s polderwater and these a

The improvement of thewindmill sb y the inventiono f therevolvin g cap made itpossibl e that fromth emiddl e of thesixteent h century lakes were drained.Thi swa s particularly sowhe n in thebeginnin g of the seventeenth century itwa s discovered that toplac e severalwindmill s in aserie s (figure 3)larg e land reclamationwork s couldb e executed.

lower mill upper mill

dike cana' f°r superfluous I poiderwateK«'!' r

poldercanal middle basin

figure 3.Ro w of threewindmill s topum p outpolde rwater .

30 In thebeginnin g of thenineteent h centurymos tpolder swer emade .Be ­ sides thewinnin g ofland s along the coast,ther ewer e twoarea s left forwhic h plans lived toreclai m them.Th e first areawa s theHaarlemmer ­ meer,a lak e in theneighbourhoo d ofAmsterdam .Thi s lakeha d grown from 9,000ha .i n 1250 to 17,000ha .i n 1800 (Ramaer, 1892).Durin g two centuriesplan sha dbee nmad e toreclai m theHaarlemmermeer .Non eo f the planswer e realized untili nNovembe r of 1836a gal eble w thewate ru p toAmsterda m and another gale inDecembe r blew thewate rint oth e streets ofLeiden .Altogethe r 11,000h awer e flooded.I twa s then that the central government decided that the lakeha d tob e reclaimed.

Thesecon d areawa s theZuiderze e and as soona s thereclamatio n ofth e Haarlemmermeerha dbee n executed,seriou splan s started toreclai m land inth eZuiderzee .A disasterwa snecessar y togiv e the finalpus h to startth eworks .O nJanuar y 13, 1916,a gal e caused floodingsi n thearea s around theZuiderzee .O n June 14,1918 ,th eac t toconstruc t theenclosur e dam and reclaimpart s of theZuiderze e passedParlia ­ ment.Ther ewer e three reasonsmentione d for thedecision : - greater protection against flooding; - improvedwate rmanagement ; -th ewinnin g ofagricultura l land.

Uptil lnow ,sixt yyear s later, 165,000ha .forme r seabotto mhav ebee n reclaimed (figure A).Durin g theexecutio n of thework sne w ideas about the land use in thepolder s havebee ndeveloped . Soi n therecen t pol­ lers,apar t from theus e foragricultura l purposes,lan d isals ouse d for townbuilding ,recreationa l areas andnatur ereserves .

Notprimaril y toreclai mne w land,bu t ofgrea t importance for thepro ­ tection against thesea,ar e themai ndelt awork s in thesout hwester n parto f theNetherlands .I nFebruar y 1953,i nthi s region 195.000ha . were flooded and almost 2000peopl edrowned .I n 1958th eDelt aAc twa s accepted,givin gwa y toth ebuildin g of largedam s and otherhydrauli c contructions and theraisin g ofexistin g dikes along theNort h Seaan d themai nrivers .

31 Figure 4. The IJsselmeerpolders.

32 While thebi gproject s tookmuc h attention alo to fwork s in thepolder s were alsobein g carried out.Owin g tosubsidenc e and toimprove dnorm s regarding thewate rmanagement ,improvemen twork shav ebee n regularly executed. Since 1954when ,th eLan d ConsolidationAc twa s accepted, several land consolidation schemeshav ebee n executed. These schemeshav e the goal toredistribut e the land among thefarmers . Within the framework of these schemes,th ewate rmanagemen tha susuall y been improved (Vande nHende , 1978).

The land in thepolder swa s normally used foragriculture .O n thehighe r parts thecitie s andvillage s havebee nconstructed .Th e growth of the population,especially after thesecon dworl dwar,mad e itnecessar y to findne w locations forurba n areas.Becaus e all thehighe r locations were already occupied,i tbecam enecessar y tohous e thepeopl e inth e polders.Altogethe r about 7t o8 millio npeopl e areno w livingi n polders in theNetherlands .

Thehistor y of landreclamationi n theNetherland s has resulted inth e differentpolde rareas : - Low lying lands 1,335,000ha . - Drained lakes 315,000ha . - Landwo n from the 350,000ha . sea. Total 2,000,000ha .

Infigur e 5 thearea s in theNetherland s thatnee d protection are indi­ cated.

Butprotectin g low lying land against thewate r onlymake s sensewhe n such anundertakin g iseconomicall y justified.Thi smean s thatth e outputha s tosurmoun t the input.Th e costs of thewate rmanagemen t system,likeinvestment s for constructions andexpense s formaintenance , are influenced by themeteorologica l situation -especiall y rainfall andevaporatio n- thegeologica l and geohydrological conditions and the degree ofwatercontro l that isrequired .Th e aspect that areo f importancewil lb e discussed.

33 IJssalmeerpolders Development Authority TT~ 0&*

area subject to flooding in the absence of sea dikes and dunes

area subject to flooding in the absence of river dikes frontier drained lakes sea dike

land gained on the sea

Figure 5.Area s in theNetherland s protected against flooding.

34 4 Meteorological aspects

TheNetherland s has atemperat emaritim e climatewit h arathe r even distribution ofrainfal l over theyear .Th emea n annual rainfalli s about 760mm .Th e rate ofevaporatio n fromope nwate r varies from 0mm/da y inwinte r to4 - 5 mm/da y insummer .Th emea n annualevapora ­ tion isabou t 700m m (figure6) .

HO

120

\ \ -^\ s 1 / s \ \ > 80 rainfall

60 K f \ i \ \ / \ N i \ 40 . evaporation / \ / \ / f N 20 / y N -.y

A S O N D month Figure 6.Mea nmonthl y rainfall andevaporatio n from surfacewater . Rainfalldata :Hoofddor p 1867-1980. Evaporationdata :D eBil t 1911-1980. (RoyalMeteorologica l Service, 1867-1980)

Owing to therelativel yeve n distribution ofprecipitatio n over the year,th eintens epotentia lévapotranspiratio ndurin g summer and the lowpotentia lévapotranspiratio n inwinter ,ther e isunde r average con­ ditions arainfal ldefici t inth esumme rmonth s amounting to 120m m and a surplus ofrainfal l inth ewinte r amounting toa naverag e of 300mm . Inrelatio n toth edesig no f thewatermanagemen t system the short term rainfall intensity isimportan t (figure7) .

35 . rainfall in mrr 160

150

,"- y s / 130 * •

• 120 A * T= 100 • y • • • /-' 4 100 • y / / / /" / / y / / / T=10 / y f y .---'

/ • ,'" T= 2 • .- / y * ,-" y /

T = return p eriod in y ears 20 winter p eriod summer period

10 days

Eigure 7.Rainfal l intensity-frequencycurves . Hoofddorp,perio d 1867-1980.

36 Whilewindmill shav eplaye d aver y important role in thepumpin g dryo f polders, thedistributio n of thewin d velocitieshas ,o f course,bee n ofimportanc e too.

5- Hydrological aspects

The discharge ofwate r from apolde rha s tob erealize d ina mor e or less artificialway .Fo r designing discharge structures like discharge sluices orpumpin g stations iti snecessar y tohav ebot h information about therainfal l surplus and about thepossibilitie s todischarg e thewater .Wate r canb e discharge to: - anotherpolder ; - acana l system; - ariver ; - thesea .

When apolde rdischarge s iato anotherpolde r iti snecessar y tochec k the combination ofbot hmanagemen t systems.Th e samehold s truewhe n a polder discharges into acana l system.Th e typical aspects ofth e river regime,i n combinationwit h thedesig nperiod s for thewate r management system in thepolder ,ar e importantwhe n apolde r discharges into ariver .Th emai n rivers in theNetherland s normally haverelati ­ velyhig hwate r inspring .Suc h ars e in levels cancontinu e for several dayso rweeks .

When apolde r ora cana l systemdischarge s into these aon e canmak e useo f theadvantag e of thetide .Durin g lowtide ,sluice s canb e opened.Durin ghig h theyhav e tob e closed.Especiall y during spring and autumn,northwesterl y winds can cause relatively highwate r sea levels during some days.

"• Geohydrologicalaspect s

Importantpart s of theNetherlands ,a sa resul to f land reclamation and subsidence,ar enowaday s locatedbelo wmea n sea level (figure1) .

37 The geological profile in the lowpar to f theNetherland s canb ebriefl y summarized as aholocen e toplayer consisting of clay and/orpea t anda thick pleistocene layermainl y consisting of sand.Th e thickness of the Holocene toplayer canb eu p to2 0m .

Due to the locationbelo wmea n sea level there isseepag e in thedeepe r polders.Normall y this seepage amounts toles s than 1mm/da y but there areexception so fu p to2 0mm/day .

In thewester npar t of theNetherlands ,a sa resul t of transgressions and regressions,thegroundwate r isbrackisc h orsalin e so theseepag ewate r isofte nbrackish .Fo r this reason thewate r in thecana lsystem sha s to be flushed regularly.Fo r thispurpos e substantial quantities ofwate r areuse d from therive r Rhine and theIJsselmeer .Fo rexample ,i nth e westernpar to f theNetherlands,th eamoun t ofwate r used during asumme r 6 3 period,partl y forsuppl y andpartl y fofor flushing,i s about 650x 10 m whichmean s 290m msprea d over thearea .

7 Watermanagemen t system

Originally only farmers lived in thepolders .Mos t citieswer e located on thehighe r ground orwher e artificial landfillha dbee n applied.Th e water control system in thepolde rwa s therefore designed and constructed according tonorm s applicable for agricultural areas.Thi swa spredomi ­ nantly the situationunti l the secondworl dwar .

After thesecon dworl dwa r intensive urban schemeswer e executed in existingpolder s tohous e thepeopl e in theneighbourhoo d of thecities . Mostlyb y landfill theare awa s "depoldered" and drained directlyint o oneo f the canalsystems .Gradually ,fo rne wprojects ,th e landswer e only raised tosom e levelabov e thewate r level in thepolder .I n these cases both thewate r of therura l and theurba narea sha d tob epumpe dout . So thedesig nnorm s for thewate rmanagemen t systemha d tob e adapted.

33 Thewate rmanagemen t system inside aDutc hpolde r consists inprincipl e ofsom e oral lo f thenex t items (figure8) . - sluice(s),windmill(s )o rpumpin g station(s); - canal(s); - main ditch(es); -ditches ; - openo r closed fielddrains .

Polders have tob eprotecte d by dikes against thewate rfro m outside.

Figure 8.Schemati c layout of apolder .

Sluices,windmill s and pumping stations

Depending on therelatio n of thesurfac e level and the level ofth e receivingwate rbody ,sluice s orpumpin g stationshav e tob e installed. Inth e olderpolder s thedischarg e ofwate rwa smainl y achieved bymean s ofsluices .Th e firstwindmil l for thedischarg e ofwate rwa s construc­ ted about 1400.Howeve rwindmill s onlybecam e common practice after the invention of therevolvin g cap and introduction of theide a ofplacin g severalwindmill s in aro w (figure 3).I n 1770th e first applicationo f the steamengin ewa s tested.Th eyear s thereafter steam engineswer e in-

39 stalled in some polders, but always in combination with windmills. It took about eighty years before a pump driven by a steam engine was trus­ ted in such a way that it was used as the only device to pump out the water. But one of the first applications was a tremendous one, since it was used to pump dry the polder Haarlennnermeer of 18,000 ha (Huet, 1885).

In the beginning of the twentieth century electrical and diesel power were introduced. These sources of energy are, generally speaking, the only ones now being used in the pumping of water from polders. Figure

9 shows the location of pumping stations used for drain~ge in the Netherlands (Rijkswaterstaat).

For a long period of time the paddle-wheel was the only divece used. It could raise the water up about 2 m. In the middle of the seventeenth century the open Archimedes screw was introduced. With this device the water could be raised up about 4 m. In recent times the screw pump, the scrP.w centrifugal pUI!lp and the centrifugal pump have been used. They can realize all nonnally occurring heights.

Drainage system \

The layout of the system of open or closed field drains, ditches, main ditches and canals in polders, is mainly based upon topography, soil conditions and on agricultural economy. Over the centuries the sizes of the plots have been enlarged. In figure 10 some representative system of parcelling out are given.

The water levels in the canals are determined by the depth of drainage required by the different uses of land. In the older polders the parcel­ ling out is often based on the natural pattern of streams and creeks. In the polders, the drained lakes and other- newer polders.. the ditches run along the long sides of a plot, the main ditches along the short side of a plot.

40 / (). :: .. _. ~ .. ., .. ; .. · .~ r

North-Sea ··1;·.· ..;;".1-~--. __ ·:· ,:.:-.

. ..

Germany

r_:<--

Belgium

0 50 100km

Figure 9. Pumping stations for drainage purposes in the Netherlands. (Rijkswaterstaat).

41 OLD CLAY POLDER PEAT POLDER

RIVER POLDER BEEMSTER

HAARLEMMERMEER FLEVOLAND

Figure 10.System s ofparcellin gout .

42 Originally, thedesig no f thedrainag e systemha dbee nbase d on trial anderror ,bu t from the thirties empirical steady state formulas could be applied. In these formulas acertai n rise in thewate r leveli s combinedwit h anaccepte d frequency and adesig ndischarge .Wit h these formulas anadequat e design of thewate rmanagemen t system ispossible . Nowadays,wit h theai d of the computers,a mor e scientific approachi s possible.Thi s approach not only leads toa nadequat e designbu tals o gives thedesigne r agoo d insight into relevantalternatives .

Theplo t sizes inne wpolder s arebase d mainly upon agricultural economy.Figur e 11show s anexampl e of the derivation of optimalplo t sizes.

:osts per ha in 10 guilders parce size in ha

28

26

24

22

^U

18 N^> ^ ^<: —

16

14

12

10 500 600 700 800 900 1000 1100 1200 1300 1400 1500 parcel length in m Figure 11.Analysi s tocalculat e optimalplo tsizes .

43 Field drains

Field drains are applied for twosuccessiv epurposes : - lowering of the groundwater-tabledurin g landreclamation; -maintainin g adequate drainage conditions afterreclamation .

For field drains there are twopossibilities : - trenches; - subsurfacedrains .

Trencheshav ebee nuse d over centuries.Subsurfac e drains date fromth e nineteenth century buthav ebee nespeciall y applied since thesecon d world-war.Nowadays ,the y areusuall ymad e of corrugated plasticpipe .

The distancebetwee n thedrain s and their depthhav e tob e choseni n such awa y that optimum growth of the crop canb e assured. Several drainage formulashav ebee ndevelope dt ob euse di nth evariou ssituations . When therecentl y reclaimed soilha s ahig h pore space,subsidenc ewil l occur,particularl y in the top-layer.Th e drainshav e tob e installed at such adept h thatafte r subsidence the soil is stillwell-drained .

8 Soilmanagemen t

Originallymos t soils in the lowpar t of theNetherland s contained brackisch groundwater.Th e soilwa s rather saline,especiall y in lands won from these aan d in anumbe r of thedraine d lakes.Whe n anadequat e drainage system is installed,unde r theprevailin g climatological con­ ditions in theNetherlands ,th edesalinizatio n of the topsoil is realized within someyears .Tw oprocesse s contribute to this,namely : - thepermeabilit y of theunripene d deeper soils isnormall y very low.Th epermeabilit y of theripene d top layeri srathe rhigh .Durin g winter there is arainfal l surplus sosalt s arewashe dout ; - themajo rpar to f theseepag e flows directly to theditche s and the canals,s oth eroo t zonei sno t affected by thisbrackis hwater .

44 Steps during the reclamation

Especially inth edraine d lakeswhe n thesoil s feltdry ,the yar e unaerated and almost impermeable.I nth eol d reclamations this caused a loto fproblem s toth e first farmers that tried togro w their crops on thesesoils .

In thene wIJsselmeerpolders,specia lmeasure s are taken tole tth e soils "ripen".Thes emeasure s consists ofdrainag emeasure s together witha nadapte d crop rotation scheme (figure 12).Wit htrenche s a first lowering of thegroundwate r tablei sestablishe d and crackfor ­ mation inth e clay soils starts.Thes e cracks result ina nincreas e in permeability.Whe n after severalyear s thegroundwate r table isdee p enough,th e trenches are replaced by subsurface drains.Th e subsurface drains realise afurthe r lowering of thegroundwate r table.Becaus e the bearing capacity of the soils during reclamation isver y low,only those crops -rap e seed and cereals- are grownwher e thenecessar y cropping measureshav e totak eplac e during periodswit h anevaporatio nsurplus .

Besides thesevera lmeasure s takendurin g landreclamation,soi limprove ­ mentmeasure s such asdee p ploughing and subsoilinghav ebee ntaken , dependingupo n localconditions .

45 reea

1 year SM J^M^^^W^^^^MS ^ R^^M 0.60

1- rape seed 2. winter wheat 3. barley

2-3 years sim /sMMsm isssssMssSi 3 (MMMPSSMM5 S /smsssp^™m /smp m 0.60

12.00

rape seed

1 year ^^5 pS^m^J pmW^i p^^^^ pamw^ iUESfcS p^m; / 1.20 '"• || u II II II

several kinds of crops

^p^S^MS^^ ^^^Sm^S^^^^ i / » i

Figure 12.Measure s takendurin g landreclamation inth e IJsselmeerpolders

46 9 Waterqualit y aspects

Over alon gperio d of timeon eo f themai n goals of thewate rmanagemen t systemwa s thepreventio n ofsalinization .Source s forsalinizatio nwer e createdby : - saltwate r intrusionb ysluices ; - saline orbrackis h seepage.

From themiddl e of thesixtie s oterwate rqualit y aspects gotmor e emphasis.Th e reason for thiswa s the changing useo f thewater ,fo r example for recreation andnatur e reserves and theincreas e inproduc ­ tiono fdomesti c and industrialwast e and coolingwate rproblems .S o thecontro l ofbot hwate r quantity andqualit y came to the forean d measuresha d tob e taken tocontro l thewate rqualit y such as: - purificationplants ; ~ separate sewersystems ; - flushing of lakes or canalswit hwate rwit h arelativel y good quality.

u Main structure of thewate rmanagemen t in theNetherland s

The situation of thewate r in theNetherlands ,wit h problems ofsalini ­ zation andpollutio n on theon ehan d and onincreasin g demand for drinking,irrigation ,coolin g andprocessin gwate r on theothe rmake s itnecessar y thatspecia l attention ispai d toth emai nwate r structure. Especially thedr y summer of 1976ha s encouraged theundertakin g of studies inrelatio n toth edistributio n ofwate r over theNetherlands . An intensive studyname d "PolicyAnalysi s of theWate rmanagemen t in theNetherlands "wa smad eb yRijkswaterstaa t and theRan d Corporation (Blumental, 1982).Durin g this study,cos tbenefi t analyses of several development alternativeswer e checked.Th e results of this study creates a solidbas e for the further development of themai nwate r structure inth eNetherlands .

47 11 Evaluation andpossibilitie s for thefutur e

TheNetherlands ,a si t isnow ,i s the result of ahistor y of landreclama- tionan d the loss of land.Fo r the future there arei nprincipl e only a fewplace s in theNetherland s wherepolder s canstil lb emade .Ther e are threeplace s forwhic hmor e or less seriousplan shav ebee n developed: -Markerwaar d 41.000h a - Slufterplan 600h a - planWaterma n 2.000h a

More futuristic possibilities canpossibl y be found inth eNort hSea . However itha s tob ementione d thatpossibilitie s are rather limited while the levelo f thebotto m of theNort h Seaha s such arapi d slope (figure 13).(Rijkswaterstaat) .

For themaintainin g of theexistin g land the riseo f these a levelo f about 0,10 mpe r century and thesubsidenc e of the landwil l gradually lead toa n increase insalin e seepage and thenecessit y toincreas e the level of the topo f thedikes .

Regarding thedesig n of thewate rmanagemen t system the following developments canb e excepted.

The drainage system ina polde r isno w almost atit s optimum.Ther ei s agoo d insight into thebehaviou r of the system and theextrem e situations that canb e expected.B y furthermechanizatio n andautomati ­ zation of the construction andmaintenanc e of thesystem ,i t canb e made and operated atminimu m costs.I na moder npolder ,o nyearl ybasis , the cost of installation andmaintenanc e of thewate rmanagemen t system is 1t o2 %o f theexistin g values of crops,building s and infrastructure ina polder .

Regarding the subsurface drains,som edevelopment s canperhap s beexpec ­ ted regarding themateria l tob euse d and in respect of the installation techniques.

48 Figure 13.Leve l of thebotto m of theNort hSea .

49 Therewil lb e afurthe rdevelopmen t towards afull y controlled water management.Tha tmean s that tohav e optimal conditions for the crops during thewhol eyea r ona larg e scale,no t only drainage,bu t also irrigation facilitieswil lb e installed.

Thepumpin g out ofwate r canprobabl yb emos t economically realized by the combination ofwin d power (back toth epast )an d another sourceo f energy.I n thiswa y theexploitatio n costs canb e lowerbu t investments higher.

Therewil lprobabl yb e developments tostor e thesurplu s of freshwate r in thewinte r tous e thiswate r during dryperiod s in thesummer .

And lastbu tno t least Iwil l finishwit h asayin gmad eb y aforme r president of theUnite d Statesmr .Lyndo n BJohnso nwh o said: " Anatio n that fails topla n intelligently for thedevelopmen t and protection of itspreciou swater swil lb e condemned towithe r because of its shortsightedness.Th ehar d lessons ofhistor y are clear,writte n on thedeserte d sands and ruins ofonc eprou d civilizations".

This statement taken in the context of thehistor y of theNetherland s in the field ofwate rmanagement ,bring sm e toth e following: " If theNetherland s fails tomaintai n theprotectio n of itspreciou s land against thewate r and tokee p astric tqualit y andquantit y control ofit sequall y preciouswater s itwil lb e condemned tone w disasters.Th ehar d lessons ofhistor y are clear,writte n onth e long listo ffloodings" .

12 Aknowledgement

The author likes toexpres shi s thanks todr .P.J . Ente,ir .R.J .d e Glopper,an dprof .dr .B .Verhoeve n for theirusefu l comments during thepreparatio n of thistext .

50 13 References

1.Blumental ,K.P . 1982.D ewaterhuishoudkundig e infrastructuur van Nederland.PT-Civiel eTechnie k septembernummer . 2.Centraa lBurea uvoo rd eStatistiek , 1981.Statistisc h zakboek 1981. Staatsuitgeverij, 'sGravenhage . 3.Hende ,W.R.J .va nder , 1978.Ruilverkavelingswe t 1954.Dee lI . Vijfdedruk .W.E.J .Tjeen kWillink ,Zwolle . A.Huet , 1885.Stoombemalin gva npolder s enboezems .D e gebroeders VanCleef ,De nHaag . 5.Roya lMeteorologica l Service, 1867-1980.Maandelijks e overzichten van deweersgesteldheid ,D eBilt . 6.Ramaer ,J.C. , 1892.D e omvangva nd eHaarlemmermee r end emere n waaruithe tontstaa n is,o pverschillend e tijdenvoo rd e droogmaking, JohannesMuller , . 7.Rijkswaterstaat .Directi eAlgemen eDienst ,De nHaag .

51 LANDAN DWATE RMANAGEMEN T INPOLDER S KanokPranic h 1/ World Bank,Washington ,D.C .

Abstract

By theen d of thiscentury , theWorld' s populationwil lexcee d six billions. Thepressur e on land forproducin g food, forurba ndevelopment ,housing ,factorie s and even forrecreatio nwil l bes o intense thana t any timei n thehistor y ofmankind . Insearc h forappropriat e land and relatedwater ,peopl ewil lb e compelled not only tomovin g up thehill sbu t also toencroac h into the swamps, plains and tidal landsb y impoldering and reclaiming them.T orea p the fullbenefi t of this latter undertaking,polder swil lhav e tob e carefully planned and executed. Also,lan d andwate rmanagemen t within thepolder swil lhav e tob ewel ldesigne d and implemented. Experience has shown thatplannin g of allaspect s of development inth e polder such asvillages ,park ,woode d area,industria lestate , irrigation^drainage,fres hwate r reservoir,far m unit,lan d parcelling, agriculture,etc ,i na n integrated manner,i s thebes twa y for achieving fullbenefits ,eve n if the implementationwil lb e carried out instages . Suchplannin g and implementation require close cooperation and coordinated effort of people of several disciplines working together.

52 Introduction

Thepresen t World population isaroun d 4.5 billion. By the turno f the century,i tha sbee n estimated that thepopulatio nwil l exceed six billion. Thepressur e on land forproducin g food,fo r urbandevelopment , housing,industr y and even for recreationwil lb e so intense thana t any time in thehistor y ofmankind . Thenee d fordevelopmen twil lb e very real and pressing. Peoplewil lb e compelled tosearc h formor e appropriate land and related water. Somewil l moveu p to the hills and somewil lencroac h into the swamps,floo d plainsan d tidal landsb y filling or impolderingan d reclaiming them.

Objectives ofWate rManagemen t

Theobjective s ofwate rmanagemen t is tosuppl ywate r tomee t thenee d ofdevelopment ,b e it for domestic,agriculture ,industr y or recreation, and todrai nof fexces swater . Inagriculture ,suppl y of theneede d quantity ofwate r forplan t growth at therigh t time isessential . Also,drainag e is important asi t allows oxidation of thesoi l (bydryin g up of soils)an d percolationo f water for oxygen supply and for leaching of toxic compounds into the subsoil,a swel l as tomaintai n theprope r depth of groundwater below thesurfac e forplan t roots development. Except for rice and some otherwetlan d crops,mos t other cropsnee d gooddrainage . Water management fordomesti c and industrial uses, i.e. tosuppl ywate r of certainqualitie s tomee t thedeman d for theseuses , isa subjec tb y itself and Ifee l iti sno t in thepurvie w of this Symposium,excep t to say that inplannin g thepolder ,th edeman dfo rthes euse swil l havet o be taken intoaccount . Water brought into thepolde rwil lhav e to provide foradequat e supply tosatisf y theneed so fal l activities planned inside thepolder . In thepast ,recreatb nwa s a fringebenefi t created after the construction of thepolder . Waterbodie s sucha s freshwate r reservoir, lake,rive r and canals inside thepolde rwer e also used for recreation — swimming,sailing ,fishing ,bir d sanctuary and the land along their banksa scampin g grounds orwoods . Inrecen tyears ,thi sha s grownt o

53 become theprimar y user and benefits from recreation even surpassed several other benefits. Inothe r cases,th e freshwate r reservoirma y beuse d forharbou r and assourc e of coolingwate r for thermalplant . The case inpoin t is in theNetherlands . Hence,i nplannin g thepolde r andwate rmanagemen t inside,al lo f theseuse shav e tob e considered. Insuc h cases,wate r level (elevation)an d quality aswel l asth e control of aquatic weeds aresom e of the important aspects. InTaiwan , somepolder s along thewes t coast sucha s theTseng-We nPolde rwa s constructed for fishpond san d oyster beds. Undoubtedly,wate rmanage ­ ment in thesepolder s had tob e geared toprovid ewate r level quality,degre e of salinity,etc. ,appropriat e for thepurposes .

Source ofWate r

TheWate r resources for thepolde rma y beeithe r oneo fthese : a) river orstrea mwhic h passes through thepolde r area orcana l carryingwate r to thepolder ; b) fresh groundwater; c) natural lakeo rpond ; d) man-madepon d or tank; e) dugwells ;o ra combinatio n of some of thesesources . Whena polde r isdesigne d toincorporat e arive r ora strea m running from theuppe r land through it,a sluic eo r aregulato r isbuil to n therive r at the lower end of theembankmen t tocontro l thedischarge , volume and levelo f thewate r aswel l as toconserv ewate rwithi n the river channel (freshwate r reservoir)insid e thepolder . However,i n this case thedischarg e and volume ofwate r entering thepolde r cannot be effectively controlled. Hencemor e often thanno t sluicesar e built atbot h theuppe r and lower end of theembankmen t tocontro l water entering and leaving thepolder . Examples of this latter casear e many: Chandpur project inBangladesh ,Chiangrak-Klongdar nprojec t in Thailand, Hachiro-gata project inJapan , and several tidallan d development projects inKore a and Taiwan. An exception to theabov e are severalproject s in themiddl epar t of

54 the Irrawaddy delta, where horse-shoe shaped embankmentswer ebuil t leaving thelowe r end ordownstrea m sideo f thepolde r openan d sluices werebuil t at theuppe r end. River floods canente r slowly through thisope ndownstrea m sidebu t thedept h of flooding and the flooded area aresmalle r thanwithou t theope nembankment . InThailan d (Chiangrak-KlongDar n Project), several canalswer edu g to conveywate r from thenearb y river into theembanke d area. These canals areuse d multi-purposely,a ssource s of irrigationwater ,fo rconserva ­ tion tostor ewate r during thewe t season forus edurin g thedr y season,an d asdrainag e channels aswell . Somepolder s are located in thedelt a oralon g these a coastwher e aquifersbearin g fresh groundwater exist. Insuc ha case ,tubewell s can be sunk toextrac t thegroundwate r forus ewithi n thepolder . However, assoil s in thedelt a and along these a coast aregenerall y alluvium, excessive pumpingwil l cause land subsidence. Examples of this canb e found in thedelta s of theTon eRive r and NagaraRive r inJapan ,an d many other places in theWorld . Also lowering ofwate r level inth e aquiferma y causese awate r intrusion into theaquifer ,i nparticula r for thepolder s along these a coast. In thecoasta l ()polder s of Bangladesh,an d severalpolder s inBurma ,farmer sals o use shallowdu gwell s (5-10m .dee p assourc e ofwate r fordomesti c supply and irrigation. Natural lakes,pond so f adequate quality ofwate r canan d areuse d as sources ofwate r in thepolder . Oftenman-mad epond so r tankshav ebee n built tocollec t and storewate r duringwe t season forus edurin g the dryseason . Thesourc eo fwate r for thepolde rma yb e either oneo f theabov e ora combination thereof.

Drainage

Inpolders ,drainag e comesbefor e irrigation and isconsidere d more important. After impoldering iscompleted , thepolde rwil lhav e tob e drained dry. The soils,generall y comprises largely of clay and silt with smallpercentag e of sand,hav e tob e ripened 2/, againb ymean so f drainage togetherwit h thecultivatio n of reclamation crops sucha s

55 rice,barley ,wheat ,ree d orgrass . Where climate issuitable ,ric ei s anexcellen t reclamation crop. Iti ssomewha t salt tolerant. Iti s grownunde r flooded conditionwhic hallow s flushing and leaching process tog oo n concurrently while land isunde r cultivation.

Drainage for Reclamation

After thecompletio n of embankments and sluices (and inman y cases pumping stations)an d the land iscompletel y enclosed, drainageb y pumping and sluicing should begin. After that the cons­ tructiono fmai n drainage canal should be started. Natural creekso r channelsma yb e used asmai ndrai n if theirelevatio n and locationar e suitable. Smaller creeksma yb euse d assecondar y drains. Shallowan d meandered creeks should bedeepene d to therequire d depth and straigth- ened asappropriat e and theexcavate d soilsuse d for filling up other small creeks and depressions. If themai ndrai n has tob enewl y excava­ ted, in the initial stage,whe n thesoil sar e still fully saturated and very soft,th edept hma y bekep t shallow and side'slo p flatter. It willb edeepene d to the final cross section after thesoil shav ebee n ripened. Secondary drainsma yb e excavated concurrently with land levelling and filling up ofunwante d creeks. Liketh emai n drain,i f thesoil sar e soft, they may bedu g smallerwit h flat side slopes firstan d made deeperwit h steeper side slopes. Thespacin g of thesedrain si s designed according to thedifferen t kinds of soilsan d isgenerall y ranged from about 400m (Thailand ChaoPhy aDelt a -heav y clay) toabou t 600m (JapanHachiro-gat a -sand y soils). For reclamation and ripening of soils,fiel d drains are generally needed. Thehighe r the clay content in thesoil swil l require the smaller spacing between the field drains. Ingeneral ,th espacin g rangesbetwee n 20m to10 0m . After a fewyear swhe n thesoil shav e been ripened fully, these field drainsma y beback-fille d togai n more land.

56 Drainage forAgricultur e

Forgoo d crops growth thegroundwate r should bekep t about 1.4 to2 m below the land surface. If thegroundwate r isbrackish ,th eminimu m levelo f 2mshoul d probably beused . Thismean s that thesecondar y and maindrain s should be adequately deep toaffec t suchgroundwate releva ­ tion. However,fo rric ewhic h isa wetlan d crop,suc h conditionma yno t be required solon g as there issom emovemen t ofwate r through theroo t zone. Hence,drainage canals inpolder s catering only forric e are generally shallower than those inwhic h dryland cropsar egrown . Ingeneral ,th e land elevation inth epolde rha s tob e sufficiently high (more than 1m abovemea n sea level)t o enabledrainag eb y gravity to beeffecte d through sluices,takin g advantage of ebb tidea fe whour s eachday . For lower elevationo fland ,pumpin g togetherwit h sluicing mayb enecessar y and if the land surface isbelo wmea n sealevel , drainage has tob eeffecte d entirely bypumping . Thismake s theprojec t more expensive inbot h the capitalan d operation costs. In thedesig n of thepolders ,location s ofpumpin g stations and sluices are important asals o theelevatio n of the sills of sluices. Sluice sillsshoul db e placed as lowa spracticabl e toimprov ehydrauli c capacity. When the land elevation is low,no tonl y drainage ismor e difficult but alsoth e construction of embankments,irrigatio n and land andwate r management becomemor e complicated andmor e costly. For this reason,severa l countries have established land elevation criteria for thedevelopmen to f their tidal lands. InIndi a (),the lowestpermissibl e levelo f land forreclamatio n ismid-wa y betweenhig h spring tidean d highnea p tide. InIndonesia , the land elevationha s tob ebetwee nmea n sea level andhig h tide.I nMalaysia ,th e elevationha s tob e about 1.2m above mean sea level.I nSr iLanka ,th eminimu melevatio n of the reclaimed coastal areas isabou t 0.3 m abovemea n sea level,wherea s inThailand , thiselevatio n isabou thig h neap tide. InJapa n (Hachiro-gata),th e minimum elevation of land inside thepolde r is4. 5 mbelo wmea nse a level. Elsewhere inJapan ,wher e land for industry and urban development was reclaimed by filling,lan da slo wa s-1 0t o-1 5m MS Lha dbee nreclaimed . There are certainkind so f soilswhic h call for specialkin d ofdrainag e andwate rmanagement . Forbot hCa tCla y (oraci d sulphate) and peatsoil s fordifferen t reasons,th egroundwate r level should not be lowered.

57 toomuch, -0.6 0to-0.9 0m should be sufficient. When soils are drained aeration occurs. Forpea t soils oxidization and land subsidencewil lb e excessive if thegroundwate r islowere d too farand,fo raci d sulphate soilsoxidizatio nwil laccelerat e the formation ofaci d (sulphuric acid)in thesoils . Incountrie swhic h aresubjecte d tomonsoo n and typhoonrainfall san d where rice isgrown ,th epadd y fieldswhic h generally have lowfiel d dikes allaroun d areuse d tostor e excess rainfall temporarily,i norde r toreduc e thecos t of thedrainag e system. Paddy can stand submergence ofu p to 7day swithou tmuc h effect. InJapan ,Hachiro-gat a polder in Akita prefecturewa s designed tostor e excessive rainwater on thepadd y fields temporarily,equivalen t to 77m m or about one-third of themaxi ­ mum threeday s rainfall of 220mm . This reduces therequire d capacity 3 3 ofpumpin g stations from 150m /secdow n to8 0m /sec. InBangladesh ,a drainage criteria of 25m mpe r dayha sbee n adopted forarea swit h an annual rainfall of about 1750m m and forothe r areas inproportio n to thisamount ,base d on theassumptio n that crops canb e submerged to a deptho f 150m mwit h little damage.I nThailand , thedrainag e systemwa s designed todrai n the threeday smaximu m rainfalls in 7u p to1 0days . For coastalo r tidal land polders,th e closure of therive rmout ho r estuary by sluices tocreat e alarg e freshwate r reservoirwil lhel p improve drainage andwate rmanagemen twithi n thepolder . If theseepag e through the seadik ei sexcessive ,a seepag e canal(drain ) mayb e constructed near the toeo f thedik e toarres t thebrackis h water or else theseepag ewil l spread further inside thepolde ran d damaging thegoo d land.Th e canalwate r can theneithe rb epumpe d outo r drained through sluices ora combination ofboth ,a s the casema yhe . In thepresen t day,mor e andmor e subsoildrainag e through tiledrain s orplasti c pipedrain s arebein g used. Although this typeo f drainage initially costsmor e than theope n or surface drain,i t ismor eeffect ­ ive incontrollin g thegroundwate r levelan d the losso f land isminima l compared toope ndrai n system. The operation andmaintenanc e costi s also lower. Inparticular , if thegroundwate r issaline ,th eadoptio n of subsoil drains should beencouraged . The average cost of subsoil drainage ranges fromabou tUS$75 0 toUS$150 0pe rhectare ,dependin g on thedept h and spacing of the drains aswel l as the typeo f soilsan d the levelo fgroundwate r during theinstallation .

58 Irrigation

Themai nprincipl e of irrigation is toprovid ewate r accordingt oplant s need. When river is thesourc e ofwate r for thepolder ,th emai n canal takingwate r from the river should be located farenoug hupstrea m beyond thereac h ofse a water intrusion.' When freshgroundwate r is thewate r source,pumpag e has tob e limited not toexcee d the rate into theaquifer , soa s topreven t land subsidence. Asmentione d earlier,natura lcreeks , ponds and tanksar eals ouse d assource s of irrigationwater .Also,fres h water reservoir canb e created asgoo d source ofwate rb y closing the downstream end of therive r or creek,o rb y closing therive rmout h orestuar y at theimpolderin g embankment. Irrigationma y beeffecte d by gravity througha syste m ofmai n and secondary canalsan d field channels,o rb y pumping fromwate r source into thegravit y system of distributory canals orb y pumping through sprinkler system (sprinkling irrigation). Theplannin g of irrigation and drainage should begin at the farm level andwor kupstrea m to themai n canal and headworks. Whether irrigation (and drainage)wil lb e effective and efficient depends agrea t deali n theplannin g and designo f the field irrigation channels and field drainsa t the farmlevel . When land isreclaime d from the sea,afte r thepolde rha sbee n drained and thesoil s ripened, irrigationwate rha s tob e supplied for leaching and flushing of salinity from thesoils . When soils contain alarg e percentage ofsand , leachingwil lb ever y effective and crops like rice canb egrow n after only afe wmonth s of leachings. InHsin-Ch u Tidal Land on thewes t coast ofTaiwa nwher e soils contain 70-90%o fsand , rice crop could be grownonl y after 2-3month s of leachingwit h fresh wateran d theyiel d in the first yearwa salmos t normal.However , if thesoil s contain largepercentag e of clay, itwil l take 1-2year s orma yb e longerbefor e the intended crops canb egrown . When irrigation isb y gravity through canals,th eamoun t ofwate r supplied asdetermine d by cropwate r requirement or evapo-transpiration, divided by irrigation efficiency toarriv e at irrigationwate r requirement, isgenerall y sufficient for leaching, tokee p thesoi l salinity under check. However, if irrigation isb y sprinkler,som e

59 additional amountma yb eneede d for leaching. Generally, if about 10t o1 5 ofcro pwate rrequiremen ti sallowe d fo rthi spurpos e, i twil lb esufficient . Most soil scientistswil l agree thati f the land comprises of potential cat clay oraci d sulphate soil, it isno twort h reclaiming. Iti s difficult and costly toimprov e the soila swel l as tomanag e the drainage and irrigation,an d yet theyiel d of cropsgrow nwil l neverb e high. However,ther ehav ebee n such land insom eo f thepolders . There are severalway s of tackling such soil: a) By theapplicatio n of lime toneutraliz e theacidity . However,a large quantity of limewil lhav e tob e applied,rangin g from 30u p to2-30 0ton spe rhectare . Also,additiona l quantitywil lb e required every fewyears . Thismake s themetho d costly and even prohibitive. b) Bypuddlin g the landwit h freshwate r and flushing and draining several timesbefor e rice isgrown . Thismetho d ispractice d in Japan and Thailand. c) Bykeepin g thegroun dwe t orsaturate d all the time,thu s reducing oxidation. In tropical countries this canb edon eb y growing two crops of ricepe ryea r orb y keeping thegroundwate r tablehig h (if thegroundwate r is fresh). d) Byploughin g and flushing the landwit h seawate r and subsequently leaching and flushing itwit h freshwater . Thismetho d isemploye d inVietna m and SierraLeone . Evenwit h theemploymen t of theabov emethods ,aci d tolerant crops should be grown on this soil. Some of these crops are rice andpine ­ apple in the tropics and reeds and grass in the temperate region. Planning of irrigation and drainage systems should start from the farm levelu p to theheadwork s or reservoir and not theothe rwa y around. Suchplannin gwil l ensure that therequiremen t at the farmswhic h are productive units,i nparticula rwit h respect to thewate r leveli n relation to theelevatio n of the land surface,wil lb emet .

60 There arevariou s typeso f layouto f farmparcel s comprising irrigation and drainage channels and farmroad s (and insom ecase swin d breakers). Theselayout sar egenerall y designed tosui t thetopography ,soils , hydrometeorology,hydrogeology ,agricultur e (crop grown)etc .o f the polder. However,th egovernin g principle of these layouts is thesam e thateac h farmuni tshoul d havedirec t access toth eirrigatio n supply, drainage and afar mroad .

Separate orCombine d Irrigation andDrainag e System

The system comprising separate irrigation and drainage channels atfar m levela sexplaine d above is thebes t foragriculture . Itgive sbette r andmor e efficientwate r controlan dwate rmanagemen t than thecombine d system. Irrigation ordrainag e ofan y oneparce lo runi t of land can be carried outa tan y time independently tosui t plants needwithou t affecting theothe r parcels. For agriculture aiming athig h intensity of cropso fhig hyields ,th eseparat e system ispreferred . However,thi s sytemcost smuc hmor e than thecombine d system and the operation andmaintenanc e costs of thesyste m isals ohigher . Hence, insevera ldevelopin g countries the combined system hasbee nemployed . InJapa n (Hachiro-gata Project),Kore a (DongJi nGang ,Yon g SanGan g andPyongtaek-Kumgan g Projects),an dTaiwa n (WestCoas tTida lLan d Development Projects),wher e agricultural development has reached high levelwit h high crop yields,separat e systems of irrigationan d drainagehav ebee nemployed . InBurm a (Paddyland Development Projects inth eIrrawadd y Delta), Bangladesh (Chandpur Project),Sr iLank a (Southwest CoastDrainag e andReclamatio n Project),wher e agriculture development isstil li n the intermediate stage,a combine d irrigation and drainage systemha sbee n adopted.I nthes epolders ,natura lstream san d creekshav ebee nredredge dan d closed by sluices toac ta sreservoir sfo r water conservation,irrigatio n canals aswel la sdrains . Inal lthes e projects,farmer s usesmal lpump s (generally 3-5 hp.)t olif t water from thenatura l streams for irrigating their lands. Moreover, theChandpu r Project inBanglades hha s alarg eprimar y pumping station

61 (34e um/sec )a t themai n sluice topum pwate r inan d outo f thepolde r foreffectiv e control ofwate r inside thepolder . Farmers in thepolde r own 1500pump s of 70 lt/sec for irrigation. A special feature of this project is that farmerswer e trained inirrigate d agriculture by actually doing itbefor e theprojec twa s completed. Hence,b y the timeo fprojec t completion theywer e ready. Theprojec t inSr iLank a also has severalmediu m sizepum p installed at themai n sluices to help improve thecontro l ofwater ,i nparticula rwate r level,insid e theembankments .

Land Consolidation

Unlike theexistin g agricultural land,th enewl y reclamimed land canb e laid outan d subdivided into rectangular farmunit s ideally appropriate forhig hproduction ,wit h eachuni t served by an irrigation channelan d a drain and connected toa farmroa d forbringin g theproduct san d implements inan d outo f the farm. Hence,i t isrecommende d that land consolidation layout be employed in thenewl y reclaimed land. Asmentione d earlier, the tidal land reclamation inJapan ,Kore aan d Taiwan,al lemploye d land consolidation. When there ispersisten t strongwin d fora lon g period of timesuc h asa t the tidallan d development projects in thewes t coast ofTaiwan ,wher e strong NNEwin d averaging 35-40k m perhour s prevails fromOctobe r toMarch ,win d breakers in the form of two rows of trees are grown onbot h sideso f the farm road toprotec t the cropsa swel l as toreduc ewate r losses in the farm through excessive evaporation. Hence,ther e are tworow so f treesever y 4-500meters . The treesgrow nar e ofvarietie s ofwhic h their leaves can alsob euse d asgree nmanure .

62 Planning ofLan d andWate r Management

Theplannin g of land andwate rmanagemen t has tob emad e at the timeo f planning thepolder . The location and sizeo fvillage , park,woode d area,industria l area,fres hwate r reservoir,etc. ,a swel la s thesiz e of farmunit ,lan d parcelling, including roads,far m roads,win d breakers,etc. ,a swel l asagricultura l development should beplanne d together asa n integrated whole,eve n though their implemen­ tationma y bedivide d into stages forshor t and long-termdevelopment .

Ihav e seenpolder splanne d and constructedwithou t proper drainage nor irrigation,an d farmersha d cut theembankmen t tole t floodscause d by rain todrai noff . Inothe r case,farmer sals o cut theembankmen t to letwate rbacke d upb y tocom e in thepolde r for irrigation. Noon e canblam e the farmers inbot h cases. As thepolder swer eno t wellplanne d and executed,farmer sha d tohel p themselves. As theplannin g and design of thepolder s isa n intricate and complex task,requirin g experienced professionals insevera l fields sucha s nydrologist,geohydrologist ,soi l scientist,engineer ,agriculturist , economist,etc. ,i t isa mus t thatcooperatio n ofeffort sb y these specialists beensure d from thestart ,beginnin gwit h collectiono f data,planning ,desig n tillprojec t implementation. Torea p substantial benefits and good return from thepolde rproject , adequatewate rmanagemen t isa must ,otherwis e therema yb enegativ e effects toth eexten t that farmersma y cut theembankmen t asafore ­ mentioned.

Footnotes

1/ Theview sexpresse d inthi spape r are theauthor' s ownan d not necessary of the institution towhic h hebelongs . 2/ Tochang e frommu d to firmer soil. The ripening of soils comprises threemai nprocesses : decrease inwate r content,formatio no f cracksan d subsidence of land surface.

63 CONSTRUCTIONASPECT S

THEDEVELOPMEN T OFTH EDUTC H POLDER DIKES P.C.Mazur e TheNetherland sWate r Defences Research Centre TheHagu e The Netherlands

Abstract

As aresul to f thevariet y inth eorigin s of polders several categories of polders havedevelope d inth eNetherlands . The specific development in theconstructio n of seadikes ,rive r dikes and belt canaldike s is illustrated inth epresen tpaper . In thepas t thecomplet edesig nwa s based onexperienc e collected ina process of trial and error. Modern designmethod sutiliz e knowledge obtained about loads acting on£ dikean d thestrengt h of the constructional elements of thedike . Inrecen t years studieshav ebee n intensified towards the probabilistic designmethod . In thefutur e thedesig nwil lb ebase d ona calculation of theris k of flooding of theprotecte d polder.Howeve r atpresen t the results of the studies todat e canb euse d toimprov e the traditional ordeterministi c designmetho d until theprobabilisti cmetho d becomes completely applicable.

1 Introduction

Themajo r part of theNetherland s consists of polders.A s aresul to f thevariet y inth eorigin s of thesepolder s andvariation s inloca l circumstances several categories of polders havedeveloped . Sincemedieva l timespeopl e protected comparatively high levelarea s along seacoasts and rivers from frequent flooding bybuildin g small

64 dikes.Drainag e of thesepolder s tookplac eb y gravity throughsluices . Soil subsidence in theolde r polders necessitated achang e from gravity drainage toartificia l drainageb ywindmill s orpumpin g stations. After thedevelopmen to fwindmill s and pumping stations polders also were constructed incomparativel y lowleve l areas,suc h aslake san d marshes.Man yo f thelake swer e theresul to f thediggin go f peatfo r fuel. Inrecen t times evenpart so f these aan d inland seashav ebee n impoldered.

Asresul to f successive impoldering activities aver y complicated systemo fpolder s anddrainag e systemsha sdevelope d (figure1) .

Yi

p4WI N

—bel tcana l iv , -2 land leveli n m belowMS L

Figure 1.Exampl e of acomplicate d system ofpolder s andbel t canals near Amsterdam

65 The levelso f thevariou s poldersrang eno wfro m 2m above to6 m belowmea n sea level (MSL). Thedrainag e system for allpolder s consists of aserie so f natural waterways and excavated canals,togethe r forming astorag e and transport system toconduc t superfluous polderwate r to the seao r to therivers . This paper dealswit h specificdevelopment s inth econstructio n of sea, river andbel t canaldike s resulting from thevariet y inorigi no f these dikes.

2 Seadike s toprotec t seapolder s

Parts of theDutc h North Sea coast areprotecte d naturally against the seab ydunes .Wher e dunes dono t exist orhav edisappeare d becauseo f coastal erosion and also alongbranche s of the sea,lo wlyin g areasmus t beprotecte d against inundationb y the seab y approximately three hundred kilometres of seadikes . Many of thesedike shav egrow nove r centuries from small embankments made of locally excavated materials (mainly clay) intoenormou s constructions made frommaterial sbrough t in,especiall y sand.Th e local soilwa sno talway s ideally suited to theconstructio no f impermeable dikes but informe rday s transport of largequantitie s of soilwa s impossible,especiall y where thesedike sha d tob e constructed intida l areas.Henc e the slopes of these "old"dike swer emad e as steep as possible tominimiz e thequantit y of soil.Th e cresto f thedik ewa s determined by thehighes t flood levelpeopl e could remember.Th e steep outer slopes,ofte nalmos tvertica lwalls ,wer e protected againstwav e attackb y allkind s ofmaterial s likewood ,ston e (glacialboulders) , bricks,rubbl e and grass-sods (figure 2);eve n compacted seaweedwa s used for cofferdam construction along thebranc h of seano w called the IJsselmeer.Knowledg e about theus eo f thesematerial swa s founded on practiceunde r the specific circumstances indifferen t areaso f the Netherlands.Thes e areaseac hha d theirow n specific construction methods,base d on localknowledg e and availablematerials .Eve n today thesedifference s inconstructio n canb eseen .

The introductiono fmechanicall y drivenbucke t and suctiondredgers ,

66 Figure 2.Cros s sectiono f anearl y seadik e hopperbarge s andothe rmean s of transport inth esecon d half ofth e nineteenth century facilitated the transport ofgrea tquantitie so f soil overgrea tdistance . Thisdevelopmen t had agrea t influence on the shape and construction ofdikes ,particularl y newly built seadike s anddams .Fro m theno n materials couldb e chosenbase d on their properties inrelatio n tothei r function inth e constructiono f thedik ebecaus e soil could thenb e obtained inlarge r quantities and from agreate rdistance .

The coreo f amoder ndik e ismad eo f great quantitieso f sand,brough t intoplac e ashydrauli c fill.Thi s sand iscovere dwit h acla y layero f a thickness of about 1m . Side slopes areno w chosena t 1:5 to 1:7 on the seaward sidean d 1:3 to 1:4o n thepolde r side (figure3) .

Asalread ymentione d theprotectio n of thedik e againstwav e attackwa s originally constructed ofvariou smaterials .Howeve r since thepresenc e of thetered owor m ruled out theus eo fwood ,protectio nwa s provided mainlyb y turf.Wher egras s could not growdu e to thesalinit y of the sprayo n lower levels theslop ewa s covered by amattres so fwillo w twigsballaste d with stones.Fro m themiddl e of the 18thCentur y the

67 Figure 3.Developmen t incros s sectiono f ase adik edurin g theperio d 1812t o 1963 outer slopeswer e protected,u p to 1.5m above storm flood level,b ya revetment of stones imported from foreigncountries . After the Second World War concreteblock swer e introduced. Thenee d torepai r great lengthso f seadike s ina shor t time after the 1953disaste r in theSout hWester npar to f theNetherlands ,th es o called Delta area,lea d toth e introductiono f asphalt revetments.Thi s has necessitated entirely newdik e constructions with asphaltrevetment * overlying directly thesan d core (figure4) .

^*r »—mmasphal t i:::::''i sand EZZ3 clay 111 i 11 mine waste "•""•" concrete blocks inn' rubble 8.70m

DESIGN WATER LEVEL • 5,65 m

MSLrOrn,

Figure 4.Cros s sectiono f ase adik ewit h asphalt revetments

68 Asmentione d earlier theheigh t of adik ewa s forman y centuriesbase d on thehighes t known flood level that couldb eremembered . Consequently after theoccurrenc eo f adisaste r due toovertoppin g or overflowing furtherheightenin g of adik ebecam e gradually lessurgent ,ove ra period of years,especiall ywher e alarg e amount ofmone ywa snecessary . Generally some limited measureswer e takenwhic h provided ane w yardstick valid for some timeunti l afloo d occurred with aleve lwhic h exceeded theol done .

It iseviden t that in thiswa y therea l risko f damageo r the probability of flooding wereunknown .Littl ewa sknow n about the relationbetwee n the cost topreven t flooding and thecos to f the damage thatmigh t result from flooding.Economi c comparisonwa sno t made;peopl e asked fordr y feetpreferabl y atn oexpense .Th eheigh t thatdike s should havewa s the subjecto f animated discussion.

In the20t h Century itwa s found that theoccurrenc e of extremelyhig h water levels at seacoul db edesciibe d adequately in termso f frequency inaccordanc ewit h the lawso f probability calculus.Howeve r the curveso f extremewate r levels,base d on arelativel y shortperio d of observations,hav e tob e extrapolated intoregion s farbeyon d the field ofobservatio n (figure5) .

The 1953disaste r provided proof for the theories developed for the probability of exceedance ofhig hwate r levels.Fro m studieso f the Dutch RoyalMeteorologica l Institute,initiate d in 1953,i twa s concluded that considerably higher flood levels than theon eobserve d in 1953wer ephysicall y possible and thatn opractica l level could be givenwhic h could neverb e exceeded; therefore therewil l alwaysb e some finiterisk .Th efrequenc y of theris ko f floodingwa s studied in relation toth eeconomi c aspects.Thi smatte rwil lb ediscusse dbelow . Aftermuc h discussion itwa s decided tobas e thedesig no f all seadike s fundamentally ona wate r levelwit h aprobabilit y of exceedance of 10 per annum.

69 frequency ofexceedanc e per annum

Figure 5.Frequenc y of exceedance of highwate r levels atHoo ko f For example the levelo f 1953,3.8 5 m aboveMS L has afrequenc y of 1/300 per annum.

Severalothe r elements also play arol e indeterminin g thedesig n leve. of ase adike : - waverun-u p dependingo nwav eheigh t and period,angl eo f approach and roughness of theslope , - anextr amargi n toth edik eheigh t to takeint o account seichesan d gustbump s (singlewave s resulting from asudde nviolen t rusho f wind), a change inchar tdatu m (NAP)o r aris e in themea n sealevel , subsidence of the subsoil and thedik edurin g its lifetime . Based on thesefactor s thedesig n levelo f ase adik e canb edéterminé e as shown intabl e 1.Th eprofil e of such ase adik e isshow n infigur e 3.Wit h thepresen tdesig n criteria the cross sectiono f amoder n sea

70 Table 1.illustratio n of determining design level

flood level MSL+ 5.00m wave run-up 9.90 m seiches and gust-bump 0.35 m risingmea n sea level (MSL) 0.25m settlement 0.25m

Design level MSL+ 15.75m dike istwic e ashig h as theol d dike thatprecede d itbefor e the 1953 disasterwit h afourfol d increase involume .

To constructmoder ndike s thecla yo f theinne r slopeo f theol ddik e isgenerall y dug awayan d stored and thesan d of thene wdik e isfille d inagains t theol d dike.Afterward s the stored clay isuse d tocove r the sand core.I nth ewav e attack zonea revetmen t of stone settso r asphalt ismade .Becaus eo f thefla t slopesno w inus e slope stability problemswil l seldomoccur .Despit e theenormou swidt ho f thewhol e dike construction animpermeabl eblanke tmad e of clayo rasphalt , applied toth e seaward slope,o r an impermeable coreo f clayi s essential topreven t seepage.

Thehistorica l development of thedesig nmetho d canb e traced.I nth e past thecomplet edesig nwa sbase d onexperienc e collected ina proces s of trial anderror . Developments inmechanic s (from 1920especiall y soilmechanics )hav e brought achang e inthes emethods .Th emoder ndesig nmetho d utilizes knowledge of thepropertie s of soilmateria l and subsoil obtained from field and laboratory tests,knowledg e of ground water flow andwate r pressures,knowledg e of thebehaviou r of thedik ebod y and therevet ­ mentunde r thewav e attacketc .

3 Riverdike s

River dikeswer emad eb yma n towithstan d thehighes t flood levels.

71 Originally thesedike swer e only small,positione d along therive r banks and carryingroads . The present form and height of theserive r dikeswa s achieved by the heightening of thecres tonly ,usin g allkind s of locally available soil and asa consequenc e the inner slopebecam emor e andmor e steep, reaching even 1:1.5 inplace s (figure6) .

AOm H Figure 6.Developmen t incros s sectiono f arive r dike in the course of time

As aresul t the inner slope could becomeunstabl e during periods ofhig h riverwate r level. Theserive r dikes are allovergrow nwit hgras s and theslope s protected by arevetmen t only onplace swher e severe erosiono rwav e attack can be expected. Thanks now tobette r transport facilitiesmor e suitablematerial s are used for reconstruction sucha s clay for impervious revetments onth e outer slopes and sandy clay on the inner slopesmakin g for flatter slopes.

In thepas t theheigh t of arive r dikewa s determined by thehighes t flood level that one could remember and only asmal l allowancewa smad e forwav erun-up . Before 1950 theconstructio n of thesedike swa smor e or lessbase d upon

72 experience andman ydisasters ,cause db y inundation and failure,wer e theresult .Inure d to inundations,peopl e learned toliv ewit h this risk and ingenera l theybuil t theirhouse s near too ro n thecres to f thedikes .Th egrowin g population and changes inagricultur e however havemad e itnecessar y tohous epeopl e in thepolder s aswel l aso n the dikes.Du e to thisa bette r protection against inundationha sbecom e essential. Today, the incidence of extremehig hwate r levels canb e represented in termso f frequency,usin g the samephilosoph y asdescribe d abovefo r seadikes . After yearso f discussion about technical and environmental aspectsi t wasdecide d tobas e thedesig n levelo f themai nrive rdike so n awate r level corresponding toa discharg e that canb ereache d or exceeded -4 8x10 timespe r year.A tpresen t areconstructio n program isbein g carried out tostrengthe n themajo r parto f thefou rhundre d kilometres ofrive rdikes .

Reconstruction of thesedike s isespeciall y difficultbecaus e of the environmental aspects.Th ereconstructio nofte n destroysvaluabl e vegetation on theslope swhic h probablywil l not return to thene w flat slopes.Man yhouse s and farmhouseswit hhistorica l value,buil t ono r into thedike shav e tob edemolishe d ordik e reconstruction minimised or executed withver y elaborate techniques inorde r topreven t demolition.

Inth eeaster npar to f theNetherland s the subsoil of therive r dikes often consists of acla y stratum of athicknes so f 2t o6 m overlying a sand stratum of 20m ormore .O nman y spots there isa nope n connectionbetwee n thesan d stratum and therive rbe dwhic h causesa transmissiono f thehig h floodwate r pressure to theundersid e ofth e clay stratum at the toeo f the inner slope.Thi spressur ema y endanger thestabilit y of thecla y stratum and can lead to itsbrea kup , followed by internal erosiono f thesan d (piping).Th ehig hwate r pressure inth e sand stratumma y threaten thestabilit y of the inner slope,addin g to the threato f riverwate r percolating through thedik e (figure7) .

73 ?'//»/>'/>/>'/;,,,,//»?/;?/:

failure mechanisms before reconstruction

design river level (D.R.L

river dike after reconstruction

Figure 7. Cross section of a river dike before and after reconstruction

In thewester n part of theNetherland s peat strata in the subsoil can cause considerable subsidence. Therefore extensive investigations of the subsoil and the soilmateria l used fordik e constructionmus tb edon ebefor ereconstructio n toobtai n data (mainly soilproperties )fo r designcalculations .

An inner slopeo f 1:3 to 1:3.5 isrecommende d with an impermeable cover of clayo n theoute r slope and on thefloodplai n adjacent to thefoo t of the slope topreven t thepercolatio n of flood water.A permeable horizontalblanke t adjacent to the inner slopewil l preventbrea ku p and theprobabl e subsequent piping and collapseo f thedike .Th ewidt h of this cover is still designed by empiricalmethod sbu t inrecen t yearsmode l studies and in situ testshav ebee n carried out toobtai n more exactdesig n rules,d eWi t et al (1981).

74 4 Belt canaldike s

Forman y centuries inth ewester n parto f thecountr y the impoldering of lakeswa snecessar y tosto p theprogressiv e erosiono f thebanks .I n additionpeopl ewh o dug peat for fuelwer eoblige d to impolder excavated areaswhic h hadbecom e artificial lakes.Anothe r process that led to theformatio no fpolder swa s thedrainag e and agricultural use of peatmarshes .I na fe w centuries the levelo f thesepeatland sbecam e solo wtha tprotectio nb ydike s and artificialdrainag ewa sessential .

In theexcavate d areas small canalsha dbee n left forwate r management and for shipping.Th e small stripso f land alongside these canalswer e used asdike swhe n drainage started with thepumpin g ofwate r fromth e lakeint o the "belt"canal . Belt"canal swer eexcavate d around large lakes andwit h thesoi ldu g from thesecanal s (oftenpeat )a bel t canal dikewa smad ebetwee n the canal and the lake.Thes ebel t canals remained part of theexistin g systemo fwaterway s to transport superfluouswate r to seao r riveran d forus eb y shipping.

During theproces s of impoldering over thecenturie s inth ewester n parto fou r country aninterconnecte d networko fbel t canalsan d thousandso f kilometreso fbel t canaldike shav e come intobeing .

The subsoil in this areamainl y consists of stratao f peat and soft clay. Becauseo f thissoi l severe subsidenceo f thedike sha soccurre d ata rat eo fu p to0.0 5 to0.1 0 m per annum insom eareas .A s thewate r levelo f thebel t canal and thewhol e systemo f canals to the seai s kept constant thisha snecessitate d thefrequen t heightening of the beltcana ldike s (up toonc e every 2o r 3years) .Heightenin g has usuallybee n carried outusin g locally availablematerials .Thi s process has resulted ina ninhomogeneou s top layerwit h athicknes so f up to4 to5 m , consisting ofdredge d mud,peat ,clay ,rubble ,ashe s and sometimes sand (figure 8). Often,th eadditiona lweigh t caused by thisheightenin gha sproduce d further subsidence.

When,b y progressive subsidence,layer so f rubble,ashe s and sand

75 polder dike - belt cana dike - deep polder M.S.L.

peat sand 'AOm Figure 8.Cros s sectiono f abel t canalwit h dikes

(whether old revetment material or road-metal)disappea r under belt canal level theyma y cause seepage problems.Whe nheightenin g isdon e simply byplacin g aca p of clayo n thecres to f thedik e the inner slope becomes steeper and stability problemsma y arise inadditio n toth e problems due to the soft subsoil onwhic h itrests .

The quest for safebel t canaldike sha sbecom emor e important sincea growing population and industrialisation has necessitated building in low level polders.Usuall y peopled ono t realise fullywha t canhappe n when abel t canaldik ebursts .Th e low levelpolde r is inundated completely by the large quantity ofwate r stored in theextensiv ebel t canal system and inadditio n damage canb edon ewhic h isdifficul t to repair.Th edik eburs t causes adepressio no f the level of theadjacen t belt canal endangering also the stability of thedike s alongside the canal.Divisio n of thebel t canal systemb ymean so f emergency weirs limits thiseffec t toa restricte d areabu tma y causemor e localdamag e to thebel t canaldike s because of thequic k fall of thewate r level in thebel tcanal . Thebel t canal dikes are covered with turf and only protected against stream andwav e attack at thewate r level.

76 A not soobviou s threat comes from animalactivities . Grazing cattle locallydestro y the turf on thebel t canaldike san d make aquagmir e of theoute r slopewhe ndrinkin g from thebel tcanal . There isa growin g problem inrecen tyears ,du e to thepresenc eo f muskrats,whic h infiltrateunchecke d into theWester npar t of the Netherlands with itsman y smallbel t canaldikes .Muskrat s arefa rmor e dangerousbecaus e theyburro w theirhole s ingroun d adjacent toope n freshwater,whethe r dike ornot . As theentrance s liebelo wwate r levelan d the tunnels canb ever y extensive thetracin go f this threat isdifficult . Theonl ywa y of combating thisproble mno w is tocatc h themuskrats .

Thedesig no fbel t canaldike sha sno t changed verymuc h sinceforme r times,a s themajo rwor k on thissor to fdik e ismaintenance .Th e crest musthav ea minimu mwidt ho f 1.5m ,bu t 3m isrecommende d tocate rfo r vehicular transport.Th e crestmus tb e0. 5 to0. 8 m above theextrem e belt canallevel . Thebel t canal level isregulate d by thepumpin g stationso f thepolder s and thepumpin g stations and sluices thatdrai n thebel t canal intoth e seaan d itvarie swithi n certain limits.Thoug h in the courseo f time theinne r slopesbecam e 1:0.8 to 1:1.5 adi po f 1:3 isrecommende d as maximum slopeangl e onaccoun t of turfmaintenanc erequirements . Nevertheless thedesig nfo r ane w cross-sectionmus tb ebase d ongeo - technical investigationsan d calculations andwil l often showflatte r inner slopes.Thi s sometimes impliesrealignin g ditches immediately adjacent toth e innerslope . Therevetment s aremad eo fwattlewor k (willow twigso rhardwoo d strips) or, simply and cheaply,dumpe d rubble.Ofte na ree dborde r growing along thecana lban kwil l suffice toprotec t theoute rslope . Itwil lb eclea r that regular inspection isneede d for theupkee p of thesyste m ofbel t canaldikes . Usually this isdon eb y thepolde r and provincial authorities.A govern ­ mental program of assessment of thestabilit y and safety of thebel t canaldike s started 15year s agoafte r thefailur e of an importantbel t canaldike .Thi s isa grea t aid toth epolde r authorities,informin g them about thecondition so f themos t importantbel t canaldikes .

77 5. New developments indik edesig n

Inrecen tyear s the statistical and economic approach todik edesig n has againbecom e atopi c fordabate . The inundation risko r theprobabilit y of failureo f adefinit edik e section areespeciall y inth eforefron t of thediscussion .Th e immediate reasonfo r thisdiscussio n lies inth e idea that thedesig nmethod s available todat e arebase d upona desig n levelwhic h sometimes leads tounnecessaril y high construction expenditure. Thepossibl e losso f areaso f outstanding natural,cultura l or scenic interestwhic h isalmos t impossible tovalu emus t alsob e seena s expenditure. To tackle thisproble m studies areinitiate d intw odirections : a)A n assessment ismad e of the "profit"o f ahighe r levelo f security. A profound understanding mustb eobtaine d of thepossibl e damage which canb e caused by thefailur e of adike ,bot h in termso f money and also the losso fhuma nlif e and thingso f cultural interest. In these studies of cause and consequence,historica l floodings (including the 1953floodin g of Zeeland)ar e analysed and scenarios of probable floodings aremade .

The aimo f these studies ist ofi x standards of safety for specific polders inrelatio n toparticula r defence requirements.I tmus tb e realized that asafet y standard canb e formulated in severalways , for example,a naccepte d risko f failureo f adike ,inundation , drowning or anoptima l ratioo f costso f dike strengthening to profits gained from areductio n indamag eb y flooding, (towhic h alsobelon g various other imponderables). The problemo f the (political)decisio n tofi x certain safety standards for specific areasha s still tob e solved. b) Studies aremad e toprovid e awel lbalance d design for aspecifi c safety standard orris ko f failure (based on apolitica l decision). Ina moder n design the impositiono f the load on all theconstruction j elementso f thedik e shouldb e arranged in such awa y that all ; elementsbea r the same risko f failure.Fo r example:I tmigh t happenj thatmuc hmoney ,materia l and land areuse d toheighte n adik e even

78 though there isstil l agrea tris ko f failureb ypipin gbefor e flood water actually overflows thecres t of thedike .Ou rknowledg e of the pipingmechanis m isstil l limited.Investigation s on thisproble m have started recently.

The first step inthes e studies is toanalys e allpossibl e causeso f dikefailure .Thes e causes (aspresente d ina "faul t tree",figur e 9) comprise four categorieso f events thatma y cause inundation: - human failure,managemen tfaults , - aggressivehuma n actions sucha swa r orsabotage , - actso fGod ,extrem erainstorms ,earthquake s andhurricanes , technical failureo f structuralelements .

INUNDATION

FAILURE

HUMAN INSTABILITY FAILURE OFTH E WHOLEDIK E EXPLOSION

SABOTAGE INTERNAL EROSION "ACTS OF GOD" EROSION OUTER SLOPE OVERFLOW EROSION INNER SLOPE OVERTOPPING

Figure9 .Faul t tree

The second step ist oanalys eth edifferen t causeso f failure in aparticular category.Onl y the technical failures arementione dhere :

79 overflow or overtopping of thedike , erosiono f thewette d slopeo r losso f stability, erosiono f the inner slope leading toprogressiv e failure, instability of thewhol edike , instability of thefoundation s and internalerosion .

For all thesemode s of failure,th e situationwher e theforce s acting arejus tbalance d by the strength of the construction (theultimat e limiting state)i s considered. Theprobabilit y ofoccurrenc e of thissituatio n for each technical failuremechanis m canb e found by employingmathematica l and statistical techniques. In thismetho d ,Bakke r andVri jlin g (1980), the probability-density functiono f theload s and thedik e strength are combined (figure10) .

FAILURE

PROBABILITY OFFAILUR E

PROBABILITY DENSITY PROBABILITY FUNCTION DENSITY POTENTIAL FUNCTION THREAT RESISTANCE

TRANSFER THEORETICAL FUNCTIONS MODELS

BOUNDARY MATERIALS CONDITIONS GEOMETRY

Figure 10.Th e concepto f theultimat e limit state of afailur e mechanism

For thispurpos emor eknowledg emus tb e acquired concerning the complex problems associated with theus eo f theoretical models relating loads

80 'andstrength . Improved knowledge of the theoretical relationbetwee nwav e attackan d thestrengt h of therevetment ,o f theprobabilit y of slope stability related to thevariou s ground parameters,an d alsoo f the theoryo f internal erosion isurgentl y needed. Studieshav ebee n initiated for all these topicsdurin g the last 10 to 15year s and havebee n intensified inrecen t years.Th e resultso f these studies canb e applied immediately toimprov e the traditionalo r deterministic designmetho d until such timea smor e insight isgaine d concerning thepracticabilit y or otherwiseo f the probabilistic design method.

It isimpossibl e at thismomen t topredic t theresult s of thestudie s mentioned above.Also ,whethe r or not theprobabilisti c designmetho d for dikes isa delusio no r arealisti c conceptha s still tob eshown .

There isn odoubt ,tha t thestudie s concerning theprobabilisti c design method result ina growin g knowledge about therelativ e importanceo f thevariou s failure-mechanismsfo r thestabilit y of thewhol e construc­ tion.I naddition , theresult so f these studies enlargeou r knowledge aboutdike s and theirbehaviou r under different conditions and also the knowledge about therisk s associated withdamag e and flooding.

References

Bakker,W.T. ,J.K .Vrijlin g 1980.Probabilisti cDesig no f SeaDefences , 17thCoasta lEngineerin g Conference,Marc h 24-28, 1980,Sydney , Australia;pp .2040-2059 . Wit,J.M . de,J.B . Sellmeijer,A .Pennin g 1981.Laborator y testingo n Piping.Tent h Int.Conf .o n SoilMech .an dFound .Eng .Jun e 15-19, 1981,Stockholm , Sweden,pp .517-520 . FROMWINDMIL LT OWIND-GENERATO R Development inPolde r Construction R. Segers Infra Consult,Soi lan dWate r Management Consultants Deventer,th eNetherland s

"Thething s thathat hbeen , iti stha twhic h shallbe ; and there isn one wthin g under thesun "

1. Introduction

Thediversit y ofconstructio n aspectsmentione d inth ecircula r iss o extensive,tha t achoic e fromth evariou s topicsha sbee nmade .I ti s undeniable that irrigationan d drainage systems,road san d shipping canals formpar t of everypolde r involved.Howeve r themos t significant structures essential tomaintai na polder ,ar edischarg estructures . Without sluicesan d especially pumping stations themajo r part ofth e Netherlandswoul d consist ofmarshes ,lake so r sea.S o life inthes e regionsdepend sgreatl y on theperfec t conditiono f thesedischarg e structures ofwhic h therequiremen t ofreliabilit y iso f thesam e importancea s the technicaloperatio n required. In this presentation severalaspect s ofdischarg e structureso fwhic h thepumpin g stations form theprincipl e partar edealt hwith .

2. Sluices

Theoldes t engineeringwork s todrai nrainfal lan d percolatingwate r from impoldered areas,wer e sluices.Thes ewer econstructe d ofwoo dan d brickwork andwer e situated at theoutlet s of smallinlan d waterways into the riverso rdirectl y into thesea .A reliabl e protectionagains t thetida lmovement s of these awa s theprincipl e requirement ofth e inhabitants of thecoasta ldistrict sa t that time.Th enee d forfixe d water levelsdevelope d gradually overa perio d of severalcenturies .

82 Itwa sobviousl y practical tocombin e theseoldes t sluiceswit h navigationlocks .

Asa result of therapi d increase inreclamatio nwork s therewa sa comparable increase inth enumbe ro fdrainag e sites required. Inmos t of these locations therewa sn olonge ran y shippingan d toimprov eth e safetyo fdik ecrossings ,th estructure swer ecovere d over (Figure1) .

Modernsluice sar econstructe d of reinforced concretewit h special precautionsagains t seepagealon gth estructure .Discharg e througha sluicei scontrolle d byon eo r twoautomaticall y operatingdoors ,whic h areopene d by thepressur ehea d of theinsid ewate r levelan d closedb y thepressur ehea d of theoutsid ewate r level.Th edoor sar econstructe d ofhar dwoo d of tropicalorigi na sa precautio nagains t pileworm . Emergency valvesar ebuil t intoth estructur e forus e incas eo fa no n closureo rothe rtroubles .

Asa resulto fgroun d settlementan d therelativ e raising of themea n sealevel ,large rdischarg e structureshav ebecom enecessary .Graduall y sluiceshav ebee nreplace d bypumpin g stations.Alon g principle rivers anda t somebi gdischarg e locationsdrainin gdirectl y intoth esea , pumping stationshav ebee nadde d tosluices .A t lowtid ean d lowrive r levelsdrainag eb ygravit y ispossibl eb yopenin g thesluices .Howeve r athig h tideo rhig h river levelsth epumpin g stationwil lbecom e operational (Figure2) .

J" Pumping stations

Asth emajo rpar to fth eNetherland s cannotb edraine d bygravit y pumping stationar emos t important structures inside thepolders .Thes e Pumpingstation shav e tofulfi lman yconditions ,o fwhic h reliability Isth emos t important.Reliabilit yca nb eexpresse d inthre eway san d yourattentio n isdraw nt oth efollowin gaspects : Reliability indesign ; Reliability ofmachiner y and Itsmaintenance ; Reliability inenerg y supply.

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85 3.1. Design reliability

During the 19thCentur ywindmill swer e replaced by steamengine san d paddlewheel sb yplunge r pumps;thi scombinatio no f steamengin ean d plunger pumpwa suse d asa weapo nagains t theoldes t enemy ofth e Netherlands,referre d toi nth epast ,a s the "".Thi swa yo f thinkingwa sexpresse d inth efirs tdesign so fpumpin g stations,whic h werebuil t likecastle swit h towersan d galleries (Figure3) . Afterwards thisaggressiv eelemen t disappeared from thedesign ,bu t aspects sucha ssolidit yan d effectivenessremained .Th epresen tpumpi n stationsar econstructe d ina purel y functionalmanne ra s efficiently and economically aspossibl e (Figure 4).A pumpin g station isi nsom e way comparablewit ha small-scal e factory,wit h theexceptio no fth e workinghours .Th eaverag eannua ldischarg e required tomaintai n polder watera ta nacceptabl e levelca nb edisplace d inabou t 1,000hours , operatingwit h fullinstalle d capacity.Th elimite d working time required togetherwit h thegrowin gpossibilit yo f theautomatio no f severalspecifi coperations ,ha s resulted inne wdevelopment s inth e construction of smallpumpin gstations .

The traditionalwa yo fbuildin g pumping stations in-situha sbee n replaced by theconstructio no fprefabricate d pumping stations (Figure 5). In thiscas e thecomplet e concretesubstructure ,compose d of different parts,th emechanica lan d electricalequipmen t and the superstructure are supplied and placed byon econtractor .A t present only smaller stations,u p to10 0m3/min ,ca nb ebuil t inthi sway . Automation,togethe rwit h thedistanc e signalizing of technicaltroubl e has resulted inth ereduce d supervisiono f smallerpumpin gstations . Most pumping stationsar e situated at lonely spots inth epolde ran d are Infrequently attended and are therefore anattractio n touninvite d visitors.Sometime s theresult so f suchvisit sca nb eharmfu lan da designerha s totak e this intoaccoun t inth edesig n toensur e pumping station security. I*

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Flg- 3. Pumping station Cruquius

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Fig. 4. Pumping station Keizersveer

88 Theaccessibilit y of thevariou scomponent so f themechanica lan d electricalequipment ,i son eo f themos t important design standards inside thepumpin g station (Figure 4). Badaccessibilit y isa principl e causeo f theneglec t of inspectionan dmaintenanc e of themai n componentso fpumpin g equipment.Secondl y itdelay s therepai ro f damagedurin gwhic h timeth epumpin gstatio ni sou to forde ran dever y engineermus t tryt oshorte nthi svulnerabl e period asmuc ha sh ecan - Inadditio n thedesig nha s toinclud eprotectio nagains tclimatologica l influences.A longlif e ison eo fth eprincipl e objectives pursued by everypolde rboard .

3-2« Machine reliabiltyan dmaintenanc e

Thereliabilit yo f thepumpin g stationi sexpresse d inth equalit yo f thepumpin g equipment and itsmaintenance .Throughou t theage s understanding betweensupplier san dengineer sha sgrow nt oa ver yhig h standard anda sa resul t theservic egive nb yth esupplier s isbase do n giving priority toal lth ekind so f repairst ob eexpecte dwit h pumping equipment.A sa resulto f thiswel lorganise d service,pum p failures canb erepaire d ina fe wday ss omos tpumpin g stationsar eequippe d withonl y two identicalpump so rArchimede sscrews .I nth ecas eo fver y bigdischarge s (saymor e than1,00 0m3/min )th etota ldischarg e is divided intothre eo rmor epumps .I nthi scas e themetho d of transportation (byroa do r ship),determine s thedimension so f thepum p runnersan d thediese lo relectrica lengines .

Protectiono f therunner sagains t pollutionespeciall y againstwoode n trashi nth epolde rwate r isprovide d bytras hracks .A sa resul to f theincreasin g population inth epolders ,th eamoun tan d thekin do f pollution isincreasing .Fo rage sth epollutio nwa smostl y soft vegetablematerials ;nowaday showeve rdomesti c rubbish,containin g Plasticsan dwood , isa constan t threat toth epum prunners .Therefor e thetras h rack isa nimportan t parto f theequipment .Cleanin go fth e trashrac ki scompletel y automatized andmos t racksar eprovide d witha mechanicaltras hremove ro rgra bbucke t (Figure6) .

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Fig.6 . Completely automatized mechanical trush remover

91 Inadditio n toth eprotectio no f thepumpin gmachiner y the inspection andmaintenanc e ofal lmovin g partso f themachiner y aswel la sth e electricalequipmen t isessential .A t least oncea yea ra n Inspection of themos tvulnerabl e partso fengines ,pump san d auxiliary enginesi s necessary.Whe n theconditio n ofon eo rmor e partso f themachiner y Is- unsatisfactory, the replacement of thisparticula r partmus tb e considered intim e topreven t asudde nbreakdown .

Awel lcompose d schemeo fmaintenanc e isa s important asinspection . This schemeshoul d bebase d onroutin eaction safte ra fixed numbero f workinghour s and should bedraw nu pb y thesupplie r of themachinery . Thebette r theinspectio nan dmaintenance ,th elonge rwil lb e thelif e of themachiner y and themor e reliable thepumpin gstation .

3.3. Reliability ofenerg y supply

Inorde r fora pumpin g station tob ereliabl e itmus ;hav ea guarantee d energy supply.A n estimate of themea nyearl y consumptiono fenerg yb y allpumpin g stations inth eNetherland s together comes to4 5x 10^kW h andalthoug h thisconsumptio nI sonl y6 %o f thetota lnationa l consumption thedeliver y has tob eassure d underal lconditions .

Theprincipl e sources ofenerg y areelectricit y and oilan d Iti s striking thatnatura lga s ishardl y relevant topumpin g station operation.A n explanation for thisma yb e that thedistributio n network ofnatura lga sha sbee ndevelope d inth elas t 15yea rperio d and itsbranche sar eno ta s finea s thenetwor k ofelectricity .A sa consequence connection toth enatura lga sdistributio n networkwoul d be expensive.Connectio n toth eelectricit y network isals oneeded ,t o operate smallauxiliar ymotor san d toIlluminat epumpin gstations , leading tofurthe rexpenses .

Thesuppl y ofelectricit y isguarantee d by theconstructio n ofa nationaldistributio n network,constructe d insuc ha wa y that failures of electricty aremostl y ofa shor tduration .Failur eo f electricity supply inth eloca ldistributio n network canb eexpecte d more

q? frequently,bu t incorporationo f thepumpin g stationint oa nlatera l electrical systemwil lsolv ethi sproblem .

Pumping stationsar e ingenera lirregula rconsumer so felectricit yan d inever ypumpin g stationa relativel y largepowe r supplymus tb e installed inrelatio n toth erelativel y shortworkin g timewhic hlead s toth eirregula r consumptiono f theloca lenerg y supply.Mos t ofth e electricity suppliers thereforehav emad e limitations inenerg y supply bychargin gextr adurin g themornin gan d evening peaks.Therefor eal l pumping stationsar eequippe dwit h lockingcontact ss otha t theof f peak timeca nb ebypassed .Th ecost so fconnectin g thepumpin g station toth edistributio n networkar evariabl ean dar edependen t firstlyo n thelocatio no f thepumpin g stationwit h respect toth edistributio n networkan d secondly onth epowe r installed. Sometimes theconnectio n costca nb econsiderabl e and thisfinancia lconsideratio n combined with the,formerly ,lo woi lcos tmad e itattractiv e toequi ppumpin g stationswit hdiese lengines .A secon d advantageo f theus eo fdiese l engines isth epossibilit y ofchangin g thespee do frevolutio nwithi n fixed limits.Thi s speed regulation influences thedischarg eo fth e pumpsan d thepowe ro f theengine swhic h isparticularl y important for drainage intoth esea .I nthi ssituatio n tidalmovemen t causesvaryin g pressureheads ,whic h results invariabl edischarges .B y raising the speed of revolution,bot hdischarg ean d enginepowe rwil lincrease , which isattractiv e fordrainin gdurin ga risingtide .

Acombinatio no fdiese lan d electricalengine sma yb econsidere d when pumpingstation sar econstructe d with threeo rmor epumps .Als owhe n twoo rmor epumpin g stationsar econstructe d orhav e tob e constructed insidea polde ri twoul d bewis et oinvestigat e thebenefit s tob e obtained fromth eus eo f twoenerg ysources .

Whenoi li suse d asa sourc eo fener*gy ,a goo d supply routeb ylan do r wateri sneeded .Th eoi li sgenerall y stored inundergroun d storage tanks,whic hhav et omee tenvironmenta lpollutio nregulations .Som e pumping stationsar eprovide dwit habov egroun d storage tanks,whic h areles sexpensiv ebu tmor evulnerable .

93 The totalcapacit y of storage tanks installed atoil-drive n pumping stations,i sa t least 150%o f theannua lconisumption .Unde r normal conditions 1/3 of thisquantit yha s tob eavailabl e atal ltimes ,i n ordert omee t thereliabilit y requirements.Onl y ina stat eo fnationa l emergency isi tpermitte d tous e thereserv equantities .Th eextr acos t attached toth e installationo f thisextr a storage capacity ismostl y paid by theGovernment ,accordin g toth eProtectio n ofCivi lWork si n WartimeAct .

Therisin go fenerg y costs inth elas t fewyear sha s resulted ina renewed interest inth eapplicatio no fwin d energy,b e itwit hsom e diffidence.Althoug h theinvestigation s areno t finished yet,th e interim reports regarding theus eo fwin d generators inpumpin g stations,ar e of theopinio n thatwin d energy canb ea usefu ladditio n toelectrica l energy (figure7) .

Wind-generators areno t operational duringcal mo r strongwind ,s oa connection toth eelectrica lnetwor kwoul d beessentia l tomaintai na fixedwaterleve l inside thepolde ra tal ltimes .Absenc e of sucha connectionwoul d carryu sbac k toth estar t of thewindmil l period,i " whichth echangin gwate r levelscoul d bekep t inhan donl yb ycreatin g anadequat ewate r storagecapacit y inside thepolder ,a nundesirabl e situationtoday .

Theeffectiv e powero f thewind-generato r islimited . In comparison withancien twindmill showever ,considerabl e improvementshav ebee n made toincreas e theefficienc y ofwind-generator s and pumping equipment;bot h theArchimede s screwan d theaxia l flowpum par eo fa higherqualit y asar eth epaddl ewhee lan d theplunge r pump today.

Both thedevelopmen t of thewind-generato r and thepréfabricatio no f small-sizepumpin g stationspromp t againth ealway s realquestio nabo<*: : i centralizing ordecentralizin g thetota ldischarg eo fbi gdrainag e } areas innewl y reclaimed land.A s thenumbe ro fpumpin g stations isf° | theonl y component inth egenera l lay-out ofa polder ,th eanswe r isJ nota neas yone .I twil lb eclear ,tha t inmos t cases theinitia lcosf f

94 HG. 7 DRAFT DESIGN

WIND-GENERATOR WITH PUMP

95 ofconstructin g onepumpin g station isles stha nth econstructio ncost s of twoo rmore .I t isals oclea r thaton ecentra lpumpin g station isalway s situated on thelowes tspo t of thepolde rcloses t toth e dike.Howeve r it isals otru e that thesoi lexcavatio n forth e additionaldrainag e lay-outwil ldepen d greatly on thenumbe ro f pumping stations involved,especiall ywhe n thelay-ou t isdesigne d in8 moreo rles sundulatin g terrain.Calculatio no f theinitia lcos to f somealternativ e lay-outs,i nwhic h thetota ldischarg e isdivide dove r morepumpin g stations,wil lb eessentia l tomak ea justified and correct choice.I tma yb eeconomica l todrai nsmal ldeep-lyin g isolated areas inside thepolde rb y seperate pumping sub-stations.Doin g this willcontribut e toenerg ysavings .

3.4. Running costs

Inadditio n toth einitia lcos to f thetota llay-out ,ar e therunnin g costo f thepumpin g stationsan d thecos to fmaintenanc e ofbot h the pumping stationan d thedrainag e system.

Therunnin g costca nb edivide d intoth eenerg y costan d thecos to f manpower.Energ y costsdepen d primarily onth eannua lrainfall , percolatingwate ran d evaporation,o nth eefficienc y of themachiner y and theconstruction ,an d lastbu tno t least onth eenerg y prices.Al l these factors aredifficul t toinfluenc e asth eclimatologica lan d geological conditions cannotb ealtered ,th eefficienc y isth ehighes t possiblean d pricesar edictate d by third parties.Th ecos to fmanpowe ' ishowever ,a subject ofeconom y studies,especiall ywhe n inth elas t decade salarieshav e increased tenfold andmore .Th eemploymen t of engineersan d otherpolde rworkme nha schange d insuc ha way ,tha ta s l result ofautomatio nan d computer techniquesan d thedevelopmen t of automatically operating trash-rackremovers ,mor e timeha sbecom e I available forne wactivities ,suc ha s thecentralize d cleaningo f drainsan d ditchesan d themaintenanc e ofmechanica lequipmen t usedf° i that purpose (figure 8). Ditchcleaning , formerly a landholder' stas" i isdon emor ean dmor eb ypolde rworkmen ,equippe dwit h alarg e assortment of selected equipment.Fo rthi sreaso n thedimension so f

96 {

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Fig. 8.Maintenanc e ofa wate r course

culvertsar en olonge rbase do ndischarg eonly ,bu tals oo nth e dimensionso fth ewate r reedcutter .A suninterrupte d sidestrip salon g thedrain s enableth epossibilit y foroperation swit hmechanicall y "operatedequipmen t eachsid editc hha s tob ebridge d orcovere d overa t theinle t intoth edrain .Al lthes ecosts ,mentione d abovear e significant inth edeterminatio n of thenumbe ro f pumping stationst o beconstructe d ina polder .

Almost fivecenturie so f interesting technicaldevelopment s arebetwee n theconstructio no f thefirs twindmil lan d thedesigne d wind-generator. Regarding theimprovement s ofmachiner yan dpumpin gequipment ,muc hha s beenachieve d anda sa resul tbot hefficienc yan d solidity areo fhig h standardsnow .Howeve r alltechnica lachievement swil lb e judged according toth erequirement so f reliability.

Atth een do f thispresentation ,a tribute ispai d totha t smallarm y ofunknow nmiller san d engine-drivers.Th e "Crugius",on eo fth eoldes t Pumping stations inth eNetherland s isno wa museu m and soar eth efe w windmills thathav esurvived . Inthi sw ehonou rou rancien t technicians,wh oreclaime d polders inth epas tages .Bu t themille ran d engine-driver,wh ob ynigh tan dda ywa semploye d onoperatin g the windmillo rpumpings-station ,ar ehardl ymentioned .H edi d hisjob , sometimesgrumbling ,alway sdutifully ,makin g lifepossibl e forth e majorpar to f thepeopl eo f theNetherlands .

97 CONSTRUCTION ASPECTS OFPOLDER S INTH EWORL D ir.M.A .Meye r Sunecon,Paramaribo ,Surinam e

Abstract

The construction ofpolder s started outside ofEurop eo na large scale inth e Caribbeanarea ,wher ework swer emainl y carried outmanually . Thephysica lenvironmen trequire d aspecia lwa y ofreclamation . Atpresen tpolder sar e constructed inquit e differentways ,requirin g 2 importantparameter s tob e taken intoconsideratio n againsta grea t numbero f factors,viz : the constructionperiod ; the costso f thepolders . Thepolde r design,th ephysica l environment,socio-economi c circumst­ ances andth epolitica l system of thecountry ,d oexercis econsiderabl 1 influences upon these twoparameters .Example sar equote d ofth e effects of such influenceso n theconstruction . Thedegre e ofmechanisatio n constitutes another factoro fmajo rimport ' ance. Countrywise ,wel l considered choiceswil lhav e tob emade ,i n order toarriv e atbalance d and justified ratebetwee n theutilisatio n of conventionalmean s andmoder n equipmenti nth e construction.I nor<3 ' tohighligh t the effectso f the factors named,a nexampl e ispresente d of the cost-components ofa polde r size 3,000ha ,t ob e constructed Ü1 delta-area coveredwit h tropical rainforest .

OR *• History

The following presentation ismainl y focussed upon theconstructio n of polders in therive rdelta-area s oftropica lSout hAmerica .Sinc eth e problems tob e solved areidentica lt othos e tob esolve d elsewhere, whati st ob e saidhere ,ma y thereforeb e attributed universalsignific ­ ance. Invariou spart so f theworl d technologies forpolde r construction were moreo r lessdevelope d independantfro m eachother . Forexample ,th eendikement s alongside thelarge r riversi nChina ,ca n beconsidere d asth e fore-runners ofth e technology intha tregion ,o f which laterdevelopment swer ederived . Uptil lno wn ointegratio n tookplac eo fal l theconstructio n techniques developed inth evariou scountries . Thispape raim sa ta modes tcontributio n toth e establishmento fon e universaltheor y forth e constructiono fpolders . For thestar t thepolder s inEurop e andSout hAmeric awer e considered. Theemergenc e of the "polder"i nEurop ewa st oa larg e extend alsoth e resulto fprim e endikemento farea sadjacen tt o the largerrivers . Themethodolog y and technology therebydevelope dwer efirs tuse do na largescal eoutsid e Europe,afte r thediscover yo f the "NewWorld" ,whe n Europeans attempted tosettl e inth eGuyana's ,th erive rdelta-are a between theAmazona s and theOrinoc oriver s inth enorth-easter n section ofSouth-America . Dutchan dEnglis h colonists founded ever since the17t hcentur ysettle ­ mentsalon g the largerriver s inthi sregion .An d thisexplain swh yth e firstpolder s constructed inthi sarea ,wer eexact-copie so fwel lknow n poldersfoun di n theprovinc e ofZealan d (Holland). UP toth epresen tth eorigina llay-ou to fth e earliestZealan dpolder s canb e foundbac k inth eolde rplantation s alongside theSuriname , Demeraryan dth eBerbice-rivers .However ,despit e thegrea t similarity inlay-ou tan d construction,th eSouth-America npolder swer ereferre d to as "plantation",a nam ewhic hprimaril yrefer st oth epurpos erathe r thant oth estructur e ofth ereclamatio neffort .

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Figure 1. Plantation

Three important differences can be distinguished, when comparing the emergence of polders in South-America with the emergence of polders in Europe. a) The first European polders, in particular those found inth e lowlands of northern Netherlands, originated as the result of the con­ struction of dams, which could facilitate overland communications be­ tween neighbouring settlements, situated on land sections above the floodline, named "terps".

The construction of these communication-dams between the terps, led to the complete endikement of the lowlands between these settlements. Later on impoldering followed, which had the purpose to reclaim flood- lands, laying above the average high water mark. Special "quais" were constructed as means to accellerate the silting-up proces. In the 17th century a third polder-type emerged, the so-called "droog­ makerij", which involved the endikement and artificial drainage of marshes and lakes by means of windmills and tide-locks. The construct­ ion of this type of polders was based upon economic considerations and took to a certain extend also place, as a means to protect densely

100 Populated orintensivel y farmedarea s fromperiodica l flooding andothe r inconveniences due touncontrolle dwater-movement s in themarshes .Th e iamous "Haarlemmermeerpolder "ca nb ename da sa n examplewhic h fits thisdescriptio n entirely. As such three typeso fpolder s canb edistinguishe d inth eNetherland s and inothe rEuropea ncountries ,namely : polders resulting from the constructiono fdam s foroverlan d communication betweensettlements ; Polders resulting fromendikemen to ffloodlands ; polders resulting fromth edrainag eo fmarshe san d lakes, ^s firsttyp eo fpolde r isth eresul to f technicalmeasure s primarily takent osatisf y thebasi c socialnee d formor e intensive face tofac e c°mmunicationbetwee n inhabitantso fdifferen tsettlements .Th e empol- dering of lowland cana s suchb esee na sa "byproduct "o fth e fulfill­ mento fa socia lneed . ^e endikemento f floodlandswa s aconsequenc e ofth e increased demand for farmland and settlementarea ,du e toth eincreas eo f thepopulation , omoo f theseendikement sver e alsoundertake n assafety-measures ,whic h c°uldprefen t theperiodi c undesiredintrusio no fwate r into thesettle ­ ments. s°cial factors assuc hwer e ofprim e importance with respect toth e emergence of thepolder s inEurope .B ycontras tthes e factorswer e entirely absenti n the considerationswhic hgav eris e toth e emergence of Polders inSouth-America .Th eSouth-America npolder swer e exclusively constructed onth ebase so fpur e economicreasons . The South-American polderswer eprimaril y constructed for theculti - Vation ofhig hpric e tropicalproduct s sucha ssugar ,cocao ,coffe ean d cotton,whic h could notb egrow ni nEurope . The rivers constituted theonl ypossibl ewa yo fdirec tacces s toarea s suitable for the cultivation ofthes eproducts .An d although theriver s offered vasthighlan d areas upstreams,th eEuropea n settlerspreferre d Settlementi n themarsh y downstream areas,becaus e of thehighe rfert ­ ilityo f thecla y soilsavailabl e inth edownstream ssections . ^ choice for themarsh yarea swa s justified by thefac ttha tdespit e hl9h costs forth e construction ofpolders ,economi cprofi twa slarger , because of thehighe rcro pyield sobtaine d from thefertil e claysoils . b) The second importantdistinctio n tob emad ebetwee nth e emergence ofth eEuropea npolde ran d theSouth-America npolder ,relate s toth e involvemento fmanpowe r and capitali nth epolde r construction. InEurop e capitalan d trainedmanpowe r forpolde r constructionswer e readily available.No t soi nSouth-America !Mos tsettler sha donl y limited funds forpolde r construction,whil emanpowe rha d tob eimport ­ ed inth e formo fhug e slave-forces,compose do fworker swit h noex ­ perience orwha t so-ever inpolde r construction-activities. Despite the facttha tsevera ldecade s earlier,sophisticate d equipment sucha sdredges ,excavator s and tipping cartswer e introduced forpolde r construction inEurope ,n ous ewa smad eo f theseequipment s inth econ ­ struction of thepolder s inSouth-America .Preferenc ewa sgive nt o manuallabor ,sinc e slave laborwa s far lessexpensiv e thanth eex ­ ploitation ofsophisticate d equipments.Thes e twofactor shav e led toa n entirely new approachwhic hdiffer s inman yway s substantially from the approaches topolde r construction used inEurop ea t thattime . Themos tsignifican tdifferenc e in thisrespec ti st ob efoun d inth e facttha tne w technology had tob e developed,fo r theutilisatio no f cheapmanpowe r inth econstructio n ofpolders ,instea d ofalread y known equipmentuse d forth econstructio n ofpolder s inEurope . TheSouth-America n system thusfeature d capital savinga tth e expenseo f manual labor,whil e inEurop e thetren d to substitutemanpowe r bymean s of capitalwa s alreadywel lunde rway . c\ InEurop e thesiz eo f theimpoldere d areawa sno tdirectl y geared toon e typeo fproduction .Impoldere d areaswer edevide d into sevetalproductio n units,eac ho fwhic hcoul d beuse d fora differen t typeo fproduction .Th e South-Americanplantatio n however,wa scon ­ structed asa singl eproductio n unit,wit ha specifi c production purpose. Whatwer e theprocedure s followed inth emanua l construction ofpolder s orplantation s inth eNe wWorld ? Atfirs tintereste dpartie swer eallotte d aparce lo f land,wit ha give n front-width,measure d in "Rhineland Rods"alon gon e ofth emai nrivers . Meanwhile itwa s thereby alsodecide d thatth erear-boundar y of the parcel shouldb eestablishe d afterwardsb y thegovernmen t surveyoro f thecolony .

102 The commonly allotted front-width,measure d at 50t o7 5Rhinelan d Rods. Thiswidt hwa sestablishe d withreferenc e toth edesir e to facilitate theestablishmen to fa sman yplantation s aspossibl ealon g theriver ,sinc e asa matte ro ffact ,th erive rwa s the solemean so f access toth earabl eland-areas . Thedept ho f theparce lwa sdetermine d byth edrainag epossibilities . But since therewa sa n entiredependenc y upon tidal-drainage,i twa sth e front-widthwhic h ineffec tdetermine d the totalacreag ewhic h couldb e drained effectively,a sw e shallse elate ron . Eachparce lwa sseparatel y impoldered.Th eimpolderin g included thecon ­ structiono fdike ssurroundin g theparce lan d the excavation ofon eo r moredrainage-canals .Ofte n twodrainage-canal swer e excavated alongside thedepth-border so f theparcel .Th epolder sthu sobtaine d arectangula r form,wit h theshor tsid eborderin g theriver . In thiswa y thousandso frectangula rpolder svaryin g insiz ebetwee n50 0 and 1,500 "akkers" (200-600ha) ,cam eint oexistenc e along themai n riversi n theGuyanas . The areawithi n theendikemen twa ssubdevide d intodrainage-unit so f 10-15 "akkers" (4-6ha) .Withi n thedrainage-unit sridge swer econ ­ structedwit ha lengt ho f 100-160meter san da widt ho f 8t o1 2meters . °fcours e therewa sa lo to fvariatio nwit hrespec tt othes edimensions , duet oth edifference s insoi ltype san dpermeabilit y of thesoil s tob e drained. Alongth eridges ,gullie swer edraw n (h=0,6-0,9m )whic hflowe d intoth e drainage canalsalon g thedrainage-unit . Because of theirpurpose ,drainag e canalscoul d notb euse d as"water ­ ways" for the transportation ofproduct s from thefiel d toth eprocess ­ ingcente ro fth eplantation .Therefor especia l "navigation-systems"ha d tob e constructed withinth epolders . In generalth emai nnavigation-cana lwa sexcavate d lengthwise inth e centero fth epolder .I nthi scana la water-leve l wasmaintained ,whic h Was usuallyhighe r thanth ewater-level so f thedrainag ecanals ,i n °rder tofacilitat e product transportation bymean so fbarges . Usually thismai n navigation canalpopula rname d "BANTAMAS"wa sgive n exceptionally largedimensions ,no tonl y tofacilitat ewate r transport­ ation,bu tespeciall y tob euse da sa mean s tostor ea sufficien tvolum e °ffres hwater ,fo rus ei n thedr y season.A ssuc h theBantama s hada

103 /) ./•; / /.,... /../,,

Figure 2.Plantatio n along arive r inSouth-Americ a

104 function comparable to thato fth eDutc h "storagecanals " ("boezemvaar­ ten"). Inth emai ndrainag e canala tide lloc kwa s constructed.Brick smanu ­ factured inEurop ewer euse d asconstructio nmaterial s for these locks. Thenorm s takenint oaccoun t forth edesig no f thetida lloc kwer emos t °ftenbase d uponsoun dempirica lprinciples . forinstance ,fo rfloodland s floodeddurin ga specia lperio d oftime , the "sillo f the sluice"ha d tob ebuil to n lowestknow n lowtid elevel , while thewidt h of the lockwa sa functio no f thenumbe r of "akkers"t o bedrained ,fo r exampleon e footo fsluice-widt hpe r 100akkers . Theconstructio no f sucha plantatio nwa scompletel y carried outi n manual labor,accordin g toth efollowin g sequenceo factivities . During thedr yperiod so f theyea r theare awa scleare dmanually . The remnants of the slashedvegetatio nwer estore d ridge-wise fora period of4- 6weeks . Porth e finaldestructio no f theseremnant sb ymean so f fire,a momentwa s chosenwhereb y conditionspersisted ,whic hcoul dminimiz e ailpossibl e dangers ofdamagin g theorgani c topsoilsb y theburnin g of the slashed vegetation.Th een do f thewe t seasonprove d topro ­ vide thebes tsuc hmoments ,sinc e attha ttim e thesoi lstil lcon ­ tained sufficientmoisture . Within thesam eyea r theplante r could alreadymak ea startwit h the Planting ofhi s first "cashcrop" ,i norde r torecaptur epar to fth e land clearing costsmade , ^e manualendikemen to f theallotte dparce lwa sals ocarrie d out during thedr y season.A ver yhig h degreeo faccuratenes s andprecisio n Was observed indyke-construct!on .Especiall y the "clearing and tubbing" ofsection swithi n theconstructio n limitswer ever y carefully Carriedout . A11 organicmaterial s sucha sbagasse ,grass ,root san dothe r undesired materialswer e removedb yhand .Th edyke swer eerecte dwit h thesoi l sPeciesobtaine d from theexcavatio no fth ecana lo n the innersideo f the polder-dyke. °Preven t seepagea centercor emad eo fpur ecla ywa s firstlaid ,aroun d whioh thedyk ewa s tob eerected .Thi scentercor e iscalle d the blinder". 11 compaction of theadde d claytoo kplac eb ymean so f trampling,usin g Fig. 3:

CANEFIELD LAYOUTS IN GUIANA

TRANSPORT/IRRIGATION CANAL SUPPLIED FROM "SWAMP RESERVOIR

ORAINAOE CANAL TO PUMPING STATION

106 slaves,cows ,donkey so rhorse sa s thetramplers . Theloc k inth edrainag e canalwa smostl ybuil ta fe whundre dmeter s landinward from theriverbank .Th e lockwa sconnecte dwit h therive rb y meanso fa canal,th e "lock creek"als ocalle d "sluicecreek" .Thi s landinward locationo fth e lockswa sa safety-measur e againstwav e attackso n theloc k aswel la sa securit y forth epreservatio n ofth e locki n case therive r started tomeander . Thenatura lriverbank-area ,als oname d "frontland "wa suse da s residence-area.Th efrontland sha dseparat e drainage systems.Du e toth e locationo fth efrontlan d areaan d thetyp eo flan dutilisation ,muc h more complicated criteriaha d tob eobserve d inth econstructio n ofth e frontland drainagesystems . The deforestation of theimpoldere dare acoul d takeplac edurin gth e wholeo fth eyear ,regardles so f thesoi l conditionspresent . Theweaknes so fth esoi lan dprolonge dperiod so fexcessiv eprecipi ­ tationdi d nothav e theeffect so nth epac eo fdeforestation ,whic har e at thepresen ttim eencountere d bymechanise d deforestation ofpolder - areas. At thetim eo fplantatio n construction onlymanua l laborwa suse dfo r Cutting and fragmenting oftree sa swel l asridgin g of theslashe d Vegetation.An d theslave sordere d tod othi swork ,coul d alwayswor k in thefield sregardles so fth eweaknes so f thesoil ,the yha d towor k on. •^econstructio n system used,thu sfacilitate doptima l employmento f the meanso f construction andoptima l flexibilityo f theconstruction - operations,sinc e therewer e alson odifference swit hrespec t toth e employmento f themean so fproductio n inth econstructio no f large canalsan d thediggin g ofsmalle rditche san dgullies , ^e slavesuse d forth e construction,coul dmore-ove r alsoimmediatel y be employed for thecultivatio no fth ecropland . T he pace of plantation constructionwa snevertheles s veryslow , ^e completiono fa plantatio n ofabou t60 0h arequire d atth eaverag e tenyear so f time.Needles st osa ytha ti f theslave swer et ob epai d wagesa ttha ttim e currenti nEurope ,al lconcern s shouldb ebancrupte d y thepolder-constructio nendeavours . There areonl y afe wrecord s leftt ous ,containin g onlysom eo fth e manyempirica lprinciple s andpractica lexperiences ,obtaine ddurin g thishig h timeo fpolder-constructio n inSouth-America . Because ofth e sorrow state ofou rhistorica l records inthi srespect , only thephysica l remnantso fth eplantation s in theGuyanas ,ar e left tou sa ssilent ,fores trampante dmonuments ,i nmemor y ofa marke d era in thehistor y of thepolde rphenomenon .

2 Consideration forpresen tpolder-constructio n endeavours

Inth e foregoingw ehav e spentquit e someattentio n toth emanuall ycon ­ structed "Polderso f theWorld" . Inthi spresentatio nmanua lconstruc ­ tiono fpolder s issee na son eo f theextreme s fromwhic h thepolder s phenomenon canb e reviewed.Th eothe r extremei st ob e found inth e presentwa y ofpolder-construction ,whereb y thejo bi salmos texclu ­ sively doneb ymean so fheav yequipments . Inbetwee n these extremes alo to fvaration s canb e found,usin gbot h manual laboran dequipment s simultaneously,bu ti ndifferen tratios . Insparsel ypopulate d countriesmechanisatio n isofte nth eonl y alternative,becaus e ofth escarsit y ofmanpower .I ndensel yover - populated countries,suc ha sfoun d inSouth-Eas tAsia ,th e utilisation ofmanua l labormus tb egive n considerance for largepart so fth e impoldering works,a sa mean st ofacilitat e thepopulatio n tobenefi t directly fromth e constructionefforts . At the same timei tmus tb eals oconsidered ,tha tth edeman d forreadil y cultivaleable croplands isals oextremel y large inessentiall y thistyp e ofcountries ,whic hma ywel l lead tolimitation s inth eutilisatio no f thevas tamount so fmanua l labor available,i nfavou ro f theoptima l utilisationo fequipment s for certainsection so fth e job,a sa measur e tospee du p theconstructio n operations anda sa measur e to satisfy the need for farmland inth eshortes tpossibl eperio do ftime . Butregardles so f thekind so fth econsideration s tob e takenint o account,decision s concerning theinvolvemen to fmanua lworker svi z equipments,wil lalway shav e tob emad ewit h reference toa contex to f soundprinciples ,t ob eobserve d inorde r toobtai noptima l realisation- efficiency atth elowes tcosts .

Inthi s section arevie wi smad eo f themos timportan telement sa tpla y incontemporar ypolder-construction .Th e factors tob e considered,wil l

108 beanalysed ,usin g asbasi c comparativeparameters : a.TH E PACEO FCONSTRUCTION ; b.TH ECOST SPE RAREA-UNIT . Needless tosa ytha tth eanalysi san d comparisonspresente d herear e both farfro m complete andfa r fromexhaustive .

2-l Thephysica l environment

It seemsquit e justified toassum e thatal love r theworld , thearea st o beimpoldere d are composed by landswhic har emor eo rles spermanentl y submerged.A sa consequenc e thesoil so f thesearea sar emostl yno t fully consolidated andma yofte nb equit eyoung . Theborder so f theare a tob eimpoldered , shouldb edetermine d onth e baseso fa soun d analysis ofprevalen thydrologica lconditions . strict observation ofth ehydrologica l conditions is theprim e andfore ­ nst importantrequirement ,t osecur e aprope rpac e andleas tcost so f theconstructio n activities. The randomobstructio n of the naturaldrainag e ofsurroundin g areas,ma y cause a loto f complexproblem sbot h during theconstructio nperio dan d afterwards. AH efforts should therefore bemad e toobtai n themos taccurat ein ­ sights concerning thenatura ldrainag e system and the topographicalan d Vegetational characteristics ofth eare ab ymean so faeria lphotograp h analysis. In any caseprio r toth einitiatio no f thepolder-constructio n a thoroughappraisa lmus tb emad eo fth efollowin gfactors : ~ Climate :Th e course ofannua lprecipitatio n and theidentifi ­ cation ofdr yan dwe tperiods . ~ Hydrography :Th e location ofswamps ,cree kan d rivercourses , gullies and tidaleffects . ~ Soil :Topography ,presenc e ofsof tlayer san dperviou s soils,possibl epresenc eo faci d sulfatesoils . "" Vegetation :A n analysiso f thevariou s typeso fvegetatio nan d vegetation layers,t ob e categorized forexampl ein :

109 :- dense forest medium forest scrub Vegetation herbalvegetatio n andgrasse s Accessibility :Al lpossibl emean so facces swil l havet ob e surveyed withemphasi so n theanalysi s of factorso flogis ­ ticalsignificance . Management :Analysi so fanticipate d social,economi c andtechno ­ logical situationswhic hma y affectbot hpolder - construction andpolder-maintenanc e activities as wella sdecision s concerning centralised or decentralised control.

Although the factors justmentione dma y seemrathe r self-evidentaffair s inpolder-construction ,i tappear s inpractic e thatthe yar eofte nin ­ sufficiently orno ta tal lobserved . Water-annoyance during theconstructio n and subsequent saggingo f machines,logistic sproblem saffectin gpersonne l transportations,fuel s and food supplies,an dpoo rworkin g conditions due toincorrectl y selected campsites areonl y someo f theman yproblem s tob e faced,a sa consequence ofneglectin g the forementionedfactors . Quite often theneglec to fa prope r approach towards the factors mentioned alsoresult s inwron g choices ofequipment s- choosing either toosmal lo r too largemachines . Suchneglect s leadt oba dplanning ,whic h inman y instances results into theescalatio no f construction costsb yhundred so fpercents . Extensive confrontation with suchproblem s and cost-escalations,i son e of themos toutstandin g aspects ofpolder-constructio n inth edelta - areaso f countries asBrazil ,Guyana ,Venezuela ,Thailand ,India , Bangladesh,Birma ,Vietna m andIndonesia . Itwoul db eerroneou s tothin k thatth e factorsname d areno to ro fles s relevance forpolder-constructions ,whic h takeplac ei na somewha t differentphysica l environment.Th erelevanc epertain s toal lth ekind s ofphysica lenvironment s ofpolder-construction . And topoin tou tanothe r exampleo fa physica l environment towhic h these factorsals oapply ,referenc e canb emad e toth eHachir oGat o polders inNorther nJapa n andt oth epolder si nth ePeople sRepubli co f

110 ÇP^T-*: *W»'W»r » 'W* »•"** ii

i » ****i^;

Figure4 . Aerialphotograp h of -Y€f •**imifca.ia^*MfcMaÉ^lhM— "ITMIWI mfmiiir flood lands

Fig. 5: Rainfall and évapotranspiration in Tropical hurud regions

Rainfall Paramaribo

111 Figure 6. Deforestratec r area

.» "f "VA C

Figure7 . -N#" '4i f Equipmenti n »«•Jk« *•»• rainyseaso n , •* y •*ii.

r--,v v* -

• ft *t.

. *•• . *

e. Figure8 . • •• f Logistics

112 (North)Korea .I nbot h countries thepolder-construction s were carried outi ninlan dsea-areas . Thewate rbalanc e inrelatio n tosalinity ,constitute d themos t importantfacto ri ndeterminin g of thesiz ean dboundarie s ofthes e Polders,whil e asothe rprim e factorst ob e taken intoaccoun ti nth e construction ofthes epolder s the following canb enamed : Permeability of thesoils ; desalination; soil compaction andseepag eo fsoils . Thetw otype s ofphysica l conditionsmentione dnamely : thedensel y vegetatedmarsh y tropicaldelta-areas ,an d inland-seas, canb esee na stw oextrem e typeso fphysica lconditions ,whic hdespit e theirdifference s require the totalobservanc e ofal lfactor snamed .

The carefull examination ofth e conditionspresente db y thephysica l environment,i s alsoo fmajo r importance forth echoic eo fpolde r design,th e choiceo f construction methods and forth edeterminatio n of thedegre eo fmechanisatio n of theconstructio noperations . Irith edelta-area sprope rmechanisatio no f theoperation sma yb ebes t Pursuedb y theinvolvemen to f conventionalmachine s such asbulldozers , dr aglines andhydrauli c excavators,whil e inth ecas eo finland-sea sth e main infrastructure canb ebes trealize db yth einvolvemen to fdredges .

F°r aprope r approach iti so fcours e necessary totak eals oothe r asPects intoaccount ,whic h areno tdirectl yrelate d toth ephysica l environmento fth epolde r area.Som eo f thesocio-economi c aspects tob e studied forthi spurpos ewil lb ereviewe db y thenex tsection .

2.2 „ • Ä Socio-economic aspects

Allove r theworld ,th econstructio no fpolder swil lhav e tob e Proceededb y ananalysi so f thesocio-economi c conditions,prevalen ti n the countrywithi nwhic h the construction ist otak eplace . Substantialinfluence s areexercise d uponth epac eo f construction activities and thecost so f thepolder-constructio n by factors suchas :

113 localexperience s inpolder-construction ; distribution of technicalknow-how ,skill s andexperienc e inmachin e operating andmaintenance ; employment conditions and customso femployer s andemployees ; wage levels andwag estructure ; time-usepattern so f skilled andunskille dmanua lworkers . Iti so fprim e necessity toobtai nreliabl edat ao fthes e factorsi n ordert ob e able tomak e aprope r assessmento fsocia lconditions ,whic h affectver y seriously both thecost s andth eduratio n ofth epolder - construction,a swel l asmatter s such as thedegre e and levelo f mechanisation tob e applied in theconstruction . Iti stherefor e no luxury tohir e awel ltraine d socialscientis twit h considerable field experiences tod othi sjob . Incas eth eloca lexperienc eprove s tob elimite d tomanua l operations only,o rt ooperation s involving traditionalequipments ,a progra mmus t bemad e for the completiono f theproject ,whic hha s taken these realities intoaccoun ti nth eselectio no f the levelo fmechanisatio n to be observed. If thepolde rwoul db e constructed inprett ymuc h thesam ewa y asdon e by thepopulatio nu pt otha ttime ,onl y relatively smallacreag e of arable landwoul db e reclaimedi n agive ntim eperiod .Th e satisfaction of thenee d for farmlandwoul d assuc h require anexcessivel y long periodo f time.B y contrast ahighl ymechanise d approach couldresul ti n a veryhig h levelo farabl e landrealisation .Bu ti ti sno texclude d thatsuc h anapproac h doesno tconcu rwit h theinterest s of the local population,becaus e ofth evas tnumber so fmanua lworker s thatwoul d have tob epu tof fside . Programplannin g forpolder-constructio n assuc hinvolve squit e alo to f exercises incompromisin g the twosocia l interests named,i nrelatio nt o factors sucha spac e of theoperation san d levelo fmechanisation . Solutions forsuc h "conflicting interests"ma yb e foundb yvariou s forms ofdivisio n of labor,linkin gth einvolvemen to fmoder nmachine s toth e construction of larger andmor e comprehensive worksmeanwhil e assigning thedetailment so f the construction tomanua lworkers . Such approachesma gpossibl ymak eth eachievemen to f thehighes t level ofmechanisatio n illusive froma technica lpoin to fview .On emus thow ­ ever consider thati n thiswa y asociall y acceptablebalanc e canb e

114 found,providin gbot h the timely completion ofth econstructio n onth e °lehan d and ample opportunities foremploymen tan d training ofloca l workerso n theothe rhand . •tnselectin g themachine st ob einvolve d inth e construction,attentio n Oustb epai d tosuc h factors aspost-constructio n exploitation ofth e equipment,fo rexampl ei nmaintenanc e activities andpossibl y alsoi n otherconstructio n activities,t ob epursue d in forthcoming timesb yth e country. Flnally inquires should alsob emad e todetermin ewhethe ro rnot ,an di f s°t owha texten dworker sneede d for theconstructio nwil lb eavailabl e auring theseason smos tsuitabl e forth erealisatio n ofth econstruction , tma ywel lb etha t theseperiod s co-incidewit hothe ractivitie so fth e Population,suc h asplantin g orharvestin go fcrops ,dwellin g construction and thelike .

•3 The relationsbetwee npolde r designan d thepac e and costs ofpolder-construction s

^ topography ofth e areat ob e impolderedconstitute s thebase s for 016 polder design.Bu tbecaus e offactor s sucha sth epac eo fcon ­ duction and thecost spe rarea-unit ,othe r factors,amon gwhic h the °Howingmus t alsob e takenint oaccount . dimensions ofcanals ,conduit s andparcel-ditche shav et ob e standarizeda smuc h aspossible ; cross-profiles ofcanal setc .hav et ob eatterne d toth emachine st o beused ,s ot osecur e theobtainmen to fth ehighes t levelo f efficiency; thevolum eo feart h speciesneede d forth econstructio n ofdam san d road foundations,ha st ob e useda sdeterminin g factor forth e establishmento f thedimension s ofexcavations . (Thisma yresul ti n dimensions forth evariou stype so fexcavation swhic h areno ti n accordancewit h theoutcome so fhydraulogica l calculations.) irregularly shapeso fparcel smus tb e avoided! (mechanised)cro p Productions require regularshaped-preferabl yrectangula rparcels ,t o be obtainedb ysomewha tmor eo fland-leveHin gi fsuc hi snecessary . The finaldesig no fa polde ri stherefor e obtainedb y cross-comparingo f theadvantage s anddisadvantage s of the followingprinciples . a) Size of the smallestpolder-uni t

The costspe r area-unito fth epolde r increase relatively toth e average-costs toth e extend thatth e sizeo f thearea-unit si sdecreased - Thisi sdu e toth e considerable increase of tertiary infrastructure, which also limitsi.e .decrease s thepac eo fth epolder-construction . Basically polders of thesam e size requireidentica lperiod s of time for construction.Difference s in construction timear eprimaril y causedb y differences between theparcellin gsystems . Thesmalle r thepolde r the larger the costspe r area-unit. The costspe r area-unit (parcel)o f thepolde r increase relatively to average area-unit costs,t oth e extend thatth esiz eo fth e area-units isdcreased . Thisi sdu et oth econsiderabl e increase oftertiar y infrastructure, which increases construction-costs anddecrease s thepac eo fth epolder - construction. b) Overlandversu snavigationa lwithin-polde r communications

A choiceshal lb e madebetwee n aroadssyste m andnavigatio n canals,a s means tofacilitat e thehaulin go fgoods/product s toan dfro m the parcels. Incas eo fchoosin g fora navigatio nsystem ,thi swil lmeanwhil e also require achoic e tob emad eou to feithe r drainage or irrigationcanals , tob emad esuitabl e forthi spurpose .I nconsiderin g thesealternatives , comparative evaluations have tob emad e ofth e followingfactors : construction andmaintenanc e costso froads ; - costs ofcana l adaptations such asraisin go fquai s andbridges , construction ofducts ; - enlargemento f thewe tprofil e ofcanal s andsubsequen t extra excavationcosts ; - purpose of thepolde r (smallholding spolde ro r single estatepolder) • c' High levelo r lowleve lwate rpresentatio n

•^ewate r levelt ob emaintaine d in theirrigation-canals ,wil lin ­ fluence the construction andexploitatio n costso fth epolde r toa con ­ siderable extend. Hlgh levelwate rpresentatio n requireshighe rdams . This implies that toreeart hwil lhav et ob eexcavate d thannecessary ,accordin g to hydraulogicalcalculations .Fo ra lowleve lwate rpresentatio n less e*cavatingi srequire dbecaus e theprofil e tob e constructedwil lb ei n closerapproximatio n toth eoutcome so fth ehydraulogica lcalculations .

secondconsideratio n isth edegre eo fefficien twater-utilisation , Slnce the farmerswil lwast e a loto fwate ri ncas eo fhig h level Presentation,whic h isi ncontras twit hth eutilisatio n ifa lowleve l Presentation ismaintained ,whereb ypumpin g costs are tob epai db y the farmer. n theexploitatio n phase centralpumpin gan dhig h levelpresentatio n mayprov e tob e far lessexpensiv e than low levelpresentatio n and lriclividualpumping . n the lastcas e the farmers themselveswil lhav e toaccoun t forth e Pumping costs,whic h ineffec tonl y impliesth eshiftin go fsom eo fth e costs.

Political factors

Ne*t toth evarious ,physical ,technica lan dsocio-economi c aspectsth e esign and construction ofpolder s isals osubstantiall y influencedb y Vari°us typeso fpolitica l decisions,o fstat e andloca lgovernments . n thedensel y forested delta-areas thegovernmen twil lhav e todecid e wh ether orno tth efarmer swil lb e allotted either readily cultivaleable °r Partly orwholl y forestedparcels ,t ob e cleaned upb y the farmers int*ividually. ext toth efac ttha tabou t1 5t o2 0percen to f theinvestmen tcost sar e tr anSferred toth e farmers,b yallottin g thempartl y orwholl y forested Parcels, otherdisadvantage so findividua l landclearin gmus tals ob e Considered.T onam ea few : Theperio d of landimproductivit yo f theimpoldere d areawil lb e extended substantially,sinc e the farmers canonl y startwit h the clearing after the completiono f theconstructio n and aftercomple ­ tiono f theprocesse s ofparcellin g andallotment .An d thosepro ­ cessesma y take a loto ftime ,mainl ybecaus e ofextensiv epolitica l deliberations proceeding them. If thepolde r isdelivere d during aperio do funfavourabl eweathe r conditions,th e farmerswil lhav et opostpon e theclearin g activities forrathe r longperiod so ftime . Thecontracto rha s theopportunit y tosecur eth e landclearin g ina highly centralizedway ,th econstructio nperio dwil l include several suitable seasons,facilitatin g the contractor tocommenc ean d continue the clearingoperation s according toweathe rconditions . The clearing costsmigh tb ehighe r inindividua lclearin go fparcel s since the clearingha s tob epursue db ymean s ofworker swhic h area t the time ofclearin g alsomuc h indeman db y other activities (harvesting etc.). Individual clearing activitiesma yresul tperiodicall y inover - demands forrelativel y scarcely availablemachine s andothe r equipments. - The farmers loose atleas ttw ocro pseason s i.e.tw ocro pharvests . Theinteres tperio d ofth e investments forclearin g isextende dwit h at leaston eo rtw oyears . Thedecisio n toallo teithe r forestedo r clearedparcel s toth efarmers / iso f course influencedb yman yothe rpolitica lan d socio-economic factors. Nextt oth e financing termsb ywhic h fundsar eallocate d forpolde rcon ­ struction,i ti sth eprim esocio-economi c roleo fth epolder ,whic hmus t besee na sa majo rimportan tfacto rwit h substantial effects uponth e decision tob emade ,concernin g theclearin gcondition so fparcel s tob e allotted tofarmers . Ifth epolde ri s constructedprimaril y asa mean s forth erapi d solution ofnationa lfoo dconstraints ,i tappear s tob emos t recommendablet o allotreadil y cultivaleableparcel s toth e farmers.I nthi swa yn o harvests are lost,whil e theeffect so f theinvestmen t canb emad e readily sensible tomajo rsection s of thepopulation .

118 In countries suffering fromforeig ncurrenc yconstraints ,allotmen to f forestedparcel sma yb e seena sth eonl ywa yt ofinaliz e thepolder - construction,o ra sa mean s tosav esom eo fth e foreigncurrencies , otherwiset ob euse d for thepurchasin g offuel san dsparepart s for machines. ^e considerations should notb e limited toonl ymacro-technica l financial andsocia laspects . ^e decision concerning theallotmen to feithe r forested orcleare d Parcelst ofarmers ,ha s alsot otak eint oaccoun tth e socio-economic Positiono fth e individual farmersa swel la sth esocia leffect s ofeac h of these twoalternatives ,i norde r toavoi dproblem ssuc ha sth e following.- n anIndonesia n landreclamatio nproject ,farmer swer e allottedrice - Parcelsstil lcontainin g stumpsan d trunkso flarg etrees ,leavin gonl y a sparse amounto fope n land forth ecultivatio n ofrice . ecause of thealmos tstil lto omodes tparcel sallotte d inthes e regions thistyp eo fallotmen tcoul d easilyhav ebrough tth e farmers existence lntoperil ,sinc e thene tcultivaleabl e areao f theparce lwa si neffec t re

119 policies followedb y the cooperative Republico fGuyan aan d those chosen by itsneighbour ,th eRepubli co fSuriname . Land-reclamation inGuyan ai salmos tentirel y financedb ymean s offund s obtained atrelativel yhig h interestrate s frominternationa l financing institutes.I nSurinam eth e land-reclamations are financed outo ffunds , donated freeo fan y chargeb y theGovernmen t ofth eKingdo m ofth e Netherlands- theforme r rulero fthi scountry . TheGuyanes e Governmentha sexplicitl y chosen fora napproach ,whic h secures high speed,efficien trealisatio n ofth epolders . Two large land-reclamationproject s are executed atth esam e time,eac h controlledb y aseparat e special appointedauthority ,wit h full fledged decision- andoperationa lcontrol . TheM.M.A.-authorit yi scharge dwit h thereclamatio no f anare ao f 50,000ha ,situate dbetwee n theMahaica ,th eMahaicon yan d theAbarr y rivers.A tth esam e timea secon d largepolde r- theBlac k Bushpolde r- isconstructe d inth eare abetwee n theCanj ean d theCorantyn eriver , underdirec t controlo fa differen tGovernmen t authority. In theM.M.A.-project ,th ereclamatio nwork s arecommissione d toon e contractor supervised by oneconsultant .Bot h areoblige d tocomplet e the total land-reclamationwithi n the shortestpossibl eperio d oftime . The approach results insimpl ean dver ystraigh t forward relations between theauthorities ,th econsultan t and the contractor,meanwhil e alsosecurin ghig h speedan d efficientcompletio n of theconstructions . Inm y opinion theGuyanes e approach appears tomak e a loto fgoo dsense . By contrast toth eGuyanes ehig hspee d construction endeavour,th e approach appliedb y theSurinam eGovernmen ti n the realisationo fth e "Multi-Purpose Corantyne CanalProject "- MC P- ,feature s a continuously ongoing concern,t osegregat e the constructionint oa sman y smallitem s aspossible ,t ob e commissioned toa sman y aspossibl econtractors . Controli sal lbu t firmly established inth egovernmen t agency charged with the coordination andsupervisio n ofth econstruction ,sinc e several other governmentinstitution s arestil l lefta voic e inth edecision ­ makingprocess .

Duet othes e factors thepac eo fproject-realisatio n isslowe d downcon ­ siderably andbecaus e ofth eto oslo wan d toosluggis hpac eo f realisation,constructio n costsescalat e substantially.

120 ^neSurinam eGovernmen tha sno w reduced the totalare a tob e impoldered as ameasur e tokee p theprojec tcost s inbalanc ewit h the available CaPital funds forth eproject . Withreferenc e toth e forementioned aspects and situations,i tma yb e statedtha tth econstructio n ofpolder si n thedevelopin gworld ,ha st o takeplac ei nsuc h awa y thata readil y cultivaleablepolde r canb e ot>tained,b yobservin g allfactor so finfluenc eupo nth ecost s andth e Paceo f theconstruction . ^is objectivewil lhav et ob eenforce db y allcircumstance s andregard ­ as ofth eway s inwhic h and thecondition sb ywhic h fundswer e stained forth e construction. In finalsom ebroa d remarksma yb emad e concerning the executiono fth e instruction activities.Mos timportan ti n thisrespec ti sth e choice etweeninvolvemen t of the localpopulatio no nth eon ehan d orth ein - v°lvemento fa foreig n contractoro nth eothe rhand . As theconstructio no fpolder s requires aver y specificknow-how ,i tma y e recommendablefo rcountrie swit hn oexperienc e inpolder-constructio n to startwit h foreign contractors rather than taking anotherapproach . Af ter the initialtransfe ro fknow-ho w joint,venture sma yb e considered as anex tste pi n theswitc h toth econstructio n ofpolder sb y local c°ntractors. At lastbu tno t atleast ,muc h attention shouldb egive nt opromot eth e WiUingness of the farmers toadap tthemselve s toth ene wproductio nan d Vlng circumstances.

Financial aspectso fpolder-constructio n ina densel y forested tropical delta-area

n conclusion ofthi spresentatio n anexampl ewil lno wb epresente d of th ne constructiono fa middl e sizedpolde ri na densel y forested,marsh y r°Picaldelta-area .Th eexampl e isfictitiou s andi sonl ymean tt o 1austrät e the costsinvolve d inpolder-construction .Th e assumedpolde r Masures 5,000-6,000meters . 1 tooofte ni toccur s atth ecommencemen to fsuc hprojects ,tha tn o 11105:6tha nincomplet e costsar epresente d andtha tth e"disappointments " as nientionedi npreviou s chapters,i nfac td oresul tint omor e extensive

121 financial consequences thanw aassume d atfirst . By the following table arevie w ispresente d ofth ecost s forth e realisationo fa polder ,generall y named "constructioncosts" .

Tableo f totalprojec t costsi n%

1 Constructioncost s 100 % 2 Contingencies à (15%) 15 % Sub-total 115 % 3 Engineering costs (13%) 14,95% 4 Legalan d administrative costs (3% ) 3,45% Sub-total 133,40% 5 Financing costs (3% ) 4 % Sub-total 137,40% 6 Interest during construction (6% ) 8,24% (interesti n 1year ! Totalprojec tcost s

The tableshow stha tth ecost s for theso-calle d "additionalelements " canamoun tt oalmos t5 0percen to fth e constructioncosts . The sizeo f theso-calle d"contingencies "depend supo nth estag eo fcon ­ structiono f theprojec ta tth etim etha tth eestimat ewa sprepared . Atenterin gint oth e financingo ra tth e application fordevelopmen t aid,referenc eshoul db emad e toth eabov ementione d cost-alignment, whichmus tb e seena sa naverage ,calculate d onth ebase s ofdat a obtained froma largernumbe ro fpolder-projects . Foreac hprojec ta separat eanalysi smus tb emade ,t odetermin eth e extendo fapplicabilit y ofth eitem sinclude dint oth e costs-alignment mentioned,becaus e thetabl epresente d assumesprojec trealisatio nb ya private contractor. Amor e extendedeleboratio no fth e "polder-construction costs"show s that thereals oexis tver ymarke ddifference sbetwee n the "directcosts " andth e "finalcosts" . The "direct costs"ar ename d "netcosts "i nth efollowin gan dca nb e specified asfollows : - generalpreparations ; - plottingcosts ;

122 - endikemento f totalarea ; clearance oftract san dexcavatio no fconduits ; road constructions (unpaved); ~ primary engineering constructions; secundary engineering constructions; ~ parcelling including deforestation. To thesene t (direct) costs,th egenera l costs forth eexecutio nafte r contractinghav e tob e added.Th e followingreference sma y servea guid e linesfo rth e costst ob e considered in thiscontext .

Item Percentage/costs ~ netcost s 100 ~ general costs 6.7 ~ construction costs 6.0 ~ management costs 3.2 - mobilisation,demobilisatio n andtranspor - 8.3 tationcost s Sub-total 124.2 Risks and profits (assumed at 15%) 18.6 TOTAL COSTS 142.8

Irith epreviou s table the "construction costs"wer eassume d at100% ,bu t inrelatio n toth ene t costs,constructio n costsd oamoun tt o1.4 2 times theestimate .A ssuc hth e finalpictur eo fne tcost sreveal sth e following

Netconstructio n (nettoaanleg ) 100 % Netdirec t costs (construction costs! 142.83% Projectcost s (1yea rconstructio nperiod l 208.01%

"^eenginee ri stherefor e compelledt ofocu shi sattentio n atal ltimes , uPon thepreparatio no faccurat e cost-estimates,whic hhav e topresen t a complete and correctpictur e ofth etota lcosts ,i norde r toavoi dhi s Principalt ob econfronte dwit hembarrassin g surprises,a tth eda yo f Project-delivery.

123 The following costs-estimate canb epresente d forth eimaginar ypolde r size 3,000ha ,t ob e constructed ina densel y forested,marsh y tropical delta-area. The costs arebase d uponexperiences ,obtaine d inric epolder san d bananapolder-constructions .

Polder-construction costsi n 1982 (example)

Item Description ofwor k Costspe rh a (gross) inUS $ 1 Generalpreparations ,surveyin g etc. 250.- 2 Endikements 250.- 3 Tractclearin g andcondui texcavatio n 750.- 4 Roadpavement s (upt oth eparcels ) 750.- 5 Primary engineering constructions 1,000.- (irrigation) 6 Secundary engineering constructions 750.- (culverts andbridges ) 7 Deforestation, levelling,clearing / 1,500.- grubbing A Construction costs 5,250.- B Projectcost sincludin g financing, _1 supervision,interes t 24% 1 Multipliedb y 170.36 duet oth eaccumulatio n ofinteres tdurin g the fouryea r constructionperiod .

From thepreviou s table itappear s thatapproximatel y 50%o f thecost s for the construction ofa ne wpolde r isabsorbe db y the deforestation of thearea . These costs areextremel y sensitive foreffect s ofth e factorsmentione d inchapte r2 . The remaining works such as engineering construction, road pavings are less affected by some of those aspects.

Note

1 R.R. = 3,6764 m

124 References

Benjamin, dr. H.D. and Joh. F. Snelleman, 1914, Leiden Encyclopedie van Nederlands West-Indië Consortium M.C.P., 1978, "Multi-Purpose Corantijn-Projekt, Voorbereiding FASE I Consortium M.C.P., 1982, Adviezen B1-B8, definitief projekt P-A.0., 1988, Survey of the Canje Reservoir Scheme Guyana Lier, prof. R. van, 1971, Samenleving in een grensgebied Rodney, Walter, 1979, Guyanese Sugar Plantation in the late 19th century Surinaamsche Historische Kring, juli 1968, Uit Suriname's historie Surgroma N.V., 1977, Vooronderzoek bevloeiingsmogelijkheden Regio 2 - Suriname Teenstra, M.D., 1833, De landbouw in de kolonie Suriname Traa, mr. A. van, 1946 Suriname 1900-1940

125 AGRICULTURALASPECT S

AGRICULTURAL ASPECTS INPOLDE R AREAS INTH ENETHERLAND S J. vande rVee n Landbouwschap TheHague ,Th e Netherlands

I amgla d tohav e this opportunity,a sChairma n of theLandbouwschap , to tellyo u something about the agricultural aspects ofpolde r areas in this country.Firs t of all,I thin k Iough t totel lyo u something about theLandbouwscha p itself.

The Landbouwschap

TheLandbouwscha p is thepubli c cooperation of the agricultural employers'an d employees'organization s inth eNetherlands .W ehav e three employers'organization s - thebigges t is theNetherland s Catholic Farmers and Growers Union (K.N.B.T.B.), then there is theGenera l Royal Netherlands Agricultural Committee (K.N.L.C.)followe d by theProtestan t Farmers'an d Growers'Unio n (C.B.T.B.),o fwhic h Imysel f amals o Chairman.Aroun d 80%o f the 140.000farmer s and growers in this country are affiliated toon e of these organizations.Th e agricultural em­ ployees' areorganize d intw o sectoralunion s -th eFoo dWorkers 'Unio n F.N.V.an d theFoo dWorkers 'Unio nC.N.V . *' These 5organization s have astatutor y organization - ascentra l agri­ cultural organization,recognize d byDutc hLaw .Th e Board ofth e Landbouwschap ismad eu p of representatives from all5 organizations . The Chairmanship atpresen t rotates between theChairma n of thethre e farmers organizations.Themember s of the agricultural organizations are perfectly satisfied with thisuniqu e form ofcooperation . TheLandbouwscha p acts asa mouthpiec e forDutc h agriculture asa whole,an d it is indeed recognized assuc hb yGovernmen t and Parliament.

*)F.N.V .= th eFederatio n ofNetherland s TradeUnio n C.N.V.= theChristia n Netherlands TradeUnio n

126 Thepositio n offarmin g inth eNetherland s

Ihisbring sm et oa fe wremark s about thepositio no fagricultur ei n theNetherlands .Ou rcountr y issmall ,densel y populated andwel lknow n f°r itswindmill s andcheese .It stota l areao fagricultura l landi s about 2millio nha . Everyyea r someo ftha t areai slos t toprovid e land forothe rpurpose s sucha shousin g andrecreation ,an dsom ei sdesignate d asnatur e area, "his lossamount s toabou t 10.000h aever yyear .

In 1950n ofewe r than 17%o fth eDutc hworkin g populationwer e employed inagriculture .Toda y that figureha sfalle n to6% . Nevertheless thesignificanc e ofth eagricultura l sector forth eDutc h economyha sincreased . Inspit eo fth ereductio n inth eare ao f agricultural land andth efal l innumbe ro fagricultura l holdings -w e n°w have 145.000- agricultura l outputha drise n substantially.A considerablepar t ofthi soutpu tha st ob esol d abroad.

Let megiv eyo ua fe wfigure s toillustrat e this.I n 1981th eNether ­ landsexporte d agricultural productswort h 31milliar d guilders.Thi s ^creased thesurplu s onth eagricultura l tradebalanc et o14. 7 nilliard guilders.Thi s contribution toth eDutc h economymatche s that madeb yth eexport s ofnatura l gas.Dutc h agriculture issmall-scal eb y nature.Th eaverag e sizeo fth eholdin g- excludin g horticulture -i s 18ha .Thi s small-scale character isoffse tb yth elarge-scal enatur e of theancillary ,manufacturin g andmarketin g sectors.I nthi sstructur e of small-scale holdings andhighl y concentrated marketing liesth e 8feat strength ofDutc h agriculture. ne agricultural land isuse d very intensively.Th ene tadde d valuepe r na ofagricultura l land isalmos t4.00 0guilders .Tha t isove r 35.000 guildersfo rever y agriculturalworker .An dtha t intur n is20.00 0 Gildersmor e thanth eaverag e figure forth eEEC .

lnce the 1950seac hh ao fagricultura l landha sbee nuse d toa n lncreasingly intensive extent.Fo rarabl e land,th epercentag eo f abour-intensivecrop s- potatoe s andsuga rbeet s- ha srise n from24 % ° over 40%.Sinc e 1960th enumbe ro fdair y cowspe rh ao fgrasslan d

127 has increased by 50%.Th e average stocking rate iscurrentl y 1.76 dairy cowpe rha .Th emil k production perh ao f grassland has risenb y 88% in2 0year s and isapprochin g 10.000k gpe rha .

Polder areas inth eNetherland s

Thisbring sm e toth e subject ofm y talk.Polder s in relation to agriculture.Mr .Schult zha s already shownyo u an interesting table explaining the three different kinds ofpolder s tob e found inth e Netherlands.H e told you that of the total 3.4millio n ha ofDutc h land, 2millio n ha arepolde r land.Tha t is tosay ,lan dwhic h isenclose d by adyk e andwher e thewate r level isartificiall y controlled.

Thegreate r part of this land consists of low-lying peat land and the oftenno t easily accessible clay land around thebi g rivers.Th e second group consists of former lakes shichhav ebee n drained,an dwhic h account for 315.000ha . The third group ismad e up of theempoldere d parts of the sea,totallin g 350.000ha .Th e agricultural production potential of this land isclo ­ sely connectedwit h thewa y inwhic h the landwa s empoldered and brought intocultivation .

From thisrevie w it isclea r that aver y largepar t ofDutc hagricul ­ tural land lies inpolders .Th ewa y inwhic h thepolde r originated,th e conditions ofwate r control,distributio n ofplots ,an d of course the type of soil arever y important determining factors for the production potential for agriculture.I wil l explain this ingreate rdetail .

Thehistor y ofDutc h farming hasbee n largely dominated by the struggle againstwater ,th e formationo fpolder s and thepossibilit y ofcontrol ­ ling thewate r level in thosepolders .Thi shistor y isreflecte d to thisda y in the life story ofman y Dutch farmers.Indeed , Imysel f can tell such astory .

Iwa sbor no na "terp" ,a dwellin gmound ,i nFriesland .Gre wu p ona farm inon eo f thene wpolders ,th eNorth-Eas t Polder,4. 5 mbelo w sealevel,wher em y father decided tostar t ane w farm,an d Ihav e in

128 fact spent the greater part ofm y life ina polder . The "terpen"o f theNorther n Netherlands are artificial dwellingmounds , whichwer e used asa refug e for thepopulatio n intimes ,whe n storm tides flooded the country,befor e itwa s protected bydykes .

Whatkin d of alif edi d our ancestors lead?The y lived inconstan t strugglewit h the sea,whic h provided themwit h fishan d deposited fertile silt,bu t at thesam e timerepresente d anever-presen t threat as thesea-leve l rose.I f these aencroache d upon the land,th eharves t was lost and the landwa s inundatedwit h saltwater .Regula r farming onlybecam e possible after seadyke sha dbee n constructed.

A seadyk eprotect s the land from thedange r from flooding.Howeve r the fact that thebuildin g ofdyke sdoe sno tmea n that all thedanger shav e been conquered isprove d by the long listo fdyk ebreache s andfloods . 1 need only remind youo f thenigh t of 1stFebruar y 1953,whe n the dykes in the South-West of this countrywer ebreache d and thatpar to f thecountr ywa s inundated by theNort h sea.Thousand s ofpeopl e drowned, ar>dman y cattlewer e lost.Hunderd s of farmswer e destroyed. The land Was coveredwit h saltwater .Year s afterwards,th eeffec t of thiso nth e structure of the soil remained noticeable insubstandar d cropyields . This disastrous night resulted in therigorou s decision torais e the height of allou r seadyke s and shorten the length of our coastline . (Thisamount s to locking thestabl edoo r after thehors e isstolen .A s amatte r of fact theDutc h saying ismuc hmor e appropiate inth econ - text. Literally translated it runs: thewel l isonl y filled inafte r the calfha s drowned).

Agriculture inth e "lowpolders "

Itlth epast,th e low-lying peat landwer e surroundedwit h lowdyke so r einbankments inorde r toprotec t them against anexcessivel y highwate r Ievel. Forman y centuries,th egroun dwate r inthes eextensiv e regions Was maintained at aver yhig h levelb ymean s ofwid e ditches,becaus e the Peoplewer e afraid that alowe rwate r levelwoul d allow thepea t to ry out andbecom e awater-impermeabl e layer,whic hwoul d seriously reduce thefertilit y of those lands.Bu t such ahig h groundwate r level

129 hasman y disadvantages for the farmer.Th e softness of thegroun d means that alo to f grass is lost throughbein g trampled by grazing cattle.Thi s loss isofte nmor e than 50%.A Dutc h farmerwil l thensay , "my cows grazewit h 5mouths" .I n the spring,gras s growth begins late, and ina dr y summer itwil l quickly dry outbecaus e of its shallowroo t system.Durin g the spring and autumn,th emor e remotepart s of thefar m areentirel y inaccessiblewithou t destroying the turf.Suc hplot s are used on aver y extensive (asoppose d tointensive )basis ,ofte nmerel y asunmanure d grassland forhay . In theextensiv e areaswit h riverbasi s clay -betwee n thebi g rivers- the situationwa s scarcely anydifferent .Onl y in thepas t fewdecade s have these regions improved,agriculturall y speaking. Thanks tointensiv e research intobette r drainage-methods,bette r opening-up of inaccessible areas,an d thanks to land consolidation or redistribution ofplots ,th eproductio n conditions ofextensiv eagricul ­ tural areas inth eNetherland swer e somodifie d thatmoder n farming became possible in those regions aswell .

Effect on thepopulation' s character

The centuries-long struggle against thewater ,th eofte n great isolation and thehar d lifeha s left its traces inth ementa lmake-u p ofth e population inman y parts of theNetherlands .Withou t going toodeepl y into thismatter ,I believ e that the independent charavter ofman y Duthmen,thei r longing for freedom and independence,thei rhabi to f acting inaccordanc ewit h their own ideas,thei r courage intacklin g problems and theirperseverenc e inconquerin g adversity hasbee ncreate d to someexten t by the constant struggle forexistance .Th e pioneering spiritwhic h characterized theDutc hpeopl e inth epast ,no t only inth e sense ofdiscoverin g unknown continents but also inth e sense of turning unproductive areas ofpea t andmars h into fertile land or draining inland lakes inou row n country hasno tye tbee n extinguished. That spiritha s certainly notbee n extinguished among the farmers,wh o were the first tomov e into the immeasurably largeexpans e of thene w land created by empoldering of the IJsselLake .

130 followingth e theme of this conference,i t is important todra wyou r specific attention to thegrea t importance ofprope r agricultural grouping ofplot s of theempoldere d areas.Afte rbein greclaimed ,th e drained landmus tb ebrough t intocultivation .Thi s involves anumbe r °fproblems ,suc has : whatwil l the landb euse d for (farming,forestry ,natur ereserve , urban area); howdee pmus t the groundwate r levelb e (thatdepend s on the future use); how largemus t theplot s and fieldsbe ,ho w largemus t thene w agricultural holdingsbe ; -wil l the landb e sold,o r leased oroperate d by theStat e itself? Y°uwil l appreciate that the state inwhic h the land ishande d overan d the conditions onwhic h the land ismad e available toth eprivat e farmerwil lb e of theutmos t importance tohim . Ishoul d like toexplai n "at toyo u inbroa d outline.

Thedraine d lakes

TheBeemste r -th e first large lakedraine d inth eNetherland s -wa s en>polderedbetwee n 1608an d 1612b y the legendaryLeeghwate rwit h the aid ofabou t 40windmills ,o n the instructions ofDirc kva nOss ,th e erector of theEas t IndiaCompan y (Verenigde Oost-Indische Compagnie), the cartel ofAnsterda mmerchant swh o financed theproject .The yprove d to haveprogressiv e ideas,fo r theplo t distribution of theBeemste r as lt was arranged 350year s ago remains suitable formoder n farmmanage - ment tothi sday .

Another example is theHaarlemmermee r -whic hwa s drained in 1850 after in22 5year s 15plan sha dbee n submitted for itsdrainage ,al l 0f whichwer ewrecke d foreithe r technical of financial reasons- Which alsoha s afor mo fplo t distribution andwate r controlwhic h makes itexcellen t forpresent-da y farming.Th e fact that thispolde r ls currently subject tosever e erosionb yhousing ,recreatio n andou r national airportmean s agrea t loss toagriculture .

As soona s these inland lakesha dbee ndrained ,th e landwa s soldt o

131 thehighes t bidder. "Ripean d green"establishe d itself here ina single area.Professo r Groenmanwrot e about this system of freecoloni ­ sation asfollows : "Although the areaappeare d richly green fromweeds ,ye t itwa s still far from ripe tob e cultivated with success".I twas ,i nfact ,a figh t to thedeat h against nature,i nwhic h the strongest,th ehealthies t and themos t fortunate couldwithstan d the struggle.Perhap s itwa s only thewealthies t Ultimately,thi s system of free colonisation,b y means of aproces s of strict selection,le d toa prosperou s society. Butnot e thewor d ultimately.'fo rwhil e the first generation had an extemely difficult,poo r andhar d life,th e second generationbenefite d from it and thenex t generation even enjoyed aver y decent standard of living,thank s toth e efforts of thepioneers .

Thene w IJsselLak epolder s

When the IJssel Lakepolder swer e constructed acompletel y different policywa s followed.Th eGovernmen t itselfbor e the risks ofbringin g thedraine d areas into cultivation,b y operating them itself forth e first fewyears .Onl y after itha sbecom e clear that there aren o exceptional risks toth eprivat efarme ri noperatin g the land individual' ly are the farmswhic h have already beenbuil t inth ene w poldermad e available toprivat e enterprise.An d thismetho d had proved asuccess .

New landhelp s theol d

Inth e course of time,th epolic y relating toth e conditions onwhic h the land ismad e available to farmersha d undergone quite afe wchanges - The firstpolde rwa s theWieringermeer ,containin g 20.000h a of land. Anybode could apply for afarm .Applicant swer e selected on thebasi s ofproficiency , financial soundness and good family reputation.

In theNort h East Polder -whic hwa s letou t in theperio d from 1940t o 1962- certai n groupswer e givenpriorit y in the allocation offarms . First came the group ofpioneers ,wh oha d helped reclaim thepolder . Then came farmers fromWalcheren ,a n island in theSout hWes t ofth e Netherlands,whic h had suffered flooding inth eWorl d War asa resul t

132 thedyke sbein g bombed. The farms onWalchere n arever y small.B y °"ering these farmers ane w farm inth eNort hEas tPolder ,th efarm s °nWalchere n canb eenlarged . 130th ene w land isutillize d forth epurpos e of improving farm structure inolde r regions.Thi smetho d ofmakin gnewl y reclaimed land serviceable for the improvement of theproductio n condition on theol d iand,ha sbee n extended toa nincreasin gdegree .

*n theFlevopolder ,hal f of thefarm swer e allocated tofarmer s from landconsolidatio n areas,tha t ist o say areaswher e aplo tredistribu - lQn programme isbein g implemented.Thi s releases land intha t area enabling the farms tob emor e efficiently parcelled. °r pasture areas inparticular ,i t ismos t important that thelan d shouldb e directly adjacent toth e farmbuildings .Thi s allows the dairycattl e tob emilke d in theparlou rdurin g thesumme r aswell . If the farms on the old land are situated too close together,th e land of afarme r on theol d land canb euse d toreparce l the surrounding ariasb y offering him afar m inth ene wpolder .I n thisway ,ever yh a of new landmake s itpossibl e for5 h ao fol d land tob e reparcelled.

n addition,som e of thene wholding s in thepolde r arereserve d for armers forced to leave theol d landb yurba n expancion orroa d instruction. Particularly ifth e farmerhold s the land on lease inth e Case ofexpropriatio n thefarme rwil ln ob e able toobtai n ane w easehold farmelsewhere .I n such cases,th ebes t solution ist omov e lnt° thene wpolder .

Freehold or leasehold?

A Politically important issue is thequestio n ofwhethe r the land sh°uld bemad e available toth e farmers ona freehol d (i.e.privat e pr°Perty)basi s oro n ashor t or long term (i.e.hereditary )lease . though Parliament originally voted infavou r of all three formso f tenancy,i twa s decided inpractice ,unde r socialist pressure,t oretai n "e land as StatePropert y and let italmos t exclusively ona shor to r °n8lease .Thi sha dmad e theStat e into thebigges t agricultural aildlord in the country. Imus t add,no t always toth e full satisfaction of the farmingcommunity .An d Parliamentary control over theState' s behaviour as landlord hasprove d tob e extremely difficult,becaus e the StateLan dManagemen t ispar t of thebudge t of theMinistr y of Finance.And ,o fcourse ,i nthi sparticula rbudge t theproblem s surrounding Government expenditure and financial economies aremor e important toth e financial experts inParliamen t than land leasepro ­ blems inth e IJsselLak ePolders. '

Size of thefarm s

Anotherpolitica l issue is thequestio n ofwhethe r toallocat e large or small farms?

Besides such aspects aseconomi cviabilit y and employment and social acceptability, themai n objective thatapplie she r is toprovid e solutions toproblem s affecting theol d land. The lesson tob e learnt from thepas t istha twha twa s considered tob e a reasonably large arable farm in 1930- 2 0t o2 5h a -i sno w toosmall - On thebasi s of thisexperience ,yo u should really start from afar m size sucha s toallo w amargi n toabsor b futuredevelopment s asye t unforeseen.Th edesir e topu t thene wpolde r tous e inorde r tosolv e problems on theol d landmean s thatwhe n that farmermove s toth e IJsselLak epolder sh emus tb e able tocontinu e to farm.An d thismean s that the farm sizemus tb e sufficient tomak e such amov e to thepolde r bothmentall y and financiallypossible .

When afar m isaccepte d inth epolde r itgenerall y involvesa considerable financiel outlay.Th eol d farmha s tob e sold to theState , thenyo u takeove r thene w farm,eithe r ona shor t of long termlease . In the caseo fa shor t lease,th e land comeswit h a"rum pbuilding" . The tenant farmerhimsel fha s toprovid e thehom e aswel l asth e equipment for the shed,surfacin g theyard ,etc .I n the case of alon g term lease,th e farmeha s toprovid e all thebuilding shimself .Th e costs involved are around 800.000 to 1millio n guilders inth ecas eo f a short lease,an d from 1-1,5 million guilders for alon g lease farm.Thi s amount isonl y economic inth ecas eo fholding swhic h are not smaller than4 0ha .

134 At thispoin t Iwoul d remindyo u that theaverag e size ofDutc h agriculturalholding s is 18ha .B y comparison,th e farms inth eIJsse l Lakepolder s are relatively large,wit h anoptimu m location,al lth e land inon epiec e around the farmhouse,excellen twate r controlan d newfar mbuildings .

Theus e ofmoder nholdings ,wit h farmerswh o areonl y allocated a farm if they satisfy anumbe r of conditions,fo rexampl e agricultural efficience,hav e asignifican t positive influence on the farmers w°rking the old land. Thepolde r thereforeha s acertai n exemplary effect.Ne wmachine s and methodso f cultivation areofte n tried out inth epolde r first.Th e relatively favourablebusines s resultsenhanc e thewillingnes s among farmers on theol d land tomak e investments and introduce improvements, Paricularly asregard s reparcelling andwate rcontrol .

The result istha t the importance ofgoo dparcellin g andwate rmanage - ment isbrough t to the attention ofman ymor e farmers.Lan d consolida­ tionha sbecom e aver y important policy instrument inth eeffort s to improve the structure ofagricultura l andhorticultura l holdings.Thi s is made evident by the fact that at thepresen t timeapproximatel y40 % of our cultivated land iseithe rundergoin g or about tounderg o alan d c°nsolidationproject ,an d that 35%o fou r landha s alreadybee n reParcelled. The State iscurrentl y investing 5.000guilder s perh a in landconsolidation .Par t of thismone y- averagin g about 50%- ha st o be repaid by the farmer orhorticulturis t after completion.Eac hyear , about 40.000h ao f land arereparcelle d and reparcelling starts ona further 40.000. The entire land consolidation procedure from thebeginnin g toth een d takesfro m 25 to3 0years .Admittedly ,i t isno tpossibl e toachiev e thesam e ideal land distribution as inth ene wIJsse lLak epolders .Th e ul timate effect dependsver ymuc h on thequestio no fwhethe r therei s efficient room to allocate every farmer themaximu m amount oflan d Mediately adjacent to his farm.Th epossibilit y ofmovin g anumbe r of farms toth epolde rmean s that thechanc e of successbecome s c°nsiderablybetter .T opu t itbriefl y thene w capacity of agricultural x and in the IJssel Lakepolder sha s afa r larger indirect effect onth e

135 old land than isofte n realised. Ihop e thatI hav e succeeded in givingyo u some ideao fho w important it is toDutc h agriculture asa whole toreceiv ene w farmland withmoder n and efficientfarms .

Changing socialview s

Over theyears ,ther e isanothe r factorwhic h influences theorganiza ­ tion ofou rne wpolders .Tha t factor isth e changingview swithi n society as to thevalu e ofnature, th ecountrysid e and theenvironment . Thisha smad e itself felt in thedistributio n of land utilization in thene wpolders . In theWieringermee r and theNort hEas t Polder,practicall y allth e available landwhic hwa s not required forbuildin g houses,i sbein g used for agricultural purposes.I nEaster nFlevolan d 75%i s agricultural land and in thenewes t polder,Sout hFlevoland ,n omor e thanhal fo f the land isbein g assigned anagricultura l function.I n these twoareas , besides thespac e allocated forhousing ,th e areasdesignate d asnatur e reserves and forest areas are 11%an d 18%respectively . Inothe rwords , aver y significant increase.

TheMarkerwaar d

This change in theappreciatio n ofnatur e and countryside also finds expression inth ediscussio n concerning theMarkerwaard ,th e lasto f the Ussel Lakepolders .I s itgoin g tob e constructed ornot ?Debat e on this subjectha sbee n continuing for thepas t 10year s inpolitica l circles inTh eHague .Man y studieshav ebee n carried outb y supporters and opponents.Actio n groupshav ebee n formed.I n theend ,th e Government decided tobuil d a40.00 0h a polder surrounded bywid e lakes covering 20.000ha .But ,firs t of all thispla nha d tob e presented to thepubli c fordebate .Th eopponent s -heade d by thenatur econser ­ vation organizations -wh o frequently find iteas y tomak e thenews ­ papers and television,stat e their argumentwit h persuasive simplicity: intervention inth e environment isa crime .A n open inland lakeo f this size suddenlybecam e represented assomethin gunique ,uniqu efo r recreation anduniqu e forwate rbirds . Itshoul db eno tb e sacrificed merely for thepurpos e ofmakin g even

136 more agricultural products,whic h arealread y inhug e surplus.Thi s fishermen,seein g their livelihood endangered,joine d in thecampaign . Public opinionwa s aroused. Certainmajo rpolitica l partiesvoice d their ejections toth ene wpolder ,other swer eno t sosure .An d yet -I consideruncertaint y tob e absolutely irrelevant tothi smatter .Th e mainobjection swhic hhav ebee n raised against theMarkerwaar d prove uPon analysis tob euntenable .I bas em y opiniono na repor t produced bY senior officials responsible fordealin gwit h thismatte rwithi n the threeministrie s concerned:Are aplanning ,Traffi c andWaterway s and Finance. Themai n objectionswhic h theopponent s have raisedare : loss ofjob s in the fishing industry; loss ofunspoile d openwate r asa natur ereserve ; risko feve nmor e over-production ofagricultura lproducts ; losso funiqu erecreatio n facilities for largeyachts .

Let me consider these arguments oneb yone .

The fishing Industry

If theMarkerwaar d becomes apolder ,th efishin g industrywil l lose 4o-000h a of fishingwaters .I twil l retain aremainin g 160.000h ao f °Penwate r inth e IJsselLak e region.Th e loss toth e fishing industry a nciliary andmanufacturin g firms,i sestimate d by esperts at2 6 miUion guilders interm s of added valuepe rannum .I fonl yhal f ofth e Markerwaard ismad e into agricultural land,tha t agriculture,includin g Hillary andmanufacturin g industry,woul d yield anadde d valueo f l50millio n guilders.Tha t isn o less than6 time s asmuc h as the loss t0 fishing. In terms of jobs aswell , the loss toth e fishing industry is more thancompensate d by theadditiona l jobscreate d by agriculture ln thispolder .

2 Thevalu e of theMarkerwaar d asa nope nnatur e reserve

The losso f the largeMarke rLake ,a large-scale nature reserve,wil l admi.ttedlyb ever y real if thepolde r comes about,bu t that lossi s offset by certain gains.Le tm ementio nhus t threematters :

137 1)i twil l create aconsiderabl y longer coastline,tha tmean s considerably more food for coastalbirds ; 2)a ne wnatur e reserve isplanne d opposite theOostvaarde r Lakes.I believe that thispossibilit y alone outweighs the losso f parto f theope nwater . 3)th e important indirect effectswhic h areofte n ignored. Empoldering means that after theyea r 2000 therewil lb emor e space forurba n construction inth evicinit y ofAmsterdam . Itmean s lessris k that the greenhear t ofHolland ,th e extensivepastur e areas inth e centralpar t of this country,wil lhav e tob e used forbuildin g houses,a t thebeginnin g of thenex t century. Iwoul d have thought that this factor isno t unimportant fromth e viewpoint ofnatur e conservation.A sevond positive effect fornatur e conservation istha tdesignate d nature reserveswhic h at thepresen t timear e stillbein g used by farmerswil lb e able tob epurchase d more rapidly and cheaplyb y the State if the farmer isoffere d a holding in thepolder .Tha tmeans :les sris ko f losing thenatura l assetswhic h arealread y there.I nbrie f theMarkerwaar d also offers a loto f advantages fornatur e conservation aswell .

3 Recreational aspects

The argument that theMarkerwaar d should notb ebuil tbecaus e itwil l result inlos so f recreational space for largeyacht s or seagoing pleasureboat s isa rathe r elitist argument.O f the 200.000h a opope n water, 160.000wil l remain.Th e resultantwid e peripheral lakewil l offer recreational facilities for far largernumber s of lesswealth y recreation seekers.Smal lboats ,win d surfers and that allclos e toth e Randstad, theWester n conurbation.Wha t ismore ,th eextende d coastline will offermor e recreation facilities.

4 Agricultural surpluses ofProduktio n

Iwil l disregard thequestio n ofwhether ,i nvie w of the rate ofth e population growth and structural decrease inth eare ao f cultivated land,w e should not expect astructura l food shortagewithi n theEE Cb y theyea r 2000.Th eare ao f agricultural land inth eMarkerwaar d polder

133 would represent 0,04%o f the total areao fagricultura l land inth e EEC. Inth eperio d up to 2000 inth eNetherland s alone it isexpecte d that 400.000ha ,i.e . ten times theare ao f theMarkerwaard , isgoin g tob e lost for agricultural purposes inth efor mo fhousin g ornatur e reserves. Surely thisdisprove s thecredibilit y of talking about the Markerwaard polder resulting inbigge r foodsurpluses .

"o:w emus t have theMarkerwaard . Thecost s of construction and developing it forcultivatio nhav ebee n estimated at 1.650 million guilders.Temporar y utilization and lease revenues over thefirs t 20year s following itsdrainag e canpotentiall y earn 650millio n guilders.Therefor e thene t costs of thedraine d polder wUl be 1millio n guilders (spread over 20years) .

What doyo u get for this: 1)40.00 0h a of first class agricultural land.Tha twork s outa t 25.000 guilders perha .I f theStat ewante d tosel l this landi t could do soa ta profit . 2)Spac e forbuildin ghouse s andundertakin g other socio-economic activities at thever y centreo f thecountry .T obuil d houses the Statewil lno t firsthav e toexpropriat e andprepai r goodagricul ­ tural land elsewhere forhous ebuilding .

1 have alreadymentione d thebenefit s interm so f recreationan d Natureconservation .

P°r farming,th epolde rwil loffer : 20 to 30.000h ao f space for ideallyparcelled ,ultra-moder n agricultural andhorticultura l holdings.Par t of thepolde rwil lb e Particularly suitable forgrowin gbulbs .

Thismeans ,directly :- extr ajob s (forabou t 1.500 persons) - extraadde d value (about 125- 150millio n guilders/year) indirectly: theeffec t onth eol d landwil lb eeve nmor e substantial.

139 Ihav e already explained howth epolde r land canb euse d inorde rt o improveth eparcellin go fth eol dland ,b ymakin g itpossibl e tooffe r farmers from land consolidation areas ane wfar m inth epolder .Thi s means that theMarkerwaar d will enablebetwee n6.00 0an d8.00 0ol d farmshav ea bette rparcellatio nwhic hwil lyiel d acos t savingo f 500guilder spe rannu mfo rever yhectare .

Inshort : TheMarkerwaar d willpa yfo ritsel f sot ospeak .I a mconvince d that this investmentwil lbea r full fruit.Th ene wGovernmen twil lhav et o make achoice .Th ene wpolder ,ne wjobs ,ne wspace ,ne weconomi c potential,o ri tca ndispla y theunenterprisin g spiritwhic h iss o often thecharacteristi c ofpoliticians .

I challenge theGovernmen t andParliamen t totak ea positiv e decision. Admittedlyw ear eshor to fmoney ,bu tw eca neasil y affordth e Markerwaard. Inth eEas t Schelde,w ear espendin g an6 milliar d guilders inorde r toconstruc t anope n stormsurgebarrie r instead ofa close d dam,merel y forenvironmenta lreasons . TheMarkerwaar d will cost less than20 %o ftha t amount,sprea d overa period of 15-20years .W ehav e theknowledg e andth eexperience . Theprojec t cannot failt ohav emajo rpositiv e effectso nemployment , space forurba n construction,agricultur e andrecreation .

I havemad ea nattemp t togiv eyo usom e ideao fth eway s inwhich ,i n thepas t andi nth epresent ,ne wpolder s aredevelope d foragriculture . And thatho wth ene wlan d ishande d overth efirs t agricultural pioneers andth ene wlan d iss ovitall y important. But alsoho wi tca nmak e acontributio n toimprovin g thestructur eo f theol dland .Ho wth emoder nholding s inth ene wpolder s generatea tremendous spin-off effect onth eentir enationa l developmentsi n agriculture inth efor mo fne wmachine s andmethod s ofcultivation . Howa polde r canals omak e asocia l contributionb yprovidin g extra opportunities foragriculture ,housing ,landscap e andrecreation .

Ihop e that Ihav e succeeded inmakin g ausefu l contribution toa ninte ­ resting discussiono nthi ssubject .

140 AGRICULTUREAN D FOODPRODUCTIO N INPOLDE RAREA S A case study fromBanglades h H.Bramme r FAOAgricultura lDevelopmen tAdvise r Dhaka,Banglades h

Abstract

angladesh illustrates polder development issues ina densel y settled, subtropical,deltai c environment.Si x types- active ;me ­ ander;estuarine ;tidal ;piedmont ;pea tbasi n -provid e different °Pportunities,need s andproblems .A 1964Maste rPla npropose d 35 einbankment/polderproject s covering 5.8millio nha .To-date ,abou t0. 5 miHion hahav ebee n flood protected and 85,000h a irrigated,increa - Slng annual riceproductio nb y about 1millio n tons (net). Slow imple- mentation isdu e toai d donors'recognitio n of technical difficultiesi n constructingembankment s andheadwork s on theunstabl eGanges-Brahma - Putrariver s and of alternative,quicker ,developmen tmodes ,especiall y smallscale irrigation. Problems ofseepage/waterloggin g and uneconomic returns resulting from farmers'slowadoptio n ofplanne d croppingpat - ems arepartl y due toplanner s'insensitivit yt obot h soil-croprelation ­ ships and farmers'cro pproductio n capacities.Firs t generation problems •"•soinclude :lo w irrigation coverage due tot seepage losses;erosio n embankments;optimu m economic designswhic h leavedepressio n sites undrained;an d lack ofwate rmanagemen t intida lbasins .Secon dgene - ration problems include:siltatio no f tidal creeksoutsid epolders ; aterlogging incana l irrigated areas;zin c and sulphurdeficiencies ; Pread of settlement onto flood-protected land;an dbreachin g ofcoasta l embankments by shrimpproducers .

14! Agro-economic surveys and landus e regulations are recommended.

Introduction

Theorganizer s of theSymposiu m onPolder s of theWorl d originally requested apape r giving anovervie w of agricultural aspects ofpolde r development outside theNetherlands .Tha t taskprove d tob e impossible within the timean d resources available to the author inBangladesh . However, is isexpecte d that theSymposiu m itselfwil l provide sucha n overview through the combined contributions madeb y delegates coming fromman yindividua l countries. The authorha s chosen to speak instead onpolde r development in Bangladesh.Th e objective of this isno t toprovid e adetaile d descrip­ tiono fpolde r development inBanglades h but,rather ,t ous e Bangladesh examples as amean s to illustrate principles,experienc e and issueso f wider relevance. Itmus tb e emphasized that theview s expressed are thoseo f theautho r alone,an d dono tnecessaril y reflect theview s either ofhi s employer,FAO ,o r of theGovernmen t ofBanglades hwhic h heserves .

Environment and demography

'Bangladeshha sbot h thephysoca l and thedemographi c environmentswher e polders aremos t needed.Alluvia l occupy 80percen to f the to" 2 toal land area of 143,000k m .I t isestimate d from soil surveys thata - bout 75percen t of the floodplain area is flooded deeper than3 0c m for 3-5 months in therain y season.I naddition ,abou t 1millio nhectare s near thecoas t formerly were subjects to tidal floodingwit h salt wa­ terbefor e embanmentswer ebuilt . Most of thecountry' s populationo f over 90millio n lives inflood - 2 plainareas .Th eaverag e population density is628/k m :regionall y itva - 2 ries frommor e than 1,000/km inComill a themos t densely settled rural 2 district,t oles s than 500/km in two coastal districts.Considerin g the fact thatmor e than 80percen t of thecountry' s total population isru ­ ral, that isa ver y high population indeed. Unlike theNetherlands ,Banglades h doesno thav emajo r areaswher e new land for settlement or agricultural production could be reclained from the seab y empolderment.Th epurpos e ofmakin g polders inBanglades h

142 ls mainly toprotec t existing settled agricultural land fromdee pfloo ­ dingo r from tidal floodingwit h saltwater ,s o that improved crops cansafel yb e grown in themonsoo n season.Often ,irrigatio n isprovi ­ deda t thesam e time ,partl y soa s tocompensat e farmers for thelos s of soilmoistur e derived fromseasona l flooding,partl y toenabl efar - mers togro w improved crops in thedr y seasonalso .

Agriculture and food production

Bangladesh's economy ispredominantl y agricultural.Agricultur e contri­ butes about 55percen t of theGN Pan d supports,directl y or indirectly, about 75percen t of thewor k force.Th emajo r cash crop juteprovide s about 70percen t of the country's exportearnings . Rice isth eprincipa l crop,occupyin g about 80percen t of thene t Cropped area,sprea d over threegrowin g seasons.Th e tworain y season cropsar emainl y dependent on rainfall and seasonal flooding,bu t almost aU the dry season rice crop is irrigated.Almos t 2millio n hectares of therain y season crop areoccupie d by deepwater ricevarietie swhic h Canwithstan d flooding depths greater than 30cm .Averag e riceyield s are low: 1.35 tons/ha.Thi s reflects the relatively lowadoptio nrat e of modern technology,a s illustrated by average fertilizer rates (for aH crops)o f around 100kg/h a (= < 5 0kg/h anutrients )pe r annum, sPread over threeseasons . Th-eaverag e size of farmholdin g is 1.4ha .However ,i twoul d bewron g to infer from this that Bangladesh isa countr y ofpredominantl y small Peasant farmers.Tha t isbecaus e land ownership isbadl y skewed.I n l978, the 8.5 percent of rural land ownerswh o possessed 2h ao rmor e held 48.4percen t of the land;o n theothe rhand ,50. 4percen t ofrura l h°useholds owned less than0. 2 ha (including thosewit hn o agricultural land at all);(referenc e 1).Lan d ownerswit hmor e thanabou t 2h a generally use share-croppers orhire d labour tocultivat e their land; often they are absentee owners.I n thepast ,suc hbi g land owners have generally shown little interest inusin gmoder n technology to lricreaseproduction ,althoug h there are indications that achang ema y e takingplac e insom eareas .

143 Progressive small farmers are foundmainl y in the south-east and centre of thecountry .

Bangladesh currently produces 14-15millio n tonso f foodgrains annually( depending onwhethe r harvestsar egoo d orbad . Thepopulatio n of9 2 millionneed s anestimate d 14.5millio n tons.A further 1.5millio n tons areneede d tocove r seed,fee d andwaste .Tha t leaves adefici t of 1-2millio n tons.Eac h year,too ,populatio n growth adds a further 400,000 tons to therequirement . In it's Second FiveYea rPla n (1980-81 to 1984-85), theGovernmen t of Bangladesh aims toachiev enationa l self-sufficiency in foodgrain pro­ duction and toexpan d theproductio n of other food and cashcrops ,in ­ cluding sugarcane,banana ,jute ,cotton ,pulses ,oilseeds ,potato , vegetables and spices.Th e foodgrain production targetb y 1984-85i s 18-20millio n tons,includin g provision forbuildin g up a reserve food stock. Inorde r toachiev e these ambitious targets,i t isplanne d todoubl e theare aunde r irrigation,fro m 1.47 million ha in 1980t o 2.88millio n ha in 1984-85,an d toprovid e flood protection and drai­ nage toa nadditiona l 600,000ha .Therefore ,althoug h priority isgive n tosmall-scal e irrigation,polder s alsohav e an important role topla y in thisplanne d development.

Physiography and soils

Most of the country comprises thecombine d deltao f theGanges ,Brahma ­ putra andMeghn a rivers.Thi s area canb edivide d into sixbroa d physiographic types (Map). a)Activ e andver y young floodplains along themajo r river channels (700,000ha )whic h are subject toban k erosion ordepositio n ofne w sandy orsilt y alluvium each flood season.Suc hunstabl e land isno t suitable forembankmen tprojects . b)Youn g and oldmeande r floodplains of themajo r rivers (5.7million - ha)whic h are characterized by aridg e andbasi n topographywit h 2-5m local difference inrelief .Predominan t soils areheav y silts toclay swit h developed profiles 30-120 cmdee p over astratifie d substratum. Such land issuitabl e forpolde r projects,s o longa s embankments are setwel l back from active river channels and there are suitable sites for irrigation/drainage headworks onstabl e

144 tributary channels. The Ganges-Kobadak (G-K) project, referred to later, is on the Ganges meander floodplain. c) Young and old estuarine floodplains (3.1 million ha),mainl y east of the Meghna river,whic h are characterized by almost level relief (< 2 m), few or no natural channels, and deep silty deposits in which soil profiles 20-120 cm deep have developed. Such land is sui­ table for polder projects, provided that embankments and irrigation/ drainage headworks can be sited away from active river channels. The Chandpur and Dhaka-Narayanganj-Demra (DND) projects, referred to later, occupy parts of the old and young Meghna estuarine flood- plains. d) Tidal floodplains occurring mainly in the south-west, locally in the south-east. They are characterized by almost level, saucer-chaped, basins with $ 1m local difference in elevation, and numerous tidal creeks. Clay soils predominate. About 400,000 ha is non-saline; about 600,000 ha is saline, (most of it only in the dry season). The Coastal Embankment project occupies most of the saline tidal flood- Plain land, and the Barisal Irrigation Project (which includes em­ bankments) occupies a part of the non-saline Ganges tidal floodplain. e) Alluvial fans and piedmont plains (1.1 million ha) occurring partly in the north-west near the foot of the Himalayas, the rest mainly adjoining the eastern and northern hills. Relief often is irregular and soils vary from sands to clays. The embankment of hill-foot rivers provides difficult problems because of the deposition of sedi­ ments within embankments following flash floods and the constant risk of embankments being breached. The Manu, Muhuri and Karnafuli Projects occupy hill-foot sites. f> (200,000 ha) occur most extensively in the transition zone between the Ganges meander and tidal floodplains in the south-west. The empolderment of peat basins is suitable so long as they are not deeply drained, which would allow the peat to shrink and oxidize. The land should be kept permanently wet or moist. 0x1 all floodplains, there is a characteristic pattern of permeable,

Us ually loamy, soils on the highest parts and impermeable, usually clay, s°ils on the lower parts. The proportions between light and heavy soils dxffer both between major floodplains and within them.

145 Generally,heav y soils occupymos t of the .Rapidl y permeable soils occurmainl y onhig h floodplain ridges,som epiedmon t fans (espe­ cially that in thenorth-west) ,an d some temporary islands onactiv e flood-plains.Th emos t extensive soils areFluvaquenti cHaplaquep't s (Eutric and Calcaric Fluvisols inth eFAO/Unesc o system). Ganges river alluvium contains lime:s o doesyoun gMeghn aestuarin e alluvium, although only insmal l amounts.Gange s tidal,Brahmaputr a river andOl dMeghn a estuarine alluvia areneutra l tomoderatel y alka­ line inreaction ,bu tno t calcareous.Alluvia l fans andMeghn a river deposits areusuall y slightly tomoderatel y acid.Becaus e of theseaso ­ nal cycle of flooding and drying out,soi ldevelopmen t usually is rapid. The seasonal changes cause rapid development of structure (where texture are suitable)an d the development of ironoxidatio nmottles .Alluvia l stratificationi s quickly brokenu pb ybiologica l activity down toth epermanentl y satu­ rated zone.Biologica l activity (roots,soi l fauna)als o increases subsoil porosity,aeration ,permeabilit y andmoistur e holding capacity. On theothe rhand ,cultivatio ntend s todestro y topsoil structure and to create a slowly permeable ploughpan.Especiall y insoi l deliberately puddled for transplanting rice.

Soil fertility

The seasonal reduction and oxidation of the topsoil -whic husuall y is cultivated,an d oftenpuddle d -quickl y decalcifies oracidifie s this layer,excep t inloam y soilswher ebiologica l activity constantly brings subsoilmateria l to the surface andwher e thedepositio n ofne w alluviumneutralize s such chemical changes.However ,whethe r topsoils areaci d oralkalin e in thedr y season,the ybecom eneutra l inreactio n when submerged and reduced. The rapid leaching ofmos t floodplain topsoils confirms fieldobserva ­ tions thatmos t river and estuarine floodplains areno t floodedb y riverwater .The y are floodedwit h rainwater or the raised groundwater tablederive d from theheav ymonsoo n rainfallwhic h isponde d onth e landb yhig hmonsoo n season river levels.Silt y floodwatermainl y depositsne w alluvium onactiv e floodplains and the immediately adjoin­ ing land,o nunembanke d tidal floodplains,an do n alluvial fans

146 (Piedmont plains)a t the footo fhills . TV*' nxs has important implications forembankmen t projects.Farmer s (and ay officials)believ e that the fertility of floodplain soils inmain - ained by an annual deposit ofalluviu m from the seasonal floods.Sinc e °st floodplain areasd ono t receive such annual deposits,an dye t clearlyar ea t least asproductiv e as those that do- e.g. , large areaso f theBrahmaputr a andGange s floodplains are triple cropped, without irrigation andwit h little orn ous eo f fertilizers - theself - evident fertility of these soilsmus tb ederive d from someothe rsource . ne ready availability ofphosphoru s and potash canb e accounted for y theseasona l cycle of reduction and oxidation in thesemineral-ric h Soils. However, thisphenomeno n cannotprovid enitrogen ,an dman y culti- vated soils contain little organicmatte r asa nitroge n source. Itno w aPPears certain that thenitroge n fertility ofBangladesh' s floodplain So Us isprovide d bybiologica l activity inth efloodwate r itself, Specially that ofblue-gree n algae.I t isprobabl e that such organisms Can provideu p to3 0kg/h a ofNitroge n annually,perhap s evenmor eo n eeply flooded landwher e deepwater aman isgrown .Sinc e these organisms are dependent on light forphotosynthesis ,i t isprobabl e thatthe y Producemor eNitroge n inclea r than insilt y floodwater.Therefore ,th e instruction ofpolde r embankmentswil lno tnecessaril y cut off farmers ronithes e sources ofplan tnutrition ,a t least on landwher ewetlan d Ce continues tob egrown . hat should notb e taken to imply thatBangladesh' s floodplain soilsd o not need or resnondt ofertilizers .Withou t fertilizers ormanure ,th e natural fertility maintains production atonl y alo wo rmoderat e equi- ibrium level.Fo r increased yields,particularl y forHYV s and irrigated Cr°Ps, it isnecessar y toad dN andP fertilizers regularly,an dsome - tin>espotas h fertilizers also.A swil lb edescribe d later,ther ei s a ls0 increasing evidence of zinc and sulphur deficiency insom eplaces .

Cropping patterns Utldernatura l conditions- i.e.,withou t artificial drainage or irri- êation - farmers'croppin g patterns onfloodplai n land aredetermine d ar8elyb y the length of therain y season and thedept h and duration °f seasonal flooding. Soilpermeability ,soi lmoistur e holding capacity

147 and thepresenc e or absence of salinity are also important,particularl y fordr yseaso ncrop s grownwit h orwithou t irrigation.Becaus e ofth e characteristic floodplain relief of ridges andbasins, variation s in soils,dept h of flooding and flood duration occur on aloca lscale , evenwithi n the areao fa village .Croppin g patterns often arecomplex , therefore.Ric e occupies about 10millio nha ,whic h isabou t 80percen t of the cropped area.I tca nb e grown in threeseasons : - aus,sow n in thepre-monsoo n season andharveste d in themonsoo n season; - aman (which isphoto-perio d sensitive),sow nbefor e or in themonsoo n season andharveste d at thebeginnin g of thedr y season;an d - boro,sow n in the firsthal f of the dry seasonan dharveste d just before orearl y in themonsoo n season. Aus and amanar emainl y grownwithou t irrigation,althoug h irrigation isexpandin g inbot h seasons,eithe r inorde r to increase security ot toallo wbot h crops tob e grown inwester n areaswher e the4-mont h rainy season is insufficient tosuppor tmor e thanon e rainfed crop. Boro traditionally was grown indepression swhic h staywe t formos t or allo f thedr y season,bu t it isno w also grownwidel ywit h irriga­ tion on relatively higher land. Within the threebroa d ricegroups ,farmer shav e selectedman y thousands of ricevarietie s to suit their specificmicro-environmenta l conditions» especially for theama n crop.Ama n includesvarietie swit h different maturity periods,toleran t of different degrees ofsalinity ,zin c deficiency and iron toxicity,an d adapted todifferen t depthsan d duration of seasonal flooding. Some deepwater amanvarietie s can elongate their stems toa smuc h as4- 5metres . Highyieldin g varieties (HYVs)o f ricewhic h havebee n introduced inth e last 15year s areno t adapted toa wid e range ofBanglades henvironments - Inorde r togiv ehig h yields,the y require goodwate r control toprovid e aver y shallowwate r depth,an d relatively high fertilizer doses.Th e farmerwil l only invest in the latterwher eh e feels there issufficien t security toensur e areliabl e return onhi s investment.Fo r thatreason » theHYV shav e spread toonl y anestimate d 15percen t of the totale rice area.Abou thal f of this isboro ,grow nwit h irrigation in thedr y season.

14S The rest isabou t equally divided between ausan daman , grown both with and without irrigation onrelativel y heavy soils on land where theris k °f damage by floods is low. It is in this context that polders areimportan t for agricultural development inBangladesh . About 75percen t ofth efloodplai n land- about 8.5millio n hagros s - isto odeepl y flooded forexistin g HYVso f rice tob e grown inth emonsoo n season. Also, some of that land cannot be used forirrigate d HYVbor o inth edr yseason , either because flood- vater recedes tooslowl y orbecaus e theris k ofearly , pre-monsoon fi„ j •, . c „u „v„o nf «hallowlv flooded tidal land near tloods is toohigh . A further area or snanuwxy t-u . i-i. „vQ mn «alin e inth edr yseaso n for the coast hassoil s orwate r which areto osaun e x» uc y •2°£°_ rice tob e grown.

Master Plan Tu ,. ,i <-jrau n im bvth eEas t Pakistan '•heMaste r Plan forwate r development drawn up Dy Haf. , o ~A in 1Q6.4 envisaged polder development water andPowe r Development Board in îyem envies r ««ending eventually over a gross area of5. 8millio n ha. Three kinds °f Project were envisaged; flood embankments with gravity draimgei n Zander floodplain andpiedmon t plain areas; flood embankments with fcidal sl.ice drainage; andfloo d embankments with pump drainage.Fo r "»at ofth eschemes , provision of irrigation wasals o envisaged, betimes asa second stage. Priority wasgive n tofloo d protection. Pi v. c i-u- -Xe, maior flood protectionan d fcx ghteen years later, only seven ofth e3i >majo r no u v iry- . • ,• n,„ Master Plan have been wholly or ligation projects envisaged in theMaste r n mai„i , •• „f reasons iti sdifficul t to quantify '"ai-nly completed. Fora variety of reasons the benefits which they have provided. °*e major reasin fortha t derives from themeanin g ofth ewor d 'comple­ ted'. Project authorities tend tous eth eter m to indicate thatcon - st»-, .• , TQ)-0^ That does notnecessaril y mean sctuction works have been completed, mau tu , tf m All theproiec t command area. that project benefits have been brought toal ltn ep j A .. „ f t-hp 'completed' Coastal A Particular problem arises inth ecas e ofth e coi v En,u , .,„protect s 1.08millio nh afro m fcn)bankmentproject ,whic h supposedly protects ,al. . „„ cpmbankment shav ebee nerode d SaW tidal flooding.Man y sections otemban k °*breache d since theywer ebuil t andman y sluices eitherwer eno t 149 Stalle°w polderd osr onlhav ye i subsequennname . tbee ndamaged ,s otha tman ypolder s are It isprobabl e thatonl y about one-third (orpossibl y less)o f the 'completed'projec t area is,i n fact,receivin g the fullprojec t benefits ofprotectio n from saline floodwater. A further problem isprovide d by the lacko f reliable crop production statistics.Eve nwher e project authoritiesmak e estimates ofcro p acreage and productionwithi nprojec t command areas,i ti sdifficul t toestimat e thene t increase inproductio n attributable to theproject , especially in thecas e of relatively older projects.Tha t isbecause , formos t projects areas,i tcanno tb e assumed that,withou t theproject , land usewoul d have remained in thepreprojec t condition. In thecas e of theG- Kproject ,fo rexample ,wher e transplanted improved ausan d amanvarietie s have replaced the formerbroadcast ,traditiona l aus and amanvarietie s (and somejute ), th ecompariso n shouldb emad ewit h areaso f similar land adjoining theproject .Undoubtedly , therehav e been significant changes in land useoutsid e theprojec t areadurin g theyear s since theprojec t started: inadditio n to the traditional aus and amanstil l grown in themonsoo n season,ther eha sbee n aconside ­ rable expansion ofwheat ,tobacco ,cotto n and sugarcaneproduction , part of itwit h small-scale irrigation.Becaus e of thedifferenc e in crops grown,a realisti c comparison could bemad e only on thebasi s ofeconomi c returnspe rhectare .Unfortunately , reliable data areno t available forthi spurpose .Moreover ,analysi swoul d be complicated by the levels of input subsidies providedwithi n and outside theprojec t area. On thebasi s of existing information,th e author'sbes t guess istha t floodprotectio nma y actually havebee n provided bymajo rproject s to abouthal f amillio nh a and irrigation toabou t 85,000ha .Th edirec t benefits interm s of increased floodgrain productionma yb e about1 million tons annually (net). In addition,becaus e of thegreate r securitywhic h flood protection provides,farmer shav ebee n ablet o provide orobtai n small-scale irrigation from surfacewate r orground ­ water sources,a s well ast ogro w additional orbette r dry-season cropswithou t irrigation insom e areas.Unfortunately , reliable data areno t available toenabl e suchbenefit s tob e quantified.

150 Plan defects

Important though the direct benefits have been, they have been much

less than was envisaged when the Master Plan was prepared. It is

instructive to examine the reasons why polder development has been so

«low. There are lessons in this not only for Bangladesh but probably

also for other countries.

The first reason'undoubtedl y is because the Master Plan and its

component projects were too narrow in concept and focus. The Master

plan is primarily a civil engineering plan . It is not an agricultural development plan'5. With the benefit °f hindsight, one can understand why that should be so. The origins of the Water Development Board and the Master Plan lie in the serious floods which ravaged what is now Bangladesh in the 1950's. Flood pro­ bation was then seen as a priority for providing security to crop Di-rM. -• -e n„ ,J>= A secondary consideration. Alter- froduction. Irrigation usually was a se^uaij nna=k -tiv e possibilitie.... s„ for agriculturai_ ^„i rioirpl developmentlonmen t wer.e not considered « all. The engineering projects in the Master Plan were considered toProvid e a panacea for the country's agricultural development. Three main factors have combined to dealy the implementation of that Plan. The major cause has been the reluctance of international aid honors to finance some of the major proposed projects because of the technical difficulty of siting headworks on such major rivers as the

G ^8es and the Brahmaputra,whos e banks can erode or recede by as much a* 600 metres in a single year, and where intake or outlet canals can silt up in a single flood season. On the G-K project, for example, it c*n take six dredgers up to three months to desilt the .,000 m intake can^i v ,. u Kofnre irrigation can begin each year; and "-«nal to the main pumphouse berore ir"Ba'- «* the Chandpur project, 20 km of river embankments had to be rebuilt before the project had even been completed, because of actual or

t-K- • • i omi,antaent. Reservations have been threatened breaches in the original embankment. e»nr , , • „uiiirv of double embanking rivers as big cxPressed, also, on the advisability or u""u and active as the Brahmaputra and the Ganges.

')T , i •„„ rnuntries, irrigation and drai- !n Bangladesh, as in many developing countries., 5 »age projects generally are planned, executed and operated by engineers with a background in civil or mechanical engineering, not m agricul- tural or irrigation engineering. The lack of international agreements onwate r use inriver s originating outside the countrywa s afurthe r constraint onobtainin g funds for projects involving irrigation aswel l asembankment . A second factor - and one also influencing donor funding -wa s the growing recognition during the second half of the 1960's that therewer e alternative (and cheaper)way s to increase cropproductio n than through costly embankment and canal irrigation projects.B y 1970,abou t 24,000 small low-lift pumps and 1,000tubewell s hadbee n installed, irrigating anestimate d 370,000ha .B y 1981-82,tha tnumbe rha d grown toabou t 40,000 low-lift pumps, 12,000dee p tube-wells and over 50,000 shallow tube-wells,a swel l asmor e than 200,000han d pumps,togethe r irrigating anestimate d 1.27millio n ha.Tha tfigur e compareswit h only about 85,000h a irrigated withinmajo r irrigation projects in1981-82 . Although the limit of easily available surfacewate r usableb y small pumpsha s almost been reached,ther e remains considerable scopet o expand irrigation fromgroundwater .Th e development of small-scale irrigation has greatly expanded crop production inth edr y season,thu s reducing theurgenc y for flood protection and drainage inman yseasonal " lyfloode d areas.Th e emphasis incro pproductio nha sbee n switched from thehazardou smonsoo n season toth erelativel y safedr yseason . A third delaying factor hasbee n thedifficult y and expenseo f acquiring land for the construction ofembankment s and irrigation/ drainage canals.I n acountr ywher e theaverag e farmholdin g isonl y 1.4h a andwher e theaverag e population density ismor e than 600pe r km2 -an d exceeds/1000k m"i nsom efloodplai narea s - tnereluctanc eo f farmers togiv eu p their land,an d to sell itonl y at ahig h price,i s understandable. This factor alsoha s influence donors'decisions ,an d itha s led to changed designswhic hminimiz e the amount of landneede d for irrigation distribution systems.Preferenc eno w isgive n toth e use ofman y small pumps along existing or improved internal channels rather than toth e construction ofnew ,gravity-flow ,channels .

Farmers' alternatives

During theeightee nyear s thathav e intervened since theMaste r Plan was prepared,ther eha sbee n aslowl y growing recognition thattech ­ nical and physical factors areno t theonl y considerations tob e taken

152 intoaccoun t inagricultura l development. Inth eMaste rPlan ,i twa s fathernaivel y assumed that landwhic h remaineduncultivate d inth e dryseaso n did sobecaus e itwa s toodry ;som eplanner s andpolic y makers still express suchviews .Planner s alsonaivel y assumed that, Wlth theprovisio n of flood protection and irrigation,farmer swoul d Quicklyadop t improvedmethod s of cultivation and grow twoo r three "ighyieldin g crops ayear .Projec t planners -an d assertive aid donors- calculated benefit:cos t ratios accordingly,showin gattrac ­ tiverate so f returno npropose d investments. Tw° thingshappene d toupse t those early assumptions.On e istha t thereha sbee n aconsiderabl e increase indoubl e cropping and triple croppingo f land,eve nwithou t flood protection,drainag e or irrigation. The second is that,i nirrigatio n and drainageprojec t areas,farmer s haveeithe rno t adopted thecroppin g patterns designed for themb y the Projectplanners ,o f theyhav e done somor e slowly thanwa s projected. In the first case,soi l surveyors have confirmedwha t farmers obviously knewalready :namely ,tha tman y floodplain soils store sufficient m°isture after the floods and rainy season tosuppor t a satisfactory Cr°P ofwheat ,pulse s or oilseedswithou t irrigationdurin g thecoo l vmter months.Th e changes from single todoubl e cropping,an d from doublet o triple cropping,hav e resultedmor e frompopulatio n pressure - and henceeconomi c pressure - than from theprovisio n ofmoder n techno- logy. Much land still remains fallow in thedr y season or in theau s season inarea swit h relatively lowpopulatio n density,eve n though c°nditionsma yb e suitable forgrowin g crops during thoseperiods . Bi8 farmers using share-croppers canobtai n asufficien t surplus from °ne croppe ryear ,wit h littleo rn omanagemen t or investment,s otha t

there is little incentive for them togro wa secon d crop or to invest ln increased production.Tha t isparticularl y so inth ecas e ofabsente e landowners . In the second case,farmer shav ebee nmuc h slower toadop t intensive Cr°Pping patterns andHYV s thanprojec t planners assumed.Figur e1 gives examples of the rateso fadoptio n ofHYV s in theboro/au s and •Sïïanseason s in theG- Kan d DNDprojec t areas.Bot h areashav econtrol - led drainage and irrigation,an dhav e soilswhic h are suitable for ricewit h irrigation.

15.1 Yet, in theG- Kare a (Phase I), it tookmor e than 10year s forHYV s tocove r even 50percen t of the area,althoug h thetren d hasbee n continuously upward. In theDN D area,i t took only twoyear s toreac h 50percen tHYV s inth ebor o season and eight years toreac h 90percen t HYVs,a twhic h level theproportio n seems tohav e plateaued;bu t in theama n season,progres sha sbee nerratic ,an d seems tohav eplateaue d at 70percent . Two lessons canb e drawn fromthi s experience.On e istha t drainage and irrigation projects shouldb e regarded primarily as agricultural development projects,no t asengineerin g projects.Therefore ,agrono ­ mists and soil scientistsnee d tob e given astronge rvoic e inth e planning and implementation of suchproject s -an d thatvoic e should be listenedto. ' The second lesson istha t agricultural development involvesfarmers . Therefore,farmer s should be consulted about thepracticalit y and acceptability of theplan sbein g prepared for them. It isth epolic y makers orplanners ,no t the farmers orExtensio n officials,wh o should beblame d ifambitiou s project targets areno tmet .I n the caseo fbot h theG- K and DNDproject s inBangladesh , theprojec t authority - comprising administrators and engineers -ha splanne d threeHY V cereal crops ayea r for theprojects ,withou t finding outwhethe r thati s what the farmerswan t tod oo rwhethe r such cropping patterns are practical for them toadopt . Recent investigations indicate that such intensive cereal cropping patterns dono t suit all farmers.I n theG- K project area,fo rexample , theaverag e sizeo f farmholdin g is2 h a and themajorit y of farmers aredependen t onhired ,migran t labour for transplanting and harvesting theau s and aman rice crops.Harvestin g and threshing (bybullocks )take s 1-2month s ormore ,whic h prevents thequic k turn-around which the addition of athir dHY V crop peryea rwoul d require.Moreover ,th e production of twoHY V rice cropspe ryea r gives farmers owning 2h ao r more ahug e grain surplus,abou t 5-6 times their family consumption needs.Ther e isn o incentive for them togro w athir d croppe ryea r merely tosatisf y theplan s of theprojec t authority. Theexperienc e of theG- K project and theChandpu r project illustrates another commonweaknes s inplanning : i.e., ignoring the soil factors

154 which influence farmers'choic e ofcrops .I n the former case,th esoi l survey report carried out for theprojec t indicates 20percen t ofth e areas asbein g unsuitable for irrigated ricebecaus e ofrapidl yperme ­ able soils.Eve n if thatwer eno t apparent from the soil survey report- which,admittedly , likeman y reports of itstim ewa smor e descriptive thanprescriptiv e - itshoul d havebecom e obvious from site examinations along thepropose d canal alignments.Ye t the irrigation layoutan d cropping pattern adopted totally ignore that information.Th emai n dis­ tribution channels are aligned along themos tpermeabl e soils- becaus e theyoccup y thehighes t part of the landscape,a s isrequire d fora gravity distribution system- bu t theyar eunlined .Als o twotransplan ­ tedric e crops ayea r are irrigated,eve n onpermeabl e soils,mainl y because thever y lowo rn o irrigation charges dono t give farmersan y incentive tous ewate rmor eefficiently .No t surprisingly,wate rdoe s n°t reach tail-end areas,an d only about 55percen t of thesuppose d command area actually receives irrigation. The Chandpur project planexpecte d farmers togro w two (orthree )HY V rice crops ayear . In fact,withi n thecomman d areao falmos t 30,000ha , farmers grewonl y 18,783h ao fbor o rice inth e 1981-82dr yseason . They grew3,50 7h ao f irrigatedwhea t and otherdry-seaso n crops;an d a further 6,347h ao fdry-seaso n crops (mainly chillies)wer e grown without using irrigation.Thi s reflects thefac t- know n toth efarmers , and described in the soil survey reports- that asubstantia l area within theprojec t boundariesha s light-textured,permeabl e soilswhic h areno twel l suited to irrigated rice cultivation inth edr yseason . Underpre-projec t conditions,som e of those soilswer e intensively used fordry-seaso n cropswithou t irrigation,especiall y for chillies,whic h formed the area'smos t important cash crop.Obviously ,farmer s find it m°re economic to continue growing chillies (and otherdrylan d crops) °nsuc h soils,withou t using irrigation, rather than tofollo wprojec t Piansblue-printe d over theirhead s fromDhak a (orfro m adonor' shead ­ waters).

155 Agro-socio-economic surveys

In this, the farmers areright .Project s should be tailored tosui t farmers,no t viceversa .However ,i tofte n appears as though project planners first calculate aneconomi c rate of returnwhic hwil l justify investment ina project ,an d then fabricate an intensive cropping pattern toprovid e that rateo f return.Admittedly , theplanner' s task isdifficult .Bu t it could bemad e easier ifagricultura l and socio­ economic surveyswer emad e inadvance ,an d ifprojec t planswer e then based on arealisti c assessment of the findings.Projec t planners raise no question regarding thenee d fordetaile d sitesurvey swhe n damsan d headworks arebein g designed. Thereneed s tob e asimila r recognition of thenee d fordetaile d agricultural and socio-economic site surveys tob emad ebefor e costly agricultural projects aredesigned . Agricultural surveys should provide information on the following subjects: a)soi lpattern s in relation to topography and hydrology,becaus emos t floodplain land isneithe r levelno r uniform insoils ; b)physica l soil properties (actual orpredicted ) inrelatio nt o irri­ gation,drainag e andnatura lmoistur e storage; c)crop s and cropping patterns inrelatio n tosoils ,includin g evidence from cropspresentl y grown in theare awit h irrigation; d)far m sizes and tenancy conditions; e)seasona l availability and costo f labour; f)preferre d staple and cash crops,cro p price relationships (including HYV versus traditional varieties), and relative production costsan d returns,etc. ; g)opinion s ofbig ,mediu m and small farmers onwhic h crops theywoul d prefer togro wwit h thepropose d project improvements,an dwha t additional inputs or servicesmigh t beneeded ;an d h)objections ,i fany ,fro m thosewhos e livelihood might suffer asa result ofprojec t implementation: e.g.,fishermen; farmers onrela ­ tivelyhig h landwh omigh t suffer frompreventio n of flooding;an d farmers indepression swhic h mightbecom e perennially waterlogged after installation of dry season irrigation.

156 •Lfth e findings of such a survey indicate that the proposed project Would not be economic, then so much the better: the funds can be better sPent elsewhere. How many projects must there be around the world by n°w that represent a drain on national economies because their plans Were not based on a realistic study and appraisal of the agro-socio- economic factors? In such a situation, project planners (or Government Policy makers) have four alternatives« a) accept the findings that the proposed project would not be economic, and divert the proposed funds to amor e economic investment (prefe­ rably within the same area); b) accept the findings and design/redesign the project to suit the Physical, social and economic conditions found; c) accept the findings, and consider whether by intensive extension activity, price incentives, improved markets, etc., farmers could be persuaded within a resonable period to adopt cropping patterns which would make the project economic; in this respect, a pilot scheme can be useful, both for the farmers and the project planners; d) accept the findings that the project, as proposed, will not be profitable, and proceed with it in the knowledge that it will need to be subsidized, temporarily or permenently, in the national inte­ rest.

First generation problems

The low irrigation coverage in the G-K project area due to seepage losses, and the erosion of sections of the embankments in the Chandpur and Brahmaputra Right Bank projects, can both be regarded as first deration problems: i.e., they result directly from the project design itself. Another example is the cutting of embankments by farmers or fishermen who feel that the project is adversely affecting their liveli- ho°d. In the latter case, advance public education about the effects of the proposed project, prompt payment of compensation or a modifica­ tion of project design could help to avoid the problem. Another example is provided by project designs which, in seeking to °Ptimize economic rates of return, prevent project benefits from being Provided to a substantial number of farmers within the project bounda-

157 Both theDN D andChandpu rproject s provide examples of this. Inth e DND area,th eoptimu m economic pump drainage design left about 10 percent of thepolde r area,i ndepressio n sites,subjec t todee p flood­ ing for awee k ormor e after sustained,heavy ,monsoo n rainfall,suc h that farmers on such land cannot risk growing transplanted aman(in ­ cludingHY V aman)o rusin g costly inputs on their monsoon seasoncrops . Sustained,heavy ,pre-monsoo n rainfall in 1980-81 also caused flooding which destroyed about one-third of theHY Vbor o crop inth eChandpu r project area andprevente d farmers fromgrowin g HYV aus inlo w lying areas.Th e solutionwoul d seem tob e todesig n projects sotha t they optimize thebenefit s tofarmers ,eve n ifthi s requires accepting a lower rate of return onprojec t investment.Tha t principlewoul d seem tob eparticularl y important inarea swher e small farmerspredominate ; (inth eChandpu r project area,fo rexample ,th e average sizeo ffar m holding isonl y 0.4ha) . The difficulty of satifying theneed s of all farmerswithi n theCoasta l Embankment project polders can alsob e regarded as afirs t generation problemwhic h could havebee n anticipated. The tidal landscape com­ prises shallowbasin swit h raised rims along creeks.Althoug h the difference inelevatio nbetwee n thehighes t and lowest pointsma yb e nomor e than 60-100 cm,suc h differences canb e critical for ricefar ­ mers,especiall y for thosewh o risk togro wdwar fHYVs . Tidal sluices inth eembankment s provide drainage of local run-off following monsoon season rainfall.Th eproble m is,ho w toregulat e thedrainage .I fth e basins are drained toleav e theoptimu m depth ofwate r on themfo r transplanted aman seedlings,th ehighe r fields dono t retain enough water.O n theothe r hand,i fwate r isretaine d tosatisf y theneed s of farmers on thehighe rmargins ,the n thebasi n land stays toodeepl y flooded.A possibl e solutionwoul d be toconstruc t low interiorembank ­ ments toretai nwate r on land atdifferen t levels,bu t experiments to. test ordemonstrat e thispractic e haveprove d unsuccessful sofar , because of lack of cooperation frombi gland-owners .

158 Second generation problems

number of problems has arisen in embankment projects some time after hey have become operational. These can be regarded as second generation Pr°blems which it may or may not have been possible to predict during pro­ ject design.

Ihe first problem of which the author became aware was the rapid situation °f creeks outside some of the coastal embankments. Under natural condi­ tions, tidal water flooding the land twice a day flows slowly off 'he land again as the tide falls, thus keeping the creeks flushed. After embankments have been completed, sluice gates prevent tidal water fr r°m entering the polder at high tide. Water in the creeks stagnates at hlgh tide, therefore, and drops some of it silt load which the slow flow of the falling tide is insufficient to pick up again. Some creeks silted UP within three years of embankments being closed. That not only re­ stricted navigation on the creeks,whic h formerly had been important, but it also caused waterlogging in the adjoining polders because of the restricted outflow during monsoon season rains. Hydraulic studies are needed to provide a solution to this problem. second early problem to develop was perennial waterlogging of some repression sites in the G-K project area. That resulted from excessive seepage losses from neighbouring irrigation channels located, as des- Cribed earlier, on permeable floodplain ridges. This problem could become more serious and extensive if full-scale irrigation were to be Produced in the dry season (so far, the project has mainly provided SuPplementary irrigation in the pre-monsoon and monsoon seasons, allow- ln8 the watertable to fall during the first half of the dry season). If the problem were to become more serious - and it is,o f course already serious for farmers whose land is affected - itmigh t be neces- Sary to introduce two measures to reduce waterlogging: lining of irri- gation channels along sections where seepage losses are most serious and if this did not provide a sufficient allegation,th e installation tube-wells to lower the water-table. ^-thin the last 3-4 years, there has been a growing awareness of zinc (arid sometimes sulphur) deficiency in rice crops grown in the DND, handpur, Barisal and G-K project areas. Recent studies suggest that

Su lphur deficiency might eventually become the more widespreado fth etwo .

159 The symptoms developwher e the rate of removal of soilnutrient sha s been increased due toth e cultivation ofon eo rmor eHY V rice crops peryear ,an dwher e the provision of irrigation forgrowin gbor o rice keeps the soilswe t formos t or allo f thedr y season inadditio nt o themonsoo n season. Farmers have found two solutions.On e is togro w aquic kmaturin gwinte r crop- e.g. ,mustar d orpulse s -befor eplantin gboro .Tha thelp s the topsoil todr y out andbecom e oxidized fora time ,whic h increases zinc and sulphur availability. The second solution ist oad d zinc sulphate fertilizer.Th eus e of this fertilizer has increased remarkablywithi n the first 18month s that isha sbee nmad e available,t o theexten t that a consultant examining theproble m early in 1982 was able tofin d littlevisibl e evidence of zincdeficienc y inth eDN D and Chandpur pro­ ject areas:mos t farmers appeared tob e using the fertilizer.Farmer s clearly aremuc h less conservative about adopting newpractice s than they arepopularl y condemned asbeing ,a t leastwhe n there areobviou s and simple remedies available. Acid sulphate soils,fortunately ,provid e arelativel ymino r problem in Bangladesh. Such soils occur patchily on the saline tidalfloodplains . The acidity problem ismos t severe and extensive in thesouth-east , where some soilshav e gone out of cultivation.However ,a substantia l areao f suchempoldere d soils inhighl y productive formakin g salt.O n theGange s tidal floodplain, the acid sulphate problem is less serious because Ganges silt in theriver s during the flood season contains lime which could beuse d toneutraliz e the acidity, ifnecessary . Peat basins inth e transition zonebetwee n theGange smeande r and tidal floodplains haveno t yetbee nempoldered,s oproblem s of subsidenceo f the land surface due todrainag e haveno tye t arisen on alarg escale . However,extensiv e parts of these peatbasin s are includedwithi n the proposed Satla-Baghda and Faridpur projects.Problem s arising fromsub ­ sidence canb e expected todevelo p in theseprojec t areasunles s the original plansmad e fordrainin g thebasin s aremodifie d soa s tokee p thepea twe t (or tobur y itwit h alluvium dredged from adjoining rivers)'

160 Land useregulatio n

Tt 0 other second generation problems have recentlybee n identified: ncroachment of settlement onto flood-protected land;an d theconversio no f Polders from agricultural use to shrimp farming.A recent FAOconsul ­ tant's study of seven,scattered,rura larea s inBanglades h snoweo that ingen e ettlement and related non-agricultural land useexpande d byonl y 0.8 Percent(in total)betwee n 1952an d 1974,eve n though thehuma npopula - x°n expanded by anaverag e of 58percen t during that period, animation of airphotos showed that thepopulatio nha d expanded almost tirelywithi n existing settlements,b y reducing theare aunde r trees waste land.Tha twa s partly explained by the seasonal flooding, lch makes itcostl y tobuil d ane wearthe n platform abovefloodlevel , nd partlyb y the farmers'natura l inclination topreserv e their land or agricultural production.However ,i n the first 10year s following he completion of theDN Dpolde r outsideDhaka ,th eare aunde rsettle - ent and industry doubled,an d the trend obviously is continuing aPidly asfarmer s (and suburbannon-farmers )buil d individualhouses , cattered over thewhol e area instead ofwithi nexistin g settlements. uhin thenex t 10-20years ,i t isprobabl e that thepolde rwil ln o °n8erb e aviabl e agricultural project;i twil lb e asubur b ofDnaka . nere isa dange r that asimila r sprawl of settlement could eventually egate theobjective s ofothe rpolde r project areas. (Evenpre-project , 28 Percent of theChandpu r project areawa s occupied by settlements). ere isth e risk,too ,tha t the spread ofsettlemen t on thefla t 1,e-» without making high platforms)coul d lead tocatastrophi c loss üfe and property if,fo ran y reason,a polde r embankment were tob e Cached during thefloo d season. Itseem s essential,therefore ,tha t he spread of settlements (and industry)withi n flood protected areas n°uld be regulated sotha t theminimu m amount ofvaluabl e agricultural atld istransferre d tonon-agricultura l uses,an d soa s tominimiz e the lsk of catastrophic casualties andpropert y damage ifa nembankmen t is Cached. At present,th eGovernmen t ofBanglades h hasn o practical e§al means toregulat e land use.Tha t isa nomissio nwhic h needs tob e ectified without delay.

161 The same lack of land useregulation s ispermittin g powerfulbusinessine n and land owners tocover t agricultural polders inpart s of theCoasta l Embankment project area toshrim p farms.Th e process issimple .Th e embankment isbreached ,allowin gbrackis hwate r to flood the landan d shrimps toente r forbreedin g and growth.Th e salinity subsequent soil either prevents the farmers fromgrowin g their traditional,single , amancrop ,o r it greatly reduces amanyield s andproduction . Isi s estimated thatmor e than4,00 0h ao f land have so farbee n lost to agriculture inthi swa y insouth-wester n polders;n o figures arereadil y available for losses inth e south-east. Shrimp farming ishighl y pro­ fitable to thepowerfu l individualswh o control it. Shrimp exports als" earn the countryvaluabl e foreign exchange.Bu t theeffec t onsmal l farmers and agricultural labourers canb e disastrous,an d thebreachin g of theembankment s negates thepurpos e forwhic h theywer e constructed. A thorough socio-economic study isneede d todetermin e thene t social and economic gains and losses.Technica l studies also areneede d to determinewhethe r shrimp farming and cropproductio n canb e combinedo r canb epractise d on separate land.Whateve r the findingsmigh tbe ,i t seems essential that either theprojec t authority,a locall y elected council or central government shouldhav e thepowe r toregulat e landuse - in thepolder s inth egreate r public interest.

Futureneed s

To-date,majo r embankment projects have contributed anestimate d1 million tons (net)t oannua l foodgrain production.Tha t ismuc h less thanwa s expected when theproject swer eplanned . It also ismuc h less than the 2.5millio n tons (net)annuall ywhic h small-scale pump and tube-well irrigation schemesprobabl y have contributed. Themajo r embankment projects included in the 1964Maste rPla nhav e been slow toattrac t donor investment.Apar t from technical problems described in the text above,donor shav ebee n reluctant totak eu psuc h projectsbecaus e of thehig h capital costs and the long gestation periodebefor ebenefit s appear.Small-scal e projects have therefore attracted more supportbecaus e of the lower investment costpe rhectare » thequicke r returns and themor ewidesprea d distribution ofbenefits .

162 Included in those smallproject s are a numbero fso-calle d early imple­ mentationprojects ,usuall y providing flood protection and/or irriga­ tion (butusuall y notpolders ) to areaso fu p to6,00 0ha . Undoubtedly,i f thecountry' s population continuous togro w atcurren t rates- doublin g inabou t 30year s- thenmajo rpolde r projects (per­ hapsincludin g eatuary closures)wil l eventually beneede d soa st o e *able highyieldin g transplanted ausan d amant ob egrow no nmos to f thefloodplai n land,7 0percen t ofwhic h currently isto odeepl y flooded f°r them tob e grown reliably during themonsoo n season. Irrigationwil l alsob eneede d toexpan dHY V crop cultivation inth edr y season and to »akeproductio nmor e reliable in themonsoo n season.B y theyea r 2000 A-D-, it isestimate d thatannua l floodgrain productionmus t increase t°2 5millio n tons tosatisf y thepopulation' s consumptionneeds , ^garding suchprojects ,th enex t 5-10year sdurin gwhic h attentioni s concentrated onsmall-scal emethod snee d tob euse d tomak e anexhaus ­ se study of experience gained frompolde rproject swhic hhav ebee n dieted. Those studies should includeno t only engineeringconside ­ rations,bu t- atleas t equally important- agricultural ,socia lan d ^ononuc considerations:wha tha s succeeded;wha tha s failed.Arme d *ithmor e comprehensive information,planner s should thenb e *Me todesig nmor e realistic andprofitabl e projectswhic h arehette r ^ilored toth e farmers'needs .Tha twil l require therecognitio n that en~- r, • »kmcclvps.The y area mean s to etl8ineeringwork s areno t anen d inthemselves .»i» y an j • or,yiVn1turaldevelopment ,a sreflec - atlend . InBangladesh ,tha ten d isagricultura l y ^ ted inoptimu m improved landus ean d awel l fedpopulatio n .

'>ç . L. , ,,„, the Government ofBanglades h has Since thispape rwa sdrafted ,tn e wv T,• „„„arins aMaste rPla n forWate r sought assistance fromUND P m preparing „*,.efo r thisstud y ismor e fully Resources Development.Th eprospectu s for this y •j riip196 4Maste rPla n. comprehensive than thatprovide d by A th u-L,e i»ofn

163 Conclusions

Bangladesh's experiencewit hmajo r embankmentproject ssuggest sa numbe r ofprinciple swhic h mayb e ofwide r relevance,especiall y indevelopin g tropicalcountries . 1.Wher e embankment projects areundertake n primarily toincreas e agri" culrural production,the y should be regarded primarily as agricultural development projects rather thanprimaril y asengineerin gprojects . That impliesthat : a)soi l scientists,agronomists ,agro-economist s and agriculturalexten ­ sion specialists shouldb e given amor e responsible role inprojec t identification,design ,appraisa l and implementation; b) inarea swhic h already arecultivated , theopinion s of arepresen ­ tative rangeo f farmers inpropose d project areas should be sought inadvanc e regarding feasible cropping patternswit h proposed project inputs; c)wher e aprojec twoul d greatly alter existing agro-ecological condi­ tions, (asusuall ywil l be the casewit h embankment projects), possiblene w crops or cropping patterns shouldb e tested anddemon ­ strated inpilo t areasbefor e the fullprojec t is implemented;an d d)objection s from thosewhos e livelihood might suffer asa resul to f project implementation should be consideredwit h avie w either to modifying theprojec t design soa s toremov e theirobjection s ort o provide themwit h adequate alternatives or compensation. 2.Becaus e embankment projects usually areexpensive ,especiall ywhe n they includepum p drainage and irrigation,the y shouldb e regarded as a development mode of last resort.Tha tmean s thatGovernment s should examine and use alternative,cheaper ,agricultura l development modes wherever possible,unti l embankment,etc. ,become s themos t economic mode remaining available. 3.Geomorphological ,hydrologica l and hydraulic studies shouldb emade ' todetermin e the optimum location ofprojec t embankments and irrigation' draina^headworks along active river channels and intida l floodplains> taking intoaccoun t thepredicte d effects of projectwork s onrive r flowan d sedimentation outside embankments and ondrainag ewithi n embankments.

164 4 T • • • irrigation channels should be sited and designed soa st ominimiz e seepage losseswhic hmigh t causewaterloggin g and prevent irrigation enefits frombein g provided to tail-endareas . • Especially inarea swher e small farmers predominate,project s should e designed soa s tominimiz e land acquisition forprojec twork s and so s tomaximiz e thenumbe r of farmerswh o benefit,eve n if thatmean s cceptinga suboptimu m economic rate ofreturn . •Soi l and crop conditions ondifferen t agro-ecological land types lthin project areas should bemonitore d regularly soa s toprovid e arlywarning s ofan yphysical ,chemica l orbiologica l problemswhic h may develop. Relevant studies should bemad e tofin d practical solu- l°ns, including solutionswhic hmigh t require themodificatio no f Projectdesig n or operation. Similarly,agro-economi c surveys should emad e regularly and,wher enecessary,appropriat e changes shouldb e made inprojec t design,operatio n orcharge s soa s toensur e thatbot h armers and project authorities can achieveprofitabl ereturns . •Eithe r atnationa l or atprojec t level,lan dus e regulations should e wade and enforcedwhic hwil l ensure that settlementan d industry do not spread unnecessarily ontovaluabl e agricultural land oront osite s wlleredisastrou s losses of life and propertymigh t occur in theeven t 0f anembankmen tbein g breached by floods;also ,s oa s topreven t ort o c°ntrol forms of land usewhic h conflictwit h projectobjectives .

165 SOCIO-ECONOMIC AND PHYSICAL PLANNING ASPECTS

FROMSPONTANEOU SSETTLEMEN T TO INTEGRATED PLANNING AND DEVELOPMENT

A.K.Constands e Rijksdienst voord eIJsselmeerpol - ders,Lelystad ,Th eNetherland s

Abstract

Thereclamatio no fne w land,whic h isuninhabited , involves internal colonization implying theestablishmen t ofa ne w society. Inth ebegin ­ ning thereclamatio n projectswer ecarrie d outb yprivat e corporations and therewa sn o clear settlementpolicy .Eve nwhe n inth e19t hcentur y theStat e tookresponsibilit y forth eoperation sn o settlementpolic y ofan y importancewa sdeveloped .Durin g theexecutio n ofth eIJsselmeer - polders-project inthi scentur y aplannin g anddevelopmen t system was built up,however ,tha t takes careo fdetaile d integrated plans,take s responsibility forth epreparatio n of the land,fo r settlementpatterns , forconstruction , forth eguidin g of immigration,th ecreatio n ofjobs , and theharmoniou s integration ofth epla n inth enationa l planning goals.

Theorigi n ofpolder s ist ob e found inth ehuma n attempts toprotec t land against flooding,wit h theai m tomak e land that could beuse d temporarily only,int o land thatcoul d beoccupie d permanently and safely. Inth eNetherland s theseattempt s started abouton e millennium ago. Why theseheroi c effortswit hprimitiv e tools insuc ha dangerou shalf " drowned countrywer emad e isa n interesting question,bu twil lno tb e

166 answered here.No tth ecause sbu tth eeffect sar erelevan t inthi s °ntext.Ou to fthi sco-ordinate d movingo feart hwhic h enabled the Peoplet ocontro lth emovin go f water,technica l aswel la sorganizationa l Killswer e developed,whic h created aselfconsciousnes s inmatter s watercontrol thatforme d thenecessar y basis forth edevelopmen t Plansfo rdrainag e ofne w land, land thatwa sno toccupie dbefore . n small-scale reclamations thisdi dno talway s implyne whuma nsettle - ent:th ereclaime dlan dwa sjus tuse dt oenlarg eth eexistin g farmso restates . n theNort ho fth ecountr y it isusual ,u p toth epresent ,tha tth e °rderlineso fa farm,standin g perpendicularly onth ecoastline ,ar e •"-ongatedint o thewate ran dal l the land thatwil leventuall y bere - aimed, lyingbetwee n those lines,belong s inprincipl e totha tfarm . Ven ifa concerte d effortwa snecessary , sucha sth edrainag eo fa ake. forwhic hwindmill sha dtob ebuil tfo rpumpin gth ewate rout ,i t ightwel l be that thereclaime d landwa sfarme d byth epeopl e living °n theborde r ofth eforme rlake .

en thedrainag e projectsbecam e largeran d technically moresophisti - ated, considerable investmentswher enecessary ,whic h couldno tcom e r°m localsources .A sa consequenc e theproject s came intoth ehand s of managers,planners ,an dwer e considered asend si nitself .Farm s ere established, villagescam eint oexistence ,peopl e from elsewhere ere moved in,sometime s fromadjoinin gareas ,sometime s from larger lstance, sometimes individually,sometime s ingroups . though the inhabitantso fth ene w land didno tcom efro mver yfar ,mos t

a tenfro m withinth e Netherlands,whic h isa rathe rsmal lcountry , fact istha tthes epeopl e came together,i nne wcircumstances ,wher e eve rythingha dtob ebuil tu pfro mscratch ,wher ea ne w society hadt o e formed.A ssuch ,th enam e 'internalcolonization 'whic hha sbee n 1Ven tosuc hprocesse s isquit eadequate .Als oth enam e 'pioneer' fcributedt oth efirs t settlerswa sno ta nexaggeration ,becaus eth e lif e ofth efirs tan d sometimes even thesecon dgeneratio n wasno ta n asy one.I nth e 17thcentur y thecompanie swhic hundertoo k thework s e formed bymerchants ,urba npeople ,wh owante d landbu twh odi d knowho w towor k itan d sometimesappointe d unskilled peoplet o •••an°ntinud e theexploitatio no fth elan dafte rdrainage .Furthermor e the was oftenbadl y drained,a sa consequenc eba dharvest scam eabout .

167 Peoplewer e struckb y diseases,lik emalaria , inunhealth y conditions atth ebeginning . Inth e 19th century,whe n some largedrainag e schemes,wit hmoder n techniques (steam engines instead ofwindmills )wer ecarrie d outb y theStat e andno tb yprivat e companies,th e living-conditions forth e peoplewer eno ta tal lgoo di nth ebeginning .Th eStat e carried outth e works forreason so fsafety-protectio n ofth earea s surrounding the lakes- an dwa sno t interested inth eexploitatio n ofth e land.Afte r initial drainage and aroug h parcelization theacquire d landwa ssol d assoo na swa spossibl e andn oattentio n wasgive n towha thappene d further.Thi swa sth ecas ewit hon eo fth e largestdevelopment s inthi s country, theHaarlemmermeer ,a nare ao f20.00 0ha , inwhic hno w Schiphol-airport islocated .Prosperou s asth eregio n isnow ,ver ypoo r itha sbee n inth e first twenty yearso f itsexistence ,becaus eo fba d drainage, lacko fgoo d organization ofth ebuildin go f thene w society, resulting inba d health-care,forma l education,housin g andtransporta ­ tion. When inthi s century theDutc hgovernmen t decided tocarr y outth e largest reclamation project everundertaken , itwa sunderstood ,o nbasi s ofth eaforementione d experiences,tha ta sth egoa l should bet odevelo p notonl y new land,bu tals oa prosperou san d harmonious society,i t should take fullresponsibilit yfo rth edevelopmen t processa sa whole , notonl y for the technical,bu tals o forth e social andeconomi c as­ pects.Thi s idea ofmor e intensive intervention by theStat ewa sno t only inspired by the ideatha t themistake so fth epreviou s century should beavoide d now,bu twa sals o anexpressio n ofth ecomin go fth e welfare-state. TheStat eha dt opla y inthi swa y adua lrole .A sowne ro fth ene wland , developed withpubli c funds,i tha d thedut y tostriv eafte rgoo d econof1 management of thearea .I tshould ,jus ta san yprivat eentrepreneu r try tomak eprofit .A sguardia n ofth ewelfare-stat e itha d toprotec t the inhabitants againstmisfortun e and topromot e public welfare.Thes e tworole sar eno talway seas y tocombine . The firstrol ewa s inth ebeginnin g considered asth emos t important one. The landwa smad eread y fornorma l cultivation by theDevelopmen t Authority. Alan dallocatio n planwa smade ,wit h fixed sizesan d types

168 of farms.Th e land remained property ofth eState ,th e farm buildings wereconstructe d byth eState .Th e farmerswer ecarefull y selected in ordert ob esur e thata ver y capablegrou p ofpeopl e would tillth e •Landi nth e new area.I fth emai nai m ofa reclamatio n project ist o increase theagricultura l production,the n thisi sa goo d policy. Iti s "thesam epolic ya swoul db eapplie db yaprivat e landowner:tr yt ofin dth ebes t enants.Thi spolic ymad ei tunnecessar yt omak eextensiv eeducationa lan d trainingprogramme sfo rth esettlers .The ywer eread yfo rth ejob .Thi si ssta ­ teds oexplicitel ybecaus ei nman yforeig ncase s themai nproble m isho w to teachpeopl e tomak e thebes tus eo fth ene wopportunities . Inthos e cases thepeopl e areno tselected : they are theone swh oar eentitle d or somereaso n toreceiv ea piec e ofland . The second role,bein g theguardia no fwelfare ,i sles seas y todescribe . Eyen on thematte ro fth efarm s itself,th ebasi so fth eeconomy ,ther e Were next toeconomica l also socio-political factorstha tplaye d arol e lr>decision-making . From apurel y economical viewpoint itwoul dhav e been possible tocalculat e which typeo ffar mwoul dgiv e thehighes t Profit.Bu tthi swoul d notgiv enecessaril y thehighes t socio-economic avantage on thenationa l level.Fo r thatreaso n arathe rcomplicate d systemwa sdeveloped ,resultin g ina mi xo fsmalle ran d largerfarms , givingopportunitie s todifferen tkind so ffarmers .

But outside the direct sectoro ffarmin g theplannin g becameals omor e human',mor edirecte d toth ebuildin go fa societ y than toth eeconomi c evelopment only.Th efarmin gpopulatio n should notonl yhav egoo dfarms , but there should beals oservice-centres ,good ,housin gfo rth eworkers , thereshoul d beshops ,schools ,churches ,medica l services,recreatio n facilities, libraries.An dal l thepersone l employed inthes e services should have agoo d basisfo rexistenc e and theservice s should have a good quality. n retrospectthi ssound s logical and simple.A tth etim eo fth efirs t development inth e IJsselmeerpoldersproject,hal fa centur y agonow , xt meant thatal lkind so frelation sbetwee n social factsha d tob e udied and quantified:ho wman y customers doesa bake rnee d tomak e living;ho wofte n doesa n averageperso nborro wa boo kan dho wman y iJ-ometersh ewil l travelt oge tsuc ha book ;youn g loversnee dsom e °°d tomak ewalk s in:ho wman y hectareso fwoo d shouldb eplante d to

1AQ satisfy theneed so fa certai n quantity of lovers? Thisdi d notonl yprovok eresearc hneeds ,bu t itals oencouraged ,eve n necessitated,government-interferenc e ina numbe r offield stha tha d alwaysbelonge d toth eprivat e sphere.Standard s andnorm sha d tob e found fora numbe r of immeasurablethings . Ofcours e researchan dnormsettin gha d imperfactions,no t inth elas t placebecaus e social changeremaine d fora largepar tunpredictable , buta nadvantag e ofal l thisresearch-wor k and striving after integrated, comprehensive planningwas ,tha tth eunderstandin g about interdependences inmatter so fsocieta l developmentwa s improved and thatbecaus eo f thatbette rplannin g systems could bedesigned . From the singlegoal ,ho w tokee p theare adr y and safe,th egoa lt o makeprofi t from agriculture,no w thegoa lwa st ogiv epeopl ea goo d life.

Asagricultura l areasth epolder s could beconsidere d asbein ga nen d in itself.O f course the internal colonization had alsoa sa goa lt o solveproblem s onth emai n land: farmers leaving forth epolder s freed space forothe r formso f landuse,o r for improving the farm-structure inovercrowde d areas.Th epolic y ofselectio n ofapplicant s fora far m inth epolder swa s inlate ryear s evengeare d totha tpurpose .Bu tth e developments within theprojec t werenevertheles shappening s ina mor e or lessclose d regional-economic system. Because inothe rpart so fth eworld , inman y ormos tcases ,polder s aredevelope d foragricultura l purposes,som emor e attention willb e given totha tpar to fth ehistor y ofth e Usselmeerpolders. Ifagricultur e isth emai n source ofproduction ,th echange s inagricul ­ turehav e far-reaching influences on thesocio-spatia l system. Inou r case themai n changewa stha tth erespons e ofagricultur e toth ecost - pricesqueez ewa sth ereplacemen t of labourb ymachines ,whic hmean t thatther ewer e lesspeopl eo n the land.Les speopl eo n the landmean sa lowerdeman d forservices . This lower demand forservice s wasquit eproblematic ,becaus e itwa s only quantitatively lower,qualitativel y itbecam ehigher .Goo d schools werewanted ,shop swit ha variet y ofware swer erequested .Thi sproble m could within the closed system only besolve d by reducing thenumbe r

170 °fcentra lplace s andacceptin g thelarge r distances from theperipher y °fth ecatchmen t areast oth ecore .Becaus eo fth e facttha tth e farmers were inth epositio n thatthe y couldposses son eo rmor eprivat ecar s the increase indistanc ewa sacceptable ,bu to fcours eno tideal . Theremarkabl e thingabou tth eprojec to fth eIJsselmeerpolder s istha t iti spossibl e tose eth eeffect so fsocio-economic ;chang ean d ofdeve ­ lopment inplanning ,rea l life,becaus e thepolder shav ebee n constructed °neafte rone ,wit htime-lag s longenoug ht ose echang eclearly :year s °fdrainag ebein g 1930,1942 ,195 7an d 1968. Inth efirs tpolde rth emai n «ffortha sbee npu tint oa goo d landuseplan foragriculture :rectangula r lots,goo d roadconnections,i nsom epart seve nwaterconnections .Bu t a Plan fora balance d settlementpatter nwa sno tmade .I twa sexpecte d that likei nth epas ta troadcrossing sservice swoul d springup .O fcours e thiswoul d havehappened ,bu tno t inth eorderl y wayan dwithou tpersona l Maniasa swa sth enor m inthi sera .Therefore ,late rth egovernmen t took care ofth eestablishmen to fvillages .I nth esecon d polder the lesson *astake n atheart :nex tt oth ecarefu lplannin g ofth e agricultural landuse,th esettlemen tpatter nwa sdesigne d onbasi so fextensiv e studies °ncatchmen t areaso fdifferen tkind so ffunction san d ondistance sfro m theperipher y ofa villag eare at oth ecentr ewhic hwoul d beacceptable . The resultwa sa hierarchica l pattern ofa regiona l centre inth egeo ­ graphicalpoin to fgravit y anda circl eo fte nvillage saroun dit . Alreadydurin g theperio d ofexecutio no fth epla n itbecam e cleartha t thedynamis m ofsocieta ldevelopmen twa sunderestimate d and thatth e asternwa s too static:th evillage sremaine d toosmall ,th eservice s c°uld not function inth eprope rwa y fortha treason ,an dbecaus eo f *nimmens e increase inprivat emotorizatio n distances counted much less as alimitin g factor,whic hcause d thatth eregiona l centregre wfaste r thanwa s expected.A paralle lo fthi swa y ofplannin g ina close d system can be found inth eLakhis hregio n inIsrae l (nota polde rbu ta forme r deo«,,.M<=sert)^ .mTh ^e sam ehierarchica .• •_• „i „«fforl pattern=;e n seitu p." i ^n abou t thesam e time ar,_, , . u-iryiat Gat- has grown while the and nowa prosperin g regional centre- Kyria tba t \ viHages have hardly afunction . In thethir d polderth eresult so fth echange sar eclearl y demonstrated. A8aina regiona l centrewa splanned . Thenumbe ro fvillage swas ,i n c°mparisonwjt hth eforme rpolder ,greatl y reduced,fou r instead of

171 tenan do fthes e£>u rori ytw owoul d bebuilt .Th eaverag e sizeo fth e farmswa s increased,th enumbe ro fpeopl e employed inagricultur ewen t downan ddow nan dsoo ni twa srealize dtha tth esyste mo fenlargemen to fscal e could notg oo n forever.Th eclose d system wasbroke nu pb y thedecisio n nott obuil d houses for local demand only inth etw ovillage s thatwer e realized,bu tjus tt obuil d and allow people from elsewhere,wh ower e not economically tiedt oth earea ,t obu yo rren ta house .Becaus e ofa shortage ofhouse s and the desireo fman y people to liveoutsid eth e big cities ina quie trura lenvironment ,thi spolic y wasquit esuccess - full. Itwoul d be interesting tokno who w thisproces swoul d havedevelope d inth e followingpolder s ifagricultura l usewoul d havebee n remained themai n function. But thiswa sno tso .Aroun d theyea r 1960th eperio d ofth eIJsselmeer - poldersproject asa n isolated agricultural project ended.Th epolder s comingneare r toth eurba n concentrations inth eWes to fth ecountr y(th e Randstado rRi mCity )wer emor ean dmor eregarde da sacompensatio n forth e scarcity ofspac e inth eurba nareas .Th eborderlakes ,designe d atfirs t forgeohydrologica l reasonsonly ,becam e ina shor t timerecreation - areaso fnationa l importance,fo rswimming ,fo rsailing ,developin ga demand behind thedyke s forarea swher e campings and holiday-bungalows could bebuilt . Ofmuc hmor e importance hasbee nth edecisio n to choose thepolder s asth e location oftw one w towns.Th efirs t one,Lelystad ,coul db e regarded asa n expanded townbecaus e thepolder s would haveneede da larger centre,a kin d ofprovincia l capital,anyway .Withou t the 'task' togro wou tt o100.00 0 inhabitants,som e 30.000woul d have lived in theplac e ifth eregiona l system had remained closed. The second one, ,designe d for250.00 0people ,i sa pur e satellite ofAmsterdam ,bu t isplayin g role ofcours e inth epolders . Ina rathe r shortperio d changeshav e takenplac ewhic hhav ea tremendous effect.Wher e asa continuatio no fathousan dyear s0 ld tradition the agricultural spaceo fth eNetherland s would be increased withabou t 10percent ,no w theregio n issee na sth ehabita t forhal fa millio n ofpeople . Inth eDutc h termshal fa millio no fpeopl e isa sufficien tnumbe rfo r

172 forminga ne wprovince ,bu tthi s isprobabl y noto fgrea t interestfo r a foreignaudience . °fmor e importancema y betha t theagricultura l function,whic hha sbee n "themos t important duringth eperio d ofreclamation ,i sno wbein gattac ­ kedb ya thir d new element:nature .I nthi s crowded,urbanize d andin ­ dustrialized country there isa genera l feartha tnatura l areas,typica l for "thelowlands ,wil l disappear.Therefore , there isa stron g (political) Tiovementtha twant st okee ppart so fth edraine dlan d asi ti s afterreclamatio n and doesno twan t thatth efift han d lastpolde r ismade ,becaus ea s a lakethi spar to fth eterritor y hasmor e value thana sland . some people state thatno tdoin g things,no t transformingth eenviron ­ menti sth eultimat e wisdom after aperio d ofruthles s destructioni n ordert omak eprofit .Other s think that thisattitud e isth eresul to f a stateo fsuc hhig hprosperity ,tha tpeopl e think they canaffor dt o ieavething sa sthe y are.Probabl y there issom e truth inbot hstatements . Ar>yway,i ti sa curiou sphenomeno n tose etha tther e issuc ha resistanc e to theattemp t tocreat ene wspac e forhuma n life sonea r toa nare a where sixmillio npeopl e livean dwh ohav e ashortag eo fspace .O fcours e thewate ra ssuc hi sals ospac efo rhuma nus ean dthi si s recognized byth e fa<=ttha t theborderlake s ofth epolder sar edesigne d widertha ni s necessary forhydrologica lpurposes .

So> asha sbee n said:eac hpolde r isa nexpressio n ofth etim e inwhic h it;ha sbee n constructed, even thelas ton eb yno tbein gconstructe dyet ! It shows that themai nvalu eo fthi stechniqu e ofdrainin g isth e acquisition ofspace ,whic hca nb euse d forman y purposes.Thi s isdemon ­ strated inth eNetherland s very clearly,becaus e this issuc ha densel y Populated country- Also theolde rpolders ,whic hhav eoriginall y been made forth eacquisitio n ofagricultura l land,ar eofte nuse dno wfo r °therpurposes :industry ,residentia l quarters ofth etown ,o rairports . The fact that thesepolder sar es oclearl y aproduc to fthei r time is Probably typical forpolder sa ssuch ,becaus epolder sar eflat ,ar e rather undifferentiated, havehardl y anyhistorica l landmarks,an dgiv e therefore theplanner sa hig h degreeo ffreedo m fordesigning .Thi si s Xn itself fascinating,bu t itgive sals oa heav y responsibility andth e a°senceo fguideline spresen t inth eexistin g environment,cause sdecision -

173 making tob eofte n laborious. On theothe rhan d the freedom ofth eplanner s islimite d by thewishe s andneed so fth e immigrants.I f improvements ofa certai n kindar e wanted, then they canb erealize d -withi n reason- inth ene wpolders , but ifth e immigrantswan tt omaintai n orreproduc e their culture inth e new environment,the nther ewil lb en o fundamental innovation.Althoug h there ismuc h societal change,thi schang e attracts somuc h attention and isdescribe d atsuc h lenght,tha tther e ishardl y anyawarenes so f continuity.T f onestudie s the so-called new society onth ene w land than it issurprisin g tose eho wmuc h continuity there is.Fo r apar tthi swil- 1 bebecaus eanumbe ro f culturalelement sfunctio ns owel ltha tther ei sn o needfo rchange ;fo ranothe rpar ti tma yb eexplaine d by tradition (whichca n berationa l aswell) . Remarkable isth econtinuit y inth esyste m of agriculture.Ther e isa nenormou s change intechniques ,th eproductio n and theproductivit y havegrown ,bu tth etype so f farms,eve nth esiz e and form ofth e farms showa resemblanc e which isstriking ,whethe ron e looks inth esixteent h century Beemster,th eeighteent h century Haarlem­ mermeer orth epresen t days Usselmeerpolders.

This internal logico fth edesig n and development ofth efirs tpolder s disappeared with thecomin go fth ene w towns.Th enumbe r of inhabitants wasn o longer theresul to fth eproductivit y ofth e land,bu tbecam e a target in itselfan d theresul to fdecision san d developments outside theregion . Thismad e theplannin gproces smor e complicated andmor e a parto f the nationalplanning . The task of thedevelope r wasn o longeronl y toequi p aregio nwit hth e necessary system ofservice san d amenities,bu t also topromot ean d create theresource s formakin g a livinga swell : byreplacemen t of activities and jobsfro m elseweher (overspill from thecities )o r establishment ofne wactivities .Althoug h thisbuildin g ofne wtown s was started by thesam eorganizatio n thatdevelope d thepolder sa sa whole, thisactivit y isi nfac tn o longer typical forpolders ,excep t that thestar tha d tob emad e from scratch:n o infrastructure ofan y kind available inth ebeginning .Becaus e thesene w townswit h their fastgrowt h involvea larg ebuildin g activity,ne wway so ffinancin g had tob e found,th efund scomin g from different andmostl yprivat e sources.Thi smean ttha tmor epeopl ean d institutionswer egoin gt o

174 Participate inth edecision-makin g process.Thi smad ematter smor ecom ­ plexan d thetimin g inth esyste m ofnetworkplannin gmor evulnerable . As building ofhighways ,constructio n ofa railway ,th ebudge t forhousin g etc. areal l subject todifferen t sphereso fdecision-makin g andhav e theirow n sequenceso fpriorities ,regiona l comprehensive planning becomes difficult. L°okinga tthi scomple x situation itbecome sal lth emor eclea rwha tth e adventagesar eo fth eformul ao fth e IJsselmeerpoldersproject:ownershi p of the land,planning ,developmen t andmanagemen t inth einitia l stage in onehand . Of 1 course agoo d organization isno ta guarante e forsucces s inal l respects.Th egenera l economic situation ina country ,th epolitica l °limate,th echange s invalue-orientation ,hav equit ea ninfluence , Specially on long-term planning and adevelopment-organizatio n hast o takethes e factors asdata .Thi sca nb esee n inth epresent :i ti spossibl e obuil d ane w town,t odevelo p ane wsociet y onne w land,bu t ifunem ­ ployment isgrowin g inth ecountr y and inneighbourin g countriesalso , lt cannotb eavoide d thatthi sphenomeno n occursals o inth ene wtowns . ut the interesting factremain s thatpolder s assuch ,b yprovidin gspace , have always avalue .Tha ti stru efo rth eol dpolders ,i twil lals ob etru e f°r thenew . It isquit epossibl e thatther ewil lb en onee d formor e new towns inth e future.The n iti sgoo d torealiz e thatw edi dno tmak e Polders inorde r tohav e space forne wtowns ,bu ttha tw efoun d aplac e 0r new townsbecaus e therewer ene wpolders .I t isquit eprobabl etha t ln the lastpolde r tob emade ,agricultur e will form themai nactivity . n thatcas ew e canunde ragai nne w circumstances,wit hne w techniques Perhaps, butwit hol d experience,continu e thiswor k thatstarte d over l0°0year sago .

175 POLDER MANAGEMENT INTH E NETHERLANDS THEMANAGEMEN T OFPOLDER S INTH E NETHERLANDS Drs.J.H.M .Kienhui s Unie vanWaterschappe n (Union ofWaterboard so r TheWaterboar d Association) TheHague ,Th e Netherlands

1 Introduction

The title ofm y paper could perhaps give the impression thatpolder s inth eNetherland s have adifferen t typeo fmanagemen tt oth eres t ofth e country. Ina certai n sense this istru e for thene wUsselmeer - polders, for example theFlevopolder .Fo r the initial functioning of thepolders ,durin g the construction and commissioningperiods , there is in facta managemen t organization which differs from the general pattern.W e dono t intend total k about thisrathe rshort - term type ofmanagemen t today,bu t rather about themanagemen t system which hasoperate d for centuries inexistin g polders.I n these pol­ ders the system ofmanagemen t isprincipall y similar to thatfoun d generally throughout thecountry .Wh y then dow ewan t total kspeci ­ fically aboutpolde r management? Well iti sbecaus e thepolder ,a sa watermanagemen t identity for centuries has alsoha d amanagement / legal identity: thepolde r aswaterboard . The Institute ofWater - boardswhic h has ahistor y ofman y centuries in theNetherlands ,ha s notbee n limited to thepolde r alone.Thi swil l be shown inth ere ­ mainder ofthi s introduction.Polde rmanagemen t forms atypica l exam­ ple ofthi smanagemen t system.

176 The formation ofwaterboard s inth eNetherlands '

ater management developed inlowe rpart so fth eNetherland s during he Middle Ages. In this theexisting ,mainl y agrarian, localcommu - ities- referre d toa s "buurschappen"- playe d an importantrole . r°m monastryrecord s iti sknow n that,durin gth e 12th century,low ­ ing areas became increasingly subjected tosurg ean d river flooding "ich, inadditio n to the tempory flooding also lead to amor e Permanent losso fland . These events demonstrated thenee d forde - er>ceo na muc h larger than local scale.Dam swer e constructed at arious places and at the same time drainage systemswer e constructed 0 remove excess water from thehinterland . Around 1200an d inth e lrst halfo f the 13th century (between 1200an d 1350)regiona l water anagement activities increased both innumbe r and extent. Inman y istricts itwa sobviou s that extension and/or furtherextensio n of °cal dikes toprotec t larger areas,wa s essential.T oensur e that hese damsan d dikesha d a long-lasting effect,maintenanc econtrol - ed byregulations ,wa s indispensable. In thiswork ,clearly , local immunities played an important role.Th eorganizatio n ofthes e regional watermanagement s workswa sgenerall y based on cooperation

etween the interested communities.Dependin g on theare a therewer e Various formso fcooperatio n practiced. Generally itinvolve d aver y °°sekin d ofmanagement .Thi swa sno t thecas ehoweve r forlarg e w°rks such asdam s (whethero rno t fitted with sluices). Thenmainte - nance had tob eorganize d toensur e thatth ewor k (onbot h sides)wa s c°ordinated. For thiswor k asupervisiona l authority wasessentia l to guarantee thatmaintenanc e was carried out toth e required standard. ut ofthi s came theregiona l waterboards,whic h developed as eParategovernin g bodies,responsibl e forregiona l watermanagement . s timewen t by,thes eregiona l waterboards gradually got ase tplac e in Publicauthorities . lnce the 15th century they havehad , inadditio n toa representativ e ody. aboar d with amanagemen t and judicial identity. n the long run,thi s board became thesupreme ,als o legislative, êano fth eregiona l waterboard.

177 Inth emeantim e thingswer ehappenin g ata local level.Alread y in the 12than d 13th centuries an increasing numbero fcommunitie s were constructing or extending embankments.B y the end ofth e 12th century newso f "poires"an d "kogen"ha d spread toth edelt a inth e south from thenort h ofNorth-Holland . Locally theseword smean t or foreshore onwhic h embankments were constructed. Thiswa s the beginning, ina technical-wate r management sense ofpolder s inDutc h history. Inth e 13than d 14th centuries datao npolderin g became more widespread. Slowly but surely atvariou s places along the coastan d the larger rivers thehabitabl e areaswer e extended. Thisproces so f poldering and land-winning continues today.Polde r construction has notbee n limited toonl y the coast,estuarie s and larger rivers.A t the end of the 13th century thisproces swa s alsouse d inth e hinterland where thenee d became urgent with thebe d settlement "inklinking"whic h occurred. Thisphenomeno n occurs inrelativel y uncompacted cultivated ground when it isdraine d bijstream san d ditches -a common situation in the low-lying Netherlands.Th e settlingproces s isaccentuate d by theshrinkag ewhic h results from oxydation ofth euppe r layers used foragriculture .

Eventually,natura l drainage was locally inadequate and then theonl y solution was toexcavat e special water courses to areas with alo w waterlevel. Inadditio n todrainage ,on e canals o lower the average waterlevel ina smal lrive rb y damming theupstrea m section.Jus t as the whole drainage situation wasbecomin gprecariou s therewa s a spectacular invention - the windmill.Earl y inth e 15th century the windmill was successfully applied todrainage .Wit h further improve­ ments inth e 16th century itbecam epossibl e to drain relatively shal­ low lakes.Subsequen t improvements lead ultimately,unde r theinfluen ­ ceo fDutc h merchants,wh o appreciated apossibl e good investment, toth edrainag e of large lakes,especiall y innorther n Holland in the 17th and 18thcenturies .

Initially,especiall y in the caseso f land-winning, the supervision ofpolde r workswa s theresponsibilit y of the local community.Some ­ times,especiall y with polder construction and the construction of

178 embankments,slice s and soo no nol d established land lying between wo ormor e local cummunities,ther ewa son ecommuna l seto f egulations,governin g theworks .Ultimately , themos tgenera l legal ystem forpolderin g was thewaterboard : thepolde r inth eadministra - ive-legalsense ;referre d tohereafte r asth e "polder".Thi swa si n aaition to the regional waterboard, thesecon d typeo fwaterboar d "atdevelope d in theDutc h lowlands.Characteristicall y agrou p or board"o fselecte d peoplewer egive n the authority to: drawu p regulations for themanagemen t andmaintenanc e dutieso f the landowners concerned; try cases ofnegligenc e and fix the charges tob epai d by the landowners:ta x assessmentsetc . Very year theboard ,a spolde r administrators,ha d toaccoun tt o meeting oflandowner s called "devergaderin g van ingelanden", aturally theprecis e form ofpolde rmanagemen t varied from region to egion, which atthi s timewer e strongly seperated. Therewer e lfferences but thebasi c pattern was that,outline d above.Thi s asically simplean d logicalmanagemen t system for thepolders ,ha s generally been applied untilpresen ttimes .

Th ne objecto f thepresen tpape r ist osho who w thewaterboar d system ln theNetherland s developed from local community organizations into a specific administration,responsibl e for theneed so floca lan d regional water management. In thispar to fth e introduction only an ütüne description canb egive n andman y interesting detailsmus t e omitted,on e ofwhic h being the interference by the"higher " uthorities with thewaterboards .Neithe r did weg o into thematte r 0f h°w, inth e 19th century and thebeginnin g ofth e 20th century, e Provincial authorities introduced thewaterboard s to improve ater-control for thebenefi t ofagraria n useo fth esoil . either can beexplaine d into detail thewa y inwhich ,durin g the ast fewdecades ,water-qualit y managementwa s appointed to existing gionalwaterboard s or tonew , largewaterboard s exclusively charged ltn this task.Th e intention istha t thisdescriptio n willb e Ufficient fora goo d understanding ofth eorigin so f the association Dutchwaterboard s inparticula r thepolde rmanagemen t system.

179 3 Thepresen tDutc h waterboard system

Theattentio n paid by theStat e towater ,tha t isth e guaranteeing ofsafet y against river and sea flooding,an d thecontro lo fwate r quality and the quantity ofsurfac e water forms,a s inth epast ,fo r theNetherlands ,a low-lying land bordering the sea,a n essential condition for lifean d survival.Withou t thecontinuin g attention ofth eStat e todam s along thecoas t and rivers,hal fo fou r country would be flooded by the sea.Th e functioning and habitability ofthi s low country hingeso n atigh t control ofrainwate r drainage and the waterlevel inwatercourses .Th emaintenanc e ofsurfac e water quality, evident especially inrecen t times,i sessentia l toliving - conditions,bot h for thepopulatio n and also floraan d fauna.Th e exercising of the essential care and attention is,i nou r land,th e responsibility of thewaterboards .

Bypubli c law thewaterboard , together with themunicipalit y belongs to the lowerpubli c administrative body of the so-named thirdmana ­ gement level,tha t isth emanagemen t levelneares t to those actually being administered to.Th eProvinc e isth e second management level, and finally theStat e isth e first.Th ewaterboar d canb e considered to be afor m of functional decentralisation within theDutc hstate . The waterboard, asa functional body,canno t take responsibility for public administrative matters,a sdoe s themunicipalit y - the general administrative body -unles s specifically decided by law.I n principal themunicipalit y isresponsibl e for economic,cultura l and educational affairs etc.Th e waterboard'sresponsibilitie s are limited to tasksrelate d towate r management matters which are specifically stated in itsregulations .Th ewaterboar d and the municipality work incoordinatio n but themunicipalit y cannotwor k independently inthos e "areas"fo rwhic h thewaterboar d hasprim e responsibility.

The function of thewaterboard , asa publi c administrative body,ca n only be in the field ofwate rmanagemen t matters.Thi sca nbe :eithe r separately or incombination :

ISO care and attention tohydrauli c structures along thecoas tan d rivers; attention tocontro l ofwate rquantities ; attention towate r quality and attention toassociate d roads. Principal more thanon ewaterboar d canoperat e inon e territory. or example water quality control in thearea so fsevera l waterboards an be theresponsibilit y ofon eparticula r board.Similaril y the °ntrolo fwate r quantity,watercourse s and excess-water reservoirs anb e exercised by onewaterboar d forothe rwaterboard s inth e re­ gion.These ,i n turn,coul d begenerall y responsible for thecontro l embankments and roads.I nothe rword s thewaterboar d system is f] exiblean d canb e adjusted tomee tth eneed so fth eregion .Th e r°vincial government is,i nth e first instance,responsibl e forth e ganization and operation ofth ewaterboard s init sprovince .Th e r°vincialgovernmen t can found and dissolve waterboards,giv e them uthority and also controls the correct exercising of theirduties . Th e Crown,tha t ist o say, theHea d ofStat e with theministe rres - °nsible, inthi s case theMiniste r ofTranspor t and Public Works in Urn has overall responsibility for thewor k ofth eprovince s with aspect toth ewaterboards . should benote d that theprovince s and theStat e inadditio n to e waterboards alsohav emanagemen t responsibilities inth efiel d of water management. TheState ,fo rexample ,th e largewaterways , th e 'Jsselmeeran d the Zeeland and SouthHollan d channels.I ndiffe - nt provinces theprovincia l governments manage thewate r quantities Certain rivers,fo r example,th e onesuse d primarily fornaviga - °n- Incertai nprovince s theprovincia l governments haveretaine d e responsibility forwate r quality control and haveno tgive n it er to thewaterboards . Ingenera l itca n be said that from early mes in theNetherlands ,th eresponsibilit y for local and regional er management has rested with thewaterboards ,takin g into account e facttha t iti s ideally suited for thedutie s and alsodécen ­ trai• J-ised- a characteristi c ofth eDutc h state system -represents , andh "asdon e for ages, apre-eminen t management system.

181 Thepresen twaterboar d comprises agenera ladministrativ e body: representatives ofth emanagemen t "board",a genera lmanagement ,a day-to-day management and achairman ,kwow n generally asa Dik e Reeve.Th e composition ofth egenera l and day-to-day managementva ­ ries, depending onth etask san d localan dregiona l situationo fa particular waterboard. Agenera l characteristic istha t they areal l composed ona functiona lbasi san drepresentativ e ofth e different interestgroup sdirectl y involved inth etask so f thewaterboard . For thehydrauli c structures,wate r quantity management androads , there aregenerall y two interested groups:th e "ongebouwd",unbuilt - group comprising owners and other legaluser so funbuil tpropert y and the "gebouwd",buil tgrou p comprising owners andothe r legal userso fdevelope d property. Thesegroup shav et opa y forwate rmana ­ gement services inth e form ofa wate rmanagemen t tax,i nproportio n tothei r interests.Th e costs incured inwate rmanagemen tmus tb e paid by the interestedparties .Th ewaterboard shav en o fixed finan­ cial relationship with theState ,unlik e theprovincia l andmunicipa l governments.Thi sdoe sno tprevent ,however ,th eStat egivin g the waterboards financial assistance,o noccasions ,fo r example after the floodso f 1953fo r the strengthening ofhydrauli c structureso n thecoas t and the largerivers .Th e costs forwate r qualitymanag ­ ement arepai d on thebasi s ofth epollute r pays. Domestic/industrial polluters pay inrelatio n toth eamoun to fthei rpollutio n witha pollution tax.

Basic interests arecentra l towaterboar d management and gowit hth e composition ofth emanagement ,han d inhand ,wit hpaymen tan d control. It isthes e three -basi c interest,paymen t and control - which form thebasi so f the composition ofth ewaterboar d management. Iti s important toconside r the task of theprovincia l government inthi s respect,whic h ist oallo w thenumbe ro fseat s and their categorieswithi n acertai nwaterboard . Representatives ofthes e categories are chosen eitherb y adirec to r an indirect system of election.Th e aim ofth eelection s isno t to fix the relative importance ofth e categories as isth ecas ewit hpolitica l elections.

182 Th ne proportion,b y which,fo reac h category anumbe ro fseat si s guaranteed, isfixe d inth eregulation s and iti sno t true tosa y "atth ecategor y paying themost ,ha s themos t seats.I tis , °wever,a vali d point that,becaus e ofth eessentia l interest in goodwate r control,o ffarmer s andmarke tgardeners ,thes e- a s ownerso fundevelope d land- hav e arigh t toa relativel y strong •Representation. isstrikin g that unlike theprovince s andmunicipalitie s which ave provincial/municipal laws,th ewaterboard s haven o directwater - °ard laws. Thisca nb e explained mainly by theprimac y ofth e Pr°vincial government inth epas twit hrespec t to thewaterboard s in he province.Som e yearsag oparliamen t decided,o n theGovernmen t Pr°posal, that such a lawshoul d bemad e for thewaterboards .Wit h e increasing significance inou rsociet y ofth e responsibilities 0r watermanagemen t and thewaterboar d institute itwa sconsidere d atth ewaterboard s should no longer remain solely within the utonomous power ofth eprovincia l government.Th ewaterboar d law reParation,whic h has involved muchhar d work,wil l ina fe wyear s °hsisto fth e legal rulesb ywhic h theprovincia l governmentswil l e*ercise their continuing primary responsibility for thewaterboar d astern.

The increase in scale/concentration

A densenetwor k of independent polder administration,varyin g insiz e 0m tens tothousand s ofhectares ,covered ,unti lrecently , thelow - ying partso fth eNetherlands .Characteristi c ofthes e administra­ tes was thedirec t involvement of thosebein g administrated to, s Pecialiy farmers andmarke tgardeners ,wit hth eworkin g ofth epol - er- Amanagemen t apparatus,and , infact ,a buildin g wasgenerall y iSsing. Thewor k of thechairma n and secretary wasgenerall yunder - ak en for a iimited reimbursement bijtrustyworth y people livingi n e Polder.Th epersonne l consisted mainly ofmaintenanc e workers

183 andmachin e operators for drainage equipment,sluice s and weirsan d alsoworker s for theexecutio n ofparticula r control and maintenance activities.Day-to-da y administration was generally carried outfro m thevillag e hall,o r some such suitable establishment or thehom eo f the chairman or secretary. Some largerpolder s had asmal lpolde r administration buildingwit h the associated staff.A n important event inth epolde r administration was theperiodica l inspection tochec k ifadjacen t owners had carried out their obligatory maintenance duties. These duties comprised clearing plants from water coursesan d maintaining thewate r management works.I ncas e ofnegligenc e the polder administration was empowered toforc e theowne r responsible to carry out thenecessar y work.Alternativel y thepolde r administration could itselfcarr y outth ewor k toth e costo fth eowner .Th e property formed -an d continues to form- thesuret y againstnon ­ payment of tax and othercosts .

During the last 20t o 25year s small scalewaterboard s have almost completely vanished.Socia l developments have led to increases in scale which haveno t leftuntouche d thewaterboar d and polderadmini ­ stration system.Muc h higher demands have beenplace d on thetask s of the waterboards,especiall y by developments inagricultur e andmar ­ ketgardenin g and by an increase in thenumbe ro frelate d activities under the authorities care inmanagement ,professional ,technica l and administrative matters.Th emanagement ,professional ,an d financial facilities of the existing waterboards could no longer cope with the demands created by the changing times.I nrecen t years thereha sbee n much discussion onwha t the response to this should be.Ther ewer e those ofth eopinio n that after somuc h time thewaterboar d system no longerha d arol e toplay .Other s supported new formso ffunctio ­ nalmanagement . Therewer e also thosewh o thought therewa s little reason tochang e and preferred thepresen t system. Particularly in poldermanagemen t thesepeopl e were attached tothei row n polderan d werever y reluctant to letg o their own interests and joinwit h bigger associations.Ultimatel y parliament agreed,wit hon e accord, thatth ewaterboar d system should bemaintained . Thepric eo fit s

184 maintenance waspai d ina n increase inscal ean d areductio n in number -thes e changes tob eeffecte d byth eprovincia lgovernments . The former 2500larg e and smallwaterboard s haveno w been reduced to about250 ,rangin g insiz e from very biglarg epart so fprovince st o waterboardso fa t least 10.000ha .Smal l scalewaterboard s and pol­ leradministration s areno wonl y tob e found incertai npart so fth e country:thes e areshortl y tob eabsorbed . Thepolder ,i na technica l waterboard sense,ha sno tvanishe d and,a s inearlie r times,stil l requires thecontinuin g specialised attention toguarante e thewate r management interestsparticularl y ofth e farmersan d market gardeners within thepolder . It isstil l important tomaintai n andeve n strengthen the involvement of thepeopl e living inth epolde rareas . There are different possibilities whichmus tb econsidere d from case to case,tw omeri tattention : within theconcentrate d waterboard there canb e acertain ,mor e °r lessfa rreachin g form ofdecentralisatio n into departments which have theirow n departmental administration with certain rights, for instance withrespec t tothei rbudget ; ~electio n districts areselecte d andgive n certain day-to-dayadmini ­ strative responsibilities under theultimat e responsibility ofth e day-to-day management.Thes e district administrations togetherwit h the landowners can be consulted onbudge tmatters ,waterboar d affairs etc;thu s keeping alive the involvement ofth e localpeopl e with watermanagemen tmatters .

Conclusions

In theNetherland s because of itsphysica l origins and its location by the sea- wit h a delta and large rivers- a specia l management Organization has developed over theage swhic h brings togetheran d Cares for the special interests connected with water management in a Particular area.Th e Institute ofWaterboard s has at itssourc e the care for,i.e .promotio n of,loca lan dregiona l interestsi n Water management. Ithas ,a s itwere ,grow n outo fth ecommunit y and

185 a typical outcomewa s the formation ofth epolders .T odate ,th e Institute ofWaterboard s hasbee n able to fulfil itsdutie s and tod o thishad ,necessarily ,undergon e arigorou s increase inscale .On eo f the fundamental characteristics ofth eInstitute : the decentralised promotion of interestswithi n the framework ofa n independent management body and inclos erelationshi p with thediffe ­ rent interested parties,ha sbee n maintained. Althoughwate rmanag ­ ement ina technical senseremains ,th epolder s ina nadministrative / legal sensehav egone .Perhap s "havegone "whe n looked at closely is toostrong . Inth eproces s of the increase inscal e ofth ewater - boards, one tries asmuc h aspossibl e toallo w thewate r management "unity"concep t- thepolde r ina technical/administrativ e sense- t o play arole .Th erecen t discussions inparliamen t have indicated that it isfull y appreciated that,particularl y inrelatio n to the various interests involved, thewaterboard s mustb e administered effectively. Polders arepre-eminentl y ofessentia l significance to life andli ­ ving inth eNetherland s lowlands.Th ewa y thatsociet y has developed has had astron g influence on the functioning ofth ewaterboar d system especially ofth epolders .I nspit eo frecen t changes,th e pre-requisite thatregiona l and local interests arebrough t together toachiev eresponsibl e watermanagement ,continue s and thisunde r theauspice so fa specific ,caring ,administrativ e organization.

)Thi sparagrap h has for alarg epar t been abstracted from apubli ­ cation ofProfesso r H.va n derLinden ,Hea d of theAncien t History LawDepartmen t ofth e FreeUniversit y ofAmsterda m andDik e Reeve of the "Groot-Waterschap" ofWoerden .

186 ECONOMICASPECT S OF SOIL CONSERVATION PROGRAMS INLDC s Alfredo Sfeir-Younis TheWorl d Bank,Washingto n DC,U.S.A .

Abstract

Th-f 8 paper Isabou t theeconomi c aspects of soilconservation . Iti s known thatmillion s ofhectare s are being irreversibly lostfo r gricultural production or forothe r economic activities. FAOha s esti­ mated that historical soil losses amount to2 billio n haan d that 5-7 J-lionh a are being completely lost every year through soildegrada - °n» The economic evaluation of soil conservation projects seemt o Se somedifficultie s both to thenatura l scientist and theeconomist . T rinda common ground between thoseproblem s related toth e natural nvironment and economic decision system,th e paper isoutline d ina ^'-containedway . After describing,ver y succinctly, thecharacteris ­ eso f soilerosion ,som e of the salient economic aspects of soilcon - ervation are defined. The paper also describes a fewapproache s for e economic appraisal of this type ofprojec t and reviews several case tudieswithi n this context. Thefina l sections dealwit hproblem s In "•Plementing this type of program in thedevelopin g countries andwit h 116mos t salient policyissues .

Introduction 1.1 SomeHightlight s

esPite the fact that soil ison eo f themos t important natural esources indevelopin g countries,n o statistics are available onth e

187 precise extent of soil erosion damages around theworld . However,i ti s wellknow n thatmillion s of hectares are being irreversibly lost for agricultural production or for other economic activities. FAOha s esti' mated that historical soil losses amount to 2billio n hectares and that 5-7millio n hectares are being completely lost every year throughsoi l degradation. This isa phenomeno n which affects both developed aswel l as developing nations. For example,losse s of productive topsoils in theUnite d States amount to 7.4 tons per ha peryear . Similary,tota l area affected inAfric a adds up to 35%an d in theNea rEas t up tonearl y 61%. Countries densely populated and highly dependent on agricultural production,lik e India and Nepal,hav e several millions of hectares affected bywate r and soil erosion,salinit y and floods. InIndia , 90millio n ha are affected bywate r erosion,9 0millio n ha bywin d erosion,7 millio n hab y salinity and 20millio n hab y flooding. In Nepal,i t has beenestimate d that nearly 8.5millio n ft^o f soilar e lost annually; these are translated into productivity losses of 1%pe r year or anequivalen t ofUS$1 0millio n per year. In middle-income countries,lik eArgentina , this isals oa critical problem: 13%o f the land isaffecte d bywate r erosion and 16%b ywin d erosion [4,15] .

To bring lands back to their productive capacity requires inman y cases sizable amounts of investments. Few countries have systematically deal' with this issue due to thenatur e of the problem (social and institu­ tional)an d the types of investment needed. Inman y developing coun­ tries, the areas which are going through heavy soil damages coincide with areas of high population density,particularl y of low-income groups. Because these people are poor,thei r need toexploi t the land toit s limits—in most cases toproduc e only a subsistence crops—poses a serious environmental threat toman y areas of theworld . Inaddition > investment packages for these soil conservation programs are usually expensive,an d their potential benefits are expected to come far inth e future (this isparticularl y truewhe n land reclamation takes place). Also,wit h often unstable political systems,decisio n makers are mostly concernedwit h investment decisions of high visibility (e.g.,larg e infrastructures,tunnels ,reservoirs )o r of quick returns. These are not characteristics of soil conservation programs. In the final

188 analysis> one findsman yLDC s suffering from serious environmental deg­ radation but where very little Isdon e toalleviat e theproblem .

The paper focuses on the economics of soil conservationprograms . Because of the nature of theproble m addressed here,an d theaudienc e f°rwhic h the paper Is Intended, the approach followed isbelieve d to keep the subject relatively comprehensive forbot h thenatura l scientist and the economist. Before getting into themai n topic,th e remainder of this sectionwil l outline very briefly thenatur e and role of theWorl d Bank.

Although theconferenc e focuses on polders around theworld , this paper d°es not specifically address theengineerin g aspects or all possible economic aspects of polders. Several reasons account for this: first, the Bank's lending program has only afe wpolde r projects,mos t ofwhic h Weredesigne d todea lmor ewit h soilerosio n and conservation thanwit h land reclamation. And second,i twa s thought useful to focus onth e analytic framework for theevaluatio n of projects affecting soil qual­ ms this applies tobot h polders and other projects (e.g.,irrigation , f°restry,agricultura l development). Sections 5.1 and 5.2mak e specific reference topolders. 1

'2 TheWorl d Bank

The World Bank is the largest provider of loans for agricultural devel- °Pment in thedevelopin g countries of theworld . Over thepas t five years, 1977-81,th eBan k has committed more than $17billio n for agri- Cultural development;thi s investment has elicited $2billio n inco - flrianclng and $20billio n from local sources ora tota l of $39billion . Thls isa ver y substantial sum indeed,bu tmos t experts on the subject agree that total Investment inagricultur e falls considerably below the Virements for thesustaine d long-term increases Inproductio n that U beneede d over thenex t 20year s orso .

^ World Bank Isa nintergovernmenta l lending agency that isowne d by its 134membe r countries. TheBan k Isgoverne d by ItsExecutiv e

189 Directorswhos e votes areweighte d by their contributions to theBank' s capital stock. The largest stockholder is theUnite d States,followe d by theUnite d Kingdom, ,France ,an d Japan. TheBan k isa multi " national institution,an d itha sa multinationa l staff drawn fromal l itsmembe r countries. Theoveral l task is toprovid e technicalan d financial resources to stimulate soundly based economic growth primarily through project lending tomembe r countries. No less important isou r commitment toprotec t the resources entrusted by the countrieswh o subscribe capital and by thosewh o buy IBRDbonds . To this end,Ban k projects must be financially viable,technicall y feasible,manageriall y sound,an d yield arat e of return at least equal toaverag e returns from other investment in the borrowing country.

TheBank' s organization and structure hasevolve d since itwa s estab­ lished immediately afterWorl dWa r II. Itno w includes three distinct legal entities (IBRD,IDA , IFC), eachwit h separate assets,liabilitie s and capitalization.

1.2.1 The International Bank for Reconstruction and Development (IBRD)

This entity uses the equity entrusted to itb ymembe r governments and earnings retained from 35year s of profits toborro w in theworl d capi' talmarket s and reiend todevelopin g countries. Loan terms arerepay ­ ment over 18years ,a 5-yeargrac e period,an d interest rates reflectie the full cost of our borrowings and administration at acurren t rateo f 11.6%. This isabou t 40%les s than theaverag e cost of recent borrow­ ings In theU.S .an d Eurocurrency markets bydevelopin g countries such asBrazil . IBRDbond s are ratedAA Aan d arehel d by investors inover . 90countries . In its 30-year history there have been no defaults. It has recently been agreed that theBan kwoul d double its capital from US$40billio n toUS$8 0billion . There areno w 134membe r countrieso f theIBR Dan d current annual commitments are about $9billion .

190 1-2.2 The International Development Association (IDA)

IDAwa s created in 1960whe n itbecam e apparent that the cost ofservic ­ ingexterna l debtswa s becoming unmanageable by the poorest countries. IDAwa s therefore set up torecycl e funds from richer member countries, includingBrazil ,an d IBRDprofits . Project credits from IDAar e pro­ vided only topoore r countries,primaril y inAfric a andAsia ,wher e the GNPpe r capita is less thanUS$32 0 (1977prices) . Lending termso f these credits are noncommercialwit ha repayment period ofu p to5 0 years,n o interest charges,an d aservic e charge of 0.75%pe rannum . IheIBR Dan d IDAar eadministere d by the same personnel,an d projects "eet the same criteria. IDAha s 121members . Commitments are running at acurren t annual rate of about $3.5billion .

l«2.3 The InternationalFinanc e Corporation (IFC)

IPCwa s created in 1956t o foster thegrowt h of the private sector equity financing indevelopin g countries. IFCobtain s funds largely from member country subscriptions and theIBR Ditself . Itha s 109 ""embers. The IFCcollaborate s with theprivat e sector indirectin g resources,bot h domestic and foreign,int o productive investment in "»embercountries . Itorganize d $3,340millio nwort h of capital forLD C •enterprisesi nFY198 1 inadditio n toothe r important activities develop- lng the domestic financial markets of thosecountries .

It:i s important toemphasiz e that theBank' s charter calls for loans to be made on the basis of economic criteria. The emphasis oneconomic s is e8sential,becaus e theBank' smember s include countries witha wid e range of political spectra: centralmarke t economies aswel l ascoun ­ trieswit h freemarke t economies. Most ofou r poorer and more populous •"embercountries ,though ,ar e in the tropics—a factor which has special 8 IgnifiCance inagricultura l development.

191 1.2.4 TheBasi c Approach

The rest of the paper isdivide d into the following sections: - characteristics of soilerosio n economic aspects of soil conservation approaches for economic appraisal - case studies - implementation problems private sector and fiscal impacts;an d - policy issues.

Themeri t inwritin g a short paper liesmor e in the synthesis of issues it requires than on the array ofanswer s itprovides . The literaturei s diverse and focuses ona countless set of technical,economic ,institu ­ tional, social and cultural issues. A substantial portion of the eco­ nomic literature has been devoted totes t behavioral relationships with the aim to assess thebeneficia l impacts of soil conservation practices« Variables such as security of land tenure,far m size,intensit y incro p production,replacemen t or substitution among crops,an d increases in theus e of inputs are some of them. Inaddition ,som e economists have attempted toasses s the impacts of suchpolicie s as taxes,subsidies , changes in land use patterns and other regulations on soil conservation practices,mostl y in the context of developed countries. Finally,a n important part of the literature dealswit h theplannin g process,par ­ ticularly with regard to land classification and land use policies of which very little issai dhere .

The examples used to illustrate some of the issues areno tgeneraliz - able. One could easily find counter-examples,whic h often existbecaus e of the nature of theproblem .

Long-term environmental considerations and the corresponding decision­ making process involve plenty of value judgments. Intergenerational afl interpersonal equity issues,compensatio n of potential losers(e.g. , programs which require postponement inproduction) ,choic e ofdiscoun t rates,an d choices of shadow prices,al l involve value judgments which relate more topolitica l and institutional choices than toeconomics .

192 2 Characteristics ofSoi lErosion 2 2'1 Types of SoilErosio n

Soilerosio n isa proces s whichusuall y includes two different steps: theremova l of soil particles and the transportation of them tosom e Place in the system. Several types of soil erosion have beendistin ­ guished,dependin g on the agent that causes the removal and transport. Themos twidel y known arewate r andwin d erosion. Whenwate r provokes theunifor m removal of athi n layer of soil, it isusuall y identified as sheet erosion. Incontras t toshee t erosion,whe n detachment and trans- Port result fromsignifican t masses ofwate r supply,i t isusuall y iden­ tified as channel erosion (i.e.,ril lerosion ,gull y erosion). Stream- hankerosio n is afor m of channel erosion,an d itma y occur on the farm, Withina n irrigation distribution system or in rivers. Inwate r ero­ sion,detachmen t of soils usually occurs due torainfal l [8,9] ,excep t instreamban k erosionwher e channel flowsprovid e large amountso f detaching energy. The transportation ofparticle s ismostl y afunctio n ofrunoff—th e difference between total rainfall and theamoun t that can Possibly be stored. Infiltration rates (amount ofwate r entering into thesoil )an d percolation rates (downward movement ofwater )wil l Steatly affect the runoffrates .

°ther forms of soil degradation should also bementioned : desertifica­ tionan d salinity. overal factors significantly affect soil erosion. Themos t important are: uncontrolled deforestation,unsatisfie d wood fuel energydemands , certainform s of intensive agriculture,imprope r agriculturalpractices , lifting cultivation,overgrazing ,fires ,demographi c and regional fac­ tors. Denuded soils left asa result of thoseactivitie s are atgrea t risk.

Theamoun t oferosio n produced by those activities depend on several actors: soilpropertie s (e.g.,permeability ,texture ,structure) , «aturalvegetatio n (e.g.,type ,extent) ,rainfal l patterns (e.g.,dis ­ tribution,amount) ,slop e of soils,an d cultural practices. Therear e also some socioeconomic (e.g.,hig h population density,poverty) ,

193 political,an d institutional factors (e.g.,lan d tenure,siz e ofth e farm)whic h affect soil erosion rates. These factors are present both in developed and developing countries. For example,a stud y inth e U.S.A. [10]conclude d that "the relationship between net farm incomean d mean levels of erosion appeared todepen d on the tenure category ofth e landowners ...ful lowne r operated ...wer e associated with lower rates of erosion" (p.1073) .

2.2 SoilErosio nEffect s

Several types of negative effects will appear when soil conservation practices are not followed,e.g. , land going out of production,defi ­ ciency innutrien t levels of existing lands,an d human and physical capital deterioration. Itma y be convenient to classify soilerosio n effects into threemai n categories: (a)intrafar m effects,e.g. ,los s in fertility,decreas e inare a cropped,decreas e incultivatio n inten­ sity; (b)interfar m effects,e.g. , silt,sedimentation ,increas e or decrease inwate r runoff,decreas e inth eproductivit y of groundwater supplies;an d (c)interare a ordownstrea m effects,e.g. , sedimentation of river basins,siltatio n of reservoirs (decrease ineconomi c lifeo f projects),cloggin g of irrigation canals (decreasing operation effi­ ciency),an d increases in theprobabilit y of flooding. While thefinal» ' cialanalysi s should beabl e tosho w if there isenoug h incentive toth e individual farmers for investing insoi l conservation programs,th eeco ­ nomic analysis should shed some light inassessin g theimpact s ofexter ­ nalities,i.e. ,interfar m and downstream effects (the fiscal impactwil l also bever y instrumental).

Although differences between intra-an d interfarm household effectsar e rather arbitrary (definition of aboundary) , this classification proves useful from an institutional and organizational viewpoint. It iscon ­ venient for identifying important benefits and costs,avoidin g double counting and assessing the institutional feasibility ofprograms .

Institutionally,whe n trying torevers e intrafarm households effects, oneneed s to focus ondecision s by one individual farmer;i ninterfarn »

194 household effects,on eneed s todea lwit h farmers associations and their working rules (e.g.,irrigatin g forestry);an d in downstream effects, °ne usually dealswit h the complexities ofpubli c interventions. An examplema y illustrate these complexities. Inman y cases,th eeffec ­ tiveness of soil conservation practices and programs (e.g.,reforesta ­ tion)depend s on the performance of suchsocia l institutions as tenure, theprivat e or common property of resources or,i nothe r circumstances, theexistin g tribal groups arrangements. Eacho f these institutional °Ptions require different treatment.->

2-3 SoilConservatio nMethod s

To remove or alleviate themajo r causes ofsoi lerosion ,policymaker s "»aydesig n investment programs or institutional changes (regulation)o r b°th. Most investment programs include components that may beclassi ­ fied in twogroups : engineering ormechanica l protection methodsan d hiologicialprotectio n methods. Although this classification is rather arbitrary,i t helps toidentif y the source ofbenefit s and costs of soil conservation projects. Among themos twell-know n engineering-related Practices in soil conservation,on e canmention : bench and channel terraces,contour-bunds ,mulching ,diversio n ditches or drains,polders , and tiered ridging.

M°st of thebiological-relate d methods refer topastur e and forest Plantations and management,alternativ e choice of cropping system, strip topping, plantation ofwin d breaks,an d sand dune stabilization. In general,on e canclassif y different land-use groups by their relative etficiency of crop cover toprotec t the soil fromerosion . Aclassifi - cation of thisnatur emus t be region-an d soil-type-specific. For •«ample,i nregion swit h specific environmental characteristics,perma ­ nentvegetatio n could bemor e efficient inprotectin g existing soils than certain rowcrops . With regard tocroppin g practices,differen t ^rinso f tillage,plantin g methods,fertilizer ,an d harvesting methods (e-g.,remova l of both crops and roots)wil l greatly affect theproduc - tlvity ofsoils .

195 Each of these methods or acombinatio n of themwil l generate important benefits and costs to farmers. Animportan t task for an economist ist ° quantify themonetar y value of potential benefits (sectionA) .

3 Economics of Soil Conservation 3.1 Concepts and Definitions

The use of benefit-cost analysis (BCA)provide s useful information for economic decisionmaking . Planners should choose soil conservation projects which showne t present values (NPV)o f incremental benefits greater than zerowhe n discounted at theopportunit y cost ofcapital . This criterion also applieswhe n selecting mutually exclusive projects. Certainly,on e has to recognize that decisions of this nature should includeman y other technical and institutional aspects. Inparticular , because of intergenerational equity considerations for example,decisio n makers maydecid e to take projects with negative NPVs.

Soil is anatura l resource. It isa comple x resource because it includes acomposit e ofman y stock and flow resources.^ Most of the relevant flow resources have acritica l zone of exploitation belowwhic " irreversible damage may occur. This composite of resources isaffecte d (i.e.,consumed )b y agricultural production systems—most of which is* 0 demand through plant growth. Because of this complementarity indemand » most scientists find it convenient tomeasur e soil quality in termso f land productivity or crop production. The loss inproductivit y occurs through areductio n inroot-zon e depth,losse s Inplan t nutrients (the subsoil left contains less nutrients),degradatio n of the soil structure (changes in infiltration rates),an d thelike .

However,change s in theproductivit y of soils areno t necessarily corre' latedwit h soil conservation,an d the lack of such correlation presents» as stated next,a particula r set of problems. Adecreas e Insoi l pro­ ductivity,du e to resource usebu t not beyond the critical zone ofth e corresponding flowresource s (e.g.,plan t nutrients),ma y be improved with theus e of economically and financially viable development progra"1 (e.g.,purchas e and application of nitrogen fertilizer). However,whe n

196 resource use has surpassed that critical zone (e.g.,dee p gullies),a return to theorigina l oreve na nacceptabl e level of soil productivity mayb eeconomicall y prohibitive (i.e.,irreversibl e process).5

Conservation of soil resources needs tob edefine d interm s ofa n assessment of intertemporal distribution ofus e rates [31. Conservation **anso r requires redistribution ofus e rates inth edirection s ofth e future,whil e depletion results froma redistributio n ofus e rates in thedirectio n of the present (this either results fromhuma n actionso r

n,.. ^ ™. n„„ r-an„ire"i making comparisons of two ormor e mature). Thus,conservatio n requires nid^x"s r timedistribution s ofus erates .

Tv. . a -,,oHr>nn f soilresource s or of anyothe r To measure the state of conservation or S»OJ.J- , ,. j.„u since itwoul d require measuring composite type of resource isdifficul fft since n. „A accusing complex interactions of theredistributio n ofus e rates and assessing cuu^ /„ r. niantnutrients ,water ,tex - several stock and flow resources (e.g.,plan t . . „„_„ „rtT-pcomple x ifon e admits that some ture). These measurements are evenmor e compos -, „v _ ••conserving "soil sunde r one system Plants or cropping patterns may be conserving while "depleting" soils underothers .

A- j IJ «r-*usuall y used tomeasur e different As stated earlier,cro p yields are usually v „ „,. Qii^ha n indicator obscures the typeso f soil productivity. However,suc ha nin a < , „„„„„c factors are believed tob emor e issue,particularl y when other exogenoustaccors , 1 , _J .A*-* changes (e.g.,weather , increase ^portant incausin g suchproductivit y changes ie.g, i „ „fnrcrani cmatters ,leachin g of plant ininpu t use)whil e disappearance of organic »i. nutrients,an d other depleting factorsma y be takingplace . T„ . c .,„,, antv isfurthe r clouded by the Iriaddition ,monitorin g of soilqualit y 3 , ^ i»nrtr,«hto between conservation and agrl- accepted definition of the relationship oeuwc Culi- * * . iA » nroiects). Investments areofte n identified "-uitureinvestment s (i.e.,projects,; . »„ .' / .„rrMse in livestock investments in as asourc e of depletion (e.g.,increas e • ( a reduced stocking)i sbelieve d Pasture lands),whil e disinvestment (e.g.a,reau c t°lea d toward conservation. This f not always the case. Thispape r *ainly focuses on investments and actions thatwil lhopefull y change the j. j .,,„fnt-ur eo r that would avoid Irrever- distrlbutiono f use rates toward the futureo r »,,, , .„„ f nhvsical investments or technologies, sihle situations. The analysis of physical 197 however,I s incomplete or meaningless without focusing on the arrayo f institutions that gowit h them.

A specific example may illustrate this point. Stevens [15],usin g the case ofNepal ,define s the "critical zone"a s the point beyond which nutrients become unavailable toplan t growth (for land cropped year after year without applying fertilizers). Beyond this point itbecome s uneconomical for farmers to recuperate the land. The critical zone varies depending on theenvironmenta l characteristics of soils. As noted inFigur e 1 [15],tw o dimensions of the problem areused : three levels of productivity (i.e.,permanen t production, threshold line,an d permanent impairment),an d time (in years).

Permanent ProductionLin e

Figure 1.Tim e period fora given land area toexcee d the threshold with agive n technique

As referred to ina sectio n later on,redistributio n of use rates— toward thepresen t or future—may also result from changes ininstitu ­ tional arrangements (i.e.,lan d tenure,taxes ,subsidies) ,wit h invest' ment being held constant. Consequently,soi l conservation programsan d policies need tob emeaningfu l and easy togras p by policymakers;other ' wise,a large portion of our effort will belost .

198 3,2 Conservation Decisions [2]

Since there are many causes that might redistribute use rates of soils toward soil depletion, conservation decisions are complex. Individual farm households are the decision-making unit at the micro level. Using a rather simple framework for describing farmers' soil conservation

A~ j . ..«.„I- 0,i^ Prisions depend on income, itistitu- aecisions, one may assume that sucn aecisiuusu<= p tions, and the planning horizon. For example, low-income farmers would be less willing to postpone consumption-and release the pressure on Intensively cultivating lands which are quickly eroding-than higher- income farmers. Several types of imbalances-biological, technological, supply and demand (for inputs and outputs), private versus social costs, social time preference and institutional-cause changes in farmers' behavior. Several farming systems show some of these imbalances: shifting culti­ vation, range burning, lack of fire protection, overgrazing, and uncon­ trolled tree cutting, all of which become depleting factors of the basic soil-carrying capacities. In addition, such economic and institutional variables as prices (in favor of "crop depleting" practices), invest­ ments, uncertainty in land tenure, too small farm sizes (making it uneconomic to adopt soil conservation„•-i, programs;™ nrofframs), . lack of public services f u\ „A

3.3 Economic Characteristics of Soil Conservation Programs [7]

Txso .theru e any characteristiL ,• ^ crh*t tha tmake maicess soi l conservation programs unique .,, . ..„, with the exception of a few, the use when compared to other projects? Witn tne ex v of v i * tnr&ï i<, as easy or complicated as in any other of benefit-cost analysis (BCA)i s as eaay Project. This section firs,-t, highlight -uj„unnVir s tnqe thrau» e mos t salient economic aspects of soil conservation projects*„„.- and=, an seconad second, ,outline s alternative aPpraisal frameworks.

199 There are several characteristics that make soil conservation projects rather unique. First,soi l conservation programs aremultiproduc t in nature. Namely,beside s their impacts on theecolog y of soils,thes e programs produce several other joint products (e.g.,forestr y programs produce fuelwood, timber,fruits ,woo d poles,fodder ,wate r catchment protection,floo d control,shade) . The nature and structure of the demand,a s it affects relative prices across products,wil l affect the extent towhic h aprogra m iseffectiv e in the conservation ofsoils .

Second,assignmen t ofmonetar y value tosom eo f the expected benefits and costs may be difficult. This isparticularl y true for environmental effects. Valuation problems are compounded by the nature of soilcon ­ servation monitoring, the lack of data,th e absence of adequate market signals, the set of transaction costs,an d thelike .

Third,externalitie s are present. Thiswil l require focusing on costs that are not revealed by farmers production functions (i.e., interfarm and downstream effects'). These externalities might result from the existing tenure system—where extraction costs are not totally absorbed by farmers,thereb y affecting the cost of every other user—the differ­ ence between private and public sector risks,an d the alternative per­ ceptions with regard touncertainty . Therefore,mos t often,lan dmarke t prices do not reflect changes in soilquality .

Fourth,th e presence of irreversibilities complicates the processo f valuation. The value of land,equivalen t to thediscounte d value ofal l future income streams from that land,doe s not take into account the value that society assigns toeac hhectar e lost toerosion . Land seems tohav e avalu e in stock. This value changes over time as a function ot theexistin g stock of land available.

Finally, intergenerational equity issues are involved adding new com­ plexities. Soil conservation programs result sometimes in benefits(<> r costs)whic h are accrued very far in the future: by futuregenerations « The planning horizon of today's farmers may significantly differ from society's,al lo fwhic h leads toconflict s in terms of allocations and

200 useo f soils. This "myopia"o f today's generation may also be consid­ ereda form of negative externality.

Asa nexampl e of thevaluatio n problem, let usfocu s onforestr y proj­ ects as asoi l conservation project. Only some of the joint products in forestry havemarke t prices (e.g.,lumber )whil e for others sometimes there isnon e (e.g.,fuelwood) . Whatever theshado w price used for fuelwood in theeconomi c analysis,i tshoul d reflect not only thenee d for energy but also the expected effects on soildepletion . To comeu p with useful estimates of fuelwood prices,on eneed s tostud y rural markets muchmore ,appl y newmethod s for determiningwillingnes s topay , andadvanc e theus e of proxy pricing (section 4.5). Moreover,down ­ stream effects of forests,lik e preventing siltation of reservoirs,o r interfarm effects,lik e preventing the clogging of canals (i.e., decrease inoperationa l efficiency),deman d datawhic h are seldomavail ­ able.

4 Approaches forEconomi cAppraisa l

Several benefit-cost valuation methodsma y beuse d depending onth e characteristics of future "with"an d "without"th eprojec t situations. Before outlining the nature of eachmetho d and inorde r todefin ean d understand thenatur e of project benefits,on emus t understand therela ­ tionship between thenatura l systemunde r study and the economic deci­ sion framework.

Because theeconomi c analysis often beginswit h anestimat e of land Productivity,economist s tend toforge t that several steps havebee n followed tocomput e yields. For example,on ema y need tokno who w losses intopsoi l affect farmproductivit y (e.g.,measure d incro p yields). Thiswoul d require first recognition that there isa rela ­ tionship between losses of topsoil and losses ofnutrients ,an d between losses of nutrients and changes inyields . TheUniversa l SoilLos s dation isofte n used toquantif y potential losses intopsoil . There isa statistical relationship between soil lossan d such factors as rainfall,slope ,soi l erodibility,cro pmanagement ,an d erosion control

201 determine the correlation between loss Intopsoi l and cropyields . This isofte n estimated by correlating soil depthwit h losses insoi lnitro ­ gen,an d then those are correlated with output. There are other formu­ lae (e.g.,soi l erosion andwin d velocity)tha t may beuse d toillus ­ trate thispoint .

Many economists do not grasp these ecological relationships. For them it isdifficul t toidentif y benefits other than theusua l cropproduc ­ tion (regardless ofho w one assigns values to those benefits). Many projects end uphavin g "marginal"economi c returns because not all the benefits have been accounted for. This also applies when identifying effects of soil conservation programs;mos t projects consider only one type of effect,e.g. , intrafarmeffects .

The choice ofvaluatio n method—as anex t step in the appraisal of proj' ects—has tob eproperl y done. Inman y instances,on emake smistake si n choosing anadequat e set of prices because noanalysi s has been doneo n present and future "with"an d "without"projec t situations. This analy­ sis (i.e.,economist' s judgment)wil l define whichmethod s tob eused .

4.1 Consumer/ProducerSurplu s Approach

Ata microeconomi c level,man y soil conservation programs have been evaluated using this method under the assumption that themarke t will reflect thenatur e of the problem. This approach uses information provided by supply and demand functions. The absence of asoi lconser ­ vation program ("without"project )woul d shift the supply curve for commodities upward due toa decreas e in land productivity. Producers may gain froma pric e effect. However, this gainma y beoutweighe d by increase inproductio n costs (land held as afixe d factor). Inth e presence ofa soil conservation program (additional costs),gain sma y result from increase inproductio n whichma y be outweighed bya n expected decrease inprice s (supply curve shifts downwards). Onth e other hand, inth e absence of aconservatio n program,consumer s maylos e due toa decreas e in supply of products. However,wit ha conservation

202 Program,consumer s maygai n bya nincreas e in the available quantityo f Products. Time asa factorwil lpla ya very important role[12] .

4.2 PropertyValu eApproac h

Twoprocedure s need tob e distinguished: (i)marke t value and (ii)as ­ sessed value (orincom e forgone approach). Both approaches imply that land rent or land values reflect tosom e extent future income streams (i.e.,productivity )fro m the land. Soilerosio nwil l affect the quality of land,and , thereby,i ti sexpecte d tob e reflected inlan d values. If land markets areperfect ,bot h approaches should give the same results.

Themarke t value approach also applies thewillingness-to-pa y principle. Demand functions are usually estimated using econometric methods. The market value approach islimitate d when applied inLDG s due to theim ­ perfections in the land markets of rural areasan d due to the fact that land priceswil l reflect several factors other than soil productivity: land ispurchase d also for security reasons,fo r land speculation,an d for increasing one's stock ofwealth .

Inth e absence of amarke t value,man y projects calculate an implicit value of land bydeterminin g itsproductio n (e.g.,alternativ e cropping Patterns)capacit y "with"an d "without"th e project (net benefits being defined by thedifferenc e between the two). This value only reflects ourestimat e of land floweffects ,an d therefore crop production esti­ mateswil l tend tounderestimat e land values. In the traditional BCA, nostoc k effects areaccounte d for inassessin g theopportunit y costo f land. The presence of soil erosion and the real risk of irreversible damagewil l also affect the stockvalu e of land.

The land value approach operates under ase t of specific assumptions, not all ofwhic h are realistic in the context of developing countries. plrst,i tassume s that changes inth e quality of land isvisibl e by consumers,and ,therefore ,th epric e of land will change ina continuum wlth changes in land quality. This continuum does not always exist

203 either,becaus e people inLDC s are attached to the land and fewtrans ­ actions take place or because quality isno t a dominant factor inth e process of land prices formation. Another factor which limits the extent towhic h land prices reflect changes inqualit y is the excessive segmentation of rural landmarkets .

A.3 Replacement Value Approach

Soil erosion results indownstrea m effects usually captured by changes in the economic life,fo r example,o f irrigation infrastructure,ground ­ water development,o r other economic activities like agriculture and fisheries (these important social costs need tob e considered). Silta- tion of reservoirs reduces their economic life,dependin g upon the existing siltation rate. Soil conservation programswil l decrease such siltation rate,expandin g theusefu l life of infrastructures. Ifn o program is adopted (future "without"th e project), the economy will have to replace such infrastructure (i.e., shadow project)soone r than expected. The cost of replacement could be used toestimat e potential benefits (i.e,"cos t saving benefits"). By the same token,replacemen t of tubewells or differential pumping costs could be accounted fora s benefits of soil conservation projects whichwoul d prevent further dete­ rioration of existing aquifers. This approach may also beuse d when changes in the economic life of soils is appraised.

4.4 TravelCos tApproac h toRecreationa l Benefit

In some cases soil erosion affects recreational facilities through decreasing the fishing productivity of lakes and reservoirs,increasin g turbidity inwaters ,creatin g fetid odors inwater s used for recrea­ tional purposes,an d others. Recreational benefits may bemeasure d by estimating consumers'willingnes s topa y revealed byexpenditure s asso­ ciatedwit h travel time and distance. Since this does not seem topla y a major role inrura l areas,n o further analysis isgiven .

204 ^•5 OtherApproache s and ProxyValue s

first,estimatio n of social demand curves has been proven usefulwhe n °ne isabl e toidentif y howmuc h society Iswillin g topa y toavoi d violating asaf eminimu m standard of soil conservation. This approach hasbee n used in theBan k toevaluat e nutrition intervention programs. Second, theus e of social accountingmatrice s may prove usefulwhe non e tries toallocat e benefits and costs and their incidence. TheBan k has used this approach insecto rwork . Finally,prox yvalu e may be used to estimate theimplici t price of commodities whose markets dono t reveal Prices.

An example in theus e of proxymethod s is thevaluatio n of fuelwood.7 Themos t frequently used proxymethod—directl y linked tosoi l conserva­ tion decisions—is todetermin e what type of products that affect soil Productivity at themargi nwil l substitute for fuelwood asa nenerg y source. In rural areas,lac k of fuelwood is satisfied byburnin g cow dungo r crop residues. Inparticular ,Ban k projects haveuse d the value of crop productivity that society loses by substituting fuelwood for cowdun g (oragricultur e residues)whe n fuelwood isno tavailable . The implicit assumption here is that elasticities of substitution between fuelwood and cowdun g arehigh ,whil e thepric e elasticities °f substitution of fuelwood with regard toothe r sources of energy is assumed tob e very lowo rzero. "

This proxymetho d cannot beuse d indiscriminately, since toadvocat e Such substitution,on ewoul d require athoroug hanalysi s of the supply and demand structure for energy "with"an d "without"th eproject . In some projects we have assumed that all these cross-partial price elas­ ticities are zero ("one must supply only fuelwood"),whil e inother sw e have assumed that these elasticities arehig hwit h respect to several other alternative sources of energy (i.e.coal ,kerosine) . The basic taskher e is todetermin e theopportunit y cost of fuelwood soa sno t toover -o runderestimat e a project'sbenefits .

205 5 ProjectAppraisal : FewCas eStudie s 5.1 EconomicEvaluatio n of Polders

Untilnow ,thi s paper has not focused much onpolders . Most WorldBank - financed polder projects reviewed for this paperwer e designed tocon ­ trol streambank erosion and topreven t floods. Only one Bank-financed project from asampl e of several projects considers the constructiono f a polder like theone s in theNetherlands ,namely ,wher e land is actually reclaimed from thesea .

The construction of polders is assumed tohav e several important bene­ fits besides those benefits stemming from land reclamation. Intrafann effects include the increase in land productivity byenablin g the land, subject to floods,t ob ecultivate d during thewhol e cropping yearan d by controlling salinity. Interfarm effects include land reclamation and the control of streambank or riverbank erosionwithi n the project area. Downstream effects include prevention of flood damages (e.g., land,houses ,capita l stock),siltatio n of reservoirs,an d decrease in the productivity of other rural sector activities (e.g.,freshwate r fisheries).

Themos t important external effect introduced by the construction of polders is the change in theproductivit y of existing freshwater fish­ eries. Polders and embankments tocontro l floods and streambank erosion would change thehabitat' s quality of fish growth through changes in salinity,wate r temperature,an d spawning habits. These rather negative effects have beenavoide d by providing thenecessar y changes inprojec t design (e.g.,fis h ladders)o r by financing fish hatcheries (i.e.,th e "shadow project"). If such investments areno t provided, important losses inincom ewoul d occur through both fishproductio n (i.e.,fisher ­ men's catchwil l decline)an d animal protein consumption.

5.1.1 Yong SanGan g IIProjec t

Theprojec t is thesecon d stage ofa pla n for irrigation,drainage ,an d land development in the lower reaches of theYon g SanGan gRiver . The

206 Project Isdesigne d tobenefi t 20,700h a through irrigation ofth e eritirearea ,reclamatio n of 5,500h auncultivate d tidal flats,an d land development on 11,900ha . The project finances the construction ofa n estuary dam across themout h of theYon g SanGang ;constructio n ofa 4.000m long sea polder;constructio n of irrigation facilities;reda ­ ction of tidal land development and consolidation;projec t building, access roads and àtemporar y pier;an d connectingservices .

The polder,extendin g downstream of theestuar y damalon g the left bank of the river,woul d be constructed toreclai m83 0h ao f tidalflats . The polderwil l be4,00 0m long and about 8m high. The body of the Polderwoul d be compacted earthwit ha rock zone on the seaward face. Asluic e would be constructed at thedownstrea m end of the poldert o Permit drainage of the reclaimed area at lowtides .

The total project cost was estimated atUS$167. 0million ,wher e the Polderwoul d costUS$2. 0millio n and the sluice gatesUS$10. 7million .

Themajo r beneficial environmental effect would be toimprov ewate r quality in the lower reaches through elimination of seawater intrusion. Two downstream effects could be expected: sedimentation inMo kP o harboran d reduced fisheries. A survey shows that about 800household s inth evicinit y of the project engage in fishing tosupplemen t farm lricome,bu t nearly all of the fishing isi nshallo w coastalwaters . Therefore,constructio n isexpecte d tohav e nosignifican t effect on fisheries (i.e.,incom e forgone is zero). As regards effects onMo kP o harbor,a stud y bya nexper t insedimentatio n concluded that the estuary damwoul d not increase,an dmight ,i nfact ,reduce ,th eannua l dredging requirements (about 130,000m 3)i n theharbor .

The economic benefit and justification procedures did not include two ad

207 5.2 OtherExample s 5.2.1 PhewaTa lCatchmen t Management Program: ALan d ValueApproac h

The PhewaTa l catchment is located InKair a District,som e 140k m from Kathmandu. The catchment has an area of 113km ^an d drainsLak e Phewa Tal. The climate ishumi d subtropical,wit h anannua l precipitationo f 3,700mm . Because of intensive agriculture and grazing in the catch­ ment,onl y about aquarte r of the original forest remains;thi s land isowne d by theGovernmen t ofNepal . Subsistence agriculture isth e resource base of the catchment with cultivation of rice,corn ,millet , wheat,potatoes ,an d other vegetables. Most familieskee p 4o r 5larg e animals for production ofmanure ,milk ,an d for plowing. Forests supply fuelwood and timber for building. Several resourcemanagemen t problems exist,namel y water supply shortages,wate r quality,erosio n problems (grazing lands being themos t critical), sedimentation inPhew aLake , grazing management (e.g.,numbe r of livestock, fodder productivityo f grazing land and development alternatives—keep animals off—and legal jurisdiction),an d forest and agricultural management (cultural prac­ tices,nutrien t depletion). The proposed program includes plantation maintenance,fores t protection,pastur e establishment and protection, gully control,stal l feeding,an d training and technical assistance.

The appraisal approach draws comparisons ondifferential s inpotentia l land values "without"an d "with"th e proposed programs. Values are defined byvaryin g degrees of land productivity over time,whic h is assumed to change depending onexpecte d output foregone. For grazing land,differen t conversion factors into animal feed and for animal feed into theproductio n ofmil k and fertilizer (net of production and other costs)wer e estimated. The fertilizer andmil k values of the grasswer e estimated atNR s 11/ha/yran d 72/ha/yr,respectively . For pasture land, itwa s estimated that itsproductivit y would be approximately five timeS that of open grazing land (for the same commodities). For scrub land, the analysis assumed that each hectarewoul d produce 500k g ofgrass , 1,500k g of fodder leaves and 4m ^o f wood. The economic valueso f grass and fodderwer e calculated asbefor e but 96m ^o f fuelwood were added. Forunmanage d forests,a productivit ywa s estimated equivalent

208 to 3,000k g of leaf fodder and 12m 3 of fuelwood perhectare . Finally, f°r plantation forestry and managed forests,coefficient s on fodder and fuelwood were estimated as before. Benefits were added upan d compared fc°th e cost of theprogram ;a B/ C= 1.7.

5»2.2 EconomicBenefit s ofShelterbelt. 9

Several benefits have been identifiedwit h the planting of shelterbelts 0t» often called,windbreak . Among the benefits one canmention : reducingwin d velocity and soilerosion , modifying air and soil temperatures, reducing evaporation and transportation, improving distribution of snow and soilmoisture , improving distribution ofwate r insprinkle r irrigation, reducingwindbur n andwiltin g of cropplants , protecing newly needed crops fromblowout ,an d protecting mature crops from lodging. In terms of specific economic benefits,dependin g on circumstances,on e "^yaccoun t reduction inenerg y requirement,buildin gmaintenance , ""educingmortalit y in livestock, improving theproductio n and qualityo f Cr°ps and fodder,controllin g soilerosion ,providin g shade,an d many others [1,16 ,17] .

^e Bank tried toestimat e theeffect s of shelterbelts on land produc­ tivity;i tha sbee n estimated that for certain crops thepresenc eo f 8helterbeltswoul d double existing productivity. These data come from e*Periments and several studies around theworld . InNige r [13],i twa s estimated that yields ofmille twoul d progressively increasewit h the height of thewindbrea k up toa certain point;th eaverag e increase in yieldswa s found tob e 29%. TheNige r report concluded furthermore that 98 a result from shelterbelts wind erosion is reduced considerably and 8°ilmoistur e and yieldwer e higher than those crops left inth eopen . In theU.S . [17],a functional relationship has been estimated between ^stance from the shelterbelt andyield s (asa percentag e ofnorma l yields). iti s shown that between 1.3m and 12m ,yiel dwoul d beabov e

209 thenorm ; thehighes t yield (over 50%)i s reached with ashelterbel to f 5m .

5.2.3 Indonesia Watershed ProjectAppraisa l ofDownstrea m Effect

TheBan k has done some crude calculations for appraising the economic value of reducing soilerosio n and siltation of streams. Here,onl y down stream effects have been clearly singled out. Itwa s estimated that only 50%o f all the siltwhic h enters the riverbasin would cause quantifiable damage downstream; this includes siltation of dams,canals » fishponds,ports ,floodways ,an d other structures. The study assumes that damage costs are at least as large as the economic cost of removal or alleviation (replacement costs). Impacts on theeconomi c lifeo f reservoirs and other structureswer e also studied.

5.2.4 Tunisia-Northwest RuralDevelopment : Intra-an d InterfarmHousehol d Effects

Thisprojec t recommended financing a4-yea r time slice of a 15-year development program for 311,000h a ofTunisia' s 1.46 million haNorth ' west Region. Project actionswil l beundertake n on 162,000h awithi n the area subject tosoi l erosion or susceptible to crop production in­ creases. The project areawa s divided into 2,000h amicrozone s distin' guished by types of land ownership and use,an d by topographicalan d agriculture characteristics. The project components include - measures todecreas e soilerosion , - agricultural development, - forestry production, - livestock development, - production infrastructure (e.g.,roads) , - social infrastructure,an d - technical assistance.

210 *hesoi l erosion production program includes changes in cultivation Practices (contour farming,continou s cropping ofcultivabl e land, Introduction of different crops onalternativ e parcels down hillsides to reduce water runoff); contour banking systems and planting ormain ­ tenance of permanent pastures,an d planting of forest inarea s where cultivation must bestoppe d and conditions dono t permit pastures to Prevent erosion;an d fencing off,supervise d grazing,wate r control w°rks,an d afforestation on land surrounding gullies and riverbeds (overgrazing andwate r runoffs causing the erosion).

^ost benefits and costs were appraised as theactivit y affects cropan d livestock production. Changes in crop production tosom e superior crops,increas e inmil k production,fuelwoo d and forest products,over ­ al increase inyield s of food crops,an d beef products. After includ- ing all costs,a financia l analsyiswa s carried out tose e the extent to which farmers had any incentive toparticipat e (other things being e1ual). The financial rates of return tofar mmodel s fluctuated between 22*an d 62%. Such returnswer e not positively correlated with farm size. However,i twa s found,a s onewoul d expect,tha t the project's rate of returnwa s positively correlatedwit h theplannin g horizon or the time slice,achievin g anoptimu mwhe n considering aprogra m of1 5 years (i.e.,ER R- 16%) .

5-2.5 Ethiopia -Wolam oAgricultura l Development: IntrafarmHousehol dApproac h

In this project,soi l conservation measures include bunding and contour Cultivation,gull y control and land rehabilitation,wate r development, and program monitoring. Twoelement swer e defined inorde r to carryou t the economic analysis: (a)a net value ofproductio n figure Br 150pe r ** and (b)a decreas e in soilproductivit y in theabsenc e of this proj- ect and a5 %dro p inproduction . Under these assumptions,th e economic rate of returnwa s estimated at 11%. No attemptwa smad e toquantif y betlefits of gully control and land rehabilitation,thoug h their benefits ete also expected tob esignificant .

21! 5.2.6 Watershed Conservation inEcuador : Economic LifeApproac h [6]

ThePoz aHond aWatershe d isa humid ,subtropica lwatershe d of 175km ^ located 2,000k m southwest ofQuit o in the coastal province ofManabi , Ecuador. Thewatershe d varies between 100-500m inelevatio n and is steep,wit h 60%o f theare a having slopes greater than 25%. Land use analysis indicates that 55%o f thewatershe d area is still innatura l forest,whil e 6%consist s of cultivated coffee and cocoa trees. Grazing land covers 22%o f thewatershe d and 3/4 of this land is subject to sheet erosion during thedr y season. Mixed farming and grazing takes place on 14%o f the land. The reservoir occupies the remaining 3%o f thewatershed .

The existing reservoir has many problems due tosedimentation ,t o climate,an d tointensiv e land use in certain areas. Sedimentation sur' veys have indicated that 20%o f the original volume of the reservoir waS filledwit h sediment;wit h 4%pe ryea r after 5years ,on e expects the reservoir tob e filled in 25years . Inaddition ,th e reservoir suffere" froma dense blue-green algae,causin g fetid odors in thewater . Under these circumstances,a progra m including reforestation,constructio n° f terraces on steep and erodable land suitable for cultivation,grazin g control and rehabilitation,an d forest protection programs were sug­ gested.

Estimation of project benefits focused ona reduction of the sedimenta' tion rate from4 %t o 2%. Such reduction was expected to increase the economic life of the reservoir from 25t o 50years . The benefitswer e estimated to comemainl y from irrigation. The analysis concluded that with a longer-life reservoir theeconom ywoul d achieve aB/ C= 1.433, -, 10 while with ashorter-lif e reservoir theeconom y achieves aB/ C =.67 « Net incremental benefits tosociet ywer e estimated atUS$30. 7million «

212 Problems inImplementin g SoilConservatio n Projects and Programs

^ough sound economic and financial analysis provide useful information °r decision makers it isonl y one of thenecessar y conditions for the successfulimplementatio n of soil conservation projects. Some ofth e efficient conditions are outlined below.

irst,i twoul d be ideal that the timingo f production practices leading oward conservation coincidewit h people's short termneeds . But,a si t ls well known,thi s is not the case everywhere. This issue isparticu - arly acute inarea swher e itma y beadvisabl e even tosto p production ( let the soil rest for awhile") ;however ,thi s issociall y unfeasible atl(I,man y times,politicall y unacceptable.

econd, there are such considerable informationalgap s that thewhol e Processma y becomeunmanageable . Inman y instances,experiment s with s°il conservation programs that will provide thenecessar y information have tob e carried out together with production programs. Under these clfcumstances,grea t distortions occur particularly when the datai s CaPturing changes invariable s other than those associated with changes n natural systems (e.g.,managemen t of individual farms).

^lr

°urth,soi l conservation programs put severe stress on local institu­ ons: most programs require theenforcemen t of rights,change s in arJrming practicespractices,anan dc change s incultura l habits. These changes may * difficult toachieve .

lfth,market s dono t always provide adequate signals to farmerswhe n adoPting soil depletion practices. Market values of land or changes in Cr°P yields dono t provide the appropriate signals toreflec t losses in

213 soil quality and,therefore ,seldo m account for the total economic cost of production.

Sixth,soi l conservation practices per sewil l not besufficien t to alter soil quality or tochang e farmers'productio n practices. Onema y need toadop t income policies;thes ewoul d affect the rate of social time preferences or farmers'biase s infavo r of crop-depleting systems.

Seventh,a financia l and economicallyviabl e soil conservation program may need changes in land tenure toenabl e farmers toexpan d the sizeo f their lands. Insevera l countries this issociall y or politically unacceptable.

Eighth,integratio n of soil conservation planning and implementation with development planning ingenera l isa mus t inorde r tohav eself - sustained soil conservation programs.

Finally, there isa lack of appropriate administration for implementing such programs. Under thebes t of allcircumstances ,thes e programsar e fragmented (e.g.,Ministr y ofAgriculture ,Publi cWorks ,Irrigation) .

7 Private and Public SectorFinance s 7.1 FinancialAnalysi s

Financial analysis of soil conservation is important,sinc e it isth e individual farmerwh o carries out theprojects . This presents problem5 in areas of subsistence farming,sinc e soil conservation decisions are clearly affected by thenee d toachiev e subsistence first and conserva' tion later (i.e.,lexicographi c decision making). Do farmers have enough incentives tocarr y out soil conservation programs? For example' the financial analysis of such programs asforestr y needs to consider carefully: (i)competitiv e uses of land (e.g.,foodcrops )an d labor (e.g.,fo rplantin g and maintenance);an d (ii)tre e species and tree planting modes ofmaximu m financial returns to farmers. Also oneshou l consider the land tenure structure as it affects farmers'adoptio no f conservation practices (i.e.,lan d sizema y be too small for farmerst o

214 adopt these programs). Finally, financial performance depends on,e.g. , fcheorganizatio n of farmers,inpu t delivery systems,credi t extension.

•2 Fiscal Impacts

^e state budget may beaffecte d insevera lways : compensating farmers toforg o certain benefits orprovidin g cash to farmers for implementing the program (e.g.,villag e forestry schemes); having toaffor d substantial recurrent cost expenditures since these programs demand little foreignexchange ;an d changing the tax structure system. Agoo d fiscal impact statement isa necessit y if oneexpect s any sustained success of this type of program. A good fiscal impact statement isa necessit y if one expects any Sustained success of this type of program.

W°st conservation programs require local currencies and resources. The "»ajorityo frura l government authorities lack appropriate funds tocarr y °ut conservation programs. One reason for such gap is the fact that 8°H conservation planning isno t integrated intooveral l development Planning.

pinally,wit h regard to taxation changes in the quality of landwil l c°rrespondingly change the capacity topa yo f this land. Consequently, Sovernments should, inprinciple ,ge t increasing resources as thecon ­ servation project develops. Due toinstitutiona l and otherfactors , however,thes e tax structures arever y rigid,thereb y not correlating (Positively)wit h increases inlan d quality. This isa problem one V1H have to livewit hit .

Policy Issues

Be*ore closing,i twoul d beimportan t toidentif y somemajo r policy issueswhic hnee d further research.

215 8.1 SoilConservatio n Planning vs.Developmen t Planning

Isolated attempts todea lwit h soil conservation are bound to fail. The environmental sustainability of soilresources ,an d of land ingeneral » should bea central subject of any development plan. Given the nature of soil conservation programs,i t isdifficul t tose eho w this integra­ tionwoul d take place,particularl y in light of tooman y development objectives.

8.2 Macro vs.Micr o Variables

Adevelopmen t policy framework needs tob e developed; this should take into account themacro -an d themicroeconomi c variables. With regard tomacroeconomi c variables,th emos t important is the sustained increase in the demand for agricultural products. This expanded demand would continue tobv.il d substantial pressure on the development of both the extensive aswel l as the intensive margins of agricultural lands. The expansion in the supply of crop landswil l require developing themar ­ gins of agriculture. In this case,i f no coordinated policies really exist, the risk of soil degradation is rather great,becaus e marginal lands are oftenmor e fragile and subject tohighe r risks of soil ero­ sion.

With regard tomicroeconomi c variables,th emos t important variable to be recognized at the policy level is the profit motive offarmers . Farmerswil l be reluctant toadop t soil conservation practices thatar e financially and economically unattractive. This isextremel y important in thepolic y context,sinc e tob eabl e tohav emor e program effective­ ness,a balanc e must be reached between public and private investments» Neither the public sector nor theprivat e sector alone will be ablet o accomplish the policy objectives outlined in thispaper .

Because the development objectives of thepubli c and private sectorma y c differ,a neffor t should bemad e torecogniz e theunderlyin g behavior ° is each sector. This iscertainl y true for augmenting the private sector

216 adoption ofne w technologies. As stated earlier,th e development of conservation technologies,t o beadopte d by the farmers,shoul d be Profitable.

8'3 TimeElement :Intergenerationa l Equity

Although this represents the core of the conservation problem,n osolu ­ tionha s been found yet. Benefits of conservation programs are usually "»aterialized far in the future. Theus e of today's generation's oppor­ tunity cost and shadow prices,withi n existing discounting techniques, Welgh very heavily against benefits received far inth e future. Several approaches have been suggested,e.g. ,variabl e and decreasing discount factors,n o discount atall ,us e ofvariabl e shadowprices ,us e ofa n °Pportunity cost of land in thepresenc e of irreversibilities,change s lr»th eBC Aobjectiv e function,an d others. None of them are fully 8atisfactory.

8*4 Administration of Conservation Programs

E*perience shows that the degree of success with soil conservation Programs is highly correlated with quality inprogra m administration. This issue hasman y facets. First,ther e isa need tocreat e public awareness about the soil erosion problem,bot h among policymakers and cltizens. Since this awareness doesno t exist,publi c funds areno t •channeled at theappropriat e rates into soil conservation programs, iscal reforms are needed.

Second, soil conservation should beconceive d as capital investment Pr°grams: investment in the land. This seldomhappen s and,therefore , m°ney available for those programs often come from the income savings account of thegovernmen t rather than from the capital accounts. The nain implication is that funds areno t earmarked for soil conservation activities,an d most of themar eunderfunded .

217 Finally,ther e Isa n increasing need for farmers toparticipat e and for thegovernmen t toprovid e extension services. The general idea of "soil conservation districts"i n theU.S.A . should be considered as aplaus ­ ible system indevelopin g countries. This systemwil l enable farmerst o participate more actively insoi l conservation efforts. However,a n important component isa nadequat e extension service. Unfortunately, most extension systems have focused mostly onagricultura l productivity» with very little emphasis onenvironmentall y sound practices. This needs achange .

Notes

The term "polder"i suse d torefe r todifferen t things. Inman y projects,polder s are used as synonymfo r embankment to control streambank erosion and reclaim land partially or totally flooded. In afe w projects (section 5.2),th e termpolde r Isuse d inth e accepted context of sea soilreclamation . Sections 2.1-2.3ar e very preliminary innature . Each typean d method needs tob eexplore d inmuc h detail thanpresente d here. Section 2relie s heavily on [8,9 ,11] . Experience in theBank' s financial Gujarat SocialForestr y Project has shown that reforestation programs inPanchaya t lands have been much less thanexpecte d atappraisal . Stock resources include,fo rexample ,texture ,dept h of soilan d line zone,an d clay pans. Flow resources may be associated to changeable features like salinity levels,p Hlevels ,bus h and tree cover,an d rock cover. The presence of irreversibility indecisio n making isanothe r specific characteristic of investment projects that affect natural environments. Shaxson [14]make s an interesting distinction betwee11 soil conservation (i.e.,buil d up thenutrien t capacity)an d soil reclamation (i.e.,bringin g back to its original stage thenatur e ot a stock resource component like texture). This subject needs tob eexplore d inmuc hmor e detail. The impHca tions are that land not only preserves avalu e inus e (flow),bu t* also has awealt h instoc kvalue . This phenomenon will affect the

218 way inwhic h projects calculate theopportunit y cost of land. Increase in relative prices ofenerg y is causinguncontrolle d use of fuelwood forests inrura l areas. This process has great effect on oil erosion not only because of depletion offorest s but also because thebul k of fuelwood is causing losses inagricultur e production. Other important factors thatma y constrain substitution at themargi n are tastes,technology ,lac k ofroads ,inefficien t distribution sys­ tems,an d prohibitive transactioncosts . Iti s important tonot e that herew ear e only describing increases in yield "with"th e project situation. Inth eBC Ao f shelterbelts,on e needs tosubtrac t the "without"projec t situation. 10 The difference inB/ C "with"an d "without"th e project reflects in addition to the change in the economic life of the reservoir,th e expected increase in land productivity resulting from the proposed soil conservation practices.

References

fl] Bogetteau-Verlinden,E .1980 .Stud y on impact ofwindbreak s in MajjiaValley ,Niger .Agricultura l U.,Wageningen ,Th eNetherlands . [2] Bromley,D.W . 1980.Th e political economy of private resource-use decisions affecting soil productivity.Comment s prepared forwork ­ shop on "SoilTransformatio n and Productivity." [3] Ciriacy-Wantrup,S.V . 1968.Resourc e conservation:economi c and policy,U .o f California,3r dEd . t4l FAO.1980 .Soi lan d conservation,Committe e onAgriculture , GOAG/81/8,Rome . t5) Fleming,W.M . 1980.Phew aTa l catchment management program,Nepal : forestry and soil andwate r conservation.Unpublishe d manuscript. (6) Fleming,W.M . 1979.Environmenta l and economic impacts ofwatershe d conservation ona MAP Sreservoir s project inEcuador . Unpublished paper.Westwate rResearc h Center,U .o fBritis h Columbia,Vancouver . t7] Gupta,S.B . Lai,R .Prasad ,an dR.K .Paudey .1973 .A neconomi c evaluation ofsoi l conservation inVaranas iDistrict ,Utta rPradesh . Indian Jour,o fAgric .Econ. ,28 ,4:205-211 .

219 [8] Hudson,N .1981 .Soi l conservation.Cornel lU .Press ,Ithaca ,NY , 2ndEd . [9] Kohnke,H. ,an dA.R .Bertrand . 1959.Soi l conservation.McGraw-Hil l Book Co.,Ne wYork . [10]Lee ,L.K . 1980.Th e impact of landownership factors on soilconser ­ vation,Amer .Jour ,o fAgric .Econ. ,pp .1070-1076 . [11]Nationa lAssociatio n of Conservation Districts.1980 .Soi lDegrada ­ tion: Effects onAgricultura l Productivity. National Agricultural Lands Study. InterimRepor t No.4 .Washington ,D.C. ,Oct . [12]Seltz ,W.D .e t al. 1979.Economi c impact of soil erosion.Lan d Economics, 55,1 ,Feb . [13]Sharp ,B .an d D.W. Bromley. 1979.Soi l as an economic resource. U.o fWisconsin ,Madison ,Oct . [14]Shaxson ,T.F . 1981.Lan d conservation measures and related costs. FAO,Worksho p onEcon .Aspect s ofLan d Cons,unde rHumi d and Semi- Humid Tropical Conditions,Rome ,3 0June- 3 July. [15]Stevens ,M.E .1978 .Lan d use pattern formargina l land and erosion» Draft unpublished paper. [16]U.S .Departmen t ofAgriculture . 1962.Shelterbel t influence onGrea t Plains field environment and crops.Fores t Service Production ResearchRepor t No.62 ,Washington ,D.C. ,Oct . [17]U.S .Departmen t ofAgriculture . 1964.Tre ewindbreak s for the Central Great Plains.Fores t ServiceAgricultura l HandbookNo .250 .

220 ENVIRONMENTAL ASPECTS

POLDERSAN DTHEI RENVIRONMEN T INTH ENETHERLAND S

J. deJon g IJsselmeerpoldersDevelopmen t Authority Lelystad,Th e Netherlands A.J.Wigger s Research Institute forNatur eManagemen t Arnhem,Leersum , ,Th eNetherland s Abstract

•Theenvironmen t ofpolder s in theNetherland s isreviewe d from twopoint s °fview .Th ehistorica l development of thepolde rarea s duringman y Centuries and thechange s inth enatura l environment aredescribed . in time thisha smean t agradua l transformation ofnatura l dryan dwe t r°rests,pea t areas and lakes inpolder s used for agricultural purposes with all the associated environmental losses andgains . Thereafter attention ispai d todevelopment s inth eus eo f the available sPace,bot ho f land andwater ,i nth eNetherland s during the20t h Century.Th e changing ofa nagricultura l society intoa nurbanize d ^dustrial society and thedevelopment s inagricultur e itself Mechanization,artificia l fertilizers and chemical control ofpest s and diseases)hav eha d and stillhav e aprofoun d influence onth e erivironment in thedutc h polder regions andpla y arol e inth eproces s of decisionmakin g about constructing and developing newpolders .

Introduction

In thispaper ,whic h dealswit h polders and theirenvironmen t inth e etherlands twomajo r aspectswil lb e reviewed. Attentionwil lb epai d toth ehistorica l development ofDutc h polder areas and of their environment and afterwards thedevelopmen t during tnis century in theus eo f theavailabl e space,bot ho f land andwater ,

221 tidâl flats, tidal gullies, rivers, and takes rich fresh marsh forests on eutrophic peatland tidal marshes, saltmarsh and reed marshes, locally sphagnum-, wet heather- and higher banks and , partly inhabited and grazed sedgevegetations on oligotrophy peatland [r-'.V'Vq complex of wet and dry forests on mineral soils, brackish reed marshes on eutrophic peatland U •:..ÓI'iJ incl. the higher flood plains of rivers

Fig. 1.A reconstructio n of the ecological situationo f theNetherland s inRoma n times (afterPons , 1974).

222 inth eNetherland s and itsconsequence s forpolde r areaswil lb e discussed.

Historical development

InRoma n times (thatmean s inth eNetherland s about thebeginnin g of thisera )th eecologica l situation ofth eNetherland s canb e described as follows (fig.1) . °nth enutrien t poor Pleistocene sandy soil forests,mars h forestsan d oligotrophicpea t forming vegetations could befound . °nth e coastal dunesan d islands,forest sexiste d on thesand ysoils . Ina largeare abehin d thecoastline ,area swit h peat forming vegetations existed togetherwit h reedmarshes andmars h forests.Alon g theriver s forests onnutrien t richalluvia l soilsexiste d aswel l asmars h forests and reedmarshe s downstream. Inth enorther n regionbehin d theisland s awadde n region,tida lflats , existed changing landwards intosalting s and reedmarshes .

From thisorigina l situationma nmad epolde r areashav ebee n developed. Iheyca nb edistinguishe d infou rmajo rgroups :polder s in thedownstrea m flat river catchment areas,polder s inpea t areas,polder s on thebotto m °fdraine d lakes and polders created bycoasta l embankments (fig.2) .

Inth e river catchment areas upper and lowerpart shav e tob e distinguished. In theuppe r part onth e levees forests grewo nric h mineral soils and in thebackswamp smarshe s and forestswer epresent , inth e lower partmarshe s and forestswer e dominating.

Inhabitation started on therive rbanks ,an d already incarlovingia n timessettlement s grewan d smallhors e shoe-shaped polderswer econ ­ structed discharging theirwate r either intoth erive r orbehin d the riverbank s using thebackswamp s and theslop eo f the land towards the sea. Inth e 12than d 13thcentur y peoplewer e ordered bymean s of"dik e letters"t oti e thedike s along theriver s together and combined polders were created.

223 higher grounds I bottoms of lakes etc, reclaimed \ coastal lowland, endiked before 1300 ^•VV-1 higheligherr river flood plain (incl. some clay on peat and peat)

tfvyH lower river flood plain coastal lowland, reclaimed since 1300

J peat land, reclaimed

Fig. 2.Th e locationo f thepolder s indownstrea m flat river catchment areas,i npea t areas,o fpolder smad eb y draining lakes ando f poldersmad eb y coastal embankments inth eNetherlands .

224 ßy theconstructio n of thesedike s and thedevelopmen t ofa n artificial watermanagemen t system thesearea swer emor e andmor e transformed into agricultural land and theorigina l vegetation of forestswa smor ean d moredestroyed . Initially the land use aimed atcerea l production combinedwit h dairy farming and fishing.A s timeproceede d the land became less suitable for cereal production andmainl y dairy farmingan d fishery remained. Inth e lowerpar to f the river catchment themarshe s andmars h forests were also gradually reclaimed.Th e originalmars hhabita twa s transformed lnto ahabita t ofwe t grasslands (onth edike salon g the rivers special vegetationdevelope d that still,thoug h oftenpartially ,exists) .Wit h thedestructio n of the tidalmarshe s birds like theGrea twhit eegret , theNightheron ,th eDalmatica n pelican and the Squaccoherro n lost their habitat toa larg eextent .

A majorpar t ofdutc h polder areas consists ofpea t soils.Th e reclam­ ationo f these areas sometimes dates from theelevent h century but the major partha sbee n reclaimed during the thirteenth century and later. *nthes epea t areas,pea t ofvariou s thickness overlaysmainl y loamy °rclaye y soils.Th epea twa s originally reclaimed for cerealproduction . As timepasse d by,du e tooxydatio n and shrinkage,th econstructio no f anartificia l watermanagemen t systemwa snecessar y tosav e thelan d fromflooding .Unde r those conditions the land could only beuse d for dairy farming. Grassland polder areasprovidin gmainl ywe tgrasslands , °rmed thehabita t forwate r andmeado w fowl.

!nthes e areas themajo r and decisive step from anenvironmenta l pointo f view is the first i.e. thereclamatio n of thesoil .Thi smean t the destructiono f the originalvegetatio n onth epea t soils and turningit , after amajo r temporary use forcerea l production,int o grassland. The other result of theconstructio n ofpolde r areas isa decreas e inth e frequencyo f flooding ofvariou s areas and control of thewate rlevel , b°th of the openwate r and of thegroun dwater . The reclamationo f the landofte n started froma ban k ofa rive ran d Penetrated bymean s of long stretched parcels into theare a tob e reclaimed.Th e origin of the formationo f these long stretched parcels is due to thecentra l government thatwa s already present at thattime .

225 Due tolegislatio n afarme r could only rent a certain (limited)lengt h of land along aban k forreclamatio n perpendicular to thatbank .Thi s resulted ina differenc e inth e intensity of the agricultural use, forced upon the farmerb ybot hdistanc e and soil conditions.I nth e oftennaturall ywel l drained areasnea r thebasi s of the reclamation (andmostl y near the farm)th e landwa smuc hmor e intensively used than the remote,somewha twette r parts at theothe r end of the reclamation parcels.The ywer e only used forha y cropping.Suc hhay-land swer ean d are froma necologica l point ofvie wvaluable .The yprovid e good living conditions forman y species ofmeado wbirds ,bu t are also importantfro m a floristicpoin t ofview . Inthes e regions birds like theCorncrake , theBâillon' s crake,th eWhit e storkwer e common although theyhav eno w almost completely disappeared from theseareas .

Figure 3show s atypica l example of thisparcellin gwhic h canstil lb e found in theNetherlands . However due toth e improvement of farming conditions bye.g . lowering of thewate r levels,th eapplicatio n ofartificia l fertilizeran d reallotment of farms,muc h of thisparcellin g has disappeared. Froma n ecological point ofvie w this isespeciall y reflected ina decreas ei n thenumbe r ofmeado wbirds ,rails ,Whit e storks,bird s ofpre y like harriersbu t also inth ediminishin g floralvalue so f theseareas .

The third group ofpolder s inth eNetherland s consists ofdraine d lakes. Natural lakeswer e present inth epea t areasbu t theyhav eals obee n formed byma n using thepea t as fuelbecaus e of lack ofwoo d or coal. Inth ewester n andnorther n parto fou rcountr y thisresulte d inth e creationo f lakes and asyste m ofope nwater swit hman y small,lon g islandso nwhic h thepea twa s dried (fig.A) ,I na numbe ro f cases the combined actiono fwin d andwave s resulted inerosio no f thesmal l islands and the formationo f increasingly larger lakes,threatenin gth e lands around them. These areaswher e lakes,smal l canals,smal l islands and hay-lands in various combinations were presentwer e important forbot h herbivorous and carnivorousbird s ofwetlands .

226 Pi8- 3.A typical exampleo f the long stretched parcelling in thepea t reclamation areas inth ewester npar to f theNetherland s (Holland -Utrech t region).

227 Fig. 4.A n exampleo f the systemo f long stretchedwater s and islands resulting frompea t digging for fuelproduction .

228 îhe invention of the revolving turretwindmil l enabled the lakes tob e reclaimed. The first lakewa s drained in the firsthal f of the sixteenth century and especially inth ewester n parto f theNetherland s many lakes havebee ndraine d infollowin g centuries.Th emai npurpos e of these workswa s the reclamation of fertile clay soils suitable forcerea l Production,a swel l as for the increase of safety against devastation °fth e surrounding peat area,reducin g shore linean d improvement of watermanagement . In time theemphasi s on theseaspect sha svaried ,bu t theyar e stillvalid . The ecological resultwa s adestructio n of thehabita t forman ywate r fowlan d birds ofmars h land,bu t also formammal s like theOtte ran d 'heBeaver . fc»th eare ao f the coastal polders adifferen t situation isfound . Here thepolder shav ebee n reclaimed from the saltings.Coasta l accretion could beenhance d bymakin g special sedimentation provisions which still canb eobserve d inth eWadden-se a (fig.5) .Th ehighe r parts ofth e saltingswer e first turned into salty grasslands providing food forman y herbivorouswaterfow l likeduck s andgeese . After embankment thecoasta l polderswer epredominantl y used asarabl e l*id.Nowaday s the land accretion areashav eprove d tob eo fver yhig h ecologicalvalu e forbot h themarin e ecosystem of theNorth-se a aswel l as forwaterfow l andwaders . The shallow,intertida l and sometimes brackish areas proved tob eo f suchecologica l value that,i nrecen tyears ,i tha sbee n decided nott o **ecuteembankmen t insuc h zones even thoughplan swer e advocated.

T*e largest landreclamatio nprojec t in theNetherland s isth eZuyder - 2eeproject. Plans for thisprojec twer e already advocated in 1657b y Henric Stevin,a Dutc h engineer,bu t itwa sno t untill themiddl e ofth e •Nineteenthcentur y before technical developments made theplan s feasible. ItK , , .. „„•„„ T-pçparchan dplannin gbefor e thefina l L tookman yyear s ofdiscussion ,researc u«u u v e dénio - ^ ,, ,„„„„ „ rakpn in 1918,b ypassin g theZuyder - ccision toexecut e thepla nwa s can-eu,m i;^, j v a ee act inparliament . The basic aims of thepla nwer e toshorte n theprimar y coast lineb y the instruction ofa barrie r dam,t o increase food productionb y the teclamation ofapproximatel y 200,000h ao fne w land (160,000h ano w 229 Fig. 5.Lan d accretionwork s in theWaddense aregion .

230 realized)an d an improvement of thewate rmanagemen t of adjacentregions , subjected tosalin e seepage from the sea,b y turning in theforme rZuy - derzee into the freshwate r lake:Lak e IJssel (IJsselmeer)b ymean so f theRhin edistributar y theIJssel . Theexecutio n of theprojec tha sha d and stillha s ecologicalan d environmental consequences. A majorecologica l consequence isth e change from thealmos t salinean d hrackish systemo f theZuyderze e intoa fres hwate r systemo f theLak e Ijssel.Thi smean t forexampl e thedisappearanc e of the typicalZuyder ­ zeeherring ,th eanchov y and ofwaterfow l livingan d feeding along the coastline and inshallo wwater s like theBrentgoose . °nth eothe rhan d there are gainstoo . The.water inLak e IJssel iseutrophi c and,althoug h under influenceo f fcheRhine ,stil lno theavil y polluted.Du e toit seutrophi c character the large lakes inthi s system are rich infoo d forwaterfow l feeding or»fis ho rbenthos .Nowaday s themollusc ,Dreissen a polymorpha,whic h was only firstobserve d here in 1937,i sth ebasi c food forbentho s feeding ducks.Th e Smelt is thebasi c food forman y fish eating waterfowl.Th e arearank sver yhig h onth e listo fvaluabl ewes t european areas forwaterfowl . Also inth epolder s part of thene w land nowadays issave d forecologica l developments;marshes ,grasslands ,wood s and forests arean dwil lb e developed providing habitats forwaterfowl ,bird s ofmeado w landan d various rare orendangere d species such asharriers ,spoonbill s and herons. In thepolde r Southern Flevoland,whic h isno wunde r development aPProximately 15,000h ao fnatur e sanctuary and forestwil lb e realized in apolde ro f43,00 0ha .Thes e developments have tob e considered in relation toth e roleenvironmenta l and ecological aspectshav e played in Physicalplannin g in theNetherland s during the lastdecennia .Whic h brings us toth e second part of thispaper ,afte r concluding thispar t with ama p of the present dayecologica l situationo f theNetherland s as iti snowaday s (fig.6) .

In theNetherland s during the20t hcentur y anumbe ro fdevelopment s took place,resultin g (asi nman yothe r countries)i na stron g awarenesso f the importance of themaintenanc e ofa goo d quality of the environment and thepreservatio n ofnatur e asvaluabl e elements for thewelfar eo f mankind. 231 NATIONALLY IMPORTANT NATURAL LANDSCAPE ELEMENTS

|^H almost everywhere or in large sections > J almost nowhere n^:=v£' in many varying to in few places ' urban use

Fig. 6.Th eecologica l situation of theNetherland s around 1975 (after Atlasva n Nederland).

232 Developments in the 20thcentur y

Th u e ~-;„u„r» 1 =ocietv intoa moder n industrialized and J-hechang e of anagricultura lsociei- y , , . , -.I,„ lov-cr pincreas e inpopulatio n and astil l urbancommunit y togetherwit h a large increase v r continuingmechanizatio n m agriculturin.T-e aroearimportant p imnortan. t inthi srespect , TU r u .-^n nf natureoriginate d fromurba narea s Theawarenes s of thepreservatio n otnatur e ULI6 aswel l as therecognitio n of theimportanc e of good environmental conditions and thenee d toreduc e thevariou s causeso fpollution . *-, . ... ,-„u „ int-h r-PTiturv(b yprivat e initiatives) Already inth ebeginnin g of the 20thcentur y \uy v M, ^- * f\,0 Naardermeer,wa s purchased.Earlie r thefirs tnatur e sanctuary,th eHaaraeim«!. , v „tr , • t. 11 \,~A fm'le dan d itwa s thenplanne d tob e efforts toreclai m the lakeha d taiiea duu •,.) , Naardermeer.th eprivat ean d filledwit h urbanwaste .Startin gwit h theNaaraerm rhô e r, nreservation acquirev d 136,000h ao f government organizations for*natur „vt-ur-pe preseiva „„,1cive« ;throughou t thecountry , nature sanctuary ofdifferen t typesan d sizestnroug i togetherwit h 293,000h ao f forests (fig.? )•

•m i. v.,,hnnk s sucha s "Silent spring"b y Theenvironmenta lmovements ,begu nb ybook s sucna ,. „„„ fonmbatin Kpollutio n injus t RachelCarson ,stresse d the importance ofcomDatin g v u o= rheNetherland sha dbecome .Pollutio n sucha nindustria l society sucha s the »emei i„„„«ic oet- c had tob ereduced , ofwater ,soil ,air ,groundwater ,bu t alsonois eetc . i j ,minn(.Hi n thepas t decennia Newlegislation s in this field havebee ndevelope nd in P K rCM-1 1man y problemshav e tob e solved, and progress isbein gmade ,bu t stillman y v inth eurba n aswel l as inth erura larea so f ourcountry . p . . . „,-„„th eenvironment ,th e legislation prior to the legislation concerning theenvi i , , • „ithin thecountr ywa smor e developed concerning thephysica lplannin gwithi n tnec y ^ oitannin e forurbanizatio n and the andelaborated . Starting fromnationa l planning j 0„;„nalan d local planningwa s adjusted development of the rural areas,regiona l ana v . , a f-imeth eproces so f planningwa s fcoon e to theother .A t the same time tnepi . graduallybein g democratized. t> . •„„^.nta limpac t assessment forne w Recently ala wconcernin g environmental imp* *.u „orliamen t bridging and covering Projectsha sbee npropose d toth eparliament , ^ g both physical planning and environmental planning.

u -, anr nf anelaborat e legislation inth e However,i nspit e of thisdevelopmen t ot aneia u „„„i „rnhpction thereha sbee nan d field ofbot hplannin g and environmental protection, x. „ , 'rnmriOTto f thepolde r areas.Thi s ^ still damagebein g done toth eenvironmen n n t oi v i,„Hpvelopment s in the land usei n canb e illustrated by considering thedeveiop f m °urcountr y during thiscentur y (fig- 8)•

233 nature areas

Fig. 7.Natur e reserves and forest areas inth eNetherland s around 1975 (afterAtla sva n Nederland).

234 Area in ha x 104 340

320 J

300 J

280 forests, nature reserves and other uncultivated area (waste land)

260

cultivated area

1900 1910 1920 1930 1940 1950 1960 1970 1980

Pig. 8.Th edevelopmen t in the land uses inth eNetherland s during the 20thcentury .

235 As canb e seen the total areao f the land inth eNetherland sha s increased from almost 3.2 millionhectare s toove r 3.3 millionhectares . This ismainl y due to the reclamation of the large Zuyderzeepolders . During the first fiftyyear s of the 20th century the total areao f forest andwast e land decreased from approximately onemillio nhectare s to abouthal f amillio n hectares mostly by exploiting thewast e land. Themajo r causeswer e the introduction ofartificia l fertilizers,larg e unemployment inth e thirties and food shortages.Durin g the last three decennia no significant changes canb e observed. However,importan t changes canb e observed in the sizeo f theurba narea . Due toa ver y strong increase of thepopulation ,6 millio n around 1900, 8.5 million in 1945an d over 14millio n in 1981,togethe rwit h an increase in theus eo f the available spacepe rperson ,resulte d ina growth of theurba n areas from about 80,000hectare s around 1900t o about 450,000h a in 1980.I tca nb e seen thatdurin g the lastdecennia , theurba nexpansio nwa s realised at theexpens e of theare ao f agricultural land.Th e average rate of thisproces s isnowaday s about 13,000hectare s peryear . Such aproces s affectsman y polder areas,sinc e themajo rpar t ofth e Dutch population lives inth ewester n parts of the country,wher e predominantly polder areas exist.Th e impact that such aspreadin g urbanization and the related infrastructure canhave ,ca nb erealise d by considering maps of theurbanizatio n inth eregio n around Amsterdam in 1930an d 1975.Nex t to the towns and villages themselves,ther ei s an increase in the zones ofdisturbanc y around themb y increased mobility of thepeople .B y setting thesedisturbanc y zones arbitrarely at 1.5k m in 1930an d 4k m in 1980,fro m theurba nborde r one canse e the increase of theeffec t ofurbanizatio n upon theregio n (fig.9 an d 10).

Next tothi surbanizatio n process,development s inagricultur e itself such as increasingmechanization ,th eus eo f artificial fertilizers, ofpesticides ,th e improvement ofwate rmanagemen t and theexecutio no f large scale reallotment plans resulted ina decreasin g ecological value ofespeciall y the grasslands.Thei rvegetatio n becamemor e andmor e uniform.Th emor e intensive use of the land caused thedestructio no f manynest s ofmeado wbirds ,althoug h some species compensated bystartle »

236 North Sea

• V l? IJsselmeer

J V\-*- M* "w • '.'•• v.- -y.: \i\ *

;;:*: .1 1 .••* ^ I . m.-

•.\ ,-V' •\

railway villages and towns urban disturbancy zona road

?• ^i. »«ttorrlamregio ni nth eNetherland s in ig.9 .Th e urbanisation inth eAmsterda m regionat 15 k m 1930an d theurba ndisturbanc y zones (arbitraraly set at 1.5k m in 1930).

237 North Sea

\ * » % .•'*•. 'm? -s)i s 1 /••.\*.. 1« '••*• i » ^ j u %r-^^:^fm"'''"'^ •t -i I_Î i .r.~.»—" --~i i 'WÈBÊt •••

4fc villages and towns road

^ ^ ' planned town railway

urban disturbancy zone

Fig. 10.Th eurbanisatio n inth eAmsterda m region in theNetherland s in 1975an d theurba n disturbancy zones at that time (arbitraraly set at4 k m in 1980).

238 breedingearlier . Excessive useo f fertilizers caused eutrophication ofcanal s and lakes and the changing of the aquatichabitat . Theus e ofpesticides ,suc ha sDD T andothers ,resulte d inth e introductiono fpoison s in foodwebs ,a sdoe s thedischarg e ofurba n and industrialwastewate r andeffluents . °nly inrecen t yearsha s theeffec t ofdumpin g industrial and urban wastes inpolde rarea sbecom e evident.Sometime s urbanextension s have beenrealize d insuc h regions.Afterward s itwa sobserve d that soil, groundwater and sometimes even surfacewater swer eheavil y polluted by, forexample ,carcinogeni c solvents sucha sbenzen e and otheraromatics . Very expensive soil improvement planshav e alreadybee n realized inth e regionsnea rRotterdam ,resultin g incost s amounting toove rhundred s °fmillion s ofDutc hguilders . Inothe r locations,suc ha s in theVolgermee r poldernea rAmsterdam , thedumpe d industrialwast ewa s recently found tocontai n thever y toxic Toxine, threatening theenvironmen t ofbot h thecit yan d theadjacen t Maturereserves .

Regarding thedevelopment s indicated above,i t isno t atal l surprising thati nth ediscussion s about the final stageo f therealizatio n ofth e Znyderzeeproject,th eMarkerwaar d polder,ecologica l and environmental *»Pectspla y an important role inth edifficul t and already 10year s orationproces s ofdecisio nmaking .Th e finaldecisio n toconstruc t *e polderha s still tob e takenb y thegovernmen t and tob eapprove d bV Parliament.Grea t effortshav ebee nmad e togiv ereliabl ean d quantitativeprediction s of theecologica l and environmental consequences forbot h theaquati c ecosystem, thatbecome s smaller,an d the increasing

P°BSibilities for nature inth e futurepolder .Th e insightha sgrown .

Whna^ t. ,• t. A„„:i;Uf« ofweighin g the twoecologica l t has remained isth e impossibility oz w<=xS 5 alternatives,althoug hmor e quantified thanever .

As awhole ,throughou t thecountry ,th e increase of thepopulation ,th e urease of industrial activityan d theurba nexpansio n result ina sPatial consumption ofpolde r areas andhenc ea destructio no f remaining ec°logical values.O n theothe rhan d theawarenes s of these processes at* apolic y aimed atpreservation ,reconstructio n andnewl y developments

239 ofnatur e and its integration intoothe rmean s of land use,ca nhel p topreven t complete destruction. As aresul t itha sbee n observed that thenumbe r of geese staying in theNetherland s inwintertim e shows amarke d increase during the last tenyears .Investigation s inwester nNetherland s during the last ten years showed that thenumbe ro fbir d species breeding thereha sincrease 0 togetherwit h the actualnumbe ro fbreedin gbirds .A nexceptio nwer eth e typicalmeado wbird s and herons.The y decreased innumbe r of speciesan " numbero fbreedin gbird s forreason smentione d above. These losseshav ebeen ,althoug h partially,compensate d for inth ene w polders.

As alreadymentioned ,ther e isstil l apossibilit y for the construction of coastal polders especially inth eWadde n sea.Althoug h anumbe ro f plansar eadvocate d in theNetherlands ,a swel l as inGerman y andDennia 1 it isver y unlikely that theywil l be executed in theNetherland san d Denmark.Whethe r thisals ohold s forGerman y isdoubtful . Inth eNetherlands ,i ti srealize d that thisWadde n region isto o important for the foodprovisio n forman y birdsan d for theecosyste m of theNorthse a and that it isto o important for shrimp fisheryan d shellfish fishery tob eembarke d upon.

At thepresen t time there isa tendenc y inou rdensel y populated country torealis e aschem e ofphysica l planning ona nationa l level thatwil l reduce therat e ofurba n expansion.I ti smor e andmor e appreciated that theavailabl e space,bot h of land andwater ,i s limited and scarce# The struggle and competitionbetwee n various land uses canno toffe r solutionswher e available space ispermanentl y lacking.I t is tob e expected that ona nationa l level agreementwil l evolveabou t the distribution of the areaove r themajo r uses of theavailabl espace : agriculture,nature ,urbanizatio n (including recreation),forest san d water.Whe n this general agreement isreache d and accepted,th e integration ofothe r functionswithi n theprincipa l onewil l helpt o differentiate theenvironmen t ona regiona l or local scale,whil eo n thenationa l level thedestructio n of thequalit y of theenvironmen t c3 beprevented .

240 Acknowledgements

The authors thank dr. ir. P.J. Ente for his contribution in preparing

the maps for the figures 1, 2 , 6 and 7 and ir. J.A.L. Barnes for

correcting the text.

References

Linden, H. van der. History of the reclamation of the western fenlands and of the organizations to keep them drained. In: Proceedings of the symposium on peat lands below sea level,ed . by H. de Bakker and M.W. van den Berg. ILRI publication no. 30,Wageningen , 1982. pons, L.J. Ecological map of the Netherlands in Roman times (1974). In: Leven met bomen en bossen, J.F. Wolterson, 1974. Sorter, E.P.R. De zilverreigers van de Oostvaardersplassen. In: De

Lepelaar, no. 66, 23-25, 1980. fc„^ , j j- ,.;i,„hinii ofwil d geese in the Netherlands R °oth, J. a.o. Numbers and distribution orwn u s 1974-1979. In: Wildfowl, december 1981. Saeijs, H.L.F. and H.J.M. Baptist. Evaluatie van Westeuropese over- winteringsgebieden van watervogels. Deltadienst nota 78-10, 1978.

~ Atlas van de broedvogels van West-Nederland. Atlas van Nederland.

241 ECOLOGICALVALUE S OF POTENTIAL POLDERAREA S M.Vannucc i Unesco NewDelhi ,Indi a

"Ifw e areabl e tobrin g about ineac h country aprope rblen d of ecological economics and economic ecology,on ewil l find that the work will turn from thepresen t mood of agony intoon eo f enduring ecstasy"- Dr .M.S .Swaminathan ,Meetin g of ICSUSpecia l Survival Committee.Ne wDelhi . 19-2-81.

From thepoin t ofvie wo f theenvironmen t - orth eworl dw e live in- thetw oprincipa l consequences ofwha t areusuall y called the"scientii 1 and theindustria l revolution"are : (1)unchecke dhuma n populationgrow t > and (2)dwindlin g natural resources,includin g decreasing genetic diversity.Th eproblem s created by thesetw ophenomon a arecompounde d by evergrowin g demands forimprove d standards oflivin gconditions , which are intur npossibl e thanks toth econtinuin g scientific- technological growth andmor epowerfu l information and communication systems.

Manynatura l resourceswere ,unti l recently,considere d tob e available inunlimite d quantities,bu t itha s finallybee n realized thatnone , absolutelynon e isso .Th eocea n cannotb e used asa bottomles s sewage sink,no r is freshwate r inexhaustible;equall y finiteo na worl dwid e scale isth e food,fibe r and energy production potential.Eac h andever y ecosystem,ever y subsystem,whethe r arive rbasin ,a mountai n range,3 forest,a villag e or apolder ,i sonl y parto f themajo rEcosyste mEaf t Ecology isth estud y ofecosystems ,wheE eb y definition and actualfact » everything isrelate d toeverythin g else;ste pb y step,whateve rhapp eI1 inth eYssel-lak epolder s mayhav e repercussions faran dwide ,i n unpredictablemanne r andwit h unpredictableconsequences .

242 Longgon eb y areth e timeswhe nEurop e orAmeric a could ignoreth e vagaries of theMonsoo n inSout h Asiaan dwhethe rmillion swoul d starve todeat h or survive andreproduce .

Thereare ,o f course,tw o possible attitudes inrelatio n toth e environment;a passiv e onesaying :"le t thingsb e asthe y arean dw e «hallse ewha twil lbecome" ,or ,i fyo uwish' ,"le t theavalanch ecom e asi tmay ,w ehop et oru nsomewhere ,fas t enough tosav eou rskins" . But there isals oanothe r attitudewhic h ismor eManl y and rational,an d this is:"le t us dosomethin g about itan d letu s avoid doingwha t shouldno tb e done".Thi s attitude ofd oan doi-a1(land/se a interface)ecosystems , °r8anisms.Man' s interference incoasta lvianu/s » K • -u„„„ci-M ib v reducing thevariabilit y h*s invariablybee n oneo f tuning thesyste m oy rea „.r jv.- ~ffn This tvpeo fmanagemen t is of Us parameters,bot h abiotic andbiotic . ihisty p ^avoidable,becaus e itmean s preparedness against natural calamities s *ch as unusuauy high tides,o r floods fromlan d drainage andrains , «*.nowadays ,th ethreat s ofpollution ;thi styp eo fmanagement ,however ,

"**als obrin gwit h itunexpecte d andundesirabl 243 econsequences ; consequences ina wa y comprablet o thoseo f agriculturalpractices , enhanced bymoder n technologies,suc h asmonocultures ,intensiv eus eo f pesticides, fertilisers and soon .

Thebuildin g upo f apolder ,ecologicall y speaking, isth erevers eo f conservation activities. It is,fo r instance,th eopposit e of establish1 abiospher e reserve.Whe nw e establish areserve ,b y definitionw eavoi d introducing changes of any sort,sinc eth e system ist ob e left undisturbed inorde r that thenatura l transfer ofmatte r and energy among components within thesyste m andbetwee n thesyste m and the adjoining onesma y proceed according toth esystems 'ow n laws.O nth e otherhand ,whe n apolde r isbuilt ,ver y often itbegin s fromscratch . Entirely newsoi l isaccumulated ,the n turned into agricultural,urba n or industrial land.Thi s iswha t theAztecs ,fo r instance,ha d donewhe 11 theybuil t the floating gardens,whic hwer e literally floating on rafts in the lakeo fTexcoc obecaus e theyneede d soil inwhic h toplan t their vegetables (theremain s may stillb e seen at Ochimilco,wher e the floating raftshav ebecom e islands,throug h trees thathav egrow ntal l and taken root). Similarly theMaldivian s enlargethei r small coral reef islands formor e spaceo nwhic h toliv eb ybuildin g san d groins to trapsand .Polder s and reclaimed land ingeneral ,ar ene w systems thatnee d tob emanage d by appropriate do's anddon'ts .

Thebuildin g up ofpolder s inevitably takes spaceawa y from adjoining systems,th e consequences ofwhic h must alsob e considered inth elon g d'' termplanning , tomake n acost/benefi t assessment;certainl y the"robb e systems alsoha d astructur e anddynamic s of their own and aproduct! 00 potential that shouldb eknown . If atin y coral reef island isenlarg ed' areawis e itwil lb e less than aspec k ofdus t inth e immensity ofth e oceans,bu t may cost aseriou s environmental impoverishment ifth e enlargement isa t thecos t of destroying slow growing corals and the rich faunaassociate dwit h them.

Polders arema nmad e systems,i nwhich ,accordin g toplac ean d circumstances,th ebiologica l elementb y rank aso fprimar y importance» ormay ,perhaps ,b e totallyneglecte d except for theconvenienc e of tn singlespecies .Man ,wh oneed s aplac e inwhic h to livean d space f°r

244 recreation. Iaothe rparts ,o f theworld ,however ,polder s are considered entirely for agricultural production,includin g inthi sperhap s also aquaculture,an d they includeman y different species,i nadditio n to man theplunderer ,th especie s forwhos eexclusiv ebenefi t thepolder s arebein gbuilt .Ther eare ,therefor e contrasting requirements -o r values,i fyo uwis h- accordin g toth eplac e andpurpos e for which Polders arebein gbuilt .Th eparameter s tob e selected,measure d and quantified for asoun dmanagemen t vary inessenc e andmagnitude .Wha t maybecom e a"don't "i non earea ,coul d verywel lb e themai n "do"i n bother. Sincepurpose s vary,an ds od ovalues ,"do "an d "don't"mus t bedefine d anew ineac hcase .

Inth emanagemen t of polders,lik e inothe r systems,probabl y thegenera l aimvaul db e tobrin g aboutwha t Swaminathan called "aprope rblen do f Ecological economics and economic ecology".Ecologica l economics hasa verydifficul t task toperform ,becaus e ecological values arehar dt o definean d qunatify interm s such aswoul db e accepted by economxsts, but it also is a challenge toth ehuma nmin d that isfascinate db y j;tt. , . , , T<„ imponderable s that determineth e Qlfficulties tob e conquered.Th elmponaei d qualityo f life forma n and that contribute inn osmal lmeasur e tomak e « any endeavour of thiskin d asucces so ra failur ecas ear eonl yto o nz^ . , i„ „noqterior i it isfoun dou t often left out of thepictur e and onlya posterior . thatsuc h factor orothe r really should havebee n taken intoaccoun t because itplay s an important previously unsuspected role in,le tu s s*y, the food chaino r inth etransmissio n ofdiseases .I nfact , f»„ ~^-;«c and every association ofspecies , everything isimportant ,ever y species anaever y ^ ^-,1 roie. itwoul dhav e longsinc e because ifi tdi dno t play anessentia l roie, beenweede d out of thesyste mb y itsnatura levolution . Siùlnc« e i..t is impossibl. .,.e, t oobtai u-oin totan t-ntalïniui linformatio . no neverythin gan d •„o vmrr v we cannotwai t tohav e Slncew e arecharacteriscall y always ina hurry ,w e r. ,• i_ fnra takine. action,a compromis e c°nvpleteinformatio n on everythingbefor e takinga c is sought and letu shop e forth ebest .

Al , „,.„, mTV where inth eworld ,ar e almostal l lifesupor t systems,almos t everywne r «„ t 'u;Bn nf noldersi scarrie d outwit h n°wadaysunde r stress,i f thebuildin g ofpoiaer s a„ • . . t~v ,-r.ct-anceadde d space forman ,o r a singlepurpos e inmind ,a sfo rinstanc eaa u v 245 economic development through industrial growth,i tcoul dbecom ea disastrous enterprise.Monotonou s ecosystems are fragile,i ti s diversity that gives stability toecosystems ,whethe rnatura l orma nma " Potential polder areasma yb e found allove r theworld ,a tlo wo rhigh er latitudes,especiall ylo w lying coastal areaswit h sandbars ,o rcoasta l lagoons,mangrov e swampso r forests,wetland s andmarsh y areas andal" n8 estuaries and deltas.San dbar s arei n fact usually thestartin gplac e where engineeringwork s for reshaping the landscapebegin ,b ybuildin g dikes andwate r level control devicesb y sluice gates orspillways . Often theimpounde d area,afte rwate r isdraine d off,i s lyingbelo w sea level,als o inman y places inth etropics .Coasta l lagoons are admirably suited and innumerable couldb e cited.Fo r instance,alon g the800 0k m long coast ofBrazil ,th eLagô ado s Patos andLagS aMiri m coverhundred s ofsquar ekms .Extensiv e reclamationha sbee n carried out allalon g itshistor y inth eBaî ad aGuanabar a (Riod eJaneiro )an d many of thecoasta l lagoons areunde r intensive aquaculture (ex.Lago a deMaricä ,nort h ofRi o deJaneiro ) throughmanage d impoundments of brackishwater ,a practic e introduced inth eearl y XVIIcentur y for thePortuguese ,wh oha d inherited theknow-ho w from theRoman s anduse d thesam emethods .Eve nnow ,gre ymulle t ponds inth eare a of,fo r instance,Recife ,ar ecomparabl e toth eacquacultur e impoundments inct l Campania,an d other places insout h Italy,wher emethod s arestil lver y muchwha t theywer e almost 2000year s ago.Values, however ,hav echan g andwork swhic hwer e carried outmainl y tomanag e thenatura l system t0 put itt oa highe r production level for those items of interest toman » like fish,hav eno w givenwa y towork s forexpandin g traffic areasan d improve communications,buil d airstrips and airports or enlargeth e industrial area.Thi swa s donever y often ina hurrie d manner,withou t due consideration toloca l physiographic conditions,speciall ywate r circulation andmajo rproblem s ofpollutio nhav e cropped up.Time s hav changed,s ohav eneed s and themean s tosatisf y them.

InAsia ,th epractic eo fbuildin g dikes for impoundingwate ran d developing low lying areas isa practic e that goesbac k toremot e tl* Thepeopl eo f theMoenjo-Daro/Harappa ncivilisatio nbuil t canalsan d AS harbours inwhic h the flow ofwate rwa s regulated according toth ene e ofnavigatio no f their large covered two-three deck ships as early aS

246 the laste fourth miUetiium BC. Inpresen t dayIndi a there are2 million hectares ofbackwaters , 30,000 hcto fwhic h areunde r aquaculture, mainly for prawns. These include thedelta s andestuarie s ofmajo r rivers as well as coastal lagoons andlakes . Lowcost , labour intensive, simple technologies arestil l inus eeve n where extensive engineering worksar e involved. Traditional methods andtechniques , that have proven their worth over centuries arestil l inus eofte n incontras t inth esam e areas, with modern technologies. Thus inth eCochi n backwaters (Malagar coast, southeast India), thebun d across theVembana d Lake isbein g built over a span ofdecade s while further north, inth esam e backwaters several polders andne wwaterway s were recently built inonl y afe wyear s for thedevelopmen t ofCochi n port andCochi n shipyard. TheCochi n backwaters area particularly interesting example. Iti sa vast area that extends from about 9°lat .N .t oles s than 7°lat .N . Extensive "bunding" (dike building, where dikes mayb esimpl e mudwall s 50-100c m hi ,. , i A ,0„al'rpiivearl v after theS Wmonsoo no r "igh above mean water level andrepaire d yeany »ajor structures built with rocks andothe r materials) hasturne d an area that includes many taluds ofthre e districts into a polder lying below sea level. In this area fields aremanage d forric e croppingan d .„, , ,, . . -1 „ ietv ofpadd y wasdevelope d over aquaculture alli none .A special varietar y f J the years which is salinity tolerant, brakish water isadmitte d during the intermonsoon period, foraquacultur e purposes. Themanagemen t of i-i•, c ,•••= nun andproblem s ofal lsorts ,no t this area hascharacteristic s ofit s ownan a pruu i .._ t-axation andsocia l relations ^ast of them those of land andwate r use taxation « n. , , „,„ K-„K-onad area ist othi s day the that become acute nowan dthen . TheKuttana a are* J. T „fkor nlaces. inth esam e backwaters rice bowl ofth eStat e ofKerala . Inothe r places, **d outside ofth eVembana d Lake protective bund, small areas which collectively cover some 5002 kmar eindividuall y diked offint o fields fi r ~„AAv cultivation andsom e fish also flooded during theS Wmonsoo n forpadd y cultiva *re reared along with paddy. After reaping therice ,whe n monsoon fresh *ater from rains andlan d drainage have ceased topou r in,brakis h water gradually inundates thebackwater swher emaximu m salinity reaches 31-32% *tmost . During this period, thesluic e gates,provide d with special n„*. . . • „,•„,*t-nrl pt oadmi t into thefield s nettings areopene d during theincomin g tidet o '»e larvae ofprawns , mainly Penaeu^indiçus. Thelarva e grow in the s **e fields wnere paddy grew during themonsoo n under 1-2%salinity . TK , „rcA hpfore theonse t ofth enex t monsoon, lhe prawns (chemmeen) areharveste d betör247e when,i f theycoul d escape,the ywoul d migratebac k tose at o metamorphose into adults and assemble ata certai ndistanc e and depth offshore,wher e thosetha t hadno tbee n trapped,ar eabl e tomat ean d reproduce. Thebund s thatmak e up the checkerboard of fields areplante d with coconuts and chinese overhang themajo r canals.Th ewaterway s are,i n addition, themajo rway s of communication, transport ofgood san d passengers aswel l asmail .Mos t of the trafficwa sdon eunti l recently and stillvastl y soa tpresent ,b y "village"craft ,unmotorise d and propelled by oars and poles.Th e owners of thefield s do theplannin g of thepadd y andharves t thecoconuts ,bu t fields are leased to fishermenwh o do thepraw n cultivation andwee d them from carnivorous fish,allowin g only thegrowt h ofharmles s species of fish inadditio n toprawns .Th e success or failure of thepraw nharves t isalmos t entirely due to theabilit y and expertise of theelde r fishermanwh o operates the sluice gates at theappropriat e time to let inth e larvae which he cannot seean d does notkno w they exist.N o fertilisers are used except human,fis h and prawnexcreta .Th e productivity in fishan d prawnaverage s 2,300kg/hct/season . It couldwel lb e increased bymoder n techniques.

Thereaso nwh y Ihav edeal t atsom e lengthwit h thisparticula r example is, first,I a mfamilia rwit h theare aan dhav e firsthan d information but there areman ymor e similar systems inIndi a andAsia ;second ,i t isa goo d example ofwis e tradionalus e of natural ecosystem,an d the human and ecological values attached to it.Th eCochi nbackwater smus t undoubtedly havebee n amajo rmangrov e area in theremot epast .Small » isolated pocketsma y stillb e found.Th e conversion of amangrov e ecosystem,whic h isa highl y productive one,althoug h of reduced direct utility toman ,int oa differen t ecosystemwit h amuc h higher producti0 rate of crops of directus e toman ,wa s achieved gradually,ove r centuries ofhar d labour and through theaccumulate d wisdom ofpeopl e who live inclos e communionwit h the system ofwhic h they areals oa n important component.I woul d presume that,a s theywer e until acoupl e ofdecade s ago,th eCochi nbackwater s havereache d theirmaximu m productionpotential ,excep t for improvements that could havebee n introduced throughmoder n agricultural practices.Troubles ,however ,

248 started when fertilisers and pesticides were used upstream and were flushed through the system with monsoon land drainage water. At the same time, other polluting agents also set in, such as oil, increased siltation, increasing sewage discharge from growing human settlements and towns and the tampering of the natural hydrographical pattern of circulation due to the construction of harbours, shipyards, airstrips, ,,.,_• i,Knnr has become more expensive Jetties and the like. In addition, labour nab while hard work is necessary to keep the structure of the system in Proper order throughout the year, including desilting of canals, repair „c -, . * ,„„;„„ the fields mud flats, tending °f bunds, sluice gates, nets, plowing, tne H, _, M„^h of the labour done by local traditional the coconut trees and so on. Much or cne experts was taken over by the Land Development Corporation that uses mechanised methods that can do the job quicker but perhaps less well. TT_ •-• ,„.fr„anl caused eutrophication of the Tne excessive use of fertilisers upstream caubeu 11, , T „.-«^c havp become covered by water lake" waters and much of the backwaters have oecom K . . • „„j M11,ine all sorts of troubles. In Vacinth, hampering navigation and causing an "old times" appropriate drainage canals removed excess salinity from the below sea level areas and the monsoon rains could wash off the A A.rina the period of stagnant waters, sulphides and the acidity produced during tne p T, • j „aA t-hroueh modern technologies have Paradoxically, improvements introduced througn m „~A ™P reason is that a natural Seated previously unknown problems and one reason - j o«t- t-ampd bv man, cannot take ecosystem, even if already domesticated ant tameü by m , . . , r adaptation and acclimatization to abrupt changes; it needs a period of adaptation tK . . ^ a lot of money is being spent on the new conditions. At present, a lot or m y ro . ™rrect the imbalances produced. The research and survey in order to correct cne ,_„„„ « , ,•„ t-hPKuttana d area and UNESCO Netherlands themselves have a scheme m the Kuttan u ,„;„rH! We might, perhaps, close »ay help in conducting some research projects, we m g .,„. if f-ould not be better than the circle and come to the conclusion that it could no what centuries of experience had achieved. T. . ,,Dra the achievements and problems If we try to compare the Dutch polders, tne a i„ v. u the Cochin backwater system, we would ln- this country, with, perhaps, the wenn ,, i ,-e risible. We would be comparing Perhaps conclude that no parallel is possible. ^ 1écrira i values and the conclusion ^sterns with totally disparaging ecological vaiu .„ i« uniaue and merits a special ls thus unavoidable that each case is uniqu .,-, ~A Ar, in practice, increase our study. Special studies that will and do, in pr , un,, . Altaic and low lying coastal areas m Utiderstan din g of estuarine, deltaic, <*"" 249 general.Th e typeo f reclamation thatma y be advisable fora territorially small country asHollan d may be theonl y solution tobi g problems of space and agriculture,eve na t the cost of sacrificing important "ecologicalvalues" .The ymay ,however ,wel lb e totally inadvisable inothe r areaswher e these sameecologica lvalues, includinghuma nvalues ,tak e theprecedence ,sinc e thewhol e system has already evolved over the centuries tosuc h aleve lo f perfection that theonl y likely improvements would be theus eo fmoder nmethod s to increase theproductio n level.Unde r thisI woul d include the production ofhighe ryieldin gvarietie s of paddy,startin g from those varieties thatar e already adapted toth econdition s at large,th e same for coconut,prawn s and other species of fish andmolluscs .Th e bundscoul db e improved materially, thehydrograph y better understood and themanoeuverin go f thedoor s (orgates )shoul d bebase d ona scientific understanding and explanation of theancien t empirical wisdom.

Theproble mwoul d always remaino f drinkingwate r supply.Typically » inth ereclaime d areasbehin d theVembana dLak ebund , tubewells only bring up foul smellingwater ,obviousl y due asexpected , to thehig h content ofsulphides .

Inconclusio n Iwoul d like tosa y that inkeepin g our eyes open toth e factn o total conservation ispossible ,w e should,a s isno wbein g done inth eNetherlands ,tr y toanalys e all factors carefully,wor k outcos«- ' tl benefit budget analyses and try tofin d out all the important factors thatma y perhaps not appear tob e sucha t first sight,tha tma y be difficult toquantif y and thatma y remain indisguis e and unperceived for a long time even if inth e long run theywil l turnou t tob e decivl indeterminin g thequalit y of lifeo f thepeople .

250 SPECIALKEYNOTE S

LESSONS FROMTH EHISTOR YO F IMPOLDERING INTH EWORL D Prof. ir.A .Volke r Delft University ofTechnolog y Delft,Th eNetherland s

Thehistory ofimpolderin g inth eworl d iso finteres t toth ehydrauli c engineer provided that technical problems were solved under different conditions with themean s available during different historical Periods.

Thehistor y ofimpolderin g inth eworl d iso finteres tt oth ehistor yo f thM. e,huma n civilizatio... . n provide•j . 1<-h<>< d tha-a nt analysia nanaiy&xs s is»mad eo fth efactor s Which indifferen t societies anda tdifferen t times inhistor y were determinant forimpoldering . Historyca nb einstrumenta l inbette r understanding thepresen t conditions andi nidentifyin g thefactor s which played arol e inhistor y andwhic h will continuet opla y arol e ln thefuture .

Thehistor y ofimpolderin g cannotb edivorce d fron,th ehistor y ofth e topics offloo d protection,drainag ean dirrigation . Indeed, impoldering isa specia l formo fintegra l reclamation andinvolve s acombinatio no f flood protection, artificial drainage andofte n irrigation. Thehistory offloo d protection, drainage andirrigatio n is,mos t ""fortunately,a littl e explored area.

In ,-u- >. -n j,«mad et oanalyz e thefact s fromth e in this essay an attempt willb emaa e LU <** j historyo fimpolderin g sotha t some factors canb eindicate d which have b*en determinant inth epas t andwhic h will alsopla y arol e in the ln thefuture .

251 1. Ancient polders

In this sectionsom e factswil lb epresente d about early impoldering activities.A n analysis of thetechnica l and socio-economic factors, which were conducive to impoldering,wil lb eelaborate d insectio n4 .

Impoldering is aspecia l typeo f land reclamation applied to specific . Itcomprise s flood protection,artificia l drainage and often irrigation and forthi s reason thehistor y of impoldering is apar to f thehistor y ofhydrauli c and agricultural engineering for achieving flood protection,drainag e and irrigation.Unfortunately : "engineers havemad ehistory ,the y have even changed thefac e of theearth ,bu t they failed torecor d it".Th ehistor y of flood proctection,drainag e and irrigation isa nalmos t unexplored field and it isonl y recently that the"Internationa l Commission on Irrigation andDrainage " (I.C.I.D.)decide d tosolici t international co-operation forwritin g thathistory .

ProfessorHitosh iFukud a fromJapa n (1976)consider s theembanke d flood basinswhic h inancien t Egypt wereuse d as retentionbasins ,an d inth e saturated soil ofwhic h acro pwa s grown after theNil e flood,a s "polders".Thes ebasin s dohav e some commoncharacteristic s with the systemswhic h areusuall y called polders and asexis t to-day,al s in Egypt, in the reclaimed lakes inth enorther n part of theNil edelta , butwhic h function ina nentirel y different way. If thedefinitio no f Professor Fukuda isaccepted ,th eoldes t "polders"i n theworl d were reclaimed inEgyp t some five thousand yearsago .

Ifhoweve r theseNil ebasin s areno t considered aspolder s oneha st o looka t those ancient civilizations where the control ofwate rplaye d apredominan t role andwhic h were denoted byK .Wittfoge l (1957)a s hydraulic societieswit h ahydrauli c agriculture.Man y thousandso f years agoembankment s asmean s of flood protection and irrigation canalswer ebuil t inEgypt ,Mesopotamia , inth evalley s of theIndu s and theGange s and in China,Per u and Central America,bu t it isno t certainwhethe r thework s canb e defined as impoldering as iti s understood to-day.

252 PaulWagre t (1959)ha s drawn attention toth ereclamatio n during the fourthmillenniu m of themarsh y low-lying areas ofMesopotami ab y the Sumerians.The yskilfull y maintained theseprehistori c polderswhic h are criss-crossed by ditches and canals.A Sumeria n text tells of the farmer Enkimdu,"Lor d of theditc h and thedyke" .Th efac t that theditche s are soexpressivel y mentioned may indicatetha t thework s comprised more than flood protection. Indeed reclamationo fmarshe snearl y always involved inpoldering.

So fara sEurop e isconcerne d Wagret considers thereclamatio nb y the Etruscans of thePontin emarshe s inItal ysom e twenty-five centuries ago as thebeginnin g of impoldering inEurope .Th eEtruscan swer e renowned as great engineers andma yhav eacquire d thescienc eo fhydraulic s through trading connections withMesopotamia .Th ework s feel indisus e after the third century B.C.an dwer eno t restoreddurin g theRoma n EmPire.

F°r thepurpos e of this study themer equestio no fsenorit y orantiquit y is not so important.Mor e canb e learnt formcase swher e informationi s Mailable as to thetechnolog y and thesocio-economi c framework inwhic h impolderingwa s carried out.Thu s twocountries ,th eNetherland s and JaPan, come to the forewher e theeminen t role theyhav eplaye d inth e hi-storyo f impoldering datesbac k to thelas t thousandyear s only.

In both cases theorigi n of impoldering and tidal land reclamation is obscure and oneha s towai t to the 16than d 17thcenturie s A.D.befor e lt canb e clearly seenunde rwha t conditions impolderingwa s carriedou t atldwhy .Nevertheles s theearlie rhistor y isstil lo fsom e significance r thepurpose .

2- History of recent impoldering inth eNetherland s

L°ngbefor e thebeginnin g of theChristia ner apeopl eha d settled on the coastal marshlands of theNetherlands .Ther ewer en ose adike san d during periodswit h abnormallyhig h sealevel s causedb y stormsurge s ln Winter they sought refuge fromfloodin g onartificia lhillock s terpen" ordwelling-mounds) . Shortly afterA.D .80 0 this systemo f

253 passive defence against these aflood swa s gradually replacedb y amor e activedefenc e inth efor mo f coastal embankments,firs t asdike s connecting thedwellin gmounds ,late r asdike s encircling land areas destined forgrazin g and growing crops so inmor e offensiveway . Inth e period 1000-1200,man y damswit h sluices inth ecreek swer ebuil t enabling somedegre e ofwate r control in the embanked areas,thu s creating thefirs t real polders inth eNetherlands . Inth esam eperio d inlandmarshe swer e reclaimed thus creating inlandpolders .

Why didpeopl ed o all this?Becaus e of increase inpopulatio n and the associated need formor e food? (Malthus).Becaus e ofa rise of these a levelaccompanie d by landsubsidenc e (challenge and response).Becaus e of cultural aspirations and thedesir e to create citieswher e lifewoul d bemor e enjoyable andwhic hwoul d made itnecessar y to reclaim nearby forfoo d production? One isno t sureabou t itbu t these incitements played arol e inman y recent cases of land reclamation.

That people did settle on thecoasta lmarshe s moretha n two thousand years ago isunderstandabl ebecaus e these lands offered better possibilities for alivin g thanman y poorsand y and dry lands inth e immediate vicinity.The y couldno t foreseetha t their situationwoul d deteriorate inth ecours e of time and that their successorswoul dhav e to face enormous problemswit h respect tosafety ,drainage ,foundation s of structures,se awate r intrusion andwate r quality. Perhaps,the ydi ° notworr y asmuc h about the future,a sman y peoplenowaday s thinkw e should do.I fon ewant s inengineerin g circles inthi s country tosho w its intelligence,on eshoul d statetha t if two thousand years agother e hadbee n aphysica l planning institute inEurope ,th e low-lying part° f theNetherland swoul d neverhav ebee n identified ason eo f themos t promising areas forhuma n settlement and intensive economic development Actually ourdistan t predecessors took therigh t decision independently

*)Th erelativ e subsidencewa smentione d forth efirs t time ina sessi 0 of theCour t ofHollan d as early as 1570.I n 1730th esubsidenc ewa s estimated at 30centimetre s in 100years ,a figur ewhic h isno t t°° far from thecorrec tone .

254 °fth ephysica l planners inafte ryear s and that decisionwa s toimpolde r ^d toaccep t all thesid e effects and consequences of thatdecision . Towards thebeginnin g of the 16th century atechnica l innovation is aPpearingo n thehistori c sceneactin g asa "vector "o rvehicl efo rth e transfer formon e technical era toanother . Iti sth ewindmil lwhic h Was made suitable fordrivin g drainagepump sb yprovidin g themil lwit h a revolving caps o thatth ewing s couldb e turned according toth e erection of thewind .

UP till then,lik e inothe rpart so fth eworld ,drainag eha d been effectuatedb ygravit y flowusing ,i n thecoasta l areas,th etida l variations. Wheren o gravity flowwa spossible ,variou s typeso fpump s Were used fordrainag e aswel la s for irrigationdrive nb yhuma no r ^imal power.Thi s technologyha s itsobviou s limitations and the reclamationb y drying upo fnormall y submerged lands,lik elakes , la8oons and tidal inlets could onlyb eachieve db yusin gwin dpowe r wllich,i nth eNetherlands ,i sreadil y available.Th etim eo f acceptance of thisne wfor m ofenerg ywa smor e thana centur y and the environmentalists of that timeoppose d theinnovatio no n theground s thatth e repidly rotatingheav ywing swoul db ever y dangerous toma n and that thebird swoul d stop laying theireggs .

^otfeertechnica l innovation,meetin g lessopposition ,wa s the Production of theso-calle dmu d mill,th eforerunne r of thebucke t dredger, enabling tomov e underwater .Als o thefirs tmanua lo r teXtbook on civil and agricultural engineering aspects of tidallan d reclamationwa s published. So thetechnica lvector swer e therebu t this condition isno t sufficient toexplai nwha thappene d inth e Netherlands towards theen d of th 16thcentur y anddurin g thebette r Part of the 17thcentur ywhe n reclamationb y impolderingwa s carried °ut ofman y inland lakes and tidal forelands andwhic h formon eo fth e Peak periods inth ehistor y of impoldering inthi scountry .

In fact thisperio dwa s also the"Golde nAge "o f theNetherlands ,a periodwit h overseas trade,succesfu lwa r against England and- a t Jeast till the latterpar to f thecentury -friendl y relations ofa "Real-Politik"-type withFrance .A ne wsocia l class ofsel f conscious

255 richmerchant s came to thefore ,busines sme nwh ower e looking for oppertunities forcapita l investments. Professor Slicherva nBath ,wh o studied theagraria nhistor y ofWester n Europe in theperio d 500-1850,ha s drawn theattentio n toth epric e revolution in theyear s 1550-1650whic hh e attributed toa n increaseo f population and an increaseo f (gold)currency .Th e first repercussion was aris e inprice s of food stuff,i nth e first place of cereals.Thi s created favourable economic conditions for agriculture and fora n expansion of the arable area.Reclamatio no fne w landwa s undertakennot - only inth eNetherlands ,o r"Unite d Provinces",a sthe ywer e calleda t that time,bu t also inEngland ,Franc e and Italy.A s far asthi swa s carried outb y impolderingDutc h expertswer e often invited topartici P and therehav e evenbee n cases of capital supplyb y Dutch business houses.

Slicherva nBat h has shown that there exists aclos e correlationbetv/ e the index prices ofwhea t and theacreag e of reclamationb y impolderinS in theNetherland s during theperio d 1500-1900.Th emos t striking featur isth esudde n dropo f thelatte r around 1675an d the small activity during the 18thcentury .Thi s goes alongwit h adro po f thewhea t price butwa s this theonl y reason?Ther eha dbee n around that datea n important change inth epolitica l relationswit h France.Loui sXI V (+ 1715)ha d abandoned therealisti c policy ofhi s predecessors like Cardinal Mazarin and Cardinal Richelieuwh oha dmaintaine d business-11* relations with theUnite d Provinces.Misle d byhi s ambitions Louis XI* wagedwa rwit h theUnite d Provinces who suffered aseriou s defeat in 1672,a blo w fromwhich ,accordin g toa nEnglis hhistorian ,th eUnite d Provincesneve r fully recovered. During thenex t century and during theNapoleoni c eraver y littlewa s achieved inth efiel d of impolderi0»'

Themos t important activity during thenineteent h centurywa s thedry 1 up of theHaarlemme r Lake in 1852,wher enowaday s Schiphol Airport is located.Agai n adecisiv e technical vector appeared inth e formo f the steamengine s fordrivin gwate r pumps.I twa s justified on theground s that thelak e threatened theadjacen t land areasb y wave erosion.Th e cultivation of thedrie d up lands almostbecam e afailur ebecaus eo f too little interest inth esocio-economi c aspects of theundertaking -

256 Inthi s century thelarges t impoldering schemei nth ehistor y ofth e Netherlandsha sbee n implemented andalmos t completed. It is theZuider ­ se project,th eenclosur e andpartia l reclamation of theZuiderzee . „ „iirhoraus eo f itssiz ebu t also Itdiffer s frompreviou s schemesno tonl ybecaus eo r k • • Hm,VAl multi-purpose scheme aiminga t becauseo f itsnature :i ti sa typica lmuiL i v ^ • _ A. eaino farabl eland ,sitin g for anincreas e insafet y against floods flnn ,ga" 1 , -, • ,it-wate rintrusion ,storag eo f newcitie s and industries,haltin g saltwate r ^ freshwater ,improvemen t ofdrainage ,shortenin g ofroa dcommunications , etc.Thi s is recenthistor y andw e could,perhaps ,no tye t take ,, „iv-ea histori c evaluation.Som e sufficient timedistanc e tob e ablet ogiv ern an - a-rpeasil y identifiable: essential independent variables,however ,ar nr e y .„.„ • resDonset o thedefea t availability ofpowerfu l technical equipment,respon s ,i„om

T„ u- triablewa s thehig h degreeo f Itappear s to theautho r that thisvariab l ^ authority and self-confidenceo fGovernmen tan d . -, „„f-f-h eZuiderze e schemewhic h '** theformidabl e decision to implement the „art 0f thecountr y forman y w°uld changeth egeograph y of alarg epar t ^furies tocome .Thi s inspit eo f theoppositio no fth e j~,,v.f-whethe rth epresen t environmentalists of that time.On ema y doubtwhet h P „rationwoul dhav e thecourag ean d deration and itspolitica l representationw o nrp^ure „ rn-rlav.Fea ro f pressure *• Power to take adecisio n of that scope today . V ,,-rinhlesproducin g nowadays 8r°ups and lacko fvisio n areth etw ovariable sp

n*gativeeffects .

3' History of recent impoldering inJapan .

T • Ton/m Itwa scarrie d out ina Soldering is anancien t technique in • ^ ^ ^ Vsical and cultural setting entirely dxff« independently

friands. For about twocenturie s evel=^ '^ ^ &

** the techniques 0f thewester nw •* ^ ^ ^ ^ Striking parallelismbetwee nJapa n andth e th* factors thatwer edeterminan t for impoldering.

257 InJapa n paddy fieldswer e cultivated moretha n 2000year s ago andal9 ° tidal and land reclamationb y thefarmer s isa ncenturie s old practice» although not asol d as inChina .Unfortunatel y little isknow n about technology and othervariable s that conditioned the reclamationb y impoldering. Inannal s theyea rA.D . 1284 ismentione d asdatf >o fth e first tidallan dreclamatio nnea rKawajiri ,bu t thisma y havebee n development of land raisedb y riverdeposit s and tectonicmovements . More isknow n about themor e recentperio d of theen d of the 16than d beginning of the 17th century,a perio d of great activity inth efiel d of impoldering,a perio d coinciding remarkablywit h thepea k period of reclamation inth eNetherlands .Thi s fact and thefac t that theDutc h East Indies Companywa s allowed from 1600onwar d toexploi t acommerci 3 house atNagasaki ,Kyushu ,ver y close toth esit ewher e tidal land reclamationwa s carried out,hav e ledsom epeopl et o thebelief ,tha t Japanese technologyo fimpolderin go ftha ttim ewa sinfluence db yatransf e ofDutc htechnology . Itma yb equestione dwhethe rthi si strue :whe nstudy 111» onlocatio ntraditiona lmethod so ftida llan dreclamatio ni nJapa nth eauth ° couldno tfin dan yindicatio nfo rsuc ha transfer .I nhi sopinio nJapanes e impolderingtechnolog ydevelope dindependentl yfro mth eEuropea ntechnol°S > whichrender si tal lth emor einteresting .However ,thing schange dcompl ete shortlyafte rth eMeij iRestoratio no f1 86 8an dagai nafte rWorl dWa r II-

Theyear s around 1600mar k aperio d of profound changes inth eJapans e political and economic system.Th e systemwa s - andwoul d remaintil l 1868- afeuda l systemwit h daimyoo rbaron s governing their fiefsw 1 only anomina l vassalageunde r theEmperor . Inth e absenceo f apower * central government the clans and lords ofcastle swer e fighting each other toconque r land and to increase theirpossessions .Th ecountr y was pacified in 1615b y twogenerallissimos ,Hideoyosh i andTokugaw a Ieyasu (+ 1616)wh o succeeded inestablishin g acentra l power,th e so-calledTokugaw a Shögunatea tYed o (Tokyo)whil e theEmpero rconti 11 toresid e atKyoto .Wherea s thedaimy o remained inpossessio n ofthe 1 fiefs theywer en o longer allowed towag ewa ran d theonl y posibili^ to increase their territory wouldb e to gain land onth esea .

Thedecisio n ofth eTokugaw a Shoguns toperpetuat e themilitar y organization of thecountr y intime s ofpeace ,a sSanso m expresses lt'

258 entailed aneconomi c problemo fconsiderabl emagnitude .Th e local economywit h payments,als oo ftaxes ,i nkin dha d tob e changed intoa monetary economy.Th e expenses of theShSgun s andth edaimy ô increased rapidly inconsequenc e of thecivi lwork so f theShögunate ,impact so f calamities,attendanc e at thecour t of the Shóguna tYed oan d double luxurious livelihood inYed oan d in theirow nfief so n thepar t ofth e daimyo.Thu sbot h partieswer e gradually driven toeconomi cstringency . T° copewit h the situationvariou smeasure swer e taken,on eo f these being thedevelopmen t ofne w land.

Inth esam e time ason e sees inHollan d agifte d builder ofwindmills , Leeghwater,i ncharg e ofimpolderin gworks ,i nJapa na talentedma n «Ppeared on the impoldering scene:Kat oKiyomasa .H ewa sno t originally a*artisan ,lik eLeeghwater ,bu t adaimyo ,an dh ei sknow n inth e history of Japana sa genera lan d asa narchitec to f fortified castles. *twa sperhap s throughhi m thatth e traditionaldesig no f theJapanes e P°lderdike swa s developed consistingo fa ston ewal lwit h astee p f acing at the outside,a cla y fillan danothe r stoneretainin gwal la t ^e land side.I t issai d thath estarte dhi sengineerin g activities *henh ewa s stillyoun g and thath esupervise d thework s personally

SDiir>-- .. ^ . n,0 TAnaneseengineer s acquired aspecia l Purringhi sfavorit ehorse .Th eJapanes e«= .& skill inbuildin g heavy stonewall so na ver y softsubsoil .

* second important stimulus for theimpolderin gwa s thewa y inwhic h «* workswer e carried out.Th edaimy Scommandeere d farmers tod o the

*«*kan d- as acompensatio n- thene w landswer ehande d outamon g them

*hen H,Ä , ,„,.„, when the landsbecam e productivemor e "="th ework swer e completed,wne n>-»« = 1=»j , j • fi„'o wav both partiesbenefitte d ia «d-taxes could be collected and inthi swa y Doenp f>. . f I.'V-f n theNetherland s -th e tr°m the impolderingworks .Thu s- jus tlik ei ntn e 17 thcentur y became apea kperio d of thehistor y of impoldering in Ja Pan. m a later stage,whe nric eprice s jumped up,tida l land rem , u„ t-radpqme nalthough ,i ngeneral , reclamationwa s also undertakenb y tradesme n n. 'j„-D,ia ca ver v attractive one thl* typeo f investmentwa sno tconsidere d asa ver y ^g to theris k ofdestructio nb y thetyphoons . In^ , „• ij0„r»I V C+ 1610), themos tpopula r itlth esam eperiod ,i nFrance ,Kin gHenr y IVI I,,- I-J .'„abou t thesam emanne r asth e *ln8 in thehistor y of France,succeede d inabou t 259 Shoguns inJapa n tohal t thewar sbetwee n the feudal lords,t ounif yc "e country andit oundertak eman y schemes of land reclamation including impolderingo fmarshes . TheMeij i restoration inJape n (1868)whic h changed thehistor y ofth e country evenmor e than the Tokugawa Shögunateo f 1615ha d alsoa prof° u effect on impoldering,especiall y on its technological aspects. In l°'u agrou p ofDutc h engineers including artisans sailed toJapa n towor k therefo r 10o r 20years .The y introduced thewester n technology inth e field ofhydrauli c engineeringwhic hwa s sot o speak super-imposed on thetraditiona l and indigenous technology.Mentio n should bemad e especially of theprojec t for theenclosur e and partial reclamation° £ Kojima Baynea r Okayama,a schem e similar to thato f theZuiderzeework » in theNetherland s which- at that time- ha dno tye t started.Th e enclosing damo fKojim aBa ywa sno t completed before 1956bu t the polderswer e reclaimed earlier.

Unlike in theNetherlands ,i nJapan ,i n theyear s twenty and inth e thirties of thiscentury , thepolitica l conditionswer eno t favourable for impoldering. Things changed completely afterWorl dWa r IIwhe n Japan saw itself confrontedwit h a shortage of food and thenecessit y tofin d a livelihood for repatriating farmers.Peacefu l conquest of ne land fromth ese awa s takenu p againan d contactswit h thewester n engineeringworl d re-established.

Twofact s ofhistorica l significance emerge from thispostwa r period- The first is the technical feasibility of impoldering of landwhic h lS normally by severalmetre s under conditions ofheav y tropical rainfall' The survival of thedee p polders created under these conditionsdepen d on theprope r functioning of theprotectio ndik ean d thepumpin g devic tokee p out thesurroundin gwater s and todrai n off excesswate r fvora localrainfall .Wit h thedryin g up the lagoonHachiro-Gat a in 1966J aP joined the groupo f countries where suchdee p polders had beenrecla i previously or came into existenceb y subsidence:th eNetherlands , P0l3*d' Denmark,Indi a (Kerala State),U.S.A . (California)an dEgypt .

Thesecon d factrefer s to theeconomi c justification of sophisticated polder projects.Accordin g toth ecommonl y usedmethod s ofeconomi c

260 evalution a comparison is made between the costs and the benefits of the project discounted according to an interest rate to the present-day values. With the present high rates of interest this means that benefits obtained in say 20 to 25 years from now represent very little money to-day. However most of the hydraulic works of a polder like embankments, canals and sluices are serving for many hundreds of years. But in the standard economic evalution it does not make any difference whether after 20 or 25 years these works would still exist or not. This is a paradox Seating, that the commonly used methods of economic evalution are n°t suitable for projects like irrigation, drainage and impoldering.

^ey may be appropriate for appraising industrial investments where ""»chines do become absolete after such a short period of time.

AniJ]l- i larg e scal-,.,,e impolderin• g projects•„*- „ ,^oT-n'pf carrield ou outi durin o"""g6 th e pasf t decades in countries like Bangladesh, the Netherlands and Japan,ar e not economically feasible according the standard criteria of benefit-cost ratio. Yet their implementation and financing were decided upon by the

0 ê vernmentg concerned because of their significance for the future of the country.

4' Analysis of the history of impoldering

Th * study of the history of impoldering in the Netherlands and Japan ha* Produced a wealth of historic facts and some consideration of factors th*t have been determinant in that history. These factors or variables are of various nature: technical, economic, social, political and Penological. This leads to the conclusion that this history has been

a c omplex matter, a fact which also applies to other fields of history.

*ecentlv the French geographer Bethemont made a classification of these tables as an approach to a new theory on the generating factors of i-ri-i» • ,, , -*.„i since the same factors must have cri8ation, drainage and flood control. Since une bee* active in the history of impoldering his study, presented in the

Rework of the I.C .I.D.-projec t mentioned earlier, is of particular devance.

^emont classifies the "independent variables"i nthre emai ngroups ,

261 viz.: the incitements for a change, the existence of favourable "vectors and a society which is favourable and receptive to changes. He considers these variables as necessary but not sufficient for the "genesis of hydraulic environments".

The incitements comprise factors already encountered in the analysis o* the history of impoldering in the Netherlands and Japan such as: population increase, economic perspectives and crisis and changes in tn natural environment but also factors like succession of dry years and cultural aspirations. Some of the incitements can be indicated as the "challenge and response" group.

Under the vectors appear the technological stimuli, also mentioned earlier, and also the traditional staple crops often associated with various forms of religious cultes like wet rice in South East Asia and mais in South America.

The societal group comprises the requirements of a minimum of stratification and coherence for the establishment of an organization for the implementation and operation of hydraulic schemes. Also the • * • faß e existence of a class of technicians. He concludes that at a certain &1- a of spatial development and technical evolution the essential element in the development of hydraulic environments is the existence of strong social structures capable to impose technical constraints like the collective management of the systems and also to assume a joint defenC of the reclaimed area.

The work of Bethemont represents an important step in the integrati°n of the history of irrigation, drainage and flood control into the geir history of mankind.

There is one group of incitements which has played a particularly relevant role in the history of impoldering. It is the group related to challenge and response. Polders along certain sea coasts &1 tor"1 certain rivers are very vulnerable and natural disasters caused by su surges at sea and river floods are likely to occur. What will be the response of man and what factors determine that response?

262 Therei sa psychologica l aspect of thatquestio na swel l asa technica l Point.Ma n isnaturall y inclined toforge t about disasters and factual experience on it isonl y toa smal l extent transferable fromon e generation to thenex t one.Bu tnatur egive sn o respitean d sooneran d later theblo w comes,ma nwake s upand ,wit h theide ai nmin d thati t shouldneve rhappe n again,ask shimsel fwha t tod oagains t it.Whethe r thiswil lb e followedb y anactua l andvigorou s responsedepend so nhi s technical capabilities and financial possibilities.Th e technical aspect of the challenge and responsesituatio n istha t experienceha sshown , 'hat inth e fight against the floods acounter-offensiv ei smor e effective thana restoratio n ofth estatu s quo.Ther ewil lalway sb e higher floods thanbefore ,highe r requirementswit h respect tosafet y a*dwate r control,th eembankment shav eentaile dhighe r flood levels, riverbed shav egon eup ,etc .Ne wline s ofdefenc ehav et ob e created to makehea d against theenem y inne wsituations .

A fewexample s of recent disasters inpolde rarea swil lsho wth e

si 8nificanceo f challenge responsefactors .

°*th efirs t of February 1953th esouthwester npar t ofth eNetherland s Wa* hitb y astor m surge.Th ese aleve lros et olevel shighe r thaneve r recordedbefor e and inten so fplace s these adike swer ebreached . Nearly 2000peopl e lost their lives and considerable damagewa s dieted toth eeconomy .Th e responsewa s acounte roffensive ,know n as theDelt aWorks ,an d consisting ofa closur eo fth etida l estuaries y dams.

Sh °rtly later, on September 26,195 9Japa n suffered froma serev e ^Phoon, the IseBa y typhoon,whic hhi t anare anea rNagoy aan d caused fln^j- _. t.-,.^ fpenaltie s andth eamoun to f ^c-odingo fman y polders.Th enumbe ro f «suau«» damn~ •. n.n ftioseo f the 1963-disaster inth e linagewer e serveral times largertha nttios e Heriands. Thevigorou s responsewa s thesam ea s inth eNetherlands : dai*ningof fo f estuaries not onlynea rNagoy abu t also inothe rplace s itlJapan . Stin „ v„, nt-h 1970Banglades hwa shi tb ya 1J-1som eyear s later,o nNovembe r ntn, '"u B J cy'cL1i°nnr,eo on th,e Ba y ofBengal .„ ..Th TUoemaximu „avimum mse a levelexceede d thecres t

263 levelo f thevulnerabl e "bunds"b y severalmetres .Th e resultwa s a terrible calamity,perhap s thewors tnatura l disaster inth ehistor yo f mankindwit h moretha n 500,000 casualties.I tpasse dby ,almos t unnotice' inth eoute rworld .Th erespons e of thecountr ywa swea k andmor e passiv than offensive.A numbe r of "kilas"wa sbuil t similar toth edwellin g mounds inth eNetherland s erectedmor e than two thousandyear s earlier- The response inth ecas eo fBanglades h waswea kbecaus e of thever y tensepolitica l situation in 1970an d thever y poor economicconditions -

5. Prospects of impoldering inth eworl d

With the analysis just presented some factorswhic hwil lb e determinant inth e future canb e indicated. Ona shor t term theprospect s inth e Netherlands and inJapa n dono t lookver ybright . Inbot h countries there isn o shortage of food;cereal s andmea t canb e imported atlo w prices from theAmericas .I nJapan ,wher e there isno w asurplu s of rice, reclamation of tidal land is continuing not for agriculturalbu t forindustria l purposes,applyin g themetho d ofhydrauli c fill.I nth e Netherlands theproces s ofdecisio n onfurthe r impoldering hasbee n paralysed, like inothe rsector s ofhe r society.

Elsewhere in thisworl d conditions are entirely different.Th eonl ywa y to relieve the food situationo f poverty stricken countries like Bangladesh andWes t Bengal is to improve thewate rmanagemen t inth e existing polders and totransfor m other upland areas intopolder swit h complete or partialwate r control.Wha t applies to thedelt a ofth e Ganges also applies toman y other large deltas and other prospective polder areas of theThir dWorld .Hig h costs of construction,deficien t methods of economic evaluationneglectin gbenefit s toth enationa l economy and lowprice s ofcereal s act for the timebein g asnegativ e incitementsbu thistor y shows that things can change rapidly.

There ison efor mo f impoldering inquit e afe wo f thedelta s andoth e iti t low-lying areaswhic hha sme t aconsiderabl e success evenfro m the V° ofvie wo f private economy. It is the reclamation of small polders in thevicinit y of large cities for thepurpos e of supply ofvegetable s a fruits. Cities likeBangkok ,Calcutta ,Saigon ,Jakarta ,etc .offe ra

264 j *-„ vrViiVh can only be grown in ready consuming market for these products which can o y g ... -.-i, a n^rfect water control and Hood Polders in the immediate vicinity with a periect w Protection.

T icr, laree-scale impoldering will be taken In the opinion of the author also large scdi r •^ .-„ inr-rease food production and the up again because of the necessity to increase «m «ill be on earth the same factors that consideration that as long as man win on «ere acting in the past will also determine our future.

• „ v,c« made a contribution to the The hope is expressed that this Symposium has made transfer of technology in the field of impoldering.

265 6. References

1. History of tidal land reclamation carried outb y theHig oClan . Toshisane Shibuya. KumamotaYear-Boo k (1954edition) . Translated by theMinistr y ofAgricultur e andForestry ,Japan .

2. Deagrarisch e geschiedenis vanWest-Europ a500-1850 . Bernard Slieherva nBath . Het Spectrum,Antwerpen ,1960 .

3. Irrigation inth eworl d -Comparativ edevelopments . HitsohiFukuda . University ofToky o Press,Toky o 1976.

A. Rice inAsia . TheAssociatio n ofJapanes eAgricultura l ScientificSociets . University ofToky o Press,Toky o 1975.

5. Sur lesorignie s del'agricultur ehydraulique . JacquesBethemont . XleCongrè s I.C.I.D.Grenobl e 1981.

6. Land development and improvement projects inJapan . ShiroSasaki . Agricultural Development Series 3.Agriculture ,Forestr y and Fisheries Productivity Conference,Toky o 1959.

7. Dredge,Drain ,Reclai m- Th e art of anation . Joh.va nVeen . Martinus Nijhoff,Th eHagu e 1948.

8. Landbelo w sea level _ Holland in itsag e- long fight against thewaters . Joh.va nVeen . N.V. Drukkerij Trio,Th eHagu e 1953.

9. History ofHydrology . Asi tK .Biswas . North-Holland Publishing Company,Amsterda m 1970.

266 '0.Histor y ofHydraulics . Hunter Rouse and SimonInce . DoverPublications ,New-Yor k 1957.

•'.A histor y ofDams . NormanSmith . PeterDavies, Londo n 1971.

•2. Japan- A short culturalhistory . SirGeorg eB .Sansom . TheCresse t PressLondo n1952 .

267 POLDERS OFTH EFUTUR E Prof. dr. ir.B .Verhoeve n International Courses onHydrauli c and Environmental Engineering Delft,Th eNetherland s

Most of the larger terrestrial mammals don't live far from somesourc e of freshwater .Ma n didno t form an exception to this general rule.A s amatte r of fact,h e cannowaday s pumpwate r over long distances tohi s dwelling places.Nomadi c tribesmove d about,eac h time thewate r ran short around theirquarter s and they still continue tod oso .However , afterhavin g collected food for afe wmillio nyears ,ma nwa sboun d to become amor e or less sedentarybein g fromth ever y moment thath e started topractic e crop growing. Indeed,som e crop growers remained semi-nomads,e.g . roaming about during theperio dbetwee n sowingan d harvesting,bu t most farmers settled down andbecam ehighl y dependent upon sources providing freshwate r throughout theyear . It isobviou s that the lowlands offered excellent opportunities for supplying the people,thei r domestic animals and their crops withwater .

Indeed somepeopl e even succeeded increatin g living conditions farawa y from openwater ,b y digging deepwell s (Northern Sahara), collecting water in tanks onmountai n slopes (SriLanka )o rb y transporting seepaS water from thefoothill s through subterraneous passages ofconsiderabl e length to their fields (Iran).However ,thos ewh o lived inth e lowlands had easiest access towater .Goo d soils and excellent fishing andhunt * groundswer eusuall yfoun di nthes eareas .Moreove rth etraffi cb yboa twa s fareasie r thanmovin g onba d oralmos tnon-existen t tracks.W efound » forexample ,tha t the former Zuiderzeewa s at that timemor e alin k tha abarrie rbetwee n thetown s andvillage s onbot h sides of thebay . Finallywate r- inparticula r rivers -wa s always awidel y used

268 receptacle for allkind s ofwastes .No t thatwast edisposa l formed a major problem inthos eol d days.

Oneparticula r disadvantage ispeculia r tomos t lowlands:th ewate r tableca n fluctuate considerably.Th ewater ,howeve r essential itma y b«, becomes adange rwhe n itrise s toofas to rto ohigh .Th e inhabitants °fth ealluvia l plains adapted theirwa y of lifet o this- usuall y seasonal- danger.The y built theirdwelling s just outside thevalley s °nth eupland ,o nhig h riverbanks ,o nprotrudin g outcrops ofolde r stratao r they simply left the lowlandsdurin g theperiod eo ffloo d

^Zard. They constructed dikes toguid eth ewate r safely todownstrea m fivertracts ,buil t theirhouse s onpole s and evenpile d upeart h to *akedwellin g mounds ("terpen"); smallone sfo rsolitar y farms andhug e

°*es for complete villages.The yha dboat s athan d and locally theymad e raised roads or even footbridges tointerconnec t thevillage s andhamlet s inthos eperiod swhe n thelan dwa s flooded. In largepart s of theworl d comparable situations stillexist .

A„ . „loc o frppfro mdee pflooding ,i t

burning that thehouse swer emor eo r lesstre eiro m v no, ,, rt.f t-hefield swer eou to fus edurin g neverthelessremaine d troublesome thattn eneius » m ,-, j^;„ oni-al wereth ebrackis h and sometimes the flooding period.Eve nmor edetrimenta lwer etu e saüne floodings inth edownstrea mpar to fdeltai c plains.Har mwa s also c*»ed by thefac t that theflood s didno t come everyyea r at thesam e ««*. Late floods could postponeth esowin g time and early floods could d~ ,- f-;.|in cbes t asthe y couldt o destroy thestandin g crop.Th efarmer s tried asDes t ,. . _ „•,_ „•„ir , Theforegoin g sentences adapt their agricultural practices toth erisks . h--, , K„f oncemore :th estatement smad e fïavebee nwritte n inth epas t tense,bu t oncemo r are stillhar d reality forman ymillion s ofpeople . l*»ie.an dGentlemen . Inth esecon d orthir d century asmal l dikewa s b "ilt on the terP ofFedderse n (Weserland,Germany) . Itprotecte d one h**e. wedon' tkno wwhethe r thiswa s thefirs tpolder ,bu t iswa sn o ***t anearl y one.Graduall y more lowdike swer econstructe d toprotec t S*all family terpen and thehouse s on theman dsometime s alsopar to f tk ., -i ~~A All thesedike swer e small the adjacent,ofte n relatively high,Und . AU these ** very local structuresbecaus eonl y thesmalles t communities showed

n * °u8h coherence toenabl econcerte d dikebuildin g activity.Th e 269 co-operation needed for dealing with larger dike projects was found not earlier than 6 to 7 centuries after the first small dike came into being' However, the Lex Frisonum does not contain any mention of dikes in the year 800. It may be that the low density of the coastal population durine the post-Roman transgression and the social changes during the migrati°n ofth enation s causedth estunte d developmento fdik ebuilding .Som e think thatth elon gan dfierc e fights againstth erepeatedl y invading Vikings unified thefreedom-lovin gFriesian sbu tmayb e this isonl ya war-glorifying conception. Whatever thecas ema ybe ,i twa sonl yi n thetent h century thata bette r cooperation enabled themt otackl eth e hugejo bo fprotectin g large fields,unti l then liablet oflooding ,b y meanso fdikes .I ttoo k indeed anothertw oo rthre e centuries before the "golden rings"surrounde d thewhol eo fth elowlands .Ye tloca lpeo p stilldi dno tplac eto omuc h confidence inth eresult so fthei rcommo n ii work; for another 100 years they continued the heigtening of the "terpe" Anyway,fro mth een do fth e10t hcentury ,th ewhol e cultivated lowland ofBelgium ,th eNetherland s andGerman ywa sembanke dwithi na fe w centuries, thankst oth eincredibl e zealan dperseveranc eo fth e inhabitants.

Obviously,th estron g co-operationneede d forth ebuildin go fth elarg e dikes also applied toth estron g changes insocia l structure.Th esmal l farming communities lost influence infavou ro fvillag ean dparis h organizations with theirmor enumerou s memberships.However ,smal luni 1- still existed locally tillfa ri nth e18t hcentury , (guaranteeing),f° r example,mutua lhel p incas eo ffir eo rfunerals .

Inorde rt oachiev ea nefficien t large-scale defence againstth e sea, rulesha dt ob edraw nu pan daccepte db yth epopulation .Th ebuildin g ofth edike swa sa collectiv e activityo fa well-structure d society of freepeople .Th ewor kwas ,a sa rule ,organize db yparishes . Monasteries and,late ron ,polde rboards ,als o tookpar t indik e building,th elatte rusin g hired labouro reve n contractors.Initial! " themaintenanc ean dsmal l repairswer eth edut yo fth elandowners .T^ ey could shiftof fthi sburde nt oth etenants ,bu tthe ykep tth eeventua l responsibility forth eupkee po fth edike . Major repairswer e thetas ko fth epolde rboards ,whic h inth eeven t°

270 calamities could even gethel p from neighbouring polders. Incas eo f emergency everyone wasboun d topersona l participation inth e dikework and inman y places thenobilit y wasno t exempted from this duty. The importance ofdikewor k was recognized; being occupied by strengthening a dike wason eo fth efe wvali d reasons forno tappearin g incourt , for example.

^rangements hadt ob emad e forth efinancia l contribution of those farmers whower e less endangered byfloodin g because they were living far from these ao ro nhighe r tracts ofland . Themaintenanc e ofdrainag e etches andcanal s hadt ob eorganized . Ittoo k centuries before well- ^nsidered rules like theRustringe r rules were recorded and polder b°ards with well-defined tasks were functioning. After that the rules h*d tob eadapte d time after tone wsocia l andtechnica l developments. S °metimes social abuses crept in,especiall y when thepolde r boards became a closed group andincapabl e andcorrup t board members inherited tne chairs from their fathers.

Mention isalway s paid toth elate r periods during which the cultivated

lanj „ nf .„.stated coastal accretions andb y and wasextende d by embankment of vegetateu DUT^- , - .„ac hadt ob e impoldered because pumpmg drylakes . Moreover, peat areas naa to »* v th= u„-:^0rif-f> which intur n resulted from Chey reached alo wleve l duet osubsidence , wnicn th-e cultivation ofth epeat . Technical skills andmean s developed:

*ind«liis with revolving caps, steam-driven pumping stations fuelledb y coai ,• i „ncinpq andelectromotor s as sources COal orpea t and,late r on, diesel enginesan a of Power. S*>ades became replaced bydraglines , bulldozers anddredgers . Manual ''«"port was superseded by, insuccession , horse andcart , narrow^ ***• railways and trucks. Tidal creeks indik e sites were successively Cl0°ed bya fast supply ofclay ,b ysinkin g a ship inth egap ,b ya sim,,!. e olivine oanels andeve n byusin g aim-ultaneous lowering ofa ro wo fslidin g pane » ca,- . ,.,(„imri weeasil y forget thatth e Caissons. Duet oal lthi s technical firework,w ee y Ut er growth of the lowland plains byne wembankment s wasb yfa r less tha» theare a which theol dcoasta l people hadprotecte d sot osa y m oRft , • 0" aa thev called these long Re S«,b ybuildin g the"golde n rings as tney ^^ ^ erin- , ,-u-hbetwee n thefirs t primitive Circling dikes. Weten d toforge t that betwee2-M n dikean d theful l protectiono f the- b y gravity drained -lands , nearly 1200year s passed away,wherea s thelas t centuries of thisperio d shouldb e seen as amos t instructive epochbecaus emos t of thedike - building was concentrated inthos e ages. Itwa s during these few hundreds ofyear s that,afte r aprolonge d and slowstart ,a changin g societywen twit h agrowin g collaborationbetwee n the lowland people, which co-operation enabled thebeginning , theexecutio nan d the completion of such agiganti cwor kwit h suchprimitiv emeans ;eve nth e wheelbarrow hadno tye tbee n invented.'A s amatte r of fact,th e later developments of poldersan d poldermanagemen t form an indispensable basis for thoughts onpolder s of the future inEurope ,bu tw ewil lse e hereafter that polderso f the futurear eessentiall y amatte r forth e thirdworl d and for thatreaso nw ehav e tokee p inmin d thesever y earlyday s of polder history.

Coming to this future,tw omor e or less inter-related basic questions are:wher e can thepolder s of the futureb e expected and whatwil lthe y look like? In thefirs t place: thepresen t polders will form anon-negligibl e part of futurepolders .W eassum e that lossesdu e toearthquakes , stormsurges, landslides etc,etc .wil lb ever y smallan d thatnuclea r weaponswil l beabolishe d before theywip eou t suchvulnerabl e items aspolders . Infact ,existin gpolder s willb emodernized .Fo rexampl e> thepowe r usually needed forkeepin g poldersdr ywil lb e provided,a t least inpart ,b ywin d energy.Studie s of thispossibilit y havealrea d" shown promising results.Mayb eothe r renewable sources of energy can ° considered too.I nindustrialize d regions inparticula r improved contr of irrigationwate r quality will lead toe.g . theus e of seepagewate r or even theconstructio n of storagereservoir s for seepagean d precipitationwate r inorde r toreduc e theintak e of polluted river water. The control of aquatican d bankvegetatio nwil lhav ebee n improved by the introduction of adjusted ditch profiles and appropria mowing rules,b ymor e carefulhandlin g of fertilizers andb y stookinS the canalswit h herbivorous fishes.

But enough about thefutur eo f the old polders.Mor e interesting are thene w ones.Wher eca nw e expect them?Hardl y anywhere herei n

272 N°rth-WesternEurope . Onmos t places thegrowt h of coastalaccreti c Lons "toppedbecaus e theproces so f sedimentation camet oa nand .Moreove r thesal tmarshe s thatwer estil l presentabou t 40year s agohav ebee n ^banked for thegreate r part.However ,th evi s inertiaeals o rules h«e. There are stillpower s active toge tcoasta l foreland (including Wlying sand-an dmudflats )embanked ,usin g allegedargument s asnee d forimprove d defence against thesea ,bette rdrainag eo f thehinterland , creation ofharbou r and industrial sites,extensio no frecreationa l ^duties andwildlif e sanctuaries and even the lacko f farmland.Bu t lightening of thedike sprovide s therequire d safety aswell ;upstrea m «orage willdecreas edrainag e problems,th egrowt h of industry «agnates and moreover somemoder n industriesdon' tas k for asit enea r deep shipping channels. Ina densel ypopulate d regio thedevelopmen to f ne'*wr-recreationa „ „• -, lr facilitie-I--- ,-rs, ia nnatur a natur eare eai aeusuall ymean s the losso f

Bv; . r „.erofrpafio n (like sailing). And listing, more distinguished, forms of recreation 1.11* s/ it seems hypocritical to look forne w farmland when governmental policy ^ to decrease the number of existing farms as quickly as possible.

H°wever, themos t decisive objection tone wpolder s came from the hi„i . , „,fC t-hat thehig h ecological value bl °logists. They were able to demonstrate that tne a g nt t,, , ..„„oc nf making even minor changes 0f this foreland outweighed theadvantage s or maicing in t-K ~ >,olH<;fo rmos t of the scarce lakes and 11th epresen t status.Th esam ehold sro i sw an>ps thatcoul d be considered forimpoldering .

UB„ ,, • „lont-vo fne wpolders ,no there , Hev ertheless , the futurewil lbrin gplent y orne w v hi,.. . .,JI„ needed for raising the food but m the third world where theyar ebadl yneeae a Prod,,,,*- , 11 vastarea s areawaitin g betterwate r »"•oauctionan dwhere ,afte r all,vas t ai» Sagement systems.

Actual! , ,.1,«,fo r thetim ebein gn orea lfoo d shortage tually, some people say thatfo r tne had to exist; that hunger ismor e a matter of poverty than of a too-low l**l of food production and that banishing malnutrition and under- tio,,„- u „ o t-prhnical problem. Whatever 0Ur ishment is a political issue than a tectmica v the -se maybe ,a stron g increase infoo d supplywil lb eneede d inth e *** futureanyway ,i nvie wo f thecontinuin g increase m world Nation. Thephenomeno n of large familiesfade s very slowly.I n 273 order toincreas e the supply of food,variou smean s canb e considered such as:cuttin g downharves tan d storage losses,replacin g industrial and fodder cropsb y food crops,increasin g yields per unit of cultivate" land and cultivating new land.

Limiting losses could indeed increase substantially thequantit yo f food available;substitutio n ofnon-foo d crops cana t least locally be of some importance too,bu tbot h subjects arebeyon d the scopeo f this symposium. Indensel y populated regions,th ebringin g under cultivation ofvirgi n land is less influential.Larg e tracts are unsuitable for any formo f agriculture orhav e tob epreserve d inthei r present state for somereaso n or other (e.g.forests) .Moreover ,th e possible extension of cultivated land by impoldering inorde r to increasefoo d production,form s onlya mino r track.

Even thisnarro w path isofte n ineffective either because thesoil s prove tob e of an inferior quality,th edikin g is too expensive or eve because the scarce localpopulatio nmake s thebes t use of thenatura l environment and cannotb eremove d since they attaina reasonable standard of living.However , themos t serious objection toimpolderin ë is that thesewetland s in theirnatura l state>ofte nprov e tob e too valuable in the long term toth esurviva l ofmankin d tob ebrough t under cultivation. Fortunately there still remains one othermetho d of increasing food production:raisin g yields perhectare .An d in thisapproac h impolder1 plays an,importan t part.I nsom e regions it is- a t leastfo r theti 111 being- no t evennecessar y toreclai mvirgi n land becausemillion s oi hectares of cultivated land are awaiting impoldering. Herew e still find conditions comparablewit h thesituatio n in theNetherland son e millennium ago.Th e people live onhighe r spots ino rnea r thelowla ° but their field areno t protected against flooding,hav e onlyver y simpledrainag e facilities and yields areprecarious . Insuc h areas a betterwate rmanagemen t isa prerequisit e for the introductiono f moderncro pvarietie s doubleric e cropping and otherne wcro p rotations,a mor eadvance d use of fertilizers andpesticides . Yields canb e increased substantially and overvas tareas .Her e the polders of thefutur ewil lb e established.

274 Problemma yb e that forpolitician s thegainin go fne w landofte n eemsmor erewardin g and less troublesome than theimprovemen to f listing agricultural land. ne regions of thene w poldersbein gassessed ,ther estil lremain s the Gestion how topla n theman d how tege t them constructed? Reclaiming ew land means the irreversible elimination ofon eo rmor ebiotopes , ut impoldering cultivated land isals oa radica lmeasure . Itmean s he definite terminationo fa geologica l development,becaus e itstop s Sedimentation. Impoldering hashydrologica l consequences,suc h asris e flood levels inth eriver . Itha s- eve n inth ecas eo fcultivate d an

11i sno tnecessar y andmayb eno t evenwise ,t ostar twit h onesmal l dlke Protectingon ehous eonl y- a s inth ecas eo fth eter po fFedderse n 800 years ago- an d it isno t possible,i nvie wo fth efoo d scarcity, 0fc akesevera lhundred s ofyear sa s theol d Friesians didbefor eth e and isproperl y protected.Bu t itmus tb eclea rwhethe r land usersar e a le teorganiz e inon ewa yo ranothe rth emaintenanc eo fdikes , structuresan d canals ofa t least asmal lpolde ran dho wthe y cancop e Vlth repairs. Itmus tb eknow nwhethe r thefarmer swil lmatc h agricultural Ptacticeswit h thene whydrologica l situation. Itha s tob estudie d Whether theeffec t of thene wpolde rwil lb esuc htha t theric h landowners 6c°raeriche r and thesmal l tenantsbecom e landless and unemployed Ub °urers. Ingenera l social commotion isno ta phenomeno n thatneed s eVelopment.

ntil ashor twhil e ago,impolderin gwa s easy:mak ea ringdike ,a sfa r 98 Possibleo na level orothe rstri po fhighlyin g land,choos ea sit e ar upstream for an intakestructure ,buil d adrainag edevic eo na 0Vnstream spot,la ydow nsom ecanal s and roads and that isthat .

275 Nowadaysw e often consider itbette rno t to startwit h thetota l elimination of the floods,bu twit h aregulatio n of thetim e andrat e of flooding.T obegi nwith ,th ehighe r parts of the area liablet o flooding canb e protected. Forth ewate rmanagemen t of the lowerparts » different courses canb e pursued depending onth eheigh t of theland . Among thesecourse s canb e included the lowering ofth esurfac einflo w fromth ehighe r partsb y catch canals;controlle d floodingb ysubmersi D dikes;accelerate d drainage;constructio n ofstorag ebasins, etc .etc .

Such adifferentiatio n inintensit y ofwate r control requires various adapted forms oflan d use,fishpond s etc.etc . Inth erive rdike s overflows canb e constructed sotha t incas eo fhig h river levelssom e water can flow off through depressions inth epolders .

In thecours e of theyear swate rmanagemen t canb e adjusted to changi™ demands of agriculture and insom eplace s thedevelopmen t mag endwit " a polder "Dutch style".I nothe r placesmayb e everyonewil l keephi s own little"polder" .Bu tno t only doeswate r management have tob esu ° andmodern :ne wway s alsohav e tob e found for theenerg y supply. Attentionmus tb egive n to techniques forproducin g energy forth epuf P from renewable resources.Solution swil l differ fromplac e to placeb u low-head turbines,windmills ,motor s drivenb yburnin gbioga s orwast e fromwoo d of formothe r agricultural products are inus eo rwil lb ei n usesoon .

Maybe thegreates t advantageo f stepb y step development of thewate t management ofexistin g agricultural areas istha t the farmers are themselves involved inth e establishment of theproject s and thatthe y learn tose t up awate rboar d forsmal lhydrologica l unitswit h a relatively simple task. Inthi swa ybi g and expensive centralized organisations canb e avoided and thesmal lwate rboard s can serveth e purposeo f increasing yieldswithou t disturbing thesocia l structure thewell-bein g of the localpopulation .

Inshort :plent y ofwor k iswaitin g for all thosecivi l andagricult u engineers,sociologist s and ecologists,wh o aredealin g inon ewa y° r anotherwit h landan dwate rmanagement .W e urgently need sound flood

276 control,efficien t irrigation systems and adequate drainage facilities, which all combined may lead topolders .An d thesepolder swil lmee t the r equirements of the future# Requirements related toa neconomi c useo f

energyant jwater ; to the development ofa decen t society and the Preservationo fa health y environment. Requirements guaranteeinga n existence forman y cominggeneration s ofplants ,animal s andhuma nbeings . e will need all our resourcefulness toreac h this goal. It istim ew e Put ourmind s toth enex t symposium dedicated completely to thefutur e asPects ofvariou s types ofpolderlik e units onagricultura l land.

277 Literature

Early ImplementationProject s forFloo d Control and Irrigation in Bangladesh.Firs t interim report, 1978.Euroconsult ,Arnhem .

Glopper,R.J . de,Aspect s ofreclamatio n plans.Lan d andWate r Intern. 24, 6-13, 1974.

Grijm,W. ,Ma n and Science inth eDevelopmen t ofWate rResources . Newsletter IHE,_13 ,22-26 , 1980.

Horst,L. ,Alternativ eDevelopmen t Concepts inPotentia l PolderArea s inDevelopin g Countries, 1982.Thi s symposium.

Liere,W.J . van,Southeas t Asia- Potentia l World FoodBasket ,Neth . J.Agr . Sc. 25, 14-25,1977 .

Odum,E.P. ,Th erol eo f tidalmarshe s inestuarin e production.Th e Conservationist ^5 (6),12-15 ,1961 .

Ohling,J. , (ed).Ostfrieslan d inSchutz e des Deiches.Krummhorn ,196? '

Veen,J . van,Dredge ,Drain ,Reclaim. -Th e art of anation .Th eHagu e» 1948.

Volker,A. ,Histor y and futureo f impoldering inth eworld, 1982.Th lS symposium.

278 GENERALREPORT SAN DCONCLUSION S PERTHEM E

279 THEMEA :POLDE RPROJECT S

SUB-THEME:VARIOU SASPECT S OFPOLDER S INA CERTAIN AREA D.S.Hesla m AnglianWate rAuthority ,Cambridge ,U.K .

Abstract

What isth eessentia l feature ofa polder ? Wehea r tenanswer s to thisquestion . Allar e quitedifferent ,bu t al1 are equallyvalid . From the'Netherlands wehav e two answers:i ti sreclamatio n of these a bedfo ragricultural ,urba nan drecreationa luse ;i ti sals o thepro ­ tectiono fdens epopulation s from accidental inundation. InWes t Germany iti sth eavoidanc e offals epolitica l and sociologica goals. InHungar y iti sth eattainmen t of theoptimu mbalanc ebetwee nminerals » wateran dai ri na soil . InRomani a iti sth eprotectio n ofa par to f thefloo d plaino fa grea riverfro m too-frequent inundation. InSpain ,Thailan d andVietnam , thecorrec tmanagemen t ofwate rt o combat toxic ions inth e soili sth ecentra lfeatur e ofreclamation . InGuine aBissau ,i ti sth eadaptio no fmoder n techniqueso freclama ­ tiont omethod sappropriat e fora nAfrica n socialstructure . InSuriname ,supplie s direct from tropicalriver smus tb e combined **x water collected from theswamp s themselves togiv e thebes tmanagem en ofreclaime dlands . Thepaper sar efascinatin g inthei rvariety ; impressive inth eunit y° resolve theauthor s showi novercomin gth eproblem swit hwhic h they & confronted.

280 Introduction

Answerst oth equestio n 'Whati sth eessentia lfeatur eo fa polder ? °°met ou sfro mdifferen tpart so fth eworld ,and ,althoug h theanswer s 8X0 sodifferent ,al lar egoo dan dcorrec tanswers ,becaus e theauthor s ha-vestarte dfro m thesam efundamenta lunspoke nassumption . Iti stha t the earth,whic hofte nappear s sohostile ,ca nb e transformed intoa homei nwhic hme nan dwome n shouldliv ei npeace ,an dfre efro mdrudger y ^ want. From thiscommo nassumption ,th econtributor shav eprovide da Set ofhighl y individualanswers . Theyar eno teas y tosummariz eto ­ otherfo reac hgoe s toth ehear to fth eloca lproble mwhic hha s tob e B°lvedfo r thatarea . A sketcho fth emai nfeature so feac hpape rther e f°re follows. Finallya tablelist san dreclamation san dcompare sim ­ portantelement s in theirdesign .

186 NETHERLANDS — TheYsselmee rPolder s- -Constandse ,d eJon gan d inkers.

^e formerZuyde rZe ebecam e theYsselmee ro rYsse llak eafte r 1932whe n a Wier dam separated itfro m theNort hSea . Fourpolder shav ebee n Claimed inth elake . A fifthi sunde rdiscussion . Totalreclaime d e ^ a will be 200 000 h£u In winter, rainfallexceed sevaporatio nbu ti n SUffl*erthi si sreversed . A largepar to fth eNetherland s Wo) depends °n artifice drainage. Soil typesvar yove rth earea ,bu ta larg e

°Portionar ever yfertil eloams . 6c *a l*nationo f thepolder si sonl ypar to fa pla nmad e in18 90an d ^Proved in 1918,whic hha d thefollowin gobjectives: - *} Shorteningo f thecoastlin e togiv emor eeffectiv e safetyagains t 0ttn surges inth eNort hSea . Reclamationo fhig h qualityagricultura lland . C) ^Proved water ^age^nt withbette rcontro lo f levelan dsalinity .

^proved roadsystems . Aa instructionha sbee nunde rwa yfo r6 0years ,ne wobjective shav e - -* UU uxuii nas ueen uuu.cx. "**J ;6en seti nth efiel do furba ndevelopment ,forestry ,natur econserva - °nan drecreation .

281 Three stateorganisation s supervise thedevelopmen t: - a) Zuyder ZeeWork sAgenc y designsan dconstruct s large scalecivi l engineeringwork s e.g. dikes,pumpin g stations,bridges ,canals ,road s b) ThePubli cBod y of theYsse lLak ePolder s isi ncharg e of local government c) TheYsselmee rPolder sDevelopmen tAuthorit y prepares thenewl yre ­ claimed landfo r itsfina luse ,includin gsocia lan deconomi cdevelop ­ ment. Reclamationwork sprocee d through thefollowin gstages: - 1. Construction ofenclosin gdike ,pumpin gstation san d drainage can*1 followingb ypumpin gdr yo f thepolde r 2. Mud surface issow nwit hree d seedsfro m aircraft 3. Smaller drains aredug ,lan d issu bdivide d intofield san droad s arebuil tove ra 10yea rperio d U. Cultivation startswit hburning-of fo free dbed san dpreparatio n° * landfo rcropping . 5. Land isfarme d for5 year sb yGovernmen t 6. Subsurface drain-pipes are installedan dfar mbuilding sconstruct 6 Water,electricit y and telephone servicesar e installed. Villagesar e built. 7. Land isallocate d inholding sneedin g1- Uworkers . Theoccupier s of thelan d liveo nthei rfarms . 8. Landscaping,forestr y andrecreationa l areasar egive nattention - 9. Finally,whe nal lwork sar ecomplete ,maintenanc e ishande dove r* ° aPolde rBoard ,an d localgovernmen t takesove rth eadministration . aC The land isdivide d intorectangula r fieldsabou t50 0m x 12OOm , e withroa d accessan dboundar y canal. A labourforc eo f about 700n> eD cultivate anare ao fabou t 20,000ha .durin gth efirs tfiv eyears . Thereafter,th elan di sle tou t tofarmers . Therear eman ymor eapP ~ licants thanfarm s soa selectionprocedur e isnecessary . Theaverag 8 sizeo ffar m isi+ 0ha ,varyin gbetwee n 20an d9 0ha . Inth efirs t twopolders ,agricultura l development waso fprim e imp°r ancean donl y thepoores t soilswer ereserve dfo rothe ruse . Inth e courseo f time,urba n developmentha sbecom emor e importantalon g wl associated recreational facilities. Inth erecen tpolders ,eve ng° ° agricultural soilsar ebein gallocate d forthes epurposes . Two larS6

282 newtown sax eunde rconstructio n- Lelysta di nEaster nFlevolan dfo r 100,000inhabitant san dAlmer ei nSouther nFlevolan dfo r125,000 . Inth eearl ypolder si swa sassume d thateac hfar m shouldb ewithi n cyclingdistanc eo fa villag e (max.7 Km )s °th. t shops,school san d churches shouldb ewithi neas yreach . Consequently,a relativel y large n^bero fsmal lvillage s ($00-2000inhabitants )wa sbuilt . Inpresen t r,*ATvrnAuetivity ,th enumbe ro ffar m circumstances,wit h greatlyincrease dproducxiv x j, , , , -J.U^o+o r motorizationth edistanc e erkersha sdiminished ,an dwit hgreate rmoxo r betweenfarm san dvillag ei sn olonge ra problem . Avillag ei sno w consideredt orecuir e 3000inhabitant st ofar ma viabl e -^and thereforeth enumbe ro fvillage splanne dfo rEaster nFlevolan dha sbee n +„„nl vthree . InSouther n educed fromth eorigina lfourteen ,t oonl y*n r ^^„/.lpflftow no fAlmer elo r Cleveland,ther ewil lb eth elarg epolynuclea rtow n i,,~n« >loca lservic e centre called 125000t o25000 0inhabitants ,plu sonl yon eloca l ^eewolde . J_>. ». ' u „»n providedo nth elake sborderin gth e Recreationalfacilitie shav ebee nprovid e „ WH ** *•** forestry. Natureaaamrareserve a shav e Poldersan di nth earea sse tasid efo rforestr y t, „a Potendhabitat sfo rplan tan dbir d been establishedt opreserv ean dexten d Ufe. m^. ' « +v,Rollan dPolde rAre aagains t ^ NETHERLANDS- Protectin gth eNort hHollan d hooding— Vernimmenan dHeyligers .

, xu.fi. tcoasta lare anort ho f *»Provino eo f»ort hHoUan doccur s« ^ lo ^ *««_ Inth .mad! ,u -« »— »"td« .^ - «-. in„pe n«« « withth e^de r »• ^ ^ 1

ä *• I*.. The „.ter of the 1*. * »» other,„ , ln th. «»*oe^ e v.„ coated .ith -* £•r -« oaiiea a **ea to form a maze ofwate r courses all at w

b0eZ6m s stem ' ' y ' . fflptres lower axe the polders. °n either side of the canals, several metres low

283 These axe tracts oflan d surroundedb ydike swit hartifica lwate rleve l control,ver yfertil e soilan dnumerou s townsan dvillage swit h some millionso finhabitants . Seawall smus tb ecapabl e of standingu p to extreme gale-sweptfloods » but theseboeze m embankmentsnee d onlyris ea smallamoun t abovenorma l water levelbecaus e therang eo fvariatio n inboeze mwate rleve li s onlya fe wdecimetres . Onth eothe rhand ,th eembankmen tmus tb ecap ­ ableo fwithstandin g thedifferenc e inleve lbetwee nboeze mwate ran d polderwate r (upt o5m. ) Investigationshav erecentl y showntha tman y of theembankment s dono thav ea sufficient degreeo f stability tomee * present-day standards. Although the samebank s canb ereinforce db yplacin gsan do nth epolde r side, it isstil lpossibl e forburst s tooccu r due toundetecte dwea k spots,pipelin e fractures,burrowin ganimal so ract so fwar . Ifa boeze m dikebursts ,th edamag e isofte nver y severe. Usuallyi * willno tb epossibl e toclos e thebreac hunti l thewate rlevel shav e equalised. There isth edange ro f losso flife ,damag e tobuilding s and services, disruptiono f industry,etc . Arapi dfal l inboeze m waterleve lca nals o causeconsiderabl e damage tobanks . A dikeburs t occurred in i960i nNort hHollan d in theembankmen t ofa smallpolde r lyingo na larg eboeze m and 2600home swer efloode dan d 1100inhabitant s had tob e evacuated. The consequences ofdik eburst sma yb erestricte d intw oways: - - byreducin gth eare atha tca nb e inundated - byreducin gth equalit yo fwate r that canflo wfro m theboeze m in*0 thepolder . Thefirs tmetho dwoul d imply theconstructio n ofa grea tman yadditio* 13"^ embankmentswithi n thepolders ,an d therefore the secondmetho dha s beenuse dver ywidely . Itwa sdecide d tocreat e afacilit y fordividin gth eboeze m into sectionsb ymean so f sluice gates. Theprojec t comprised theconstru e tiono f 37ne w sluices and 23ar eno wcomplete . Emphasisha sbee n placed on isolatingmajo rbodie so fwate r ,suc ha slakes ,fro mth e remaindero f theboeze mnetwork . Various typeso f sluicehav ebee nconsidered ,dependin go nth ecircum - stancesa t eachsite . Forus e inth ewide rwatercourses ,a ninflatab 1 weirha sbee ndeveloped . Thiswei rconsist so fa fla t steelbo x lyin^

2S4 onth ebe do fth ecanal ,containin ga folde denvelop emad eo fnylon-re ­ inforcedrubber . Thewei ri soperate db ypumpin gwate r intoth efolde d „ bo xan dretain sth eboeze mwate ra s envelope. Itthe nemerge sfro mth *•-eDO +h*X awuJ . J „w^^i-a+pc,a nautomati cmonitorin gan d a solidrubbe rdam . Thesyste m incorporatesa na .- , 4.,-^v, flowmeter shav ebee n instal- varningsystem . Atimportan tlocations , floQ wm e ,-, . .*,•/,»! nan bescanne d electronically ledwhereb yth erat eo fflo wan ddirectio nca n scam T -, <+-,,evreed sa certai nprese tvalue ,a n ttfo ra certai nperiod ,th evelocit y exceedsa * Mob decreeo fprotectio nagains t alarmi sactivated . Inthi sway ,a hig hdegre e y « * 4.V. *«*m*lvcopulate dan dlow-lyin gpolde r floodingi spreserve dfo rth edensel ypopux * landi nth ewester nNetherland s

^ T, !„q+aü-e so fth eHerman nGorin gPolde r ^T GERMANY- Th eOrigi nan dEarl yStage s0 1 (TumlauerKoog )i nSchleswi gHolstein .— J..

Iri1n . ahorten thecoastlin eo nth ewes t coast In193 1a pla nwa sdraw nu pt o ***** the dlkes mä esta_ <*Schleswig-Holstein ,reclai mth emudflat s behi vv ,_ Bv 19tómos to fth epla nha dbee n re­ lishne wvillage si nth earea . By W? varvinKi n •Uud, 7polder so nforme rmu dflat sha dbee nreclaimed ,varyin g

£.. from 500t o13 00ha . Molf ^ ^

ebes tknow npolder swer e«^ ^ ffien who initiated themi n *•Herman nGorin gKoog ,name d after ^^ ^ 193S- ^ -e nowknow na sMeksande rKoo ga n ^^ ^ ^ *•*th eNationa lSocialist s tookpowe r«1933 ^ ^ ^ ^^ ^

«Wfcm could serve someo fth e ™™°J strengtheningo fagricul ^ »creasing homefoo dproductio ni nG rman y ^^ ^ tural communities,selectio no fsettler s w«

^racteristics. ^^ Koog> each stage

^oughout thecours eo fdevelopmen to f ^ ^^ ^^ A W ^ markedb ydifference so fopinio n ^^ developffientan dselec t Clement companywa sforme dt ocarr yo u ^^ ^ gemment ^ newsettlers ,bu tit sview swer eo settlement through- ^cies. For example,th eCompan ywa ne d ^ settlements.

J* the polders,bu tth e*> ^ J^«^ styleo ffax» *i nth e

^ buildingswer e constructed m xn because therewa sa lo to f of ^Shbouringol dland ,wit h thatched*> * Sooialism. Initially Uganda forthi s stylei nth etim eo fNationa l

285 31+settler s came toliv e inth eTumlaue rKoo g ($00ha. ) Manywer e selectedbecaus eo fpart yaffiliations . Soilswer emuc hheavie r thanth e settlersha d expected and cultivation wasver y laborious,harvest swer e disappointingan d thegovernmen tha d toprovid e subsidies topreserv e thepropaganda -valu eo f theproject . After thewar ,a ne wgeneratio n gradually tookover . Farmshav emerge d and theaverag e farm sizeha s grownfro m 11+ha .t o 31ha . Theinitia l ideological aimso f thereclamatio nhav eno w disappeared andfarmin gna S adapted itself toth epatter n inth eres to f thesurroundin gland .

HUNGARY -Hydroamelioratio no fAgricultura l Lands inHungar y — M.Szina y

Hydroamelioration isdefine da s thebranc ho f sciencean d technology whichdeal swit h improvement of thenatura l conditiono f soilfo rpla 11 growth,b ycontrollin gth esoi lmoistur ebudget . Theai mo fhydroamel ' ioration ist omanag e the soilmoistur e in sucha manne ra st oallo w plants togro wa t theiroptima lrate . Theke yfacto rwhic hwil lulti ­ mately controlagricultura l development inHungary ,an d inmos to fth e rest of theworld ,i swate r supply. Agriculture canprogres s intw o ways:- 1) 'extensive'- ie,bringin gint o cultivationne w tractso f landfo rexampl e insemi-ari d zones. 2) 'intensive'i egainin gbette r cropsfro m existingcultivate d land,b yprovidin goptima lmoistur e conditions ateac h stageo fplan t growth. Ineithe rcase ,hydroameÜ 0" ration isexpecte d toperfor m twobasi c functions,namel y theremova l ° excesswate rb y drainage andth e supplyo fwate r tocove rshortage s W irrigation. InHungar y there isa nare ao f5 millio nha .i nwhic h soilfertilit y ie impaired andwhic hca nb ecorrecte db yprope rwate rmanagemen t inth e soil. Inapplyin g theprinciple s ofwate rcontro l iti simportan tt o remember that thesoi l isa 3phas e systemo fminerals ,wate ran dai* » andwhe nan yon eelemen t inth esyste mi schanged ,th eother sar eal s° affected. For example,salin e soilsexis tove r 1millio nha .i n Hungary,mos to fwhic h couldb eimprove db y leachingwit h irrigation water

236 ROMANIA- Som eo f theDanub eFloodplai nPolde rProjec t Criteria - I-Mihne aan dM . Clarian

In Romania,th eare abelo wrive rfloo d levels isabou t3. 5millio nha . ** of this 2.2million ha .i sagricultura lland . There istherefor e a lo«ghistor y of embankment schemesalongsid e theDanub ean dothe rmajo r rivers,whic h aima t theprotectio no fpolde rarea si nth efloo dplain . At firstmos t of thelan dwa sprotecte donl yb y lowsubmersibl edikes , 8°ae 3m.abov e land level,wit ha cres twidt ho f5 m . Thesegav ea standardo f protectionu p toabou t theonce-in-ten-yea rflood . More recently,ne wpolder shav ebee nreclaime db yconstructin gdike su p to theonce-in-a-hundre d yearfloo d levelplu sa 1m.safet ymargin . In 1962a decisionwa s takent oreclai m150,00 0ha .i nth eDanub e fl °°dplain in thisway . An areao f2 90,000h adivide d into 17polder s is included in thefirs t stage of thisscheme . Thedike sar ebuil t ab°ut 200m.fro m theoute rlimi to f therive rbe dwit ha cres twidt ho f Sm- Drainage channels andpumpin gstation sar eprovide d toevacuat e excess water in thepolder s themselves. Fielddrainag e isprovide db y »**•o fope n ditcheswit ha minimu m spacingo f IfiQm. Thecapacit y is c^culated togiv ea rat eo f dischargeo f5 to6 mm/day . Insom eplace s la**sfo rfis hfarmin gwer e integrated into thereclamatio nplan . The nee

**» - Basic Informationabou t theMarshe sa t theLowe rGuadalquivi r ive*— R.Bella s Rivera

* «* *outho f theGuadalquivi rRive ri nSout hWes tSpai n therei sa la*eeare ao fmarshlan d covering 136.000ha .a tabou t theleve lo f ***tide ,3. 6 m abovemea n sealevel . Insummer ,evaporatio nfa r

287 exceedsrainfal l and irrigation isrequire d to sustaincro pgrowth . Moreover,groundwate r issalin ean d slightly alkaline and thesesalt s mustb ekep t outo f therootin g zone. Reclamationwor k istherefor e seena shavin gfou r aims:- 1) Prevent inundationb yimpoldering . 2) Provide adrainag enetwor kwhic hallow srai no r irrigationwate r ^° pass through the soil,washin gou t injurious salts 3) Maintaina wate r tablewhic h allows roots todevelo p anddoe sno t allowcapillar y riset o thesurface . U) Loosen the soilb y cultivation to increase permeability. Successha sbee nachieve d indecreasin gsalinit y and increasingagric " ulturalyield su p tolevel s obtained in thesurroundin gdistrict swhi" 11 dono thav e salinityproblems .

GUINEA-BISSAU -Natura l andSocia lConstraint s toPolde rDevelopmen ti fl Guinea Bissau— R.J.Oosterbaan .

Guinea-Bissau isa coasta lstat e inth eextrem ewes to fAfric awit ha ^ areao f 36,000K m . There arecoasta lmudflat s extendingt oU00,00 0 ha,an d 100,000ha . havebee m empoldered. Theremainin gare ai s coveredb ymangrov eforest ,bu ta sther e isa nee d to increaseric e production,th eGovernmen t isconsiderin gextensio no f thereclaime d area. The traditionalmetho do f reclamation ist oconstruc t dikes 1.5 to 2m' highalongsid e the tidalcreeks ,althoug hmor erecentl y damshav ebee » built across thecreek san d thisreduce s thelengt ho f dikerequired « By custom theme nconstruc t andmaintai n thepolder swhils t thewome n cultivate therice . Water supply inth epolder s isentirel y dependent oninciden t rainf»1 andn o irrigationwate rfro moutsid e isused . A systemo fcultivât* 0 inridge s isfollowe d and this seems tob ever ybeneficia l incontrol ' lingth epresenc e ofnoxiou selement s inth eacid-sulphat e soils,a n inusin gth eavailabl emoistur e toth ebes tadvantage . Drainageo f areai sb ymean so f surface drainsan d thesear eals ouse d toretai n water. Thereha sbee na failur e tobrin g someo f thenewl y reclaimed landi °

238 cultivation, andi ti sthough t that emphasis should nowb eplace do n improvement of existing polders rather than onreclamatio n ofne warea a

EILAND - Land Reclamation inThailan d -Ruanglek , Chaveesukan d ?oolsup

Tl* Klongdarn Drainage Project wascarrie d outbetwee n 1921 and193 1a s 911 irrigation scheme covering 200,000 ha. close toBangkok . Nowi ti s tended toreclai m 2^,000 ha. ofmarin e clay aspar t ofth esam e pr°dect. In6CP/ 0o f this area, soils aresaline , andth eai mi st omak e these soils suitable forcultivatio n ofrice . Themethod s used ist o ^ovide surface drainage andallo w irrigation byfloodin g duringth e **y season toflus h thesalt s down beyond therootin g depth ofth eric e (2° -3 0cm. ) Evaporation andupwar d movement of salts from saline ^oundwater must bekep t toa minimum bydoubl e cropping. Iti shope d to Produce 2.5tonnes/ha . inth edr yseason . A *ea dike hasbee n constructed along thesouther n edge ofth eare at o k6eP outse awater . Inth edik e there areassociate d discharge sluices 90d Midges. Irrigation water isconveye d toth eare a from thenort h al°«g theRaphipha t Canal. Drainage channels aredesigne d to dis- Ch^ ata rate of1 * mm/day, andirrigatio n canals axeprovide d with a capacity of 7 mm/day.

V^AM - The Experimental Polderfo rResearc h onAci d Sulphate Soils the Mekong Delta — E.Stamhuis .

In +u • Tr,-=+yiam there isa very flat area the delta ofth eMekon g River in Vietnam tnerex W L-.,,, . „v, aBaci dsulphat esoil san da 4 million ha. Half of this areaha saci a s^ ""ethort • ,. •„« +hese soils insuc h awa ya st o give "n°d is being sought ofmanagin g these b«^ rea8ed production of rice, ^anrt, • •„„ „ nverflow inth ewe tseason , . lQ isno tembanked , andwhe n rivers overixow x ,.,... f ie-M ' , A c ?m This iso fvalu e toth e iel shallowdrainag esystem st ogiv eprove d leachingo ftopsoi l by Wanting acid-tolerant varieties ofric e andb yth eus eo f fertil- 289 isers,bu tusuall y thesemethod sar eto oexpensiv ean dlarg earea s remainwit h lowyields . Anexperimenta lpolde rha stherefor ebee nse tu pb y theUniversit ya t CanTho ,wit hassistanc e from theDutc hUniversit y ofWageningen . The area,8 ha .i nextent ,ha sbee nsurrounde db ya cla ydike . Itha sbee » providedwit hdrainag e andirrigatio n channelsan d sub divided into smallplots . Withineac hplot,drainag ean dinundatio n depthca nb e controlled. Thep Hvalu eo f theirrigatio nwate rca nals ob evarie d& s required. Tillage depth andrat eo ffertilise rapplicatio n arefurthe r variables tob e investigated. From thesetrial s iti sexpecte dtha t improved techniques canb edevise d forth emanagemen t ofpolder s inth e ItekongDelta ,an d thatagricultura lyiel do f theare aca nb eincreased »

SURINAME- Presen t stateo fWate rResource sDevelopmen t in N.W.Surinam e— A.Spie r

Theexten to freclaime d swampland inN.W .Surinam eha sgrow nrapidl y since 1950t oa nare ao fabou tlj.0,00 0ha .mainl yuse d forth ecultiva ' tion ofrice . Amuc h greaterare a( 180,00 0ha. )o fver yfertil esoi l ispotentiall y available. Much technical dataha sbee ncollected ,^ u* themos t difficultproblem sar econcerne dwit hlan downershi pan di* s legalan d socialimplications . Waterfo rirrigatio nca nb emad e availableb ymean so flo wbank st o buildu p theleve lo fwate r seepingacros s thelan dtoward s thecoas* * Thistraditiona lmetho d isstil luse dbu tmor eefficien tway so fwate * resourcemanagemen t axeno wbein gsought . Themos t promisingmetho d ofdevelopmen t seemst oli e ina n intégrât6* systemo frive rwate r intakesan dcanal s tocu tof f seepage fromswaï" P Onth eCorentyn eRive rwor kha s startedo na multi-purpos eproject . Somewate rmus tb elef t topreven t saline intrusion,bu t 50cu.m./sec canb ewithdraw nb ya pumpin gstatio nan dconveye dalon ga cana l6 7* ^ inlength . Thiswil lallo wreclamatio no f 12,500ha .o fne wpolder s andprovid e irrigationwate rfo r 33,000ha . Theyiel dcoul db e increasedby: - a) Installationo f extrapumpin gcapacit y tooperat eonl ya t low** * b) Flowregulatio nb ymean so fa da m tob e constructedupstrea m for

290 hydropower. \ f^m theNann ian dCoroni eswamps . «0 Collectingwate rwhic hseep sfro ,th e^ ^ ^ ^ Th»latte roptio ni smoe tpromising . Caxemus x . +„„™, hbecaus eonl yth eto pmos t thewate rleve li nth eswamp sb yto omuc h oeca r x „™ hle. Bycombinin gth eyiel do f layerso fsoi l (mainlvpeat )ar epermeable on, w " «verso i son vmainJ-y v** i integratedresourc eca nb e therive rwit hth eyiel do fth eswamp ,a ninte ^ate .i j „»»tPT thanth esu mo i "ie ^eloped, whichha sa combine dyiel dgreate rtna n ..A total polderare aca nb eincrease dt o componentparts . Inthi swa yth etota lp o 5?,000ha .

291 VARIOUSASPECT S OFPOLDER S INCERTAI NAREAS . LISTO FAREA SDESCRIBED ,AN DMAI NDESIG NFEATURE S Region Authors Subject& Mai nThem e DesignParameter s Netherlands, Constandse Comprehensiveagricul - R=750E-68 0 Ysselmeer deJon g turalan durba ndevel - A1=166A2=U 1 Pinkers opment A3=207 Netherlands, Vernimmen Floodprotection:Safet y N. Holland Heyligers fromaccidenta l inunda­ tion W.Germany , Smit Effects of socialpolic yA1=0. 5 Schleswig- onorigi no fpolder s (TypicalP ° Ide^ Holstein Hungary Szinay Hydroamelioration: R=580 optimisationo f soil A3=£000 moisture budget Romania Mihnea Planningpolder s in D=5t o6 Danube Clarian floodplaino flarg e A1-29A2=U2 6 river A3-U55 ^ Spain, Bellas- Improvement of saline R=570 E-U3° Guadalqui- Rivera alkaline soils A3=13° virMarshe s Guinea- Oosterbaan Constraintso ndevelo p R=2300 Bissau ment:findingappropr ­ A1=100A2=3° ° iate technology A3=Uoo __^ Thailand S.Ruanglek Regulationo f quantity R=1200E=7 12 S.Chaveesuk andqualit y ofsoi l D=U61= 7 ^ M.Poolsup moisture A2=2UA3-20JU - Vietnam, Stamhuis Experimental polder: D=86 Mekong controlo f acid sulphate 1=20t o3 ^ Delta soils A3=U000 Suriname Spier Waterfro m swamps A1=[;0 integrated withrive r A2=12 abstraction A3=57

*R=Annual rainfall in mm. E=Evaporation D-^Designrat efo rdrainag emm/da y I=Designrat efo r irrigation A=Areas in 1000's ha. A1-=Complete. A2-rProceeding.A3 Ultimate.

292 SUB-THEME: VARIOUS ASPECTSO FPOLDER S INA CERTAI N AREA (CONTINUED) E. Allersma Delft Hydraulics Laboratory,Th eNetherland s

Abstract

ThisGenera lRepor tdeal swit hte npaper s, nin eo fwhic hdescrib easpect so f th*construction , amelioration andmanagemen t ofpolder s while the re- mainingonepicture sth edisposa lo fdredge dsediment si ndee p polders.

2 Pou ur PaperTÏ-, s discus,• s th, elarg e (13.50/i-at;n nUVm km; 1aej.u deltaa development andrecla -

^ion projects in the densely populated andnaturall y hazardous coastal Pt °vinces of Bangladesh. Smaller, butpursuein g similar purposes,i s the atneHoration scheme ofth eLezfri a Grande inPortugal , ^igns ofne wpolder s areth esubjec t ofpaper so nth eTan a River ^rni . ...,ii o^^-io^t-i nNieeria :bot h situated _r°Ject inKeny aan dth eHadeji a Vally Project innige i , n a semi-arid climate. AT w « ~r solders that have developed ^tch paper surveys thefou r typeso fpolder s Vi»g thepas t tencenturie s abovean dbelo wse aleve l inth elo wan d s l0»ly subsiding coastal Netherlands.Th ework s required tocomba tth e e £fer.(- r ,t „oc-iupus eo fgroun d waterar e the lects ofsubsidenc e caused byexcessiv eus e0 1 & A Je ct ofa paper from Taiwan. PaPer from describes themethod so fdisposa l ofth elarg e ,U**itie,o f (partly heavily polluted) dredged material fromth e harh^, . . „.„I acripctso fthi sus eo fpolders . b°urs inpolder s andth eenvironmenta l aspects ui Thevin« , , .„.„jcocia lcondition sencountere d inth e W1aerang eo fnatural ,economi can dsocia l wn Pt °^tarea slea dt ointerestin gcomparison so fway spolder sar elai dou tan d 0Perated. Dutch consultants were involved inmos to fth eprojects . 293 1 General observations

Definitions ofpolder s all contain theelement s of land andwate ran d their jointmanagemen t ina wel ldefine d area.Thi s separation fromth e surroundings isa direc t consequence of thecontro l ofprocesse s with10 thepolde r and theexclusio n of external influences.

The element "land"lead s tovariou s aspects sucha s location,geology » soils and land usewhil ewate r leads toassociation swit hclimate , hydrology andwate r control.Th ejoin tmanagemen t presupposes agoa l whichmus t be feasible and which leads toa technica ldesig n and an organisational structure for theoperatio n andmaintenance .Thes easpe ° of polders are the subjects of the tenpaper s tob e reviewed inthi s Report.

The locationno t only points toa plac eo nou r globebu t evenmor et o thevertica l positiono f thepolde rwit h respect toth e surrounding water level.Difference s of afe wdecimetre s inaltitud e canhav ef ar reaching consequences for thetechnica l realisation of the supply anc^ evacuation ofwater .Th edevelopmen t ofhydrauli cmachiner ywit h in- creasing head and capacitymultiplie d therang e of lands suitable f°r reclamation asa polder .I nth eNetherlands ,wit hdrainag ea s themai n problem, the successive steps inth econques t of thewate r were (see Bakker and Kooistra). - construction ofdwellin gmound s (2000-1000BP) ; - embankment of the surrounding high grounds (1000-1500AD) ; - embankment of naturally accreted areas (1200-present); - drainage of lakesu p to6 m below sea level (1450-present),an d - reclamation of large areas of seabotto m (since 1930). The first three could stilld owit h gravity flowbu t the lattertw oty P required thepowe r ofwind , steam,combustio n engines and electrica' Notwithstanding theavailabilit y of thisrang eo f technicalmeans ,tli e isa nunderstandabl e (economy,reliability ) tendency to solutions wiu •t h the soleus e of gravity (see Brouwer).

Thepapers ;locatio nan d climate

294 e tenpapers ,whic h are the subject ofthi sGenera l Report,ca nb e assified,accordin g tothei r locationan d theclimate ,int ofiv e Categories.

')Bangladesh . Deltadevelopmen t inBanglades h byShafiqu lHa q Polderdevelopmen t inBanglades h 1 Past and present byMd .Mohsi nUddi nan dS .Isla m H The land reclamation project byA.T .Chowdhur y HI Thedelt adevelopmen t project byMd .Ab uQuasse m all pertaining to 13.500km 2 along theestuarie s and thecoas to f thedelt ao f theriver sGange san dBrahmaputr awit ha tropica l monsoon climate:precipitatio n 1500-3000mm ;evaporatio n 1200mm .

' Taiwan. Problems in stratum settlementdu e togroun d water exhanstionb y SinMong-Hsiung . Ab°ut anare ao f 40km 2 inth esout ho f the island ofTaiwa n ina sub-tropical humid climate:P = 1300-3000m m fromJul y toOctober .

TheNetherlands . - Marine polders in theNetherland s byH .d eBakke ran dM.J .Kooistra . ~ Polders asa disposa l site fordredge dmateria lfro mRotterda mb y H.J, Groenewegen. Pertinent toabou t 10.000km 2 (onethir d ofth ecountry )i nth e c°astal part of theNetherland s ina temperat emarin eclimate : 760mm ;E = 69 0mm .

} Portugal. Land reclamation andagricultura ldevelopmen t ofth eLezïri aGrand e (Portugal)b yL .Santo sPereir a andM.G .Bos . '3°km 2 inth eestuar y of theTagu sRive ran d ina dr y sub-tropical cUmate p= 400-110 0mm ;E = 1200mm .

A]l these polders are situated intida lareas .I nmos t cases,th elan d ,SU5rface isabov e themea n sea levelo reve nabov emea nhig hwate rbu t be low fchehighes t floods caused by thetides ,th espate s ofa rive ro r

295 storms. The polders in Taiwan are gradually subsiding and some of the Dutch polders are dry lake bottoms up to 6m below sea level.

5) Africa. Irrigated rice polders in the delta of the Tana River, Kenya by H.W. Appel and M.M. Vierhout. Hadejia valley irrigation and drainage project, Nigeria by R. Brouwer. Areas of 100 and 200 km2 respectively near the Indian Ocean in Kenya and in the North of Nigeria in a semi-arid tropical climate: P = 600-700 mm; E = 2000-2500 mm. Both project areas are situated in the flood plains of rivers some ten of metres above the ocean and Lake Chad. They are subject to seasonal flooding.

3 Objectives

In all cases, the construction of a polder means protection of the lan against inundation: by embankments (bunds) against intrusion from the outside by floods of fresh river water and tides,an dsurge s of saline sea water, and by a drainage system against an excess of local precipitation and seepage. Contrary, an often temporary shortage of water is met by irrigation l0 Africa, Portugal and Bangladesh. An excess of salt,whic h mainly occur in coastal areas (Bangladesh, Portugal, Netherlands) is fought by the prevention of inundation by salt water and by flushing with fresh( ir gation) water.

In most cases, the empoldering of an area is an offensive act: land 1 age withdrawn from "Nature" and made to (a better) use. Along the Dutchc and on Taiwan also defensive aspects are important because subsidence the area increases the natural dangers. the Generally, the protection of inhabitants, property and crops against various catastrophes is expected to increase the usability of the la or of the bottom of a lake or sea.

296 j1 A -icnqp d foragriculture .A n in- Mosto f thereclaime d or improved land isuse d tor g c fu rrorï food isth emai nobjectiv e ofth e creaseo f theproductio no f (better)too a ! ,„jAfric a Other expected berufit sare : Projects inBangladesh ,Portuga l andAfrica ,u „„I forth e localpeople ,mor e betterlivin g conditions (safety,economy )fo r f room in adensel y populated contry (Bangladesh,th eNetherlands) ,a better infra-structureo f thearea ,change s of thesocia l structure (landtenure ,co-operatives )a s inBanglades h andPortugal .

j • nanoladesh.ar eexpecte dt oyiel d Pilotareas ,suc ha sbein gdevelope d inBangladesh , .. ^ used inth efutur edevelopmen t experiencewit h certaintechnique s to beus e *•t- nh eexample s fora large rarea . °fth evhol eprojec t and they aremean t tob eexam p

„A Rotterdam tob efille d inorde r *»exceptio n areth edee p poldersaroun dRotter d material t0 . • „f Partly polluted)dredge dmateria l dispose of thegrea t quantitieso f (partly v fr°rath eharbours .

Geology and soils

Rß • nbiectiveo fth econstructio n ofa ^ause land improvement isa ma m object ^ m of

-lder, the ge0logy of theare aan d the^ uitable,,i nord ert o ***tinterest .Th elatte rshoul db e"suitabl eo rhig hy ^Projects,asdesigne di nBangladesh ,Afric aan dPortuga l e-ble. r «.lat-ivelyfla tare aan d the Co *trolo fwate r levelrequire s arelat i ^ ^^ MMtal plains Pliability ofwater .Thes erequirement s po« ^^ ^ ^^

^ alluvial plains along ^'^^^ Taiwan, Portugalan dth e Fr °m thediscusse d areas theone s in g the rg in Irland, are situated along coasts and ""»"^^

JW. and Kenya areprojecte d in ^J^ ^vements o£ thesoi l iS0 invie wo f thewate r control, EH _ rhese aleve lalon g surf Therelativ eris e0 1 rr ace areo fmayo r importance. sea th oi, va eustati cris eu i ne coast of theNetherlands ,cause d compaction of the subsoil l (1«* l (1mm/year) ,a tectonic subsidence " ^ ^ ^.^ types o£

erosr "Wyear), compactiono f (local)rece n ^^ ^ ^ ^^ ^^ ion of the surface,ha smounte d up u the same occurs ro inc«ioe thnoe Dutcf theh surface started, habuildin smounte gembankments du p to- . ^ ^ ^^

297 inBangladesh .Artificia l subsidence,cause d by theminin g ofnatura l gas and ground water add toth eproblem s inth eNetherland s and aret n main subject of thepape r aboutTaiwan .

The complex process of deposition and thesubsequen t soil formation generally lead toa ver y complicated soilmap .Th e oneo f theLezfri a Grande inPortuga l isa goo d example.

The soils of thecoastal ,lagoona l and estuarine areaso f Bangladesh, Taiwan,Portuga l and theNetherland s aregenerall y described asclays » sands and somepeat .Th e salinity of the soils ison eo f theproblem s tob e solved by their empoldering.Th e soils aremor e or lesscalcareo u depending on their formation.Olde rmarin enon-calcareou s soils tendt develop into acid sulphate soils (cat clay).

The soils inth eproject s inNigeri a and Kenya arealluvia l and aeoliafl depositso fclay san dsands .Som eo fth eterrac esoil si nKeny aar esaline .

5 Land use

Inal l cases agriculture is themai nus eo f the land.Detail s depend° n location,climat ean d soil conditions,a brief review shows thegrea t variety. - Bangladesh: 60%i sunde r cultivationwit h crops asrice ,betelnut » jute,fruit ,vegetables ,condiments ,pulses ,sugarcane ,oi lseeds » tobacco and sesame;th eres t iswast e land,forestry , shrimpsan d saltproduction . - Taiwan:no t specified except fish farming. - Kenya:mechanise d riceproduction . - Nigeria: sorghum,millet ,co wpeas ,maize ,groun d nuts,wheat ,co 1- vegetables andrice . - Portugal:presentl y 50%fodde r and pasture;th eres twheat ,othe r „ill cereals,tomatos ,melon ,etc. ;th eproductio no f irrigated rice bepromoted . - TheNetherlands :pastur e land,arabl e land,horticultur e and frul

293 Generally some of the land is used for the infra-structure sucha sroads ,

canals, towns, industry, etc.Speciall y mentionedar erecreation , natural

reserves and the dumping of dredge spoil.

6 Hydrology and water management

T"e purpose of water management ina polder is to influence the local urologie phenomena in a favourable way.Briefly , the following means

are available (or not):

- „ • . • A OÛOT,PCTP within the polder can hardly Precipitation, evaporation and seepage WICIU.II v

be influenced; 11 ~A rrit-hin the limits of the source supply from outside canb e controlled within tne

(rivers, ground water); - drainage to the outside depends on external conditions, and ^ the storage in the polder (soil and open water) is given with the

design. Irr,- . , -A„A sv technical means. They areth e ligation and drainage canb e aided by teenmea -in instruments of themanagement . Irrigation is needed whenth estorag e is insufficient to fill thega p between evaporation and precipitation

(and x • A anrf drainage should remove an excess; vand seepage)durin g adr yperio d anddrainag e bom •,. c„ hmMSU res aremean t tosafeguar da uotn withina reasonabl e time.Suc hmeasure * Cr°P or even toallo w fora nextr acrop . With «.». • -„A andi n vieuw of the great variety in ACn these observations in mind,an ai n vie . , . . Cl*-te and land use,i t isn o wonder that the polders described in the "Per. show great differences in the water management. From the three ei„ . „A irrigation - the first two 6 lements - flood protection, drainage and irrigatxon a Ppear in all areas under consideration.

&iv*r «, • ,-„rpa s in Nigeria (once a year) and iVer floods occur in the project areas in «J-B RB„ ' •> ^^ro enrees are themai n problem Ketl Va (twice a )# High tides and storm surges in Tai , A «nrh areme t with in Bangladesh and P Taiwan and the Netherlands. Both are me., or«- ,.„ «vnected to protect the polders rtugal. In all cases embankments are expected v a&a,- a „«riod varies between 20 years êainst floods of which the recurrence period var (Bangladesh) and 10.000 years (theNetherlands) .

Mo,* »f thedescribe d polder areas are drained by gravity flow into the

299 river or (at lowtide ) into tidalwater . Inth eNigeria n case aspecial - buffer,i nth e lowerpar t of thepolde r provides storage capacity to facilitate aprope r drainage toth e river and toa lower flood plain; avoiding apumpin g station.Suc h stations are indispensable in thever y deeppolder s inth eNetherland s and inth e subsided area onTaiwan .The y areconsidere d inth e amelioration scheme for theLeziri aGrand e in Portugal.

Irrigation isno tver y common inth eNetherland s with an evenlydistri " buted precipitation,relativel y little evaporation and a large storage capacity ofmos t soils.I nBangladesh ,wher e 90%o f the annualrai nfal- 1 inth emonsoo n frommi dMa y tomi d October irrigation isapplie d insof f areas for the flushing of salt.I nal lothe r schemes,irrigatio n isa n important aspect. - OnTaiwan ,especiall y the fishpond snee d vast quantities ofwater ! also outside therain y seasonwhic h lasts fromJul y toOctobe ronly - Theus e of ground water for thispurpos e caused ashortag e andsev e subsidence of thearea . InKenya ,th etw owe t seasons around April and December areto owea k and need assistance by irrigation tofacilitat e thegrowt h of two crops.Wate r canb e takenfro m theTan aRiver . InNigeria ,th eprecipitatio n of 700m m inconcentrate d squalls£ r° August toOctobe rmus t be supplemented by irrigation from theHade J River inwhic hwate r isretaine d by aserie s of reservoirsupstrea m from theproject . - InPortugal ,th eperio d of lowprecipitatio n and high evaporation during the summerwil l bebridge d by irrigation from theTagu s rive Thiswil l facilitate thegrowt h ofrice .Pumpin g stations will W1 thewate r into and through thenorther n half of thepolder .

Salt,whic h poses problems inBangladesh ,Taiwan ,Keny a (onlylocally' ' Portugal and theNetherlands ,i sgenerall y expected tob e combated vl thedrainag e of excess rainwate r during thewe tseasons .

A special feature of theLan d Reclamation Project inBanglades har e largepond s tob euse d for the storage ofdrinkin g water forvillag eS' Theywil l be filled bywin dmills .

300 7 Environmental aspects

Thereclamatio no f land,b y itsnature ,change s thehydrolog y (surface andunderground) ,th eflor aan d thefaun awithi nan dprobabl y alsoout - . _•„ „ai d tothi saspec t m the «ideth earea .Relativel y littleattentio ni spai d Papers.

„ „hirh however,deal smor ewit h Anexceptio n isth epape r of Groenewegenwhich ,how e , 0i nf heavily polluted dredged fcheenvironmenta l problems of thedisposa l of VP f a„olde r Itdiscusse s thepath san d Materialtha nwit h theeffect so fa polder . ., .- thp ormmd • „i-c ,'nth esoi lan d inth egroun d theeffect s ofa multitud e of contaminants m „„,.„.„effect so nwate rquality , Water within and outside thedumps .Variou s fl°ra, faunaan d structureswer estudied .

Feasibility;economi c and social

Aw afe wo f theauthors . Thee economic feasibility isbriefl ydiscusse d by f Th, e -rything with an estimated costo fabo u UI • partg ^ ^ C °St ratios of 2.35/1 and 3.88/1 are- » ^ ^^ ^ ^ ^ the Project.Fo r theTan aRive rprojec t ' ^ ^ $ g7Q ^

** net ha i8 estimated atU S$ 6,67 0wit hrunnin g^ ^ ^ ^^ ^ an ^m. various alternatives lead tointern a ^^ national level)o f 3 ' -82. The final evaluation (onfar m levela n ^ reclamation

"* U.fri.Grand eprojec t inPortuga l """* adopted plan is alternatives and three farm structure alternat! • 6xPected tohav e an internal rateo fretur no f ..

TK par insom emor epapers .Structure s 6 ^£ial aspects of theproject s appeari n

and objectives vary greatly. landlords ispropose d toshif t Il »Banglades h the system of (absen ^ ^ farmers inco-opera ­ organ a tesmal l land-ownership witha n ^ ^ructure of villages ando f tives. Alsoothe r changes inth esoci a s ,., ,.. „resul t fromth escheme . fc newhol e area areexpecte d tor e ^ ^ ^ ^^ of fche In Portugal theownershi p of theproje c agricultural company. "Companhiada sLezfrias "whic hals o isa

301 It ispropose d tomaintai n thepresen t structurebu t topromot eth e settlement of small farmers onplot so f 12t o 100ha .dependin go n thetyp eo fcrop . Inth eNetherland smuc h of theol d landwa s empoldered andmanage d W associations of landowners.Th e empolderings of lakebottom swer e private enterprises under charter from theGovernment .Th eZuiderz e polderswer e constructed and reclained by theGovernmen t and fort h greater part rented inparcel s of 12t o6 0h a tofarmers . InKeny a the threepolder s inth eTan aRive r project willb eowne d a runa sa stat eenterprise .

9 Design,area l planning and details

The areal planning isa wel l considered compositiono f all elementsc ° stituting apolde r sucha s thedrainag e system,th e farmplots ,th ei rr gation system,roads ,villages ,etc. ;al l taking intoaccoun t thenat u conditions.Technica l skillshav egreatl y improved inth e courseo f history;jus t tomentio n theArchimedea n screw,th ewin d mill,variou s pumps,moder n power sources,automotiv e transport,fertilizer san dm°o e •ji g farming equipment.Thes edevelopment s arereflecte d inth earea l plan of the successivepolder s inth eNetherland s (deBakke r andKooistra ^ well as inth eamelioratio n schemes for thepolder s inBanglades h an^ Portugal. For the latter case,th eautho r gives somedetail so ftheal c uitb nativedrainag e and irrigation schemes.Tertiar y units of 30-40ha .w 25 to 30farmin g families,livin g ina typica l circularvillage ,ar e contemplated ina pilo t polder inBangladesh .

The technicaldesig n of theproject s issparsel ymentione d inth eP aP Themos t important aspect is the flood protection.Th eprojec t inB anë desh provides for 4050k mo fbund s of three typesviz .se adikes ,r l dikes andmargina l dikes.Eac hha s itsow ndesig nbase d upon thehy< * a*1 liecondition so nth ecoast ,i n theestuarie s and along lessercanal s» tob econstructe d from locally availablematerials .I nth eTan a Rive project (Kenya),th efloo d embankments are combined with amai n dral detials (alsoo f amai n canal)ar egive n inth epaper .

302 Drainage sluiceso fa specia l typewer edesigne d inBangladesh ;th e numbero fvent s (1,5x 1, 8m 2 each)t ob eadapte d toth eloca lcondi ­ tions.Th eus eo fbambo o field drains ismentioned .

A . . „f rv.econstructio no fdredge d material A special casei sth edescriptio no fth econstru e j, , •„•„„ ,-n«Pttlin ebasins ,th estimula ­ is around Rotterdam:Th edepositio n insettlin g v .-• ,„i . j^oinoo,.o fth ewate r fromth etran ­ en ofth eripenin gproces san dth edrainag eo rcn ew Station ofth esediments ,fro mth ecompactio n proces„„t-lr.-rtsnrores san dfro m normal precipitation.

10 Management andoperatio n

<5„ ,.hav ~ already beenmentione d as b°measpect so fth egenera lmanagemen t havea *• ^oTit-an doperatio no fth edrain ­ ants ofsocia l development.Th emanagemen t ando p ^ ^x.„ konris of public bodies in aSean dirrigatio n systemsar eofte n inth ehand s pub . ui,- 6 7 voidercommitte e (consisting v "ichth efarmer s havea say .I nBanglades hapoia e vVlll,nrfl1 of • , . co-operatives andth eagricultura l 0f representatives ofth eproject ,th ethfc oop e H ^-,. aBOistedb ysu bcommittee sfo r dePartment)wil l overseeth emai n system assisted oy ^ «* sluicesan dloca l canalsa swel la sfo rth ewate rcontro li n t-tiary units.I .Keny a theestat emanagemen t authority

^le f0r everything.O nTaiwan ,a Provincia lWate r Conservancy Bure

*.. . O,on1ca swel la sth esea-wall , —ains thedrainag ean d ^^»^« ^ ^ fch. ** s^easpect s are looued afterb yth e A- ^ ^ Le ^-ria Grande in Portugai. inth eNetherlands ,th ew ^ cfc hef1 n , . . • rriehand so fwate r boards inwhic hth e -«and1 P-tection isi nth ehand s operateunde rsupervisio n ^ittee ischose nb yth elandowner s andwhic h P co-ordinationo fprovincia l authorities.

303 SUB-THEME:GENERA LDESCRIPTIO N OF POLDER PROJECTS D.W. Rycroft Institute of Irrigation Studies University of Southampton,U.K .

1 Introduction

The elevenpaper s describegenera l featureso fpolder s inarea sa s widely separated asCanad a and Indonesia,fo robjective s asdivers ea s thedevelopmen t ofprim e agricultural land (U.K.)t oth efloo d protection ofdensel ypopulate d urbanarea s inSout hEas tAsia . Inessence ,polder s aim to isolatearea so f land hydrologicallyfro m their surroundings whilst controlling thehydrologica l processeswith 1 to enable thedesire d human activity toproceed . Theyar eusuall y situated on low lying landsadjacen t toa majo r element ofth e regi°na open water system, i.e.th e seaand/o r arive r estuarywher eth e construction ofdyke s lessens the incidence offlooding . Soils in landsborderin g sucharea sar eofte n highlyfertile , comprising theproduct s of erosion carried down from higherlands . Their evenness,fertilit y and easeo facces smak e them highlyattrac t fordevelopmen t either foragricultur e orurba ndevelopment ,th etw o competing uses not always inharmony . Inestuaries ,progressiv e raising ofmars h levelsb ydepositio ncré a conditions well suited to small stepb y step impoldering and their a continued successful development isusuall y assured by thepresenc e 0 of aj-e firm existing agricultural foundation. Elsewhere,larg ene wpolder s developed mainly byth e state either toexten d existing agricultural strengths as inSpai no rt o createne w strengths as inEgypt . Thepaper srevea l thaturba nan d agricultural polder developments

304 ^•u j^^nWc degreeo fcontro lt ob e create conflicts concerning thedesirabl eaegi e ^ exerted onth eexterna lan dinterna l hydrology. Citiesnea ro rwithi n Poldersprovid ea read ymarke tfo rproduc ewhils t creating problemso f , i,.„tpn dt odra wpeopl eawa yfro m Pollutionan dwast edisposal . Theyals o tend P tu • t Tbppaper sals orevea l that thelan d toth eurba n environment. Thepapei s *u natural ecologyo farea san d Soldering involvesmajo r changes inth enat u ,__.,...... naturalhabitat s ismakin g ^creasing concern aboutth epreservatio no fnatun nf r • *r, create furtherpolder si n !tincreasingl y difficult tocontinu et ocreat e Europepurel yfo ragricultura l development. P purely agr ..resting problemsan dfo rreporting , Thepaper scove ra numbe ro finterestin g p ^ & ^ havebee n grouped around linking themes. The ThP second groupdescribe s general descriptiono ffou rpolders . Theseco n ,. tnrH crroupconcern spolder s Puders within peat landswhils tth ethir d group A further challenging paper "»inlywithi n developing countries. Aru r

««Ue „au,, uestio»s«h .P^^* ^ p."« —.3 Productiono fwha tar esee nt ob efairl ysopt u l Wo developing countries. cnP(-ificallyestablishe d T hefina l group of papers deal witha polde r spe ^

* assist ina populatio n relocation^«whils t ^ ^ ^ *°stunusua lan dinterestin g technical pro e ^ ^ ^ ^ deals withth eproblem soccurrin g m ap o e ^ ^^ ^ an «inferential subsidencean dlyin g«thx n ^ ^ the proMefflSo £ a

Venezuela). Thesecon d andfina lpape r exp managementan d

2 1detail so fpolder s Papersdescribin g general ^ ^^ 2-1 Reclamationo flan do nth eEaster n byP.D .Coo k oaricultural land fromth e The ofprim eagricu-n-uj- " Paper describesth ereclamatio nu v ^^ shallow estuaryi n marar '" shes bordering theshore so fth eWash ,a essiveiy risesdu e

^ Eiland. Theleve lo fth eseawar d ^ ^ ^^ vegetative 0 thedepositio no fsediment saccélér a ^ ^ ^ ^ ^^ the '°Ver. Theare ai sreclaime db yconstructin ga

305 marsha spossible . Later,th eprim e silt soilsar eunder-draine db y pipedrains . The reclamation isprivatel y financed byth efarmer s bordering the reclamation and forthi s reason theminimu m width of 'economic' reclamation tendst ob eabou t40 0m . Thedyk e isconstructe d fromth e locally available siltymateria l and isprotecte d fromwav e action firstly bypreservin g sufficient protectivemars h to seaward and secondly,b ycoverin g thedyk eb ya thic k grass sward. On arecen t reclamation thefailur e toestablis h aswar d rapidly andunusuall yhig n tide levels (1978),resulte d indamag e toth edyk ecostin g approximately 50% of itsconstructio n cost in1977 . Inrecen t years,pressure st o maintain themarshe s inthei r natural statea sa sanctuary forwildli* e aremakin g it increasingly difficult toconside r futurereclamation .

2.2 Dykelands (Polders)alon g the Bayo f Fundy,Canad a byC .Desplanqu e

Inth emaritim e provinceso fCanada , largearea so fgrassland ,i n particular bordering the Bayo f Fundy,wer e endiked by French settlerS inth e sixteenth century. Today,muc h ofthi sare a liesbelo wth e existing seaward marsh which has,lik eth eWas h areaso fU.K. , continued to risedu e todepositio n of sediments. This suggeststha t theendike d areascoul d beprogressivel y extended as inth eWash . Tne land is surfacedraine d bya system ofcambere d beds leading to shall0 drainage channels,thi smetho d being chosenbecaus e of thehig hrain* 3 intensity inautum n (20cm.day ") an d becauseo f iceformatio nwhic h blocksope n channelspreventin g groundwaterdrainag e bypipe s discharging intoope n collectors. Sinceth e 1950's,dyke shav ebee n raised incertai n areaswhils t tidal sluiceshav ebee n installed in 'Aß others torestric t the flowo fwate r and hencecontro l theris e int: L level thusreducin g thenee d torais eth edykes . Itwoul d beo f interest to learnho w thedecisio n toop t for the sluiceo r the raisl ofth edyke swa smad e and tokno wwhethe r the installationo ftida l sluicesha s increased problemsdu et odepositio n elsewhere inth eB 3''

306 2-3 Polderso fth eVistul a River by P.J. Kowalik

T , „•„.„1.Rive r havebee n reclaimed Largearea so flan d bordering theVistul a Rivern a overth e centuriesb yladdering . Inrecen t years,th etendanc yha s teent oamalgamat e areasan deve nt oinstal l intermediatepumpin g .u - ^irlprs Theclos eproximit yo f dations thus creating polderswithi npolders . «*ba„area s (Gdansk)ha sprovide d aread ymarke tfo rproduce ,thoug h th j, . *J,AHrif to fpopulatio n fromth e is advantageha sbee n counteredb yth ed m F r ra„Kiria i +ai imnacto fth etow ncausin g la"dt oth etow nan db yth eenvironmenta l impact eran dai rpollutio nan dproblem so fwast edisposal . *ateran dai rpollutio nan dproblem so fwast edisposa l „<-0Hrelatin g predicted grassland *-_ .Figur e2 ,a detaile d graphi s.presente. d*~A relat relatinig p g predicted grassla ««•utilizer Itwoul d oe ^eld towate r tabledept han dnitroge n fertm i • V„TP been tested intn e neiu helpfult olear n whether theseprediction shav e a"dho wth einformatio ni suse d inpractise .

T„e soiU and-« , «Me ,** °f «» """ "* "CastilloD eDon aBianca " byV .Gomez-Migue l et_al_

Tu A.Timatologica ldat afo ra polde r

^ Wth paper describes soils andc ^J^ ^ Spain. The area d eve'elopmeni tborderin gth eGuadalet e ^^ ^^ Two opment borderingth eGuadalet e ^^ ^ ^^ Two is tob eirrigate d using lowt omoderatel ys

^»orpoint s require elaboration. - ^ periods o£ P **ly. Figure 2depict s anannua l water » ^ ^ ^

•**s.an dwate r deficit. Theexces swhi c ^ dependsupo n the

**a,ional efficient leachingo fth eso i •* ^ would like this efl eit beingmad e goodb yirrigation . ^ ^^ ^ been t0 be confirmed,t okno w whethera para l e ^_^ ^ ^^ developed,an dho wsalinit yi st ob econtr o ^^ ^ ^ ^^ ^ ^

Secondly,th esignificanc eo fth ecommen t• t e eam from the **•tha ntw ometre si nth eda mcalle d LaCorta , lin>ito fth epolder "i sno tclear .

307 3 Paper involving thereclamatio n ofpea t soils 3.1 Peatland polderso fNorth-Wes t Germany by R.Eggelsman n

Thispape r isbroadl y arestatemen t ofth econsiderabl e bodyo f knowledgegaine d inth edevelopmen t ofpea t lands inLowe r Saxony. l"e restatement of existing knowledge onth e shrinkage and oxidation of Ve isjustifie d and timely invie wo fth epotentia l developments insuc h soils inth etropic swher ethes eprocesse s are accelerated.

3.2 Drainage ofpea t soils inth epolde r ofPega-Oliva r Alicante,Spai n by I.G.Sanche z andJ .Martine z Beltrân

Thispape r isa goo d example ofth e extent towhic h sound hydrophysic survey (Figures 2,3 ,4 an d 5)combine d with a stepwise approacht o reclamation anddrainag eca n lead to sounddrainag emeasures . The soil inth e area ischaracterise d by acla y layer 0.5m deepunderla i by layerso fpea t (upt o 3.0m thickness) sand and clay. Trialswit" 1 subsurfacedrain shav e indicated apreferenc e fordrai ndepth su pt o 1.8m deep. Invie wo fth e first paper,i t seemstha t thepea t will shrinkan d oxidise and so some elaboration on thispossibilit y and itseffect s° theprojec t would berelevant . In 1976,a socio-economic surveywa sundertaken . This indicated tha* benefitswer evirtuall ydoubl e thecosts . Thereporte r would liket " evaluation tob e elaborated,particularl y bearing thefollowin g fact0 t0 inmind . Doesthi sevaluatio n includeal l thecost so r just some* : nd which group ofparticipant s inth epolde rdevelopmen t do thefigure 5 relate,th e farmers,th edevelopmen t authority, etc.? Also,t owha t extent havecos t evaluations and changes since 1976altere d this projection ?

308 3-3 Reclaiming Muturajawela, SriLank a by S.H.C, de Silva

T*is paper deals with thepossibilitie s forreclaimin g Muturajawel swamp temptingly close toColombo , thecapita l ofSr iLanka . This 2400 ha swamp runs parallel toth ecoas t for1 0K m immediately y ferth of Colombo. Theswam p consists ofaquati c vegetation overlyi ng substantial depths ofpea t (3-10 m) overlying sand. Theswamp s surface ^s below mean sealeve l whilst itsperimete r isringe d bycanal san d ro *ds. Up t0 the present dav, theshee r costs have prevented reclamation. Thepossibilitie s investigatedare : l) sand pumping torais e thelan d above mean sealeve l J replacement ofpea t by sand 3) impoldering andlowerin g ofth ewate r table îh0 t.. ,-,.t it«; cole usefo ragricultu n he high development cost mitigates against its soie anri , -0 mnt-t likely justificationfo r nd sourba n development seems tob eth emos t iitceiy j ** *eal developments. Itwoul d beo finteres t tokno w what usesth e *l»ed peat, obtained aspar t ofth esecon d proposal would have beenpu t t0 and whether a time scale forshrinkag e andoxidatio n hadbee n eluded in thethir d proposal. Also, itwoul d behelpfu l ifth e aUt Ws could elaborate onth estrengt h ofth eargument s infavou ro f ePing theswam p init spresen t form.

4 u- cinod Blain planning ona crossroads

Kafue Flats, Zambia :Floo d plain v by w.T. deGroo t andM . Marchand

Tin • m0r,tal study of developments 0,15 «Mutating paper concerns m environmental study r ">«> .Kafu e«ive ,floo d plain nearLusaka ,capita l ofZ„b. a I»th e "«»«I state, theplai n is s„.l,o,.y«««• - «" •"«' "" "* •"»««ly. The flooded area supportsa rar eAntelope ,th eL , ,.

abii- _, 0v«c ituniquel y ablet oexploi t Ulty tograz e inth efloode d landsmake s itum q tïiei» , ,wtiono fherbag e thatwoul d 6lr grazing potential whilst thereductio n otl^ «.i. inundated areas abundant her ' wiSe decay, enhances andsupport s theinundate d fishlif • „ traditional human society dependent ilfe. Theare a also supports a traditi Up °n catti • . A in„^ fishing andsmal l scale dryland cattle grazing thedrylands , ns"i»s

309 agriculture. In recent years, the Kafue River has been regulated by means of dams for hydro-power generation resulting in considerably reduced areas of annual flooding and an increase in the permanently inundated areas. Cattle now have access to grasslands throughout the year, whilst the areas suitable for Lek have been severly curtailed. Within Kafue Flats up to 70,000 ha of land could be impoldered and developed. However, the main contention of the paper is that it islT 1 the nature of polders to strengthen the arm of the central organising body, in this case the State, and at least in a developing country, weaken the existing pattern of life. This phenomenon is ambiguously described as the centre-periphery complex. The paper argues that polders should develop organically, that is to say, in small units based upon existing agricultural strengths as happened traditionally in the Netherlands and still occurs in the Wasn area of the U.K. The paper also points out that economic analysis can be targeted to produce answers ranging from the optimistic highly profitable to a pessimistic annual loss. It is in the nature of development to feel persuaded to the most optimistic forecasts although in the reporte? s view, realistic ends to the economic spectrum should be identified before final decisions are made. Furthermore, in viewing Kafue Flat5» one might question the value of traditional accounting to such a complex situation. How is the cost of the existing situation and social order to be deduced and can accounting allow for the reality that many large projects in developing countries fail to realise the e aspirations of Northern hemisphere planners? Perhaps the time has cofl to invest finance wisely though not necessarily economically in developments that will build strengths without disrupting the status quo; that will succeed albeit on a small scale where larger schems would fail.

The final three papers deal with impoldering as part of a trans-

310 Migration programme (Egypt), with apolde ro nlan d thati s differentially subsiding (Venezuela)an dlan d which issubsidin g rather lessbu tentail s impoldering adensel y populated urban area (Jakarta)

S-l Polder areaso fNorther n localitieso fth e Nile Delta, Egypt by M. ShDia b

This large polder lies right atth e Northern baseo fth e Nile Deltai n *n area ofpredominantl y heavy clay soilso flo whydrauli c conductivity. "T_ •„».!„ _0 6m below meanse a Th he elevation ofth elan d isa tapproximatel y u.b mD 1 i j.u i i K mbelo w ground level anevdel , the groundwateri sa tshallo w depth, 1-1.* » De « nd itan dth e overlying soil arehighl y saline. Though not stated, it

»°uld seem that these leveis areindicativ e ofinseepag e via the deep sandy aquifer. Theare a which isrequire d for resettlement ofpeople s •c L. irrigated anddrained . tr°m densely populated Southern areas ist oD e s TK ni ™Pn ditches some 25m aparta t The planned drainage relies onparalle l open ditcne 1m depth. . . T*e reporter would like further elaboration onth e P°ten*ia^T Claiming andcontrollin g salinity inthes e soils. Also w a an^entived s andplan s have been made toattrac t themigrant st osta y -A1 eworn environmentk what areevidentl . y difficult soils inwha tt othem , must

Polders andDyke so fth e Bolivar Coast, Venezuela byJ .Abi-Saa b Soto eta l

111Venezuel a oil extraction from beneath Lake Maracaibo ^ A rvr-norpssive subsidence, bounding lowlyin g polder areas hascause d progress

"Pto 4.5m i ncertai n areas. eXtraction zonesan d The subsidence decreases with distance from the ext "*tes severe cracking ofth e land atth e pointso f^ * Mature, i.e. theedge so fth earea so fsubsidence . £ c ci j ,•,,.„ inth eimpolderin g dyices -ny poses hazards o£ piping and fa " P ^ "hllst thesettlemen t causes problems foran y rig Pipen u •», „Hvk e In addition, the area lies within ^Pelines, passing through the dyke.

311 an earthquake zone sotha t theacceleration s and consequent stresses resulting from earthquakes posemajo r stabilityhazards . Thedyke s havebee nprogressivel y increased inheigh t asth e land level, thoughno t the lake,ha s subsided. The increasing deptho fwate ro n the lake sideo fth edyk e has sharpened therisk s ofwav eattac k whilst theorigina l useo frigi d concreterevetment s against wave attack hasbee ndiscontinue d infavou r offlexibl erip-ra p whichi s more able toadjus t todifferentia l settlements. Nowadays,pipeline s and jetties have topas s freelyove r thedyke s toavoi d settlement problemswithi nth edyke . An additional problem istha t thedrainag e within thepolde r continues tochang e as levelschang edifferentially - A finite element analysis hasbee ndevelope d to identify theprobabl e sequenceo f stresspattern s inth edyke s during adesig n earthquake. Consideration ofth e effect of thesecycli c stresses onundraine d samples ina triaxia l test apparatusha s suggested that thedyk ei s prone to liquefaction inth e sand layersa t theupstrea m anddownstrea m toeso f thedykes .

Further elaborationo f studiesunderwa y into the 'field significance of these findingswoul d beo f interest. Also,i twoul d beo f interest to find out howan d bywhom ,th ecost so f theremedia l works forth e polders aremet . Onepoin t ofdetai l requiring further explanation concerns thecommen t that the soil isunlikel y to crack, i.e. inth e dykes, ifth e capillary zone isles stha n 3m thick. Thereporte rwa s unsure whether thisreferre d toth edept ho f thewate r tablewithi nt " dykes ingeneral ,o r thedept h oftha tpar t of thedyk e above lake level.

5.3 The "Pluit"urba n polder byJ.H . Kop eta l

The finalpape rdeal s ina mos t comprehensive waywit h thedesig nan d operation ofth e "Pluit Urban Polder"i nJakarta , 2760h ao f lowlyi n2 land containing apopulatio n of 1.5 millionpeople . Theacut eprobl e posed by theare a include high rainfall,a largely impervioussurfa c area,th enee d to alsous eope n channels todispos e of foul water containing largequantitie s ofgarbag e anddebris .

312 Station isno wrefrehse d

Themai noutfal l drain leading toa p uP ^ ^ ^^ ^^ wMlst daily. Automatic screensa tth e sa ^ ^ ^ external diversion

stormsan d floods arehandle d bya co m ^ retentionreservoirs . canalsand ,within ,pump sassiste d by e maintenance andi t u-^+i rate doperatio n<*» "

Thesyste m dependsupo n sophistical r^^ ^ elaborate onth e

wouldb eo fgenera l interest forth eaut^ o ^^ ^^ meaSures. Also,

organisational framework established toi ^^ ^ stand_

itwoul d be of interest tokno wwha tprovisio n *>ypum po r generator capacity.

313 CONCLUSIONS BYTH ECHAIRME NO FTH E THEMES.

THEMEA :VARIOU SASPECT SO FA CERTAINARE AO RPROJECT .

General reportsby : Mr. D.S.Hesla m Ir.E .Allersm a Dr.D.W . Rycroft

Conclusions byProf.dr . I.Mihnea , chairman.

Thediscussion s during theworkin g sessions dealtmainl ywit hcon " struction,improvemen t andmanagemen t ofpolder s although some sociai' economic and environmental aspectswer e discussed too.Bot h the reclamation ofne warea san d the improvement of existing polders received attention. The conclusions canb e summarized asfollows : 1.Investment s formakin g newpolder s or the improvement ofexistin g polders canb emad e only if theeconomi c and social analysis justify suchprojects . 2.Polde r projectsmus t bebase d on local data coveringnatural , social,economi c and environmental aspectswhil e applying local standards. 3.Th edecisio n tomak e ane wpolde r or toimprov e anexistin gpol<* e should be takenb y the local government since this government knows exactly theneeds ,an d controls theinvestments . 4.Polder s require considerable investment which can onlyb erepai d by asubstantiv e leap inagricultura l production.Thi s invariably requires asophisticate d technological responsewhic hma yb ebey 0 thecapacitie s of thefarmer s concerned.Thi s constraint cant> ea majorobstacl e tosuccessfu lpolde rdevelopment . Consideration should be given inthes e circumstances toincreas i thefarmer s technological capabilities and cropyield s byothe r means before necessarily embarking onne wpolders .

TIA •Experiment s and pilotproject s arerecommende d ata nearl y stageo f thestud ywhe nmajo rdifficultie s and constraints inth e technical and/or social fields areexpected . 6- Special attention should be given toth emaintenanc e ofpolders .Thi s isa n important task for the localorganization s and the farmers.Th e farmers should be instructed accordingly. •Al l possible sources ofenergy ,includin gwind ,sunshine ,an d tidal energy canb e considered forus e inpolders .

315 THEME B 1: LAND AND WATER MANAGEMENT

SUB-THEME:WATE RMANAGEMEN T SYSTEMSAN DDESIG N CRITERIA M.J.Hal l SirWillia mHalcro w and Partners Shortlands,Londo nW 6 8BT,U.K .

Abstract

Thewate rmanagemen t ofpolde r areas isessentiall y amultidisciplin ar" activity, involving among others elementso f civil engineering, hydrology,agricultur e andeconomics . Systems analysisprovide sa convenient frameworkwithi n which toconside r alternative strategies forprovidin g drainage and irrigation systemstha t are optimal according toa specified design criterion. Such criteriama y be expressed in termso f thecost s and benefitso f the scheme,bu t invariably theeconomi c factorsar e implicit rather than explicit owing to theus e of objective functions such asth emaximisatio n of cropyield so r theminimisatio n of irrigation water supplies. The economic performance of the schememus t also beconsidere d atfar m level aswel l asprojec t level. As thepowe r of small micro-computer systems continues to increase,th eus e ofmanagemen t techniquesbase d upon systems analysis islikel y tobecom emor eprevalent .

1 Introduction

Inwha t isperhap s themos tgenera l definition of theterm ,a polde r may be considered asa well-delineate d arealuni t whose resources of land andwate rma yb emanage d independently ofothe r adjacentunits - The size and complexity of apolde rma yvar ywidely , from the simplicity of asmall ,bunde d ricepadd y toth e sophistication and

316 ,j o vptdespit e thisdiversity , areal extento fth e Ijsselmeerpolders . Yet P •ïoc ; Aswit hman y facetso f theirmanagemen t invoKes=o- „ prxncxpl ^ water resources analysis,polde rmanagemen tha sbe n «f theflexibilit y andpotentia l could take further advantageof , ^^ ^ majority Qf affordedb yth edigita l colter xnx e thepaper swhic h for,th e subjecto f and their «*thi strend ,wit hthei r relianceo n- ^ ^ ^ ^ emphasis,implicitl yo rexplicitly ,o n

optiont oa desig nproble m ^ physical nature of a ftnimportan t consequenceo tt w ^input san doutput sca n

Polderi sth e extentt owhic hth ehydrologie s ^ ^^^ degree of beeithe rmeasured ,controlle do restimat e „f landan dwate rmanagement , the accuracy. However,i nterm so tia i behaviour, v, T„ onepertinen t aspecto r hydrologyo fth epolde r isonl yo n y ^ ^ leveie (orstandin gwate r T he responseo fa give n cropt osoi l"""^^ ^ with regard toth e l «vels inth ecas eo flowlan d rice), P«txcu ^ ^ ^ ^^ deductionsi nyiel d thataccru e from ax ^ equally if notmor e

Requirementsa tdifferen t stageso fgr o , analysiso fcost san d be^Portan; ti neconomi c terms. Thes us e regQurce managementan d sebefit si sanothe r essential xngre exercise. iniinarynatur eo r rvest oemphasis e theinterdiscip i As eallocatio nproblems ,polde rmanagemen ti s withman y similar resourcea n ^^ ^ developed in tenablatien et oa system s analysisapproa c • polderwate r c- n• o *representatxo no r« v action 2,alon gwit ha generalise dJ ^framewor k withinwhic ht o "Sagement system. Thelatte rprovxde s ^^ ^ ^^ Reporti n teview theeleve npaper s that form general <5 jn section 4 wit" action 3. The Report concludes i» ^ ^_^ management of Nervations on the role of computers in t ew Pol^er areas

2 *cht opolde rwate rmanagemen t Systemsapproac ht oP

. a seto fcomponent stha tcollectivel y

t*it sbroades t sense,a syste m xs ^^ ^ ^ .„ its

tan sform aninpu t into anoutput . ,ssume awid e varietyo f COl^exity, and both inputs and outputsma y

317 forms,dependin g upon theproble m under study. Inpractica lterms , thecomponent so f the system and their inter-relationships are described bya serieso fmathematica l and logical statementswhic har e readily translated intoa computer-compatibl e form. The analysiso f a system isgenerall y carried out either by simulation oroptimisation . The former approach isparticularl y relevantwher e ahig h levelo f detail on system behaviour isrequired . A simulationmode l provides the time serieso foutput sproduce d byth e system operating on agive n serieso f inputs according toa predetermine d strategy. Thisapproac h tends toplac e largedemand so n computer core storage,an d the locati°n of anoptimu m operating policy hast ob eundertake n on atrial-and* - error basis,whic h canprov e both expensive and time-consuming and carriesn oguarante eo f absolute success. Incontrast ,optimisatio n ishighl y appropriate fordeterminin g astrateg y that isth e"best " according to some specified criterion. This approachma y alsob e demanding on core storage,bu t lesss otha n simulation. Inaddition , caremus tb e taken indefinin g the system inorde rt oensur e thatth e problem isamenabl e totreatmen t by astandar d solutionprocedure . For example,wher e all relationships describing the system arelinear » the techniqueo f linearprogrammin g may beemployed . A schematic representation ofa polde r watermanagemen t system is presented inFigur e 1. Thecor eo f the systemma y be seen toconsis t of twomathematica l models,on eo fwhic hdescribe s thehydrologica l* " hydraulic component and theothe r theeconomi c component. In its simplest form,th ehydrologica l modelma y consisto f a single equati°n which accounts foral l inputsan doutput sdurin g successive time increments. Thiswate r balancema yb edescribe d incompatibl eunit s J anequatio no f the form:

H (n+1)= H(n ) + (RF+IRR)- (ET+INF+DR) ( where H (n)= soilmoistur e (orwater ) levela t theen d ofth ent h ti®e increment RF =precipitatio n IRR =amoun to f irrigation ET = evaporation

318 MODEL AVAILABLE CLIMATIC START WATER INPUTS PARAM. SUPPLIES X DRAINAGE IRRIGATION H SYSTEM HYDROLOGICAL MODEL SYSTEM DESIGN DESIGN

SOIL MOIST./ GW LEVEL/ SURFACE ROj WAT.LEVE L

INFRASTR. SYSTEM SYSTEM CROP DAMAGE COSTS COSTS YIELDS X ECONOMIC MODEL

c END

DRAINAGE IRRIGATION

water management system n9ure 1. schematic representation of a polder

INF seepage loss DR = amounto fdrainag e

Of v«,derive d from climatological these: variables variables,,R R FFan an ddE E TT»a ma yy b e ^ ^ ^^ eitfte^ r °bs«ovations , butIR Ran dD Rar edesig n « périment, be Choseno nth ebasi so fexperienc eo rdete r

scriE,eth ewate r Balanceo fa J**aWh,r ^s equatioequation (1(1)mama ybb eadequatadequat e t o^ ^ ^^^ ^ ^^^^ ^ ^ ^^^ ^ ^ re ciWiselE y delineated cropped area,suc ha sa ^ ^ example,

--ou^uslsly inadequatinadequate tt oodea dea ll^Z\::tlZ wit» ^ e systesystemm gervinservin gg

°*tart odescrib eth ebehaviou ro f ^ ^ saturatedan d er IVe'^aall suc suchh lan landd parcels parcels,,accoun accoun tt musmus .t e ^^^ ^^^ ^^ ^^ ^^ ^ ^^ un ^^turated groundwater flowa swel l «j^ layered conceptual er ieso fth echanne l network, A .f representationo f c atoK -^a moreappropriat ere p ucnmentmode l would thenprovid ea thig system component, .. , _ ter levels corres* öavi„ . „f soilmoistur eo ro r wa ln9 produceda tim e serieso fso n 319 ponding to agive ndrainag emodulu so r configurationo fdrainag e system,thes edat a become the inputs toth e economicmode l formingth e secondmajo r system component. Themoistur e statusthroughou t the growing season isa principa l determinant of cropyield . Similarly» * supplementary information isavailabl eo ngroundwate r and surfacewate r levels,estimate sca nals ob emad e ofan y infrastructure damage resulting from periodso f excessive flows. These benefits and costs may becombine d with the installation andmaintenanc e costso fth e drainage system and (ifprovided ) the irrigation system,an ddiscounte d toa commo n economicbasis . Theadequac yo fth eoutcom eo fthes ecomputation s isdependen tupo nt n formo f thecriterio n ofoptimality ,o robjectiv e function,unde r whicn the study isbein gperformed . Thepossibl e formso fobjectiv e functi0 areman y andvarious ,bu tth emos t commonly applied would appear tot> e minimum annual costso rmaximu m difference between benefits andcosts - Frequently,thes ecriteri a are implicit rather thanexplicit . The designvariable sma y becontinuall y updated until theobjectiv efunc t issatisfied . Havingme t thecriterio n ofoptimality ,a further ,bu tequall y • it y important,phas eo f thecomputatio n isentere d inwhic h the sensitiv1 of theoutcom e to thebasi c assumptions anddesig n variables canb e tested. In itssimples t form, such sensitivity testsma y consisto f repeated application of the systemsmode l with individual design variables sett odifferen tvalue s withal lothe r variableshel d constant. Sucha n exercise mayofte n provide insight intoth eleve l detail towhic h each system componentneed s tob e represented. F°r example,th erelativ e importance of the individual terms in equati°n (1)i nrelatio n toth emagnitud e of the cropyiel d may beevaluate d 1 thismanner . Bydrawin g attention to such issues,th e systems appr° isabl e to isolate those aspectso f aproble m where additional . .-teil information willyiel d themaximu m dividend. Inparticular ,cro p wa yield relationships,whic h form an important linkage between the hydrological and economic components of the system model,woul d apPe tob ea fruitfu l area for further investigation.

320 3 Reviewo fpaper s

, -4-v,* ranaeo fdivers eproblems , The groupo fpaper s underrevie wdea l« h J ^ ^ butal l are concerned withsom easpec t J ^ watermanagemen t systems. Thecontribution sma yb Y ,• v ,=^rP<5se sproblem so fric e W t„ ,„ups, the fir«to £->»=> >*» • f ^ syatims.

~tl,.tl„ .»d the -co- the" /rlco paaay a„lnM, . the »«e of the authors ««at theprobl. » ^^ ^ ^.^ ^

l M ^ « <* — "°"*". " :;tHl so^tion Ptooe*«, «— - "ahmenrel yo n acomputer-aide d re surface storage v,,- nwhic hth echang ex » opted for astatistica l approachi n ^ ^ ^ ^

trivalent to acombine d ter»HU * >"^ ^^ analyses for ^dependentvariabl e ina serie so comparatively ,„ roundwaterflow . i" groundwatertabl e elevation anag * „•„„- Darticularlyi n forthes eequations ,F " p °orexplaine d variancesobtaine d elevation interm so f c °mparisonwit hthos e forgroundwate r ta e ^ QI closing of Ia 9ged rainfalls andnumber so fday s sine ^ whether a more the irrigation system,raise sth equesti o ^ ^^ movementi n

Physiically-base dapproach ,takin g m ^reliabl emodel . the upper soil horizons,woul dn o

of riCe in Suriname is based upon a AcWordin g to Buijs, the cultivation o ^^ little account of Strict water management schedule that a ^ ^^ drainage reSU lowing season rainfall and therefore ^ ^^ wifch fche diScharges

r6 quirement. The return flows are a reused, subject to In the rivers to which they drain, but c „r cling.. assists in Cer tain water quality considerations. ^^ _^ bringing the m ^imi3ing the use of the available water suPP lar 9est possible area into cultivation. ^^ problem of determin- The Paper by Dahmen, in treating the more ge in crop yieids, ln 9 the drainage modulus which minimis ^ economic considerations, ts tanc stable for its emphasis on the imp°* ^^ levels. The th at the farm level as well as P identifiable in the PrD>-~o - - „uno• pBs iiss readiJ-reaaiJ-y ---- >cedure which the author outline ^ timely warning is 9ergetlvera l framework of Figure 1- ma1 ^ ^ available

S Ut relia ° >âed on the need to assess the ^taking any analysis. ci lmatological information prior to un —«"-oiogical intormatiw» r--

321 Riceproductio n isals oth etopi c discussed byWiersing aan d Sudibjo, whodescrib e the reclamation of atida l swamp area in Indonesia forth e cultivationo f rainfed crops. Thisprojec t gave rise toa serie so f design objectives,includin g thedrainag e ofexces swate r and noxious compounds;th emaintenanc e of adequatewate r and soilmoistur e levels inth ecroplands ;protectio n against saline flooding;an d theprovisio n of access and effective transportation within thedevelope darea . Thoseauthor sdescrib e the structuralmeasure s thatwer edevise d to meet theseobjective s andoutlin e themanagemen t practices thatar et o be followed within thedevelope d area. The latter areheavil yrelian t on theoperatio n of structureswit h flapgate s and stoplogs,whic har e notoriously subject tohuma nerror . The second groupo fpapers ,whic hdea lwit hvariou s aspectso fpolde r drainage, isnotabl e forth ewid e spectrum ofdesig nproblem stha ti s discussed. In somecases ,th edesig n criteria arelargel yqualitative - For example,Hebbin kprovide s adetaile d discussion of thedifferen t typeso f subsurfacedrainag e systemstha thav ebee n installed inth e Flevoland polders,an d elaborateso nthei r advantages anddisadvantages - Currentadvic eo npreferre d systemswoul d appear toplac e greater emphasiso n avoidance ofdisruptio n thano nminimisin g installation and maintenancecosts . Amor equantitativ e approach topolde rdrainag e design isprovide d bv Dorai. Again,th ecro p isrice ,an dth edesig n criterion forth e drainage system isth eminimisatio n ofperiod so f inundation. This objective isachieve d byvaryin g thedimension so f themai noutfal l sluice, subject todownstrea m tidalvariations . Inminimisin g the durationo f submergenceo f theric eplants, th eeconomi c component of the systemsmode l (Figure 1)i simplici t rather thanexplicit .

A similar implicitcriterio n iseviden t inth ewor k ofKurod a andCh

322 ^ automatic optimisation procedure isals o used bySchult zt o determine thevalue s of five design variables that together characterise a polder drainage system. This contribution provides a clear example ofth eapplicatio n ofth esystem s approach. The hydrological andeconomi c components arecomprehensivel y described,an d the objective function, which involves theminimisatio n ofannua l costs is explicit. Furthermore, theautho r presents inhi sFigur e 4th e results ofa sensitivity analysis which reveals theimportanc eo f aiding theunderestimatio n ofsubsurfac e drain depth andwate r level.

E*ch ofth eabove-mentione d contributions relates topolde r areas h*ving a single agricultural land use. Thereminde r provided byva nd e Ve" andVe no fth econtrast s instor m runoff response that exist

between rural and urban areas is therefore apposite. Theeffect so f the enhanced peak discharges from theurba n areas aremitigate d by the active useo fth eassociate d urban canal systems as detention s<-~ ,. „,-^n= nf thelatter , includingth e st°rages. Determination ofth edimensxon s ottn e ^•t width ofth eoutfal l weir andth esurfac e area ofth ecanal , also institutes anoptimisatio n problem inwhic h theobjectiv e function Solves thelimitatio n ofth emagnitud e ofth efloo d lift to that a eclated with a specified frequency ofoccurrence . B * virtue of their physical characteristics,polde rarea sar e W=> • „ „Anarent toa coastline . Inthes e Variably located inlow-lyin garea sadjacen tt o 0i ^umstanceS/ the wind fetch fromcertai npoint so fth ecompas sma yb e C0 *siderable. The elongated openwate rbodie stha tcompris e thepolde r linage systemma y thereforeb e subjected towin d set-up. This P ^lem iB treated cornprehenSively byBouwkneg t andKroon . Whereasth e ^tter- „ -u „Hnnal hydraulic model based uponth e Ler authors employa computationa liiy " S^t venant equations,Tanak aan dShikash otrea tth eproble m offore ­

sting the depth of unsteady open channel flow bya n approximate ^thod involving theextende d Kalman filter.

Concluding remarks s *veral „ . A in section 3abov e have described e*al ofth epaper s reviewed in Seen" a , „ater management problem. naal f a ' yt1Cal approaches toth esolutio n or a

323 Thesecontribution s havedemonstrate d avariet y oftechniques ,rangin g from sequential solutions toth ewate r balance equation to automatic optimisation techniques and numerical solutions toth e SaintVenan t equations. Whilemuc h canb e accomplished with hand-heldprogrammabl e calculators,a saptl y illustrated byDahmen ,th edemand so ncor e storagemad eb y themor e sophisticated modelling procedures inevitably involve theus eo fa large r computer. Unfortunately,acces s toth e largermin ian dmainfram e computers isfa rmor e restricted inth e developing countries than inth edevelope d partso fth eworld . in these circumstances,mor e consideration should perhapsb egive nt oth e transferability oftechniques . The authorsma y care toreflec to n how dependent their approacheswer eo n the availability of aparticula r typean d sizeo fcomputer . Interm so f anappropriat e level ofcomputin g atwhic h todisseminat e analytical techniques toadvantage ,th edifferen t typeso fmicro ­ computer thathav ebecom e availablewithi n the last 3-5 yearswoul d appear tohav emuc h tooffer . Manymake s areno w capable ofhandlin g mathematical programming problemswit h 40-50variable s and asman y constraints (seeAnnesle y et al, 1982), and several ofth eproblem s considered in thepaper sunde r discussion would fallwithi n their scope. As their capital costcontinue s todecreas e asthei r sizei n termso f random accessmemor y increases,micro-computer s would appear toprovid e ahighl yversatil e tool for futurewate rmanagers .

Reference

Annesley,T.J. , M.J. Hall andN.A .Hil l 1982.A maste r water resources and agricultural development plan for theStat eo f Qata 2. The systemsmode l and itsapplication .Wate r Supply and Management,i nth epress .

Papersreviewe d

Bouwknegt,J. , andL.J.M .Kroon .Win d influenceso nth e watermovemen t inope n channelnetworks .

324 UlJs, J. Irrigation requiremento frice ,retur n flowsan d theireffec t on the irrigation capacityo fa river , ahmen,E .Drainag e and irrigation requirements: an integrated approach. °rai, M. Design considerations forth edrainag eo fpad ipolders . arzon,R.s .Th e influence ofshallo wgroundwate ro nth edrainag e Problem of theKabaca nRive r irrigationschem e ebbink,A.J . Drainage ofurba narea s inth eFlevopolders . Kllroda,M. ,an dT .Cho .Wate rmanagemen tan doperatio no f irrigation system inlo wlyin gdelt aare awit hcreeks . chultz,E .A mode l todetermin e optimal sizesfo rth edrainag e system ina polder . Tanaka, K., an d S.Shikasho .Applicatio n ofth eextende d Kalman filter for forecasting thechanne lflow . en' F.H.M.va n de,an dG.A . Ven.A compariso n betweenth e runoff from arura l and anurba nbasi n inFlevoland . le rsinga,R . Th.,an d S.Sudibjo .Lan d andwate rmanagemen t intida l swamp landdévelopper ,t project s inIndonesia .

325 SUB-THEME: WATER MANAGEMENT SYSTEMS AND DESIGN CRITERIA (CONTINUED) J.J.A. Feyen Laboratory of Soil and Water Engineering Catholic University of Leuven,

Abstract

The paper summarizes 11 submitted articles dealing with traditional a new approaches in the design and watermanagement procedures of polder and pumped catchments. The review goes from the classical agrohydrol0» cal experiments, resulting into drainage criteria and watermanagement •tie s concepts, through the definition of design levels and pumping capaci based on the statistical processing of hydrological data collected °v a long period of years. Both approaches assume in their design steady flow conditions. Often the criteria as the design procedure are modi* to engineer's experience and/or to the failure of existing systems. According to the increasing need of reducing the investment and ope*"a tion costs of water control works for the agricultural improvement ° low-lying parts of river basins in deltaic andcoasta lareas , new tec niques have been introduced for the refinement of design and manage"1 tfte To those belongs the technique of modelling which allows to simulate water level in existing or designed arterial drain networks of pump catchments in function of a rain event with given characteristics. powerful approach, based on the modelling of the unsteady flow cond age' tions in polders permits to examine alternative design concepts, ma ment and maintenace schedules in terms of level control, quality c0 of the boezem waters and cost estimates. According to some of the viewed papers, the general application of simulation models offer c

326 *,+• thPdesig nan dmaintenanc e policies derable scopefo rth erefinemen to fth eae&i r.r g i„ vofiprtine intoa noptimizatio no f ofpumpe dan dfre e drainage networks,reflectin g the economic accountingo fth eengineerin gwork sneeded .

1 Considerationso fexistin g designprocedure s for in-field drainage systems

• Altaic andcoasta l areasar econti - Low-lying partso frive rbasins ,m «iw , *4- „waterloggin g conditions,eithe rb y nuouslyo rfrequentl y subjected towateriogg i* u 4-v. ^charge of water fromth esurroundin g Lepage, floodingo rthroug hth edischarg e ,.... 4.«* >*-hi< 5areas .I nadditio on n «Plands, limiting agricultural developmento fthi s , .„th p seepage orfloo d water is brackish salinized soils mayb eforme d if theseepa g , „ i j „-t-^table mayals onPfb enecessaril P sari v y in composition. Lowering ofth egroundwatertabl e y , + rontrol thesal t balance ofth e lr» irrigated agriculture inorde r tocontr n o rOot7ono * .„ work s thebenefit so fth eengmee - Asgenerall y accepted inengineerin g *«** ^ ^ ^ ^ ^^ y masures shouldb ebalance d again ^^ ^ *«Tk8. Drainage andwate r control (dik s ^ ^ ^ ^ ^ -asures require rather high investmen c ^ ^ ^^ ^ ^ tlvely exact estimate canb emade . Howe ^ lainage works areno ttha t clear. nticipated from flood control and ^ inundations, salinity, ** adverse effect ofpoo r drainage, *may hampe^ ^ rsoi fll_ul -.,o ncro pgrowt hi s^ :^ 2^ ~ ^ ofth ecro p stress. Additionally, detoriation of the structu-' iage, transport ofmachines , leading to ^ conditions ofth esoil . on waterlogging. Increa- **ther fewdat a areavailabl e ofcro p r-po^ ^ ^^ ^ ^.^ Si "g efforts have been made recently to expr^ ^^ ^ ^ ^^ ^ lr > increased land workability. From ^^ ievels for salinity. C ^teria have been forwarded ofcro p o ^ ^ ^ experimen_

*** thepaper s torevie w onepape r of rice.Th e expe_ ^ termination of tne salinity-yiel re^ ^ ^ ^ ^ l «*nt. were runi nth ecoasta l area o when in an unri_ toa^i,, ,.4-j-ionercolatio n C=H>- ri ne origin, with very little pe ^ only adchieved through P **<* state. Leaching onthes e soils seems peak y.elds ln ten8ive drainage together with sprinkling

327 occured atsalinit y levels around 0.4 mmho (EC-valueswer emeasure d on 1:5 soilwate r extracts,an d converted tostandar d EC-values), arela ­ tively decrease inric eyiel d occured over theE Crang e0. 4 -1.15mmhoS > and atEC-value smor e than 1.15 mmhos,ric eyiel d fell sharply.Accor ­ ding to the author thesalinity-yiel d relationship isinfluence db y other factors astyp e oflan d preparation andpH-leve l ofth e soil. Until recently most ofth efiel d drainage experiments wereru n toesta ­ blish field drainage criteria.A classical example ofsuc h astud y is givenb y VIEIRA etal .Th e agrohydrological experiments were run onsom e experimental plots situated inLeziri a Grande,a n island of1307 4h ai " the lower TejoValley ,2 5k m upstream from Lisbon.Th e soilso fth e area aremostl y heavy,salin e and alkali.Base d on theresult s ofa de ­ tailed investigation of thepotentia l drainage area three experimental plotswer e installed in theSouther n parto f theLeziri a Grande.Th e plots differing incomposition ,permeabilit y andgroundwate r regimewe r surface drained with 60c m deep ditches installed every 20m ;subsurf aC drained with corrugated PVCpipes ,5 c m indiameter , installed ata n average depth of1.2 0 ma ta varyin g drain spacing of10 ,1 5an d 20m . Inadditio n halfo f theplot sreceive d agypsu m treatment inquant:tie 5 varying from 10t o4 0 tonpe rh a depending from theESP-value .Gypsu m was applied toverif y itseffec t on thealkal i condition,an d indirectly on the internal drainage capacity of the soil.Fro m rainfall,drai n dis' charge,EC-value s ofdrainag ewate r andwatertabl e level measurements following drainage criteria and design recommendations for theagricul ' turalexploitatio n ofth eare awer e derived by theauthors :

- Subsurface drainage controls thewatertabl e better thansurfac edra* ' nage. Narrow drain spacings aremor e effective andgypsu m applica' tions favouriseswatertabl e control by improving soil structure through sodium replacement by calcium. - The leaching ofsalt s insurfac e drained plotswa s remarkable infe~• rior to tile drained plots.Sal t leaching seemsno t tob e influence by drain spacing and ascoul d be expected gypsum effectspositivel y ondesalinization . - Adrai nspacin g of2 0m an d drain depth of 1.20 m isrecommende d f°r themarin e soilso fLeziri a Grande.Th eheav y andpoorl y drainedf vial soilsneed sa drai n spacing of3 0m .Fo r the fluvial soilsw i hile intermediate conditions adrai n spacing of6 0m isrecommended ,w '

328 •i« with high elevation dono tnee d drainage, the sandy andloam y soils with nign ma^nf, qolla • j o^0 9 Sl. s .ha for themarin e soils - Thedrai n discharges derived are d.s i o n l «T1 ha" for themarin e soils withsu b with surface drainage,

surface drainage. . th rp^iria ~A oalinitv problems m tne wiiiiä Kor theimprovemen t ofth edrainag e an^sal ^ ^^ ^ ^

Grande future drainage works shou ^ ^ ^^ irrigation Pipes (which does noto rsligh t y ^^ ^ ^ ^^ ^^

network), concrete collectors an P^ ^ installed at an average depth by pumping stations. Drain pipes shou ^ ^^ ^ ^^ ^ ^ ^ of 1.20m , while thewate r level m open ^ complemented m below ground level.Th efiel d drainage^ystem

by land levelling andb ygypsu m applica i • Jarikaba (Suriname) • oi pxoerimentwa siu " An analogous agrohydrological exp ^^ drainage criteria forbanan a from 1966t o197 2i norde r toderiv e research asre - i 'n Theconclusions ,u * Plantationsi nth e coastal plain. „„elation between rooting •a positiv e coiicia Ported bySO EAGNIE' s paper are. v ^ decrease with agewit h

and drainage depth; agreate r effect in ^ optifnum lifetime ofth e incr6 ^creasing drainage depth,an da n ^ ^ optimal field lay-outfo r -1 Plantation with increasing drainage • „ Q m.day isa „h-nitv between l.b anu heavy clay soils with apermeaD m y „roundwatertable • mpter wide depths, »'" c ambered bedsyste m with six meu -nationwit h adischarg e capa­

bel at8 0t o9 0c mbelo w surface in^^^ ^ on the agrohydrologi- 1 1 °ity of2. 3 l.s" .ha' . Farm management ^ ^^ ^ ^^ low_permea- cal plots revealed thatn osoi l ti ag machineryi s K- ,-iavev,marin e soils. bl lity, low-stability, young ciay y, unreversible compactation n°t permitted forth esam e reason o ri ^^ empoldering, Tearing "trieJ- <-"-,~ a r "d physical degradation even for ^^ ^ ^ for the transport for themaintenanc e ofth edrainag e system,

Df fruits atharvest . discharge criteria,th e Having defined fora give n region predicting drain ae sign watertable level,a variet y ctivity andgeometr y ofth e

facings, based onth esoi l hydraulic ^.^ spacing •ri H Themos twioeij r u°w domain have been developed. eauilibrium between . tvDe assuming equo. Nations areo fth estead y state ^ circumstances, ^ -foil However, even drain discharge anddesig n ramfaii. rainfall, which Wh^e drains areinstalle d primarly 329 often israrel y uniform long enough toestablis h astead y state,drai ­ nage design ismostl y based on theus eo fth estead y stateequations . Thealternativ e useo ftransien t equations hasbee n exploredb y ARMSTRONG.Bu tstil l theunstead y approach hasno tye tbee n developedt o a procedure that canb e used routinely.Th e limited application of transient equations isdu e toth ecost so fth e investigatory workneede d for scientific drainage design,th espatia l variation insoi l properties and cropping practices.Becaus e of this,ARMSTRON G and others developed a rational drainage designprocedur e suited for the drainage ofth e English fenlands.Thei r approach isbase d ona desig nrainfal l rate (taking into consideration climate,croppin g and drainage type), on soü profile examination and experience.Accordin g tothe m theexperienc e of advisors and contractors isno t tob e despised. Insom e casesth edogma " tic insistence ofclos e spacings couldb ewippe d outthroug h the appÜ" cation of therationa l drainage design concept.Fo r afiel d varying in soil composition they advice tomak e thedesig n for thedominan t soil type,an d tomodif y iti nrelatio n toan y included soil variation.A s forexampl e adominantl y peat soilwoul d normally be drained at fairly wide spacings (inexces s of2 0 m), whichma yb e decreased tosa y 15o r 10m inth epresenc e ofcla ylayers . The drainage design of thepea t soils,a spresen t inth e fenlandso f Eastern-England, should take into consideration specific problems asth e lowering of thesurfac e by shrinkage and oxidation ofth eorgani cmatte r when drained.A sa consequenc e the drains tendst obecom e shalloweran d risk to loose theirgrading . Ifth eoutfal l cannotb edeepene d the soüs have tob eredraine d periodically atsuccessivel y greater depths,th e pumping requirements tob e increased and ifafte r some time theunder ­ laying clay willbecom e exposed thedrainag e characteristics have tob e adapted. Beside peatwastag e blocking of field drains by irondeposit s andsil.t a' tion can cause total failure ofdrainag e schemes.I nth eU.K . siltati°n ofdrainag epipe s seems according toARMSTRON G not ofnationa l signifi~ cance and canb e circumvented by theus eo fpip e filters,whil e iron deposition seemst ob e acommo n fact inpea t soils.Onc e itoccurs , remedialwork s areparicularl y difficult,an d theonl y solutionaccor ­ ding toARMSTRONG' S paper seems tob ea programm e ofrepeate d drainage until the store of iron isexhausted . Inaddition ,th eus e ofdrai n

330 lines tosuppl y water-c oth eplan t inth esumme rmonth sha srecentl y been investigated. Technically itseem st ob epossibl e tomaintai n the watertable inth efenland sa ta specifie d levelb yreverse ddrainage , but tob e effective foragricultur e thelan d should belevelled ,whic h isno tonl y expensive,bu tma yals oexpos eunripene d subsoilmaterial . Mosto fth eproblem s encountered indrainin g thefenlands ,howeve rhav e n°tye t resulted intoa fir mse to frecommende d procedures.A s forothe r areas, it israthe r impossible tobas eth edesig n toa larg eexten tupo n equations,eithe r ofstead y ornon-stead y state.Loca lknowledg ean d skill, suggestsARMSTRONG ,wil lalway sb eessentia l fora prope r dealing °fth eparticula r seto fproblem s encountered locally. Due toth e traditional approacho fpoldering ,renderin g optimalcondi ­ tionsfo rhabitatio n and agriculture,polde rdevelopmen t oftenresult s intohig h technicalrequirements ;hig h investment costs,hig horganiza ­ tionalrequirements ,lo wrat eo fimplementation ,socia lan denvironmen ­ talrepercussions ,incompatibl ewit hloca leconomic ,socia l andenviron ­ mental conditions ofth edevelopin g countries.HORS T inhi scontributio n advocates strongly thatothe rdevelopmen tconcept sgeneratin g agreate r Participation ofpeasants ,resultin g intoa lowe r investment costpe r ha, corresponding betterwit h thetraditiona l farming systems,causin g iessdisturbanc e toth eecologica l equilibrium should beexplored .Som e Possible alternatives thatar eworthwil e tob econsidere d are improved lainage only, improved drainageplu ssubmersibl e dikes,complet e diking withoutpumpin g and/orwit h lowpumpin g capacity,th epractic e ofhors e shoe dikes,th eintroductio n offloatin gric eo rdee pwate rric e inth e flood period, etc.Th eeffec to fthos ealternative so nth epossibl e length of thegrowin g season isbee nillustrate dgraphicall y byHORS T in hispaper .I ti ssel feviden ttha tth eapplicabilit y ofthos ealter ­ ative formso fwate r controlwil l depend onlan d use,o n theloca l topographical and hydrologicalsituation .

2 Design considerations ofpumpin gplant s

Traditionally iti saccepte d that6 t o1 3mm.day -1 should bedischarge d fr°m polders.Fo r the Usellakepoldersa genera laccepte d startingpoin t for theestimatio n ofth epumpin g capacitywa s thedeman d that4 0m mo f

331 rainfall during fiveconsecutiv e dayswithi n the sameperio d shouldb e discharged. Ifth e land isuse d for theproductio n ofhig h valued crops discharge rates aretake n insom e caseseve n equal to1 8mm.da y (BERAN). Itwoul d bepreferabl e ifth e design ofpumpin g stations could bebase d on therunof fbehaviou r ofpolder so rpumpe d catchments similar insize f composition and land use.Slightl y thecollectio n ofhydrologica l data becomes amatte r ofroutine . Inhi spape rDIJKSTR A isanalysin g the yearly totalrunof fvolume s ofth eWieringermee r and northeast-polder, collected during alarg enumbe r ofyears .Th epum p capacities ofth e different polder sections analysed ranges from 8.4 to1 7mm.da y .Th e meanpumpin g capacity ofth e IJsellakepolders isclos et o1 2mm.da y From themea n value of the totalrunof f during ayea r itcoul d becon - -1 eluded that the entire installed capacity ofapproximatel y 12mm.da y isoperatin g appears tob e 1440hour s during ayear .Fro m theanalysi s of long time series ofrecorde d water levels itcoul d beverifie d ifth e pumping capacity of1 2mm.da y be on average sufficient tomaintai nth e water level inth editche swithi n permissible limits.Accordin g to DIJKSTRA following conclusions could be drawn from the frequency of occurence ofextrem ewate r levels:th edesig n assumption of thepumpin g station iso r isno t inaccordanc e with thestatistica l distributiono f thewate r rise;th eeffec t of increase inpumpin g capacity on the dimi­ nish ofextrem e levels canb e estimated,a swel l as theeffec t ofin ­ crease ofope nwate r storage on theretur nperio d ofcertai nlevels . While DIJKSTRA'S study was devoted to large polder areas,BERA N tried t0 formulate flood frequency curves forsmalle r areas,10 0t o 15000h a large,situate d inth e fenlandso fth eU.K . His findings arebase d on theprocessin g ofdail y discharge data collected on 15pumpe d areas f°r atminimu m 5years .Fro m the flood frequency curves,i.e . therelation ­ shipbetwee n acertai n magnitude ofrunof fan d itsretur nperiod ,th e degree ofutilizatio n of the installed pumping capacities could bederi ­ ved.A s aresul t a1 0m m pump capacity seems tohav e a2 0yea r return period protection inth eEas tAnglia n fensbu tn omor e thana 5 yea r returnperio d protection elsewhere.Th e current design standard ofl 2-5 mm,a s imposed bypum p technology,wil l provide evena 3 0yea rprotec ­ tiona t theEas tAnglia nstations . Oneo fth epumpe d areashav ebee n studied more intensively byBERA N in

332 „+- octor mrainfall .Therefor e order toestablis h thecatchman trespons e tostor m •4-., ^statu shav ebee nrecorde d si- water levels,rainfal l andsoi lmoistur estatu s notable featureo fthi s multaneously atsevera l locations.Th emos Thtsn moso t 11„oint si nth ecatchmen ta lon gth e researchwa s the tendency foral lpoint si n t-A^r,tha tth elag-tim e ofth e arterial drain tomarc h together suggesting that g ,. A ,-i-t-hth elag-tim eo fth ebasi na sa field drainrespons e mayb eequate dwit hth ela g onfall eventss ofa rstudie d range whole.Th erunof fcoefficient s fromrainfal l • tinn, seem tob erelate d toth esoi ltyp eo f from 5t o4 0% and thevariation s seem ,<.a+,m Thp = andth estor m precipitation.Th e the catchment,th ecatchman twetness ,a n idpntifv „hshoul db econtinue d toidentit y author suggests further thatresearc hshoul d officient.Confirmator y studiesar e the factors controlling therunof fcoei i inrludinathe offloo d frequency relationships,includin g the alsoneede d on theslop eo ffloo d ^ ^ ^ ^^ _ aspecto fseasona l dependency.Thos e Precisely pumpsize .

Modelling asa desig nan dmanagemen tai d

., ..bein guse dar ebase do nth eresul t Up tono wmos t ofth edesig ne n er ^ ^^ __ ln ofagrohydrologica l studieso fp o ^^ ^ engineer's experiencean d addition these criteriawer emodifi e ^^ hydrologicalstu - adapted toth e failure ofexistin g ^^^ of existing level and dieshav e tried througha statistic a ^^ ^^ differentextrem e freqUe Pumping data toestablis h the "^erent periods oftim ehav ebee n levelsan d volumes ofpumpin gwithi n i ^ for pumped catch_ experienced. However,th eexis t ë extreme arbitrary fre- mentswit h itsassumption s ols x inadequate forrefine d . .level sseem sTO U ^ quency ofexceedanc e ofwaxe i étudieshav ebee naime da t .l-i-^nmDlementar ys economic design.A s aresul tcom p ^ ^^ deterministically. modelling thewhol eo fa pumpe d drainage^^ ^ ^ ^^ ^ drainage T hehydrodynami c modelapproac hperm i ^ erforms duringa nunstead y l 0 network togetherwit h itspumpin g sta ^^ permits tosimulat eth e event occuringwit ha give n frequency. arterial drainsan d effecto fsmal l changes toth ebas i frequency andduratio no f 6 °fchange s inth emaintenanc e s^ ^^ fine tuning, donewit hde ­ baterleve l exceedance inth en e nificantlysaving s incon - n toreduc esig" 11 terministic models has proven ^ drainagenetworks . struction,operatio n andmaintenanc eco ss

333 Of the papers in the subtheme B 1.2, I had torevie w 4 papers that were. dealing with the development of model concepts for the computation of total water demands for level control and control of chloride concentra­ tion, for the hydrodynamic simulation of flows and salt distribution in boezem systems in pumped catchment areas and in tide-driven drainage networks. In most of these papers various design alternatives were com­ pared in terms of specific impacts on water and salinity level, flow conditions in the canals, pumping performance, costs of construction, operation and maintenace.

VAN BOHEEMEN describes in his contribution a numerical model to calcu­ late the water supply needed for level control during the growing sea­ son, April 1 to October 1. The water requirements are calculated per timestep of 10 days and per bloc of 25 ha. To each of the distinguished blocs, in which the polder districts have been subdivided a representa­ tive land use, soil type, and various hydrological characteristics have been given. For each timestep data have been collected on precipitation« global radiation, and potential évapotranspiration. Then the water re­ quirement of each bloc of 25 ha is calculated. For five different type3 of land use a separate method has been developed to compute the water requirement. In a next step the water requirements of the blocs are added to obtain the water supply of the entire area.

A validation has been made for two polder districts, the polder district of Rijnland: 106,300 ha large and Delfland: 35,875 ha in size. As vali' dation criteria the simulated water supply was compared to the actual one. The comparison has been made for the summer periods 1975 through 1978. Ingenera lth e model results are slightly higher than the actual values. According to VAN BOHEEMEN the differences are due to following model assumptions: shortages and surplusses are replenished, respective ly discharged immediately so that no fluctuations in open water level occur; an optimal water supply sytem and a full-grown crop being prese° during the entire summer.

Due to the presence of large scale glass house horticulture in the p°^" der districts inth eNetherland s and toth ewate r supply for level contr-0' an additional water supply for water quality control became oi'growin g importance, with special emphasis on the chloride content of the polde1" and boezem water. GRUSEN et al. carried out a study to assess the additional water needs for flushing the internal and external salt l°a

•534 of polders.I nadditio n theyanalyse d various technical alternativeso f water supply systems toDelfland .Amon g thealternative s compared,com ­ prised suchpossibilitie s asth econstructio n ofa ne wcanal ,recon ­ struction ofexistin g canals,constructio n ofpipeline s andsyphons , constructiono fa reservoi r and useo fpurifie d wastewater . with ahydrologica l model,comparibl et oth eon edescribe d inVA N BOHEEMEN'spaper ,'th ewate r demandsfo rleve l controlwer ecompute d for each decadeo fth esumme rhal fyear s inth eperio d 1911 to1978 ,bot h for thepresen t landus epatter n inth eregio na swel l asfo rth eon e anticipated for theyea r2000 . Ina nex tste p thewate r demandsfo r flushingwer e computed foreac hdecade .Heret oth ehydrodynami cmodel , AB0P0L (Analyzing aBOeze m POLdersystem)wa sused .Thi smode l calculates thechlorid e distribution inth eboezem san d theadditiona lwate rdeman d for keeping thesal t levelo fth eboeze mwate rbelo w thestandar d for salt concentration. In afollowin g step theyearl y extremewate rdeman d figureswer esub ­ jected toa frequenc y analysisusin g theGumbe ldistribution .Wate r demandswit h aretur nperio d of3 5year swer etake na sdesig n flowfo r thewate r supply systems.Th epresen tstud yresulte d toa tota lwate r demando fth eregio n forleve l and chloridecontro lo fonl y 73% o f earlier made estimates.Previou s improvement inth eestimat eo ftota l Water demand waspossibl e since ina dynami c approach thesam equanti ­ ses ofwate r servevariou spurpose s atth esam e timean dsinc eth e niJmericaldescriptio n ofth epolde rregim ebecam efa rmor edetaile dan d

comprehensivea sbefore . Si*ce in themode lAB0P0 L thesomatizatio n ofth eprojec tarea ,o fth e C*nalsan d theboezem sha s tob e imputed,i twa spossibl e tochec k the effect ofalternativ ewate rsuppl y systems interm so fth echlorid e Xevel. The costestimate s ofth ealternativ eproject srange d from 54t o 224 million dutchguilder s compared toth eestimate d 137millio nguilder s for theorigina lplanne d water supply canal.Whic ho fth estudie dalter ­ atives should berealise d dependshoweve r fromman yothe r non-technical asPects,„hic hcanno tb econsidere d withAB0P0L . Pr°m theconcer n thatan y investment inimprove d drainage should-b emad e Pr °Perly, pRICE etal . ofth eU.K. ,argu ei nthei rcontributio n thatw e Sh °uld getri d of the semi-empirical designprocedur e forpump s (=ar e bas*d onrunof fo f0.3 4 m^s"1.»«.-2)an d ditches <= a fal lo f1 0c mpe r

335 km andwate r velocitiesu p to0. 3 m.s ),wit h itsassumptio n of steady flow and an extreme arbitrary frequency of exceedance ofwate r levels.A s aresult ,a comprehensiv e procedure for thedesig n andanaly ­ siso fpumpe d drainage systemshav e beenworke d outan d presented in PRICE etal' spaper .Th eprocedur e isbase d onth e simultaneous useo f twomodels :th e first todesig n the dimensions of thearteria ldrains , which isregarde d asa dentriti c network and thesecon d model aimst o simulate theperformanc e ofth e complete system, theoperatio n ofth e pumping station included. Thehydrauli c design ofth earteria l drains isoptimise d insuc h awa y that the costs ofexcavatin g and ofth e land lost for agricultural purposes beminimal .A discrete differential dynamic programming method isuse d toobtai n aminimu m value of thecos t function.Fro m ates to f themode l onth eNewboroug h catchmentwa s found that :th eoptima l design corresponded with thecritica l slope that is,th e smallestgra ­ dient defined by themaximu m permitted water levela tth eupstrea m end ofan y drainan d thewate r levela t thedownstrea m end ofth ebranch ; themaximu m velocity constraint isa critica l factor indeterminin g tne geometry ofth edrains . Asimulatio nmode lwa sdevelope d for thedescriptio n of theunstead y flow ina pumpe d drainage network.Th emode l isapplicabl e ona desig° e orexistin g system andpermit s toexperimen twit h various alternative changes interm so fth ecapacit y ofth earteria l drains tostor erunoff ' pump capacities,setting s of thepumps ,etc .Th e simulationmode li s being used tosimulat e theperformanc e of these alternative changesi n design,operatio n andmaintenanc e schedules on thewate r level atseve ­ ral locations ofth edrainag e network foran y arbitrary rainfallstor" 1' which mightb e characterised by agive n duration,intensit y andretur n period. Ina las tpape r YANES etal . presented asimulatio nmode l for theim ­ provement of thewatermanagemen t of tide-driven drainage networks, wit application on theGuar a island, situated inth edelt a ofth eOrinoc o river.Guar a likeal l other islands inth edelta ,hav e their lowestl an levels towards thecente r and embankments towards theperiphery .Th e maindrain swer edesigne d todischarg e into therive r channelssurroun ­ ding the island,drive nb y thewate r slopeproduce d during low tide in therive rchannels .

336 The simulation model,describe d inYANE Se tal . 'spaper ,fo r theopti ­ mization ofth emanagemen tpolicie s hasbee nbase d onth eapplicatio n of theSaint-Venan t typeequations .Vi a thecombinatio n ofth econservatio n °fmas s andmomentu m equation,usin gManning' s expression todefin eth e fractionalslope ,a syste m ofnon-linea r equations isformed ,wher eth e unknowns are thestage s (waterlevels )a tth ediscretizatio n pointsan d theknown s are formed according toth eboundar y conditions imposed.Th e system ofequation s issolve d using theNewton-Raphso nalgorithm .Th e simulation issimplifie d byfixin g theupstrea m boundary conditiona sa slowly varying hydrographgive n byth estag eo fa reservoir .A tth e downstream boundary avaryin g tidal stagehydrograp h of1 2hour sperio ­ dicity istaken .A stage-discharg e functionha sbee nuse d todescrib e thedownstrea m discharge through theon ewa y tidecontro lgate . The rapid growth ofaquati c macrophyteswa s taken intoconsideratio n in thehydrauli c model by increasing theroughnes s coefficient ina wa y which depends on density andplan tstructure .I tha sbee nobserve d name- *ytha t three ofth emos tabundan t speciesdispla y verystrikin gdiffe ­ rences in increasing theroughnes s coefficient.Th epape rshow s thedis ­ charge of the island Guaraversu s timea sobtaine d bycompute r fora c°mplete tidelperiod .Beside s thatth eauthor sclai m thatth emode lca n Ser"e toanalys e alternative management strategiesan d tooptimiz ewate r levels.

References

Armstrong,A.C. ,1982 .Th edesig no fin-fiel d drainagesystem s inth e English fenlands.1 0p . Beran, M.A., 1982.Aspect s offloo dhydrolog y ofth epumpe d fenland

cathmentso fBritain .1 0p . Boheemen, P.J.M. van,1982 .A mode l forth ecomputatio n ofwate rrequi ­ rementfo r level control ofpolde r areas.1 3p . Di Jkstra, j., 1982. watermanagement inth eUssellakepolders .lip . Donker, s.M.K.,1982 .Th einfluenc eo fsoi lsalinit y onric eyield si n theWageninge npolder ,Suriname .1 1P « GriJsen,J.G .an d G.Miedema ,1982 .Wate rsuppl y toth emid-wes t ofth e

Netherlands.1 2p .

337 Horst,L. , 1982.Alternativ e development concepts inpotentia l polder areas.6 p . Price,R.K .an dJ.E . Slade, 1982.A mode l for the design,analysi san d operation ofpumpe d drainage systems.1 1p . SoeAgnie ,I.E. , 1982.Lan d andwate rmanagemen t inbanan a cultivation inSuriname .9 p . Vieira,D.B. , A.E.Pissarr a andJ.G . Pombo,1982 .Drainag e and desalini" zation studies and design inLeziri a Grande,Portugal .1 2p . Yanes,A.G .an dM.F.L .Acevedo ,1982 .Tide-drainag e networks:th ecas e ofGuar a island.1 1p .

338 SUB-THEMEtfATER: QUALITY ,GEOHYDROLOG YAN DSOIL S J.Wesselin g Institute forLan d andWate rManagemen t Research Wageningen,Th eNetherland s

Abstract

Thi srepor t discusses papers onwate r qualityan d changes insoi lprop - e*"tiesan d their influence onwate rmanagement .A totalo fseve npapers . fr°m Australia,Egypt ,Iraq ,Japa n (2x),th eNetherland s and fromFA O (Rome)wa s received. he latter paperdeal swit hplannin g programs forirrigate d areaswit h emphasis on theeffect s onwate r qualityo fdrainag ewate r from irrigated areas. The Australian paper describes thewate rmanagemen t problems inrelatio n to riverwate r quality of theMurra y riveri nSout hAustralia . The Egyptian paperdiscusse s theproblem s encountered byreclaimin gan d lrrigating astri p ofdeser t lando fsom e 17,500ha . The Iraqian d Dutch paper treatchange s insoi lphysica lpropertie s asa c°nsequence ofreclaimin g saline landan dpolder s respectively.Th e latter paper gives amode l tosimulat e thesoi lripenin g tob eexpecte d in future. The twoJapanes e papers dealwit hdesalinizatio no fnewl yreclaime d land al°ng Tokyo Bay and thedesig n offres hwate r lakesalon g these a resPectively.

1 Introduction N

The Papers falling under thecongres s themeB l (landan dwate rmanage - me*t) that included the topicswate rquality ,geohydrology ,soi l

339 ripening,- subsidence ,- physic s and -improvemen t couldb e divided into three groups namely: papers dealingwit h seepage problems inpolde rareas ; papers discussingwate r quality aspects inirrigate dareas ; papers on changes insoi lphysica l properties during andafte r reclamation ofpolder s and saline soils in irrigatedareas .

The report onpaper s falling in the first category isgive nb yRomijn , thepaper s falling in the latter twocategorie s arediscusse d inthi s report. Although irrigated areas areno t always polders in theorigina l sense ° theword , theyhav eman y things incommo nwit h polders,th emai npoin t being theautonomou swate rmanagemen t system. Both reclamation ofpol ­ ders and saline soils in irrigated areashav e incommo n that theyfor m the cause of changes insoi lpropertie s thatar enecessar y tomak e the soil suitable for cultivation and thegrowt h ofagricultura l crops. These changes areo f utmost importance for thewate r management systems tob e applied.

Watermanagemen t problems inirrigate d areas

Introduction of irrigation inari d regions inevitably brings abouta rise of the groundwater,a n increased salt load in thegroundwate r3 nc* deterioration of thedownstrea m surfacewater ,du e to thedisposa lo f drainagewate r from the irrigated areas themselves. Because of theeve r increasing demand for food there isa worl dwid e tendency toenlarg e theproductiv e agricultural areab y introducing irrigation. Inman y areas good quality of irrigationwate r isscarce . Moreover,agricultur e has often tocompet ewit h domestic and industri3 water demands in thedistributio n of thescarc eresource . Control ofwate r quality leads tocleane rwate r and an increase in agricultural production. Itma y provide extrawate r tomee t additional demands by agriculture, industry andpopulatio n and it can reduce energy consumption. Improvingwate rmanagemen t practices candiminis h the salt load fromagricultura l areas,leavin g abette rwate rqualit y for thedownstrea m sections of the riveran d savingwate r forus ei n

340 theseareas .A bette rwate rqualit y itself canincreas e cropproductio n considerably and reduce thehazar d of soilsalinization .Preventio no f soil salinization in turnca nsav e largeamount s ofwate rotherwis e needed for reclamation ofsoil sonc esalinized . Kadry(1 )i n his paperwarn s that tooofte n reclamation and irrigation Projects inari d and semi-arid regionsar edesigne dwithou t considering theeffect s of implementation of theseproject so nothe r regions.H e advocates acarefu l analysis ofwate rqualit y problems inal l thearea s °fa rive r system. Such ananalysi s should startwit h aninflow-outflo w analysis of surfacewate r and groundwater foral l thesubareas .O nth e basis of thisanalysi swate r and saltbalance s should be setu pt o detect themagnitud e and sources ofsalinity .Nex ton e should consider °n-farmwate r usesystem s toobtai nappropriat e solutions forminimu m salinization ofsoi lan dwater .Fro m thesepossibilitie s acceptable Practical solutions should bechose no nwhic h acost-effectivenes s analysis has tob eapplie d toarriv e at thebes tmanagemen t practice for salinity control ina rive rbasin . The paper gives planning frameworks fordevelopin g bestmanagemen t Practices insubbasin s and inrive rbasins ,bu tdoe sno tg o intodetai l as fara s it concerns necessary datao rresearc h toobtai n them,tha t are needed for implementation. Intha t respect thepape r leavesa numbe r of questions tob e answered. Tomentio nsome : - For implementation ofplan s and application of technologiespartici ­ pation of thefarmer s isnecessary . Theautho r chooses for thesolu ­ tion of this problem trainingan d field demonstrations.Coul dcooper ­ ation of the farmers notbette rb esough t inparticipatio n of them

m irrigation districts? ~ The author points several times toth enecessit y of systematic moni­ toring of flows andwate r qualityparameters ,bu tdoe sno t indicate whomus t organize thisan d take responsibilityfor .Moreover ,moni ­ toring alone isno t sufficient.Wh o takesactio nwhe n results indi-

cate problems? ' The author states that remote sensing techniques canb euseful^t o guide the selection ofmeasurin g points,th ecarryin g outo fsoi l surveys and land evaluation activities,bu tdoe sno t indicateho w this should bedone .

341 How farwant s theautho r tog owit h respect tocost so f designan d accompanied research,sa y expressed as apercentag e of the total investment costs of aproject ? - What organizational framework isnecessar y torealiz e theplannin g frameworks included in thepaper ?

An example of theman y problems that appear inwate r management and the control of salinity is given in thepape r of Schrale and Desmier(2) . They discuss theproblem s of thewate rmanagemen t of theMurra y riveri n South Australia.Thi s river delivers 90%o f the irrigationwate r in SouthAustrali a and isuse d as asourc e for drinkingwate r forAdelaide - Due toretur n flowo f irrigationwate r and underground seepageo f groundwater the salinity of the riverwate r is increasing.Annua l costs forurba nwate r users increasewit h $A7 9 200 foreac h additional EC-unitwhil e irrigation farmers loose $A 18 100fo reac h additional mg saltpe r litre.Polder s along therive r areuse da spastur e landwit " a potential production of 27.5 tonnes drymatte r proha .Th eactua l production is less than 50%an d isdecreasin g due tosalinizatio nan d water logging of thesoi l causing changes incompositio n of thegrass " land.

Analyses of return flowvolume s revealed that irrigation efficiency is only about 50%,bu t also that theamount s of salts removed are 2t o5 times ashig h as the inlet amounts.Thi s leads theauthor s to thecon ­ clusion that themai n reason for the increasing salinity of therive r lS groundwater seepage.Measurement s of groundwater seepage during the nonirrigation season showed thatseepag e intensities arebetwee n 0.1 atl 14.2m mpe r daywit h anelectrica l conductivity up to 34.2m Spe r eta. Further research on improved drainage and irrigation combinedwit h resowing of thegras s should lead to the solution of theproble m in t polders themselveswhil e alternativemethod s of drainagewate r disp°sa- have tob e considered after reduction of itsvolum e as asolutio n f°r eliminating the effect of thedrainag ewate r on the riverwate r salinl

The paper gives interesting datao n theeffec t of salinity forbot h drinkingwate r and agriculture.A nactua lproductio n of grassland of about 13tonne s perh adr ymatte r isver y reasonable.A potentia lP r°

342 auctiono f27. 5 tonnes ina nin emont hgrowin g season iscomparabl ewit h Dutch data ofabou t 16tonne s fora fiv e tosi xmont h season.Takin ga transpiration ratioo f 30k gD Mpe rm mo fwate rwoul d demand roughly 900na no fwater .Subtractin g theundergroun d seepage from thisdemand , !tbecome s clear that the irrigationmetho dmus tb e themai nsourc eo f the trouble as fara s itconcern swaterloggin g and theaccompanyin g salinizationo f thesoil s in thepolders .Drainag ema y solve thisprob ­ lem,bu t isno ta remed y for theundergroun d seepage.Peculiarl y the authors dono tmentio n furtherresearc ho n thissubjec t asa possibilit y tofin d asolutio n for the increasing salinityo f therive rwater .

A second exampleo fwate rmanagemen t and salinity problems isgive nb y Korany andHussei n (3).I tpertain s toa 1750 0h aare ao fdeser t land west of therive r Nile inEgypt . Theauthor s give adescriptio n of thegeohydrologica l andclimatologica l conditions in thearea .Ther e isa 67t o 100metre s thickaquife ro f Holocenemateria l underlainb y impermeable Tertiary formations from Pliocene,Miocen e andEocen e origin.Rainfal l isrestricte d to2 2t o4 5 »»»Pe r annum andhig h temperatures areaccompanie d byrelativel y strong *inds. Potential evaporation inth eare a isestimate d tob e 1450t o '°40m mpe ryear . Waterbrough t into theare aan doriginatin g from therive rNil e iso f Scellent quality.Afte rreclamatio n of theare ai n 1965groundwate r ievels rose to 19.6metre s and insom espot seve n to0. 1 mbelo wsur - fiacape.. Th„,e groundwate , r i.s somewha .of t.i,bracKis ra^,'qhnbu »t^mixe dwit h surfacewate r itgive s 25%o f the total amount of irrigationwate rapplie d inth earea . The authors report onresult s ofpumpin g testsan d groundwatermap s indicating thedirectio n ofgroundwate rflow . ^fortunately they dono tg o intofurthe rdetai lo n theresult so fthei r findings.Som e remarks on thispape r couldbe : - The authors report that thek-valu ei n theaquife rrange s from 15.4 to3 2m perday .Takin ga naverag eo f2 5m pe rday ,a gradien to f n •> , _• „A „re 0 15-0.26m pe rkm )an d athicknes s U.2m pe r km (datamentione d areu.i- >«••< • r ~c , __,-„oo at anundergroun d lossof^O.3 8 of theaquife ro f 75m ,on earrive s ata nuuu c ë n,2 , , ,nnofh of 80k m this comes to 3040 0 m perday .Fo r aboundar y lengtno i ou N3 perda yo r0. 5 m3 persecond .

343 - Apotentia l evaporation of 1650m m ayea r as anaverag e leads toa water requirement of 9.14 m3 per sec.whil e the authorsmentio n 10,273+ 10,846= 21,11 9 m3 per sec.Therefor e seepage losses from conveyance canalsmus tb eo f utmost importance indeterminin g the water need unless theundergroun d seepage outo f the area ishighl y underestimated. Thementione d water requirement means a total irrigation of 3850ram per annum. From this roughly 40%evaporates .Sinc e the concentration of the surfacewate r isgive n as 555pp m thiswoul d give asal tcon ­ tent in thegroundwate ro f 2jx 55 5= 1400ppm . Theauthor s give values between 1467an d 4789 ppm.Apparentl y fossile salts inth e profile play an important role and thequestio n iswha twil lhappe n with both the groundwater table and the salt content of the groundwater in the future underprolongue d irrigation. Sowha t doth e authors expect thatwil l happenwit h the future salinization of the soil and thepossibl e seepage losses from thearea ?

Changes insoi l physical properties

Asmentione d earlierbot h reclamation of saline soils and reclamation oi polders imply changes insoi lpropertie s thatar e of utmost importance forbot hwate rmanagemen t andwate r quality. Okazaki (4)report s on the land reclamation in theeaster npar to f Tokyo Bay.Her e land is reclaimed from these ab yheightenin g thesoi l with theai d of sand pumping from thesea . The soil in the land obtained is saline due to theseawate r fromth e dredging activities.Wie n themateria l is sandy, leachingb y natural rain israpi d enough to allow after some time treeplantin g andcon ­ structionworks .Man y areas reclaimedwit h finermateria l had a toop° ° drainage tob e used. Inaddition ,unequa l shrinkage of the land leads depressions that arever ysaline . Shrinkagewa s found tob ehighl y dependento nsoi lmateria l and starte with crack-formation upon drying, the largest cracks occurring athig " clay contents.I nplace s with fine-textured subsoil and lighter tops°a no cracks occurred. Due to the lowpermeabilit y of the subsoil layers leaching of salts didno t occur.Salt s accumulated theno n theedg e oi

344 thedepression s due toevaporation . Movement of chloridewa s found tob eeasie r than thato fsodium ,causin g differences inpH .Thi swa s oneo f thereason s fordifference s inth e halophyticvegetatio n foundo n theland .

From thestandpoin t of soilformatio nan d therelatio n betweensalinit y and vegetation type the conditionsprevailin g in thereclaime d landar e very interesting. Technically iti swell-know n thatsan dpumpin g leads tover y heterogeneous soilprofiles ,th eheterogeneit y depending onth e speed ofpumping , typeo fsediment ,drainag e etc.A solutio n forth e Problem that soils areno t leached thereforeha s tob e found at least Partly indevelopin g better techniques fordepositin g thesoi lmateria l during the sandpumping . Al-ani et al. (5)repor t onexperiment s concerning theeffec to f sodium salts on thepermeabilit y ofsoils . salts inwate r dono tonl y change theirphysica l and chemicalproperties , but bring into contactwit h soils such solutions thatar e liablet o échange of chemicalswit h theadsorptio n complexo f thesoil . Therefore changesma y occur insoi lpropertie s andwate rmovemen t inth esoil . The authors saturated undisturbed soilsample s ofa nonsalin e siltycla y s°ilwit h solutions of sodium chloride,sodiu msulphate ,sodiu mcarbon ­ ée and calcium chloride.Nex tpermeabilit y testswer e carried outwit h the same solutions until constantvalue swer eobtained .A s anex tste p theexperiment s were proceeded using tapwate r tose ewhic h changes took place. The ratioo f thevalue s foundwa s used asa nindicatio n forth e changes inhydrauli c conductivity thatma yoccu r during leachingo f Saüne soils. Authors found thatespeciall y highconcentration s ofsodiu msalt s inth e Soil will reduce thehydrauli c conductivity upon leaching.O n theothe r ha"d thepresenc e of calcium andmagnesiu msalt s does notsho w this effect. The authors point out thatalthoug h theresult s of theexperiment s cannot be used fordirec t application in leachingprocedures ,the ygiv e an ideaabou twha t canb e expected upon the timeo f leaching ofsalin e s°ils.

345 A complete different problemo f soil formation,namel y theripenin go f newly reclaimed polders in theNetherland s isreporte d by Rijniersce (6)- Soil ripening isnecessar y toobtai n enough bearing strength and tomak e growth of plants possible. Inth eDutc h practice of reclamation ofpol ­ ders reed is seeded as apionee r crop toobtai nmoistur e extractionfro m the soil as astar t for theripening .Afte r someyears ,whe n the soil lS dried sufficiently toallo w theconstructio n ofa furrow drainagesystem » thisvegetatio n isremove d and replaced byagricultura l crops.Th esoi l ripening is important for thedesig no f therequire d drainage and to predict the rateo f subsidence of the land thatha s tob e taken into account for construction of canals,ditches ,roads ,buildings ,etc . Theautho r gives theprinciple s of anumerica l simulationmode l for physical soil ripening. The soilprofil e isdivide d intoa numbe ro f layers ranging from0. 5 cm in the topsoil to5 c mi n the subsoil.Th e watermovemen t in the soil is thensimulate d toobtai n soilwate r con­ tents and accompanying shrinkage and cracking. Openwate r evaporation (Penman)correcte d forsoi l cover isuse da s evaporative demand. Transport ofwate r through theprofil e (bothupwar d and downward) is then computed forever yperio d of ten days. Computed soilwate r suctions arenex t transferred intoa moistur e profilewit h the aid of relations between organicmatte r content andbul k density onon e side andwate r contents atgive nsoi lwate r suctions on theoth e hand. Amodifie d Terzaghi formula isuse d tofin d thecompactio n due toth e Ik load excerted by thedryin g soil layers.Thi s gives the increase inbu i density upon drying.Th e increased bulk density results into subsidence and crack formation. Bymean s of adistributio n factor changes inbul k density are distributed over subsidence and cracking. Themode lfinall y predicts thesubsidence ,th edept ho f the cracks and theamoun t of wate stored in the soil profile.Example s of comparisons between computed a measured data show that themode l gives areasonabl e prediction. Themode l offers thepossibilit y toobtai n datao n soil ripening in a relatively simpleway . Ituse s anumbe r of relations between parameter derived for conditions in theDutc h IJsselmeerpolders. This impliest h the available model cannotb e used forothe r conditions withoutprope r adaptions as theautho r points out inhi spaper .

346 Water quality inreservoir s

paper that issomewha t beyond the topicso f thisrepor t is thato f ohara (7).I tdescribe s thewate r quality ina reservoi r that issepa - ated from these ab ya nenclosur eda mprovide dwit ha drainag e syphon 0 letwate r out.Du e toseepag e through theenclosur e damsal twate r accumulates in thereservoi rbelo w the levelo f theoutle twhil e the °P layerha s freshwater .Unde rth einfluenc eo fwin d thediffusio no f Salt from thebotto m layer into the top layer isaccellerated .Th e author gives amathematica l descriptiono f thisphenomeno nan ddiscusse s thevariou s parameters included. n the basis of this theoryh edevelope s asimulatio nmode l for thecas e that thehorizonta l distribution ofsal t inth ereservoi r ishomogeneous , y dividing thedept h intoa numbe ro f layersan d applying thefinit e difference method,bot hvertica lvelocit y andsalinit y changes causedb y xt, canb e found numerically. Inorde r tomaintai n thewate rqualit yi n thereservoi r theamoun t ofwate r causing thesal tmovemen t has tob e counterbalanced by anequa lamoun to f freshwater . ODIexperiment s and simulations theautho r finds that inorde r tokee p thechlorid e content ina reservoi rwit hsurfac eare aA (ha)belo w 500 Ppm, theamoun to fwate rQ require d isQ/ A = 123H"1-8 (m3.ha_1.d"1). nderwin d velocities u> 5 m.s" 1 thecritica l deptho f thereservoi r topreven tmixin g of salts isH =0.7A u- 2.6 .Unde rpractica lcondi - f c lQ ns inJapa n onegenerall y usesH £ =5 lo gu - 1.0 .

This paper is interesting forproblem swher e freshwate r reservoirs cl°se to the seaar e used forwate r intakeb yfo rinstanc e agriculture r for theproductio n ofdrinkin gwater .

References

'•Kadry ,L.T .Soi lwate rsalinit y relationship environmental factorso f land reclamation. 2- Schrale,G . and R.E.Desmier .Salin egroundwate r inflowint o irrigated polders along theMurra yRiver ,Sout hAustralia .

347 3.Korany ,E.A .an d S.A. Hussein.Geohydrologica l status and controlo f land andwate rmanagemen t in the reclaimed desert areas,Wes to f theNil eValley ,Egypt . 4.Okazaki ,M .Accumulatio n and evaluation of salts insoil so f reclaimed land along Eastern part of TokyoBay . 5.Al-ani ,A.F. , S.R. Daghistani andB.A . Takessian. Effect of different salts on thehydrauli c conductivity of soil. 6. Rijniersce,K .A simulationmode l forphysica l soil ripening inth e IJsselmeerpolders. 7.Tohara ,Y .Wate r qualitymanagemen t of adesalte d reservoir.

343 SUB-THEME:WATE R QUALITY,GEOHYDROLOGYAN DSOIL S (CONTINUED)E .Romij n Provincial WaterBoar d ,Arnhem ,Th eNetherland s

Abstract

Seepageproblem s inpolde r areashav ebee na majo rhydrologica l research itemfo rman yyears ,especiall y inTh eNetherlands .The y stimulated the developmento fgeohydrolog y ofsemi-confine daquifers . Thepaper s ofKoche v &Yovko van d ofDianko vdea lwit h theproblem so f riverpolder s along theDanub e inBulgaria .Bot hanalytica l andnumeri ­ calmode l techniques areuse d fordrainag edesign . !norde r todesig n themos teconomi can deffectiv edrainag e system,th e fluctuations of therive r levelan d theseasona lprecipitatio n excess "»ustb e taken intoaccount . trends calculateswit h ananalytica l formula therespons eo fa ste p function in therive r leveloutsid e thepolder ,wit h steady statea sa Parting point.Th e leakagefacto rA ha sbecom e timedependent ,increas ­ ingwit h time to the limit /KDc afterseveral.years . °» theothe r side the total seepageint o thepolde r increaseswit h time Until themaximu mvalu e atstead y statei sreached . We sseling.s paper dealswit ha nextensiv e study inth eprovinc eNorth ­ land. As aresul to f thehydrologica l computations the contribution of various sources toth esurfac ewate r quality couldb e calculated na *ely from the saline underground (deep)seepage ,effluent s of industry a»d households,artificia lgas-wells ,inle twater ,agricultur e andrai n Vater and saltuse d inwinte ragains t iceo nroads . ^ paper ofKirkha m falls somewhatbeyon d thesubjec t of thisreport .

349 Thewrite r has developed apotentia l theory for the shape of thecon e ofdepressio nfo r theclassica lproble m ofa nunconfine dwel l centered ina circula r island.

Introduction

Seepage problems inpolde r areashav ebee n amajo r hydrological research item forman yyears ,especiall y in theNetherlands .The y stimulated thedevelopmen t of geohydrology of semi-confinedaquifers . Thehydrogeologica l scheme,consistin g ofa sand y aquifer abovea n "impervious"cla y layer and coveredb y a"semi-pervious " claypeat complex (the aquitard) isofte ncalle d theDutc h Polder Profile.Becaus e of therefractio n of thestreamline s of the ground water flowa t theboundar y of the aquitard and the aquifer,fo r simplicity the flow isassume d tob evertica l in the aquitard and horizontal in the aquifer.Furthe r basic assumptions are: - Darcy's law - thela wo f conservation ofmas s - aspecifi c set ofequation s of statewit h respect todensit y and viscosity of the system asa functiono fpressure ,temperatur e and chemical composition Inal l thepaper s presented, temperature effects areneglected ,th e water is incompressible,th epressur e only effects thesoi l and thepermeabilit y of the soil is time independent. As anexampl e letu s examine the transmission of tidalwave si na n extensive Dutch Profile.Cas e studies of this typewer e inth e Netherlands alreadydescribe d by e.g. Steggewentz in 1933,Bosc hi n 1951 andWesselin g in 1959.Takin g intoaccoun t the compressibility of theaquifer ,an dusin g symbols as innex tFigure,

350 the following equations hold

TIDE

MEAN LEVEL M

AMPLITUDE U UJ-.2JL xxxx ;

Darcy's law

\ = -K2 3((>/3x q = (-h)/c

~ Mass balance

D div qx + qz = -D3n2/3t = -S3

% = U3h/3t

"ith c= d/K . (hydraulic resistance),S = PgD a (storage coefficient), =PgDnja ,a ascompressibilit y coefficient of thesoi lmatrix , u thedrainabl e pore space,n theporosity ,K th ehydrauli c conductivity.

TV» e flowequation s become

(*-h)/c = u3h/3t, KD32.(./3x2 = S3

Vlth boundary conditions

x = 0 = h = M + U sin wt; x = » Ztyfdt = 0 rhe formula for thepiezometri chea d is

* =M +u exp(-p x)si n(cot-Qx )

351 2 2 2 2 pc(y-Z)a) (JJ(U+S-Z+U c Su ) p Q = ? 2 2 • 2PQ = m (1+p c iß)KD (1+VJ c ui )KD which illustrates that atdistanc e xth epiezometri chea d $show s a reduction of amplitude exp (-Px) and aphas e shiftQx .

Discussion on thepaper s presented

The papers ofKoche v &Yovko van d ofDianko v dealwit h theproblem s of riverpolder s along theDanub e inBulgaria .Bot h analytical and numericalmode l techniques areuse d fordrainag edesign . Inorde r todesig n themos teconomi c andeffectiv e drainage system, the fluctuations of the river level and theseasona l precipitation excessmus tb e taken intoaccount . Kochev &Yovko v define acritica l drain spacing such that thephreati c levelmi dbetwee n thedrain s isjus t at the levelo f thepiezometri c surface of theunderlayin gaquifer . Their drainage formula for steady flow takes into account theradia l flownea r thedrains ,a horizonta l flow component and avertica l onedu e to thepiezometri chea d inth e underlayingaquifer .Th epiezometri chea d itself iscalculate dwit h a finite elementmodel .Als o subirrigationwa s studied. Diankov'smode lha s inadditio n ahorizonta l groundwate r inflow from thehighe r partsnea r the river polder.Hi s results showver y clearly theattenuatio n of theamplitud e and thephas e shifto fth e piezometrichea dmentione d earlier.

Barends extends the theory as illustrated inparagrap h 1wit h the compressibility and subsidence of the semi-pervious layer.Recal l thatunde r steady conditions the total seepage intoa nextensiv e DutchPolde r Profile isequa l to

Q= (M-h0)/KÔ7^

withM as the steadywate r leveloutsid e thepolde r andh 0 the controlled polder level,wherea s

352 <(>-h = (M-h )ex p (-X./X), X= vICD c

Barends calculateswit h ananalytica l formula therespons e ofa stepfunction in the river level outside thepolder ,wit h steady state asstartin gpoint .A t thebas e of thecoverin g semi-pervious layer,a formul a for (-h) quit e comparable toth eabov e mentioned holds,onl y the leakage factor \ hasbecom e timedependent , increasingwit h time toth e limit /KDcafte r severalyears . On theothe r side the total seepage into thepolde r increaseswit h timeunti l themaximu mvalu e at steady state isreached .On ema y askhoweve rwhethe r inthi scas e theassumptio n of timeindependenc y of thepermeabilit y of thesemi-perviou s layerholds .Consolidatio n of the claypeat layersma y result after severalyear s ina highe r cvalu e and alowe r total seepage into thepolder .

Wesseling'spape r dealswit h anextensiv e study in theprovinc e North-Holland.Th ehydrogeologica l scheme consists of three leaky aquifers above each other,covere d by the claypeat complex. The resistance of theseparatin g silt layerswa s calibratedwit h the aid ofwate rbalanc e studies andpiezometri c data. As aresul t of thehydrologica l computations thecontributio no f various sources toth e surfacewate r quality couldb e calculated namely fromth esalin e underground (deep)seepage ,effluent so f industry andhouseholds ,artificia l gas-wells,inle twater , agriculture and rainwater and saltuse d inwinte r against iceo n roads.Mai n contributors for chloride are seepage (62%)an d inlet water (21%), fornitroge n natural leachingplu s fertilizers (35%) inletwate r (23%)an d seepage (18%)an d forphosphorus : households (46%)natura l leaching plus fertilizers (28%)an d seepage (10%), stressing the important influence of seepage on water quality.I tshoul db enote d that leaching fromsoi lan d losso f fertilizers combinedwer eobtaine d asclosin g entry of thebalanc e and notb y directmeasurements .

Thepape r ofKirkha m falls somewhatbeyon d thesubjec t ofthi s report.Th ewrite rha s developed apotentia l theory for theshap e of thecon e ofdepressio n for the classical problemo f anunconfine d

353 well centered ina circula r island.A t thewel l face,wher e ground water leaves the aquifer,a seepag e surface exists,nevertheles s the formula ofDupui t for thewel l discharge iscorrec twhic h can be easily seenb y considering the function

hr 2

= n withh r asphreati c level,(r,h r) r> giving

hr El =/ ii dz = =9* dr o 3r 2irKr with boundary conditions filled out and integrated

$r = ih^KQ^irtCHnR/r 2 2

Qw = _1TK ln(R/r ) w

Kirkhamcompare s his resultswit h laboratory model data ofHal l (LaHouill e Blanche, 1955)

References

Kochev,K &Yovkov ,B .Som emethod s for selecting and designing ofa prope r drainage system ina rive rpolde r Diankov,Z.I .Groundwate r flowdynamic s inBulgaria n riverside polders -a numerica l model investigation Barends,F.B.J .Seepag e induced surface leakage inan d around polders Wesseling,J .Hydrologica l conditions and their influence on surfacewate r quality in theDutc h polder region Kirkham,D . Free surfacepotentia l theory fora gravit ywel l

354 THEMEB SUB-THEME B1:LAN DAN DWATE R MANAGEMENTASPECT S

General reportsby : Prof.dr.J.J.A .Feye n Dr.M.J .Hal l Drs.E .Romij n Dr.ir.J . Wesseling

Conclusions byProf.Em .D .Kirkham , chairman.

The twosession s inthi s sub-themedeal twit h watermanagement systems anddesig n criteriarespectivel ywate r quality,geohydrolog y andsoils . Thereporter s reviewed 37papers ,submitte d by authors from 15 countries:Australia ,Bulgaria ,Egypt ,England ,Indonesia ,Iraq ,Japan , Malaysia,th eNetherlands ,th ePeople' s Republic ofChina ,th e Philippines,Portugal ,Surinam ,th eUnite d Statesan dVenezuel aan d from F.A.O. The subjects of thepaper s included awid erange . Someo f the studieswere : - thedesig no fpolde r drainagesystems ; - ricean dbanan a cultivation; - sourceso fwate rpollutio n inth eprovinc eo fNort hHolland ; - compression and subsidence of thesemi-perviou s layer; - development ofpotentia l theory for the shapeo f thecon eo f fora nunconfine dwel lwit h thetheor y applicablet o upward seepingwater ; - therelationshi p of soilwate r salinity toth e environmental factors of landreclamation ; - theeffec t ofdifferen t salts on thehydrauli c conductivity ofsoils ; -wate rqualit ymanagemen t ofa desalte d reservoirwher ewin d influences saltdiffusion ; - astud yrecommendin g drainagemethod s that fitwit h traditional farming systemsan d ecological equilibrium;

355 - modelling studies done inEngland ,th eNetherland s andVenezuela ; - drainage and irrigation problems ofcertai n regions,suc h as:th efen - lands ofEngland ; theMurra y River ofSout h Australia;reclaime d desert areaswes t of theNil e valley inEgypt ;polder s along the Danube River inBulgaria ;th eLezir e Grandepolde r ofPortugal ; reclaimed land along theEaster n parto fToky o Bay;soi l ripening in the IJsselmeerpolders;growt h ofbeac h land and reclamation atPear l RiverEstuar y inChina ;reclaimin g againstQiantan g Bore,als oi n China. Methods of research described in thepaper s varied from classical agrohydrological experiments,throug h systems analysis andmodelling . Sometimes therewa s acombinatio n ofbot hmethods , Themajo r conclusions thatca nb edraw n from thepaper s and discussionsare : 1.Wate rmanagemen t ofpolde r areas isa multidisciplinar y activity, involving elements of civilengineering ,hydrology ,agricultur e and economics. 2.Knowledg e and techniques onwate rmanagemen t should be transferred internationally. 3.Microcomputer s areno wbecomin g of lowenoug h cost,s o that theymay , insom e cases,b euse d instead ofpocke tcomputers . 4.T o aid inpolde r design,physica lmodel s ofwate rmanagemen t should be constructed and solved,wit h realdat a supplied,a s fara s possible,fo rinput . 5.Thos epeopl e involved insystem s analysis used inpolde r designan d thosepeopl e involved ingatherin gphysica l data should learneac h other's language and objectives,a sa nessentia l aid tothei r effective cooperation. 6. Often financial resources tod oenoug h research arelacking . Therefore it iso futmos t importance tobrin g together any available information.T o do this requires cooperative sharingo f data collected by all departments of agovernment . 7.I nman y cases irrigation causes underground seepage of salinewate r toward other regions.Therefor e inpolde r andwate rmanagemen t design one should not restrict himself to theprojec t inself,bu tals o consider theneighbourhood .

356 8.Polde r technology aspractice d insemi-humi d climatesmus tb e strongly modified for the tropics,becaus e of torrential rainstorms. 9. Concerningmodelling , this designmetho d mayb euse d indata-scarc e situations,provide d that it isuse dwit h asensitivit y analysis. Results of sensitivity analysis canassis t indesignin g future data collectionprograms .Result s also can showdeficiencie s of existing models andpoin t outdirection s for future research. 10.Waterqualit y isa majo r item tob e dealtwit h inwate rmanagement . Salinity from ocean seepage or fromexces s evaporation ofwate r from the soil canb e amajo r source ofpollution .Sedimen t inwate r is alsopollution . An interesting tablewa s presented ina stud y ofwate r quality of thepolde r areao f theprovinc e ofNort hHolland .Thi s table shows theamount s of chlorine,nitroge n andphosphoru s fromth e following sources:inle twater ,households ,industries ,gas - wells,rainfall ,traffic ,seepage ,natura l leachingan d fertilizers,an d leakage throughdikes .

357 THEMEB 2 :CONSTRUCTIO NASPECT S

SUB-THEME:DIKE SAN D EMBANKMENTS J. vanDuivendij k Haskoning,Nijmegen ,Th e Netherlands

Abstract

Therear eman y thousandkilometre so fdike s surroundingpolder sal love r theworld .Ver yhig h overallcost sar e involved ininvestmen tan dmainte ­ nance. Iti sencouragin g tose etha tth escientifi cbas e fordik edesign / construction andmaintenanc e isbroadenin gbecaus e inth elon gru nthi s willresul t insaving st oth epeopl e living inthes epolder swhil eals o their safetywil lincrease . *) \,o Fourteen paperswer e submittedo nthi s sub-theme.Subject streate d intn e papersconcerne ddesig na swel la sconstructio n andmaintenance .Majo r featureshighlighte db y thepaper sare : - abette r scientific approacho fproblem s inth ehydro-geologica lan d geo-technicalfiel d thanpractice d inth epast ; - agrowin g understanding of thenee d forregula r inspectionan dmainte ­ nanceo fdike susin gmoder ngeo-technica lequipment ? - introduction of scientific designo frevetment s in seadefences .

*) B Asfou rpaper sar edeal twit hb yMr.Hammon dth eoveral ltota l forThem e is20 . 1 Introduction

Theoutside r looking atth e sometimes somewhat shapeless ridgeso f earth surrounding ane wpolde ro ra tth etre e lined friendly looking lowem ­ bankmentscovere db y grassan dwil dflower swhic har etypica l forol d polders^willno t seethes e "structures"a sdike sperformin g anecessar y function.Mos tprobabl y thisoutside rwoul d laugh ifyo u toldhi m that there ismuc h engineering involved indesigning ,aligning ,buildin g and maintaining thesedikes .Nevertheless ,th eengineerin g ofdike s isth e subjecto f thisrepor tand ,lookin g atth eman y interesting reports sub­ mitted,on eca n saytha tman y engineerswit h dedicationar edail y devoting their timean d skillt oth ematter .

Whyd opeopl ebuil d dikesaroun d theirpolders ?A genera lanswe r is easy togive :t okee pth ewate rout.Bu ta s usuala genera lanswe r is never completely correct.I twoul dappea r thatther ear efou r reasons whypeopl ebuil ddike saroun dpolders : 1)T opreven t flooding of thereclaime d landdu eto : -hig h astronomical tides inestuarie san dalon g thecoast ; -win d set-upcause db y stormsurges ; -hig h riverdischarge s causedb y rainfallo nth ecatchment . 2)T opreven t salinewate r intrusionalon g estuarine and sea/oceanic coasts. 3)T olimi t seepage fromoutsid e toinsid eo fa polder . 4)T opreven ta furthe r regressiono f thecoastlin eo rmeanderin g ofth e riverbank. Inshort :a dik e isa protectiv e deviceagains tth eforce so fnature , thelatte rbein gdemonstrate d inth ebehaviou ran dconsequence so fth e tides,th erainfal l andth ewind .

359 2 Design requirements and subjects tob e studied

Theauthoritie s anxioust ohav e sucha nembankmen tbuilt ,generall yhav e three requirements inmind : a)th eabov ementione d reasons 1)t o4 )inclusiv emus tb eborn e inmin d andth edesig ndevelope d accordingly; b)th edesig nmus tb e "economical",i.e .a smuc ha spossibl eus emus tb e madeo f locally availablematerial swhil e thedesig n criteriamus tb e metwithou t "over-designing"th eembankmen tprofile . Moreover,a neconomi c evaluationmus tb emad eo f investmentan dmain ­ tenance costsfo ralternativ e designs inorde rt o selectth e least costsolution ; c)a genera lhuma n feelingo f safetymus tb e established through design and safetymargi n (freeboard,safet y factor)and ,subsequentl ymain ­ tained through regular inspection andmaintenance .

Bearing thesethre ebasi c design requirements inmin d aproces so fdesign » construction,management ,operatio n andmaintenanc e ofpolde rdike sca n start.I norde r tod othi sa numbe ro fdifferen t subjectsask sou ratten ­ tion.W ewil l list sevenher e (Table 1)bu tth enumbe r caneasil yb eex ­ tendedb y listing lessrelevan tone so rb y sub-dividing theorigina l seven subjects.Mos to f the subjectshav ea bearin g on thevariou sstage s ofa nembankmen tprojec t (design,etc. ,u pt omaintenance) . How importantal l these subjectsan daspect sar ei nrelatio n toeac h other isno tknow na sthei rrelativ e importancevarie s fromprojec tt o projectan da si tar ei n factth e localcircumstance swhic hdetermin e for eachprojec t themajo r issuest ob e looked into.However ,on ethin gmus t bever y clear:thoug h the subjectsar e listed asseparat e items the designproces s requires the integrationo fal l subjectsan daspects . Thismean stha tdurin g thedesig nproces scontinuou sadaptatio n ofpart s of thedesig n is necessary inorde r toarriv ea ta noptimu m solution without "conflicting"parts .A s suchthi sproces so f iteration isa typicalengineerin g methodwhic h isno talway s found ino rappreciate d byothe rdiscipline s involved inpolderization .

360 Table 1: Seven subjectst ob e studied inth ecours eo f designan d implementation ofa n embankmentprojec t

Subject Aspects involved

1Coasta lan d riverhydraulics , - waves - frequency ofhig h water levels hydrology andmorphology . -erosion/sedimentatio n -win d set-up - local rainfall

2 Hydro-geological and soil- - seepageunderneat h and through dykebod y mechanical characteristics of - stability sub-soilan d embankment - embankmentprofil e tob eselec ­ ted materials. - construction method

3Availabilit y of construction -dambod y - revetment materialsfor : - toeprotection - closurework s

4 Structuraldesig no frevet ­ -wav e impact - perviousness ment. - flexibility versusdifferentia l settlements ofdambod y - construction intida l zone

5Environmenta l issues. - road-rail connections - erosiono fforeshore ,mean ­ dering -urba nan drura l settlements - ecology - landscaping

6 Constructionmethods . - closurework s (ifany ) -manua l labourversu s equipment - dry/wet construction

7Managemen t structure, - inspection procedures -dat acollectio n andprocessin g operation andmaintenance . - floodwarnin g system - maintenance

361 Inth e following sectionsw ewil ldea lwit heac ho f the seven subjects mentioned and seeho w they aretreate d inth epaper spresente d forthi s sub-theme.

3 Papers submitted

On thesubjec to f dikesa tota lo f 14paper swa s submitted.Fo rcon ­ venience sake fourpaper s (nos94 ,96 ,14 2an d 329)ar edeal twit hi n Mr.HammondsReport .Thes e fourpaper swil ltherefor e onlyas k forsom e global remarks fromou r side.Al l fourteenpaper sar e listed inTabl e2 .

Table 2: Papers submitted ondesig nan d construction ofpolde rdike s

Ref. Authorsan d their "ountrywher e Titleo fpape r no country oforigi n project(s) situated 88 SadamiKuwan o Effectiveprotectio no fpolde r Japan (Japan) dike. 94 L.S.A.vanElze n Possibilitieso fdik eenlarge ­ Netherlands and H.L.Jansen ments increasedb y Colbond (Netherlands) verticaldrainag e system. 96 G.J.Flórianan d Calculation ofhydrauli c head Netherlands H.J.Vinkers forrive rembankmen tdesig n (Netherlands) usinga numerica l groundwater method. * 142 J.vanDuivendij k Designan dconstructio n of the Guyana and J.R.Pieters seadefence so fGuyana . (Netherlands) 144 J.J.L.M.Enneking Designan dconstructio n of Morocco andM.M.Vierhou t flood control dikesaroun d (Netherlands) 43000H Ao firrigatio n areas inth eRhar bPlain ,Morocco . 151 G.W.Beetstr a and Reliability ofDutc h Netherlands P.V.F.S.Krajicek Polderdikes. (Netherlands) 152 W.Broeders,J.Hui s Strategics andmethod sfo r Netherlands in 'tVeld ,J.Stui p closing dykebreaches . (Netherlands) Table 2 (continued)

Ref. Authorsan d their Country where no country oforigi n Title ofpape r project(s) situated 161a F.Smith Managemento f catchwater Netherlands (Netherlands embankments in "DeOud e Veenen"drainag edistrict . 187 R.Dresnack, Statistical riskassess ­ U.S.A. E.B.Golub, mento fpolde rprotectio n j.R.Pfafflin structures. (U.S.A.) 209 G.P.Bourguignon Reclamation indeltai c Various (Netherlands) regions. 287 Dr.BélaHajó s Useo f hydromechanization Hungary (Hungary) forhydrauli c earthworks inHungary . 296 A.M.vanNispe n TheZuiderze eproject ; Netherlands totPannerde n construction ofdikes . (Netherlands) 329* D.L.Gudgeonan d Theraisin go f thedefen ­ United Kingdom M.E.Hannah ceso fConve y islandt o (United Kingdom) resista on e in 1000yea r tidalsurge . 501 B.Wesseling Labour-intensive polder Indonesia (Netherlands)an d construction inIndonesi a Ir.Madsalim (Indonesia)

*) ssereport sar ede a Ltwit hb yMr.Hammon d inhi s Report. ' Th

Contentso fpaper s inrelatio n tosubject st ob e studied

InTabl e 1 (Section 2)seve n subjectswer egive nwhic hnormall y require ourattentio nwhe ndesignin g and constructing adike .I nth efollowin g sub-sectionsw ewil l reviewwha tth eauthor so f thepaper shav e said abouteac ho f thesesubjects . 4.1 Coastal andrive rhydraulics ,hydrology ,morpholog y

Though this subject isa s important for dikedesig na sth eothe rsix , onlya fe wauthor srefe r toit .Thi s isunderstandabl e asbot h coastal and riverhydraulic s aswel l ashydrolog y andmorpholog y areth esub ­ jecto fperiodi c congresses,conference san d seminarswhic h arehel d allove rth eworl d anddurin gwhic hal laspect smentione d under this subjectar ediscusse d indetail . This isprobabl y thereaso nwh yth eauthor so fpaper s 142,144 ,29 6an d 329onl ybriefl y touch this subject.On ema y saytha tth eoutcom eo f hydraulic andhydrologica l calculationsan d considerationsar econ ­ sideredb y thedik edesigner s (mainlycivi l engineers)a sa boundar y limit,a conditio n imposed byothers . Theauthor so fpape r 187ar e infac tth eonl y oneswh odiscus s in detailon eo f theaspect srelate d tothi s subject i.e. thefittin go f data (water levels)t oth eprope r statistical distribution.The y state thati ti spossibl e tosupe r imposea nextrem evalu edistributio no f storm surgesove ra norma l distribution ofastronomicall y generated tides. Becauseo f the interrelationship ofcres televatio no f dikes,(deter ­ mined in first instanceb yhydraulic/hydrologica l considerations) construction costan dmaintenanc e requirements iti srecommende d to discussthi saspec tdurin g theafternoo n sessiono nOctobe r 4th.The n alsorelate dpolitical, socia lan d safety implications canb ediscus ­ sed.

4.2 Hydro-geological and soilmechanica l characteristicso f subsoilan dembankmen tmaterial s

Not lesstha n eightpaper s (88,94 ,96 ,142 ,144 ,209 ,296 ,329 )discus s oneo rmor easpect so f this subject.Paper s 94,96 ,14 2an d 329ar e reviewed inMr.Hammond sRepor t towhic h reference ismade . Theothe rpaper sar eno wbriefl y summarized.

364 Paper 88present sa n interesting caseo fmeasure s carried out inJapa n fordecreasin g the seepage through a dikebuil tu po f rather coarse material.B ydrivin g 19.0m long steel sheetpiles intoth ecentr e line of thedik eove ra lengtho f approx.60 0metre sth edail y seepageo f 1000 0m decreased to20 0m . Itwoul db e interesting tokno w thecos to f theseremedia lwork si n relation toth eorigina l construction costo f thepolde r dikean dwha t extra initial construction costwoul dhav ebee nneede d topreven tth e leakageal ltogether . TheReporte r ishapp y tonot etha tth eauthor swer ewillin g topresen t indetai la cas eo f something which wentwrong .We ,engineer snormall y learnmos to fmistake s eithermad eb y ourselveso rb y othersan dan y discussiono n suchmistake san d subsequent remedialmeasure s takeni s verywelcome .

Paper 144describe s in somedetai l thedevelopmen to f the cross-section of dikesi nth eRhar bplai n inMorocc o onth ebasi so f twokind so f availablematerial .I t isinterestin g tohea rabou tth e special problems posedb y theus eo fmontmorilloniti ccla y andwha texperiment swer e carriedou t inthi srespec tbefor ea decisio nwa smad eabou tth ecross - sectiont ob eadopted .

InPape r 209i ti spointe d out that settlemento f the soft subsoilunder ­ lying adik ebod yma yhav e seriousconsequence san dwha tmeasure s canb e considered toreduc e this settlement asmuc ha spossible .

Paper 296provide sa noveral lpictur e of thedesig nan d construction of the dikeso f theZuiderze e (nowcalle d IJsellake)includin g the dikesaroun d thepolde r inwhic h the "Polderso f theWorld " seminari s held.Thes e dikeswer ebuil tove ra perio d of 50year san d their total length amounts to severalhundred so fkilometre swhil e theirheigh t inplace sexceed s 15metre swhic h intur n signifiesthe ma s "large *) dams" .Fo r theconstructio n of thepolde rdike s softlayer s inth e

According toth edefinitio no f ICOLD.

365 sub-soilwer e removed firstan dreplace db y sandt oavoi d stability and settlementproblems . Forman y centuriesth edesig nan dconstructio n ofpolde rdike sha s beenbase dmainl y on emperical data.I ti sencouragin g tonot e that morerecentl y the establishmento f asoun dgeo-technica lbas eo fin ­ vestigations,test san dcalculation s isbecomin g agenera l feature of dikedesig nan d construction.

4.3 Availability of constructionmaterial s

Infac tonl ya fewauthor s (papers88 ,142 ,144 ,287 ,296 )indicat e thatth eavailabilit y ofa certai n construction material inth e neighbourhood of thedike' s alignmentha sbee na facto r of importance inth eestablishmen t of thedik e design.I tca nnevertheles sb econ ­ firmedtha t indail ypractic e thedesigne r firstlook saroun dt ose e what isavailabl e andthe nensure s thathi sdesig nan d construction arematche d toth epropertie so f theseavailabl econstructio nmaterials . Thispractic e isfollow d also for largeearth -an drockfil l damsan d itwoul d appeart ob ea mus t foreconomica l engineering. Iti showeve r pointedou ttha tus eo f largedredgin g equipmentma y sometimes allow todiver tfro mthi sprincipl e (Paper296 )whil e suchdiversio nma y alsob e comtemplated forothe rreason s (recreational constraints,onl y limited loadingo f subsoilpossible ,etc.) .

4.4 Structuraldesig no f revetment

Generally speakinga revetmen t isonl y requiredwhe nth e seaward/ riverward/lakesid eslop e issubjecte d tocontinuou swav eaction . This iscertainl y notth ecas efo rman y dikesbuil tfo r non-frequent high waterso ralon grivers .Consequently ,onl y typical seadefence s (Papers88 ,142 ,209 ,329 )an dth e dikesborderin g largelake slik e theIJsellak e (Paper 296)requir erevetments .Als oher e forman ycen ­ turiesan dunti l 30year sag oth erevetment sconsiste d ofope n type revetments:ope nfilters ,ston epitching ,ri pra pwhil eals oconcret e

366 wasuse dwit hdifferin g results.Thicknes so f layersan d size/weight of individual unitswa spurel y amatte r ofexperienc ean do favail ­ ability ofmaterial s (Papers 142,209 ,296 ,329) . Nowadays,a neffor ti smad e toreall y design therevetmen twit h theai d ofwav e formulesan dmode l testswhil ea tth e sametim ebitume n isintro ­ duced (Paper88 ,142) .

Ingeneral ,moder n revetmentdesig n isconsidere d tob ea par to f coastal engineering and iti stherefor eunderstoo d thatonl y limitedattentio n is given tothi s subject inth epaper spresente db y theauthors .

4.5 Environmental issues

Only twopaper s (144,329 ) indicatetha t theenvironmen tma ypla y arol e indesig no rre-desig no f thepolde r dyke.Mos tprobabl y there ismor e onthi s subject inth epaper s submitted underThem eB- 5 ("Environmental aspects").

4.6 Constructionmethod s

4.6.1 Closure works wnena polde r isconstructe d ina nare ao ftida lcurrent s (aswam po n thecoast ,a n island ina rive rdelt ao ra sandbank ina n estuarium)i t mightb enecessar y toemplo y elaboratemethod sfo rclosin g thelas ttida l channelb ymean so fa dike.Suc ha closur ewil lals ob enecessar y when thedike so f low-lyingpolder sar ebreache d during storm surgesan dso - called flowgap sdevelo p (Paper152) . InTh eNetherland san dals oelsewher e (Bangladesh)variou smor e orles s elaboratemethod shav ebee ndevelope d through thecenturie s toclos e tidalchannel so fvariou ssizes . Papers 152an d 209summariz e thesemethods .As ,again ,thi s subjecti s consideredb y theReporte ra sbelongin g toth efiel do fcoasta l engi­ neeringh ewil lno ttrea tthi s subjecti nfurthe rdetail .Provide d

367 thedike s of apolde r are safe (noovertopping ,n ocollapse )closur e workswil lonl yas k forattentio ndurin g initial construction andno t againdurin g its lifetime ofman ycenturies .

4.6.2 Equipment and labour

Theauthor so f Paper 501giv ea n interesting reviewo f labour-intensive construction ofpolde rwork s inIndonesia .The y conclude thatalthoug h manualexecutio nwa s slightly more expensive thanmechanica l execution thequalit y of themanuall y constructed embankmentswa s considerably better thantha to f theembankment s constructed byheav yequipment . Theadditiona l costwa sals ojustifie db y increased employmentoppor ­ tunities. Theothe rpaper s touching the subjecto fconstructio nmethod s (144, 287, 296)invariabl y refer toth eus eo f equipmentfo rconstructio no f earthworks.

Papers 287an d 296bot h refer toth eplacin g of fillb yhydrauli cmeans . Paper 296wa salread ybriefl y reviewed inSectio n4. 2 towhic h reference ismade .Pape r 287describe s theplacin go f fillborrowe d fromth e riverbe d infloo dcontro l embankmentsalon g theriver s inHungary . Theautho r states thatno t lesstha n420 0kilometre so fdike s arein ­ volved.H edescribe s indetai l theplannin go f actual fillplacin gan d theadvantage s anddisadvantage so fvariou smethods . Itwoul db e interesting tohea rfro mth eauthor so fbot hPaper s 287an d 296mor e specific informationo nweekl yproductio nrates ,pip ediamètre s used,grai n sizeo fmaterial ,capacit yan d typeo fdredger sused , transportdistances ,etc .

4.7 Management structure,operatio nan d maintenance

Designers,i ngeneral ,hav ea tendenc y nott oworr yto omuc habou tmain ­ tenance.Firstly ,th ecos to fmaintenanc e doesno tcoun tmuc h ineconomi c

368 evaluations (becauseo f theconventiona l discounting methoduse d and theapplicatio n ofhig h interestrates )and ,secondly ,mos tdesigner s dono t seewha tthe y cancontribut e towardsthi s subjectanyhow . A third reason istha tonl y during the last 30year sadequat emean s (instrumentation,geo-technica l equipment)hav ebee ndevelope d to actually inspectembankment sothe r thanpossibl eb ymean so fvisua l observations. TheReporte rwoul d liket oas kmor eattentio n forth e relationship initialdesign/maintenanc e ando n thenee d forgoo d regularinspections . A gooddesig n and costly initial constructionma y saveo n future maintenance costswhil e achea pdesig n andba d constructionma y result inver yhig hmaintenac e costs.Th ewhol ematte rwoul db e easy ifdik e. behaviour couldb epredicted . Practice ishoweve r thatdike sbecaus e of their length are subjected toa statisticalproces so f deterioration causedb y loading,qualit y ofconstruction ,damag eb yma nan danimal , propertieso f construction materialsan d subsoilcondition ;eac ho f thesereachin g valueswhic h area function of timean dplace . Only regular and thorough inspectionsma ybrin g toligh twha t iswron g andwhe n (Paper 151)an dwher e action isurgentl y needed (Paper 161a).

TheReporte r assumestha tman y thousandskilometre s ofpolde rdike s are inoperatio n allove r theworld .H eknow stha tfo r instance largedam s in some countries arealread y inspected regularly topreven t seriousaccidents .I twoul db e interesting tohea rdurin g the seminar what isbein g doneoutsid eTh eNetherland so n theregula r inspection ofpolde r dïkes.-

369 SUB-THEME:MISCELLANEOU S CONSTRUCTION ASPECTS T.G.Hammon d Binnie andPartners ,Londo nS W IP1R X

Abstract

Report onpaper s dealingwit hmiscellaneou s construction aspectso f Polders of theWorld . This group of 10paper s dealswit h geotechnical, hydrogeological aspects ofpolde rdevelopmen t togetherwit hpaper so n thecontro l and testing ofpolde rpumpin g equipment. Thepaper s range widely from schemesdealin gwit h theprotectio no fpolder s fromse a attack toth epossibilitie s of theus eo fundergroun d storageo fwate r insuitabl e geological formations for irrigation. The engineering approach inal l thesepaper s isinnovativ e and interesting tothos e engaged inconstruction .

Listo f papers ThemeB2 :Constructio n Aspects

Authors Title Location 142 J.va nDuivendij k & Designan dConstructio n Guyana J.R. Pieters (Netherlands) of SeaDefence s 329 D.L.Gudgeo n &M.E .Hanna h Raising of theDefence s UK (UK) ofCanve y Island 39 L.van' t Leven Construction ofPolder s Suriname (Suriname)

370 11 M.A.Viergeve r Foundation on Soft Netherlands (Netherlands) Marine Deposits ina Recently Reclaimed Polder 94 L.W.A.va n denElze n& Possibilities ofDik e Netherlands H.L.Janse n (Netherlands) Enlargements increased by useo f theColbon d Vertical Drainage System 96 G.J. Florian &H.J .Vinker s Calculation ofHydrauli c Netherlands (Netherlands) Head fora Rive rEmbank ­ ment Designusin ga Numerical Groundwater Model

503 PeterH .Reite r Test Runsan dAcceptanc e Finland (Finland) Testso fPolde rPumpin g Stations 132 D. Dejas,A .Reinhar d & Control ofPumpin g Poland W.Trzecia k (Poland) Aggregates andMeasure ­ ment ofDischarg e in PolderPumpin g Stations 23 Arata Masumoto Possibility of Using S.E.Asi a (Japan) Underground Dams to IrrigatePolder s in Tropical Areas 108 AntoninoVazque z Guzman ConstructionAspect s in Spain (Spain) thePolder s of theLef t Bank at theLo w QuadalquivirMarshe s

In thegrou p ofpaper s onconstructio n aspects ofpolders ,tw orelat e to theprotectio n of land from the sea inth edifficul t foundation conditions found inestuaries ; fourpaper s relate to thedrainag ean d consolidation of embankments and their stability problems; twopaper s dealwit h theprovisio n ofpumpin g plantan d itscontrol ; onepape r givesa n interesting insight toth epossibilitie s ofundergroun d storage ofwate rnecessar y forpolde r irrigation and the lastpape r dealswit h theconstructio no f apolde r development inSout hWester nSpain .

371 The first paper on thedesig n and construction of these a defencesa t Guyana byva nDuivendij k and Pieters dealswit h thedesig nmethod s adopted for constructing seadefence s ina nexpose d coastal areao f Guyanawher e erosion ofprotectiv e mud banks issubjectin g the coastline toheav ywav e attack andhighe rwav e run-up. The author setsou t the inter-dependence of theparameter s causing erosion and thereason swhic h led to the selection ofa ne w seadefenc e line inshore of theorigina l embankments. This newalignmen t gave theengineer s anopportunit y of designing a seadefenc e systemwhic hwoul d stand up fora minimu mo f 100year swithou tmajo r repair. Thepape r detailswav eobservations , thedesig no f slopes forwav e run-up,surg eetc .an d themode l testing whichwa s carried out,give sa nexplanatio n of thepossibl e reasons for thepreviou s failures and the steps proposed toensur e the securityo f thene w defences on theexpose d Guyaniancoast . Theproblem s inGuyan aar e repeated on theThame s estuary where apape r by Gudgeon and Hannah setsou t themethod s adopted toprotec t theCanve y Island areao f thenort h easternThame s estuary against thecontinuin g ground settlement and increase in tidal levels in thiscorne r of theU K together with the increasing frequency andheigh t of surge tides inth e North Sea. The verywea k clays underlying theembankment s inbot h Guyanaan d Canvey Island pose thegreates t problems to theengineer .I t is interesting tose eho w theseproblem s have been solved. In thecas e ofGuyana ,th eus eo f sheet piling driven at the toeo f the embankment hasbee ndiscontinued ,wherea s atCanve y Island thepilin g isuse d to create ane wraise d coreo n thecentrelin e of theembankment . Thiscor e iscantilevere d toac t asa to e to theraise d downstreamembankment .

InGuyan a anembankmen t profile isuse d witha substantia l berm located at lowwate r and thenrelativel y steep excavation at the face of the bermprovide s the fill for theembankment . At Canvey Island analterna ­ tivearrangemen t usingpulverise d fuelas h fromloca lpowe r stationswa s considered for theupstrea m segment of the raised embankment,backe db y sandfill,bot hprotecte d by suitable drainage layers. Themethod s at Canvey aremor eelaborat e than thosea tGuyan a and thisn o doubt is justified by thenee d toprotec t arelativel y largepopulatio n livingo n the island and theassociate d major industrial base. TheGuyan aprotec -

372 tion is tailored in some respects to thevalu e of thepolder s protected and of the likely consequences of failure. Judgmento f thevalu eo f protectionwork s isdifficul t and in theen dmus t be subjective.

Thenex t group ofpaper s relate to theproblem s ofpoo r foundations, drainage and consolidationme twit h during construction. Thepape r "Construction ofpolder s inSuriname "b yvan' t lieven gives an interesting description of thecondition s found during poldercon ­ struction in theinlan d coastal region of Suriname. Itdescribe s the methods adopted toenabl e drainage canals tob e excavated inriverin e junglewher e thebearin g capacity of the soil iss o lowan d thefores t

sodens e that normal construction equipment cannot bebrough t intous e initially. The step by step approach setsou t themethod s used,firs t toprovid e access and then todewate r the zone tob eexcavated ,an d the final consolidation ofembankments . The load bearing capacity of the soilan d presence of non-cohesive layers in theexcavatio n itself coupled with ahig hexterna l groundwater tablemak e theproble mo f the stability of channel sides amajo r one. The gradual approach onexcava ­ tionadopte d and themetho d developed towor kwit h nature paid off so that thecos t ofne wconstructio nwa skep t toa minimu m and theprojec t properly programmed tocompletion . Thepape r byViergeve r entitled "Foundations on softmarin e deposits in a recently reclaimed polder"deal swit h similar settlement and stability problems encountered onwor k inHolland . Theautho r setsou tth e methods adopted toadap t the fixed structures,suc ha sbridges ,pipe ­ lines,buildings ,etc .t o thehig h settlements encountered innewl y reclaimed land. He dealswit h theproble mo f takingpipeline s or sewers into relatively stable areas froma zon e inwhic hmovemen t iscontin ­ uing. Someexample s ofmethod s developed for overcoming differential settlement are setou ta sar e the investigations necessary togiv e the engineer an indication of thedeformation s tob eexpecte d and the likely magnitude of settlement and subsidence. Thepape r byva n denElze n andJanse n covers a specificmetho d of enabling existing embankments tob e raisedwher e theyhav e settled or newembankment s constructed onpoo r foundationsb yutilizin g drainage methodswhic h reduce foundation porepressure sb y the introduction ofa

373 proprietary "Colbond"vertica l drainage system. Verticalhole sar e first augered,reame d ordrive n into the foundation toa fixe d depth and thedrainag emembran e consisting of anoute r filterjacke t anda n innercentra l corewhic hallow s thefre ereleas eo fwate r isthe n slipped into thehole . Thevertica lhole sar e interconnected bya horizontal drainage layerbefor e the surcharge of theembankmen t is placed. Theconsolidatio n occurring from thepor epressur e reductions due todrainag e canb ecalculate d by theTerzagh i formulae and the eventual stability ofan yembankmen t raising carried out on thedraine d foundations canb eestablished . The "Colbond"system isforme d from polyester fibres forbot h thecoars e inner layeran d theexterna l porous filter. This typeo fproprietar yvertica l drain isuse d inplac eo fth e moreconventiona l sand drainan d isa commercia l applicationo fthi s wellknow ntechnique . Thepape r byFloria nan dVinker s dealswit h thecalculatio n ofth e hydraulic head actingunde r anembankment ,th efoundatio no fwhic hi s connected bya perviou s layer to thehighe r head ina nadjacen triver . Themetho d used adapts anumerica l groundwatermode l todetermin ehea d loss. Inth ecas e studied,a permeabl e coarse sand and gravel layer is intersected by arive rbu t continues asa confine d aquifer underneath adjacent continuous surface claydeposits . Thehea d in therive r thus exertsuplif tpressure s on thecla yo nwhic h construction of embankments was totak eplace . The slip circle analysis of the stability of these embankments had totak e into account theuplif tpressure s occurring beneath them. Theseuplif t pressureswer e reduced by thehea d loss occurring inth eperviou s strata interconnected with theriver . Thetw o dimensional groundwater flowmode l hasbee ndevelope d so that the figuresobtaine d from themode l canb e utilized in the conventional stability analysis of theembankment . An interesting contour projection hasbee nmad e showing thecalculate d hydraulichead s tob eexpecte d from theperviou s layeran d thezone s inwhic h thesehead s could prove critical.

Of thepaper s dealing withpumpin g plant atpolde r pumping stations,th e firstb yReite rdetail s themethod s used tomeasur e the discharges from polderpump san d theproblem s tob eovercom e inth emetho d ofmeasure ­ ment of largequantitie s pumped atrelativel y lowheads . Reiter details

374 the information required and therang e ofaccuracie s whichca nb e expected andwhic hmus t be takenint o account inassessin g theabilit y of thepum p tomee t contract guarantees. Theautho r sets out anumbe r of suggestions for suitablemeasuremen t equipment and points outth e additional requirements to test toensur e thatcavitatio n isno t taking place and that thepowe r inputmeet s specified limits. Thepape r on the control ofpumpin g aggregates and themeasurement so f discharge inpolde r pumping stations byDejas ,Reinhar d and Trzeciak describes ametho d ofmeasuremen t developed inPolan d toachiev e the automatic control of thequantit y pumped byutilizin g a system ofelec ­ trodes in thepumpin gwel l linkedwit hmeasuremen t of thepum p flows

fromventur i system. Theautomati c control systemha sbee nworkin g for twoyear s in threepumpin g stationswit h satisfactory results. The method outlined inth epape r issimpl e and appears relatively robustan d canb eadapte d tomee t therequirement s of anumbe ro fdifferin g inputs andoutput srequire d froma polde rpumpin gstation . Thepape rb yMasumot o dealswit h thepossibilit y ofconstructin gunder ­ ground dams inperviou s formations toprovid e storageo f irrigation water forpolder s intropica l areas. Thepape r gives somedetail so f theexperienc e obtained on theconstructio n ofundergroun d storage in thepermeabl e areaunderlyin gMyak o Island onOkinaw a and suggests that thismetho d of operation could beadopte d inothe r partso f theworld . The author suggests that the large limestone orpermeabl e volcanic zones underlying irrigation areas inIndonesi a offer suchpossibilities . If potablewate r canb ehel d in thesepermeabl e areas rather thanallowin g freedischarg e toth e sea,th ereservoi r created canreduc e thenee d to takewate r for irrigation fromslightl y salineestuarie san d soimprov e riceyield . Themethod suse d atMyak o are setou t in somedetai l including themethod suse d torestrai n groundwater outflow to these a by theconstructio no f groutedmembrane s in thepermeabl e layer. The author suggests theprovisio n of anundergroun d spillway torestric t the retention ofwate r in theaquife r toa nacceptabl e level. Theautho r setsou t themean sb ywhic hundergroun d water supplies canb e conserved and augmented inarea so fhig h intensity rainfall and longdroughts .H e suggests that thisapproac h could proveusefu l ina numbe r of tropical areas,particularl y onisland swher eperviou s zones sucha scora l are

375 present. Similarwor k to thatdescribe d atMyak oha sals obee n successfully carried out inth e southo fFranc e incavernou s limestone areas adjacent to the sea. Theprovisio n of storageb y theconstructio n ofundergroun d dams isinterestin g andunusua l and theextensio n of this method to thecoral s and volcanic ashes intropica l countries deserves furtherattention . Thepape rb yGuzma no n theconstructio n aspects ofpolder s on thelef t bank at theLo wQuadalquivi r Marshes inSevill e gives aver ybrie f des­ cription of themethod s used inconstructio n of thepolder s and the irrigation system installed. Thepape r outlines thedrainag emethod s adopted tocontro l salinity and gives somedetail so f theacces s arrangements to thepolde r zones. Thepape r as submitted isi ngenera l termsan d iti shope d that theautho rwil lb eabl e toexpan d hiswritte n paper atdiscussio n and thusgiv emor e information at the Symposium.

Conclusion

The tenpaper s reviewed inthi s section on theconstructio n of polders arevarie d and interesting and iti shope d that theywil l stimulate discussion.

376 THEMEB SUB-THEME B2: CONSTRUCTION ASPECTS

General reportsby : Ir.J .va nDuivendij k Mr.T.G .Hammon d

Conclusions byDr.ir .H.S .Adhin , chairman

Twenty-one paperswer e submitted on "Construction aspects".Mos to f thesepaper s (15)deal twit h one ormor e aspects ofdike san d embankments.Other s concerned designan d construction issues related to thewater-managemen t systems ofa polder ,suc h aspumpin g stationsan d drainage canals,o rwit h theparticula r problems posed by the founding of structures on recently reclaimed marinedeposits . From thediscussion s held during twoafternoo n sessions the following conclusions canb edrawn : 1.A mor e detailed and more scientific approach isnowaday sbein g used inth edesig nan d forsolvin g construction problems in the fieldso f hydrogeology andgeotechnics . 2.Ther e isa nee d forbette r integration of all factors involved inth e determination of thecres t elevation of anembankment .Thes e factors formpar t ofdiscipline s ashydrology ,hydraulic s and civil engineering,bu t also factors likeenvisage d operationan d maintenance procedures should be integrated into thedesign . 3.Thoug h local circumstances will toa larg e extent determine the designo fearthwork s and structures,a numbe r of generally applicable principles and criteria cannotb e disregarded when designing and constructingpolders . 4. Itwa s apparent from the reports that awid e range of returnperiod s isbein guse d fordeterminin g thecres t elevationo fdykes .I nfact , designwate r levels are selected insuc h amanne r that,i nsom e cases,exceedanc e can takeplac eonc e in2 0year s and inothe rcase s onlyonc e in 10,000years .Fo r the selection of acres t elevation therelationshi p betweeneconomic s on theon ehan d andpsychological ­ lyacceptabl e safetymargin s on theothe rhan d clearly needs tob e considered infurthe rdetail . 377 THEME B 3: AGRICULTURAL ASPECTS

AGRICULTURAL ASPECTS J.W. vanHoor n Department ofLan d andWate r Management University ofAgriculture ,Wageningen ,Th e Netherlands

Abstract

Polders possess some characteristics thatmak e them different fromothe r agricultural areas:soil s ofhig h fertility thatar edraine d systemati­ cally and oftenbette r thanelsewhere ,plo tdimension s designed to obtain lowcosts ,an d selected farmers.Th e combination of thesecharac ­ teristicsma ywel l lead tohighe ryields . Introduction Themajo r aimo freclaimin g polders isagricultur e and,indeed ,farmin g is themai nactivit y inpolder s inTh eNetherland s and inothe rcoun ­ tries of theworld .Hoeve' spape r on thesignificanc e of agriculture in theDutc h IJsselmeer polders shows thechange s in land use infou r polders reclaimed insuccessio nove r aperio d of fortyyears .Eve ni n themos t recently reclaimed polder,mor e than5 0pe r cent of the landi s used foragriculture , theres tbein g reserved forurbanization ,forestr y andrecreation .

Only relatively fewpaper shav ebee npresente d onagricultura l aspects ofpolders ,warrantin g theassumptio n either that thenumbe r ofpaper s is inversely proportional toth e importance of the topico r thatagri ­ culture inpolder s isno tparticularl y different from agricultureelse ­ where. Indeed noneo f thepaper s reveal any systematic difference between polders and other areas,i ncrops ,soi l tillage,sowing ,cro pprotec ­ tion,an dharvesting .A s elsewhere,part so fpolder s canb euse d for forestry.I n theearl y IJsselmeer polders,forestr ywa s limited tosoil s unsuitable for agriculture,bu t in thelate rpolder s forestry coversa larger areabecaus eplanner s aredevotin gmor e attention torecreationa l needs.

378 Nevertheless thepaper spresente d at thissymposiu m show that therear e somesignifican t agricultural differences due to the intrinsic natureo f polders.

Soils

Soils inpolder s arealluvia l inorigin ,eithe rmarin e or fluvial,s o their topography isflat .Sinc e thewatertabl e isalread y shallowunde r naturalconditions ,artificia ldrainag e isalway snecessary .Wit h the systematic application offiel d drainage,watertabl e control inpolder s isusuall y better thanelsewhere .Th edrainag e systems areeithe rsur ­ faceo rsubsurfac esystems . Surfacedrainag e isgenerall y applied in tropicalregions ,e.g .i n Surinam and Indonesia.Ther ear esevera lreason s for this:hig h rainfall intensity,lo wpermeabilit y ofcla y soils,o rn onee d for adee pwater - table inarea swher eric e isgrown .Th epape r of daCosta ,'Agricultura l aspects ofbanan a cultivation inpolder s inSurinam' ,underline s the need fordrai nmaintenance ,notwithstandin g itshig h cost,sinc eepxeri - enceha s shown thata deterioratio n of thedrainag e system results ina rapid decline inproduction . InWesterhout' spaper , 'Agriculturaldevel ­ opment of tidal lands inIndonesia' ,wate rmanagemen t isconsidere d the key factor for successful development.Aci d sulphate soils posea specialproblem .The y require acareful ,gradua l lowering of thewater - table tocontro l theacidificatio nan d theremova l ofacids . Traditionally, surfacedrainag ewa s also applied inDutc hpolders .Grad ­ ually,o narabl e land,i twa s replaced by subsurfacedrainage ,wherea s ongrasslan d itcontinue d tob eapplie d for alonge r time.Th erapi d development ofhigh-intensit y dairy farming inth epas t thirty years required improvedwate rmanagemen t toincreas e thebearin g capacity of grassland and tominimiz e thedamag ecause d bypoaching .Thi s explains the tendency of lowering thewate r level in theditche s and ofreplacin g surfacedrainag eb y subsurfacedrainage .I nth eIJsselmee rpolder s subsurfacedrainag e isapplie d everywhere,o ngrasslan d aswel l aso n arableland .

Polder soils arenormall y fertile soils.Wher epea t soils occur,oxida ­ tiono forgani cmatte r releases aconsiderabl e amount ofnitroge nfo r

379 thecrop sbu t isals o themai ncaus e of subsidence.A spointe d outb y vanWallenbur g andWestervel d in theirpape r 'Peatpolder s inth e westernpar to fTh eNetherlands' ,maintenanc e of theditche s by dredging and deposition of themu dmixe d withmanur e gradually changed thecompo ­ sition of the topsoi lb y increasing theminera l components,san d and clay,an d in thiswa y led toa chang e inlan d use suitability.

Crops

The choiceo f thecrop s inpolder s depends onwatertabl e control.I n shallowwatertabl e areas,gras s is themai n crop ina temperatehumi d climate and rice ina tropicalhumi d climateowin g to their shallowroo t systems.Arabl e crops and treecrop s require adee pwatertable .Th e paper presented byva nGoor ,Groenhuis ,an d Jacobs: 'Forestry andfor ­ estry research' shows the importance of thepopla r as apionee r species inth eIJsselmee rpolders .

Plot dimensions

Newly reclaimed land offers theopportunit y of choosing optimumplo t dimensions. Aspointe d outb yMoen s inhi spape r 'Agricultural mechanization and plotdimension s inpolde r development projects',plo t dimensions havea n impacto nyiel d levels,o n thecos to f constructing andmaintainin g road and drainage systems,an d on thecos to f agricultural production.Th e problem inplannin g consists indecidin g onplo t dimensions thatoffe r thebes t solutionfo r the immediate futurebu t dono t impede long-term developments infar m size andmechanization .Va nDijk ,Erdman ,an d Idoe, in theirpape r 'Mechanized riceproductio n inSurinam' ,sho w theeffec t of largemechanize d estates on themechanizatio n level of smallfarms .

Farmers

In theselectio n of farmers for theIJsselmee r polders,technica l

380 skills,financia lmeans ,an d personal qualities sucha s leadership are takenint oaccount . Westerhout'spape r on 'Agricultural development of tidal lands in Indonesia'mention s spontaneous and transmigrant settlers,bu tn oselec ­ tioncriteri a areapplied .Th eai mo f thisdevelopmen t is toprovid e landless ruralpeopl e andpoo r farmerswit h apiec e of land.On emay , however,assum e thatonl y themos t active among landlesspeopl e andpoo r farmers arewillin g totransmigrat e and thus form themajorit y of the new farmers.Thi smean s thathere ,too ,th efarmer s in thepolde r area selected group.

Yield level

Young polders often showa highe ryiel d level thanelsewhere .Fo r example,th eyield s inEaster nFlevoland ,on eo f theIJsselmee rpolders , are 20 to5 0pe r centhighe r than theaverag e forTh eNetherlands , winterwhea t showing thesmalles t difference and potatoes thelargest . Vande rZaag ,comparin g EasternFlevolan dwit h older polders inTh e Netherlands inhi spape r 'Yield and quality ofpotatoe s produced inth e newpolder s inTh eNetherlands' ,point sou t thatno t only is theyiel d betterbu t also thequality .H eascribe s thedifferenc e toa bette r water supply,which ,i n turn,lead s togreate r root activity and deeper rooting of thecrops .

On theothe rhand ,shortcoming s inth ewate rmanagemen tma y cause seriousdrawback s infurthe r developing agriculture inpolders . VanBoheeme ne t al.,i nthei rpape r 'Effects of freshwate r supplyo f SchouwenDuiveland ,Th eNetherlands 'discus s amode l thatallow s the need for fresh-water supply ina polde r tob edetermined .The y provide datao f theeffec t that supplying fresh surfacewate r toa polde rma y have on theagricultura lproduction .A n important itemo f this typeo f forecasting isth epossibilit y for thefarmer s tochang e their cropping patterns by including inthe mcrop swit hhig hmarke t values.Whe n fresh water isavailable ,eve nunde r humid climatic conditions,farmer s can thusrais e theirincome .

381 References

Boheemen,P.J.M ,van ,P.J . Kusse,C .Maa s andJ.W .Wesseling .Effect so f freshwate r supply ofSchouwe nDuiveland ,Th eNetherlands . DaCosta ,I.Chs .Agricultura l aspects ofbanan a cultivation inpolder s

Suriname. Dijk,A.D .van ,J.W . Erdmanan dM.J .Idoe .Mechanize d riceproductio n in Suriname. Goor,C.P .van ,B .Groenhui s andL .Jacobs .Forestr y and forestry research. Hoeve,H .Th e significance of agriculture in theDutc h IJsselmeer- polders. Hoeve,H . Criteria for thedeterminatio n of themomen t of suitability forprivat e agricultural land useo f clay and loamy clay soils inth e DutchIJsselmeerpolders . Moens,A .Agricultura lmechanizatio n andplo tdimension s inpolde r developmentprojects . Wallenburg,C .va nan dG.J.W .Westerveld .Pea tpolder s in thewester n parto fTh eNetherlands . Westerhout,J .Agricultura l development of tidal lands inIndonesia . Zaag,D.E .va nder .Yiel d andqualit y ofpotatoe s produced in thene w polders inTh eNetherlands .

382 THEMEB SUB-THEME B3:AGRICULTURA LASPECT S

General reportby : Dr.ir.J.W . vanHoor n

Conclusions by Dr.R.J.A .Dudal , chairman

Notwithstanding the fact thatonl y alimite d numbero fpaper s on specific agricultural aspects ofpolder swa spresented , itwa s still possible toarriv e ata numbe r of important conclusions and recommendations. 1.Th emajo r aimo fpolde r reclamation isagriculture .Thi s implies that polderproject s should be regarded primarily as agricultural development projects and that soilscientists ,agronomists , agricultural economists,agricultura l extension specialists should begive na mor e responsible role inprojec t identification,design , appraisal and implementation. 2.Thoug h agricultural practices inpolder s areno t particularly different from thoseo nothe r farmland itshoul db e realized that for the farmers thepolde r environment isofte n strikingly different from the conditions of the landswher e they came from.Possibl e new crops orcroppin gpattern s shouldb e tested and demonstrated in pilot areas and farmers should be given full support toadap t toth e newconditions . 3.I narea swhic h arealread y cultivated, theopinion s ofa representative range of farmers shouldb e sought inadvanc e regarding the future farmmanagemen twit h thepropose d project inputs.I t should especially be assessed if larger farm sizesan d projected intensificationar ewithi n theirreach . A.Wit h the transfero f technologies itshoul d be takenint o account thatpolder s and lands tob e reclaimed occur underver y different agro-ecological conditions invariou s partso f theworld ,no tonl y with regard tosoils ,climate ,micro-fauna ,wate rquality ,whic h all have aninfluenc e onprojec t designan dmod eo f development.Throug h land evaluationon e should appraise the type(s)o f landuse tob e

383 recommended inaccordanc ewit h theproductio npotential . 5.I ndevelope d polders soil and crop conditions on thedifferen tagro - ecological land typeswithi nprojec t areas should bemonitore d regularly soa s toprovid e earlywarning s of anyphysical ,chemica l orbiologica l problemswhic h may develop (e.g.deterioratio n ofsoi l structure,acidification ,subsidence ,salinity) .Practica l solutions will have tob e applied,possibl y including solutionswhic hmigh t require themodificatio n ofprojec t designo roperation . 6.Agricultura l aspects ofpolde r development should not be separated from socio-economic aspects sucha s theestablishmen t of services and institutions,credi t andmarke t facilities,mobilizatio no f human resources andpricin gpolicie s soa s toensur e thatbot h farmers and investors canachiev eprofitabl e returns.Concurrentl ya selection of the settlersma yb e desirable inorde r toobtai na n optimum response and promote acollectiv e approach. 7.I t issuggeste d that anumbe r of criteriab e developed,fro mth e angle of agriculture,t orationall y determine desirable cropping patterns,far mmanagemen t systems,labou r inputs,level so f technology,need s for training and research,t ob e applied ina specific polder development site.Suc h criteria couldb e testedb y studying these factors insuccesfu lpolder s and inpolder swhic h have failed.Suc h criteria could alsob e used as indicators to monitor progress innewl y developed areas and to initiate adjustmentswher eneeded .

384 THEME B 4: SOCIO-ECONOMIC AND PHYSICAL PLANNING ASPECTS

SUB-THEME:PHYSICA L PLANNING H.J.Groenewege n PublicWorks ,Rotterdam ,Th eNetherland s

1 Introduction

Relating toth edevelopmen t of theDutc h IJsselmeerpolders Constandse states: "The fact that thesepolder s are soclearl y aproduc t of their time isprobabl y typical forpolder s as such,becaus e polders areflat , Prerathe r undifferentiated,hav e hardly any historical landmarks,an d give thereforeth eplanner s ahig hdegre e of freedom fordesigning .Thi s isi n itself fascinating,bu t itgive s also aheav y responsibility and the absence of guidelines present in theexistin g environment,cause s decisionmakin g tob e oftenlaborious "(Constandse , 1982). This statement clearlymark s thefeature s of the challenging task peculiar toplannin g innewl y reclaimed polders.Moreove r itapplie st o theplannin g task tob e executed in large reclamationprojects ,no t necessarily comprising polders as such,example s ofwhic h canb e found throughout theworld ,e.g . theextensiv e transmigration schemes in Indonesia aswel l as the desert-reclamation-projects inEgypt . Therefore it should beborn e inmind , that thepaper spresente d inthi s report,a swel l as thediscussio n points evoked, inprincipl e dohav e significance concerning thesepolderles sprojects .

Considering the statement cited above asmarkin g the specific features ofphysica lplannin g inpolder s it appears that only three out ofth e eightpaper spresente d within this themedirectl y dealwit h the subject involved. These paperswil lb e discussed inpar .2 . More indirectly covering someo f the features presented are twopapers ,

385 tob e presented inpar .3 . Physicalplannin g andpolder s appear tob epu t together ina rathe r differentway , inth eothe r threepaper sreceived . Thispaper s actually dealwit h theproces s ofphysica lplannin ga tth e national level,puttin g up therelatio nbetwee n (aspects of),th e nationalpolic y and thedevelopmen t -o r non-development- o fth e IJsselmeerpolders.The ywil lb e dealtwit h inpar .4 ,usin g the last IJsselmeerpolder-to-be (Markerwaard) asa n illustrativecase .

2 Physicalplannin g inpolders , methodologies used

Within thepas tmillenar y ofDutc hpolder-developmen t major changes have takenplac e (Constandse, 1982) successive scale-enlargement Starting from small-scale reclamations inorde r toenlarg e one's own land,larg epolder su p tohundred so f squarekilometre shav e been reclaimed

- monofunctional tomultifunctiona l Frompur e agricultural use tocomple xus e ashousing ,industry , agriculture,recreatio n andnatura lareas ,

growing state-involvement While enlarging scaleo f thepolder s andmostl y due toth e growing complexity of thegoal s set,involvemen t of the statet o develop acomprehensivel yplanne d society became indispensable.

Considering (polder-)reclamationproject s throughout theworl d onema y observe that inmos t countries the first twochange s did occur in little timeo rn o time atall ,whil e appropriate state involvement within the task of comprehensive planning isn't amatte r ofcourse , mostly due tolac ko f "planninghistory" . Thepaper s reported upon inthi sparagrap h dooffe r somevaluabl e history-based experienceswhic hma yb eapplicabl ei ncurren t reclamation projects.

386 ft * ft Rijpert in "Shops and shopping centresi nth e IJsselmeerpolders" deals with the approach developed to obtain a balanced retail trade composi­ tion within the IJsselmeerpolders. Although directed, specifically, to the retail trade sector, this approach in an adapted way may be of use in planning other sectors in a reclamation area.

Rijpert goes through the shopping history of the 20th-century Dutch polders seeing with respect to the Wieringermeerpolder (1930). "The only statement was to be found on the allocation of shopping facilities in the new polders said that it was to be expected that settlements of people would arise on the main crossings of roads and canals and that possibilities had to be created for the establishment of shops. And that was all there was said to it".

The planning effort confined itself to the monofunctional agricultural purpose of the polder and due to non-planning the retailtrad e sector shopkeepers without enough professional knowledge could open a large amount of shops and "for a long period of time there was a chaotic situation during which supply and demand were completely out of balance". Concerning the North-East Polder (± 1946) it is pointed out that a, theoretical demand and supply model has been applied - looking at things after the event simple and imperfect,bu ta t the time 20 years ahead of common use in the Netherlands - being "effective in the sense that the chaotic and unbalanced situations of the Wieringermeer did not exist" and developments could be kept in sight and regulated to a great extent. A crucial role in the model's implementation was played by the Development Authority,whic h built a certain amount of shops and thoroughly selected the shopkeepers. At first only based on general experience, the theoretical side of the model used, was built upon the practical experiences of shopkeepers and customers, this being the starting point of distribution planning "Gradually a policy was developed to establish retail trade facilities in a responsible way based on theoretical principles". And during the colonization of Eastern Flevoland (± 1967) this model - outlines presented by Rijpert - was used to "determine at any moment in the future the amount of square metres necessary for shopping

387 facilities inth edefine d area".Rijper t inhi spape rmor e indetai l discusses the regular surveys,carrie d out,t oadjus t themode l applied. Concluding this report Iwoul d like topu t forward somemor e general theses: Toestablis h awel l functioning retail trade (oran y other)secto r ina ne wpolde r (reclamation area)carefu l selection,o r adapted education of tenants isneeded .A state-owned Development Authority isth ebes twa y tod oso . Planning developments ina polde r (reclamation area)- force db y the special circumstances -ar e commonly farahea d of the developments inthi s field ona nationa l scale. (Rijpertpresent s evidence to this thesis,wit h respect toth eplannin g ofretai l trade). Itha s tob e attempted toadjus t theexperienc e based Dutchpolder - planning for appliance incountries ,confronte d with relatively sudden,larg e scale,multifunctiona l impoldering (reclamation) projects.

A * * Inthei rpape r"Lan devaluatio n foragricultura l development inLeziri a Grande,Portugal" ,Reis ,Perdiga o and Perdigaopresen t acas e inwhic h the F.A.O. Land evaluationmethodolog y was applied inPortuga l forth e first time. In thisprojec t the following goals had tob e reached: "increasing land productivity,providin gmor e employment opportunities, obtainingmor e export produces and avoiding imported ones,a swel la s promoting abette r incomedistribution" . As the authors already signal thenearl y impossible task toclearl y present themethodolog y inthei r limited paper -howeve r actually succeeded in trying this- Iwon' t try tod o so ina neve nmor e restrictedway .Thei r conclusion however iswort h tob e cited asb y using themethodolog y described itappeare d that:"th epresen tproduc ­ tivecapacit y ofLeziri a isver ymuc hbelo w itspotentialities .Wit h the land improvements some of the limitations canb e totallyo r partially removed,resultin g inhighe r yields,landus e intensification, increasing irrigated area aswel l as introduction ofne wcrop san d landusesystems" . Inspit eo f the formulated multifunctional goals,th edescriptio n ofth e methodology used aswel l as theconclusio n drawn,d o give the impression

388 of arathe rmonofunctiona l (agriculture) macro economic approach.I n thehistor y ofDutc hpolde r planning on thecontrar y gradually nextt o economical,sociopolitica l factorshav ebee n taken intoaccount ,whil e multifunctionality replacedmonofunctionality . Inm yvie wbot h approaches arevaluabl e up toa certai n "moment".Th e question ishowever ,whic h features do indicate this "moment". Isi t the size of the reclamation project,th edistanc e toth enearb y already structured "old land",th e structure of theol d land assuch , thecountry' s availableplannin g capacity, the origin of the future population,th eregiona l ornationa l market conditions? Ord oothe r features play arol e and how should thedesire d extensivenessb edeter- « minedo f theapproac h tob eapplied . *

"Qualitative spatial planningmodel s forne w urban fringe areas"ar e presented inWezenaar' s so-called paper.Thi spape r actually reflects theplanners 'hig hdegre e of freedom indesignin g and the laborious decisionmakin gproces s inpolde r pLanning. With respect toAlmere' s Buitenruimte (OuterArea )Wezenaa r sketches the sheer infinite opportunities presented by the site itself,whil e on the other hand theabsenc eo fguideline s in theexistin g environment and the inexperience with theplanne d rateo f growth dohampe r theplannin g task.

Theplannin g philosophy,wit h respect to theBuitenruimt e -base d upon theprinciple s of coherence and diversity - iselaborated . The future usersbein g involved in theplannin gprocess ,b yplayin g aso-calle d preference budget game.Thi s involvement -i nwhic h the future inhabi­ tant isaske d to select anumbe r of attractive environments,considerin g a limited purchase capacity -appear s tob e asucces sbot h topartici ­ pants aswel l as toplanners . "For future urban fringe areaswher e not yet adevelopmen t likeaffores ­ tation took place,anothe r elaboration of the general development strategywa shandled . Reason for thiswa s thepreferenc e budget game model beingbase d upon certain recreaction designations. Itgive sn o cluefo ral lpossibl e urban fringe elements ofnon-recreationa l character. Soa structura l theme,a "leitbild" isneeded .Th e following concept has

389 been chosen: thephenomenologica l orientationwit h regard to thetown . Itha s toorganiz e the spatialplannin go nmicr o level.Th ebas efo r thisconcep t isth e idea that cities are artifacts andworld so f artifice placed atvaryin g distances fromhuma n conditions close to nature". Wezenaar extensively dealswit h thismode l and finally concludes "The described model hasbee n tried out infou rhistorica l old land urban fringe areas.Becaus e themode lmatche s therea l situation itca nals o be used outside thepolders" . Another evidence of the innovative potentialities of the challenging tasko f "polder planning"?

3 Opportunities and restrictions

Braaksma in"Polder san d landfills asalternativ e sites formajo rair ­ ports"briefl y considers theopportunitie s ofpolder s and landfills in locating space-consuming airports.Thi sbecaus e of "many of themajo r citieso f theworl d are located adjacent tobodie s ofwater" . The landfill concept appears tob e applied for several airportexten ­ sionswhil e alsopart s ofne wairport s havebee nbase d uponlandfills . Several examples are sketched. "The polder concept canb euse dwher e thedept ho fwater ,o r theavaila ­ bility of fillpreclude s the construction of a landfillalternative" . Although severalfeasibilit ystudie shav ebee nperforme d- depth s from< 5 to4 0metre sbelo w sea-level-"to date thepolde r concept hasno tbee n used ". Presenting(off-shore)sit eevaluatio n criteria,a summary of (dis-) advantages isgiven ,bu t actually Braaksma's last conclusion totally explains thepresent-da y situation."Economically ,offshor e airports appear tob edifficul t tojustify .The y require huge capital investments. Inth e light ofth e current economic state of theworl d it istherefor e not surprising tonot e thatver y fewoffshor e airports havebee nbuilt" .

* * In "Dopolder s adapt tothei renvironment "Bo s states "itmus tb e clear that ane wentity ,e.g . apolder ,ha s got itsow n spatial identity and

390 that isfull y appreciated.Bu t life cana tan y scalemak e social, functional and through these also spatial linksbetwee n old andnew , making old and newon ediver sbu t organic pattern".Example so f different scale arepresented .Wit hrespec t to theHaarlemmermee r ".... the subur­ banizationpressur e of these twocitie s (Amsterdam and Haarlem)wa s such thatne wresidentia l areaswer ebein gplanne d inth epolde r ....". TheNort hEastpolder : " East of thepolde r theare a iso fpoo r agricultural value and poorly populated,bu t ofhig h touristicvalue . This caused the twowood s along theeas tborde r tobecom e centres for recreational activity"an d " threevillage s inth e southeas t sectiono f thepolde r attract quite afe wpeople ,commutor sfro mth e old land ". ThusBo s shows that "through quite afe w functions old andne wlan d mutually influence eachother ,thu s integrating thepolde r init s environment". With respect toSingapor e andAlmer e iti s shown that city planning techniques arequit e able totranscen d theborde rline . Ica nendors e Bos'answe r "they should"t ohi s ownpose d questionwit h respect to the socialan d functional linkage of old andne w land. But inm yview ,n oconvincin g arguments -a t leasto n the larger scale- havebee npu t forward toendors e thisanswe rwit h respect toth e spatial linkage,althoug h from theexample s given it isobviou s thatpolder s "could"adap t tothei r environment.Can' t ashar pborderin g linegiv e asmuc h spatial satisfaction asa n integrated one?

4 TheMarkerwaar d case

At theBarrie r Dam of the IJsselmeer there isa monumen t onwhic h is sculptured the famous slogan "Anatio n that isalive ,build s for its future".Reclamatio n of theMarkerwaar d - the lastpar t of the project -a t themomen t however isn o longer amatte r ofcourse . The Markerwaard,bein g themai n issue inth eNetherlands ,whe ndiscus ­ singpolder s and physical planning ona natio nwid e scale isdiscusse d inthre epapers .

391 EUROPE / HOLLAND âA S /( H, « f ( chjjM/ AmsietdarP^ Tht Hagut O Rottirdim

GERMANY 7 y^VvN BELGIUM y^ —*«sr

Figure 1: Realised parto fth eZuiderze e project and theplanne d Markerwaard alter­ native.

392 * * Spierings in"Urbanizatio n inDutc hpolders ;th eevolutio n of theRand ­ stad conception"onl y incidentally mentions theMarkerwaard ,howeve r his paper is important when trying toretrac e thedevelopmen t in therol e of thepolders ,wit hrespec t to thenationa l physical planningpolicy , within thepas t twentyyears . Ina ver y compactwa y Spierings dealswit h the "continuing contest between contracting andwidenin g forces"withi nDutc hphysica l planning policy. With respect toth e roleo f thepolder s in thispolic y he showsth e significant change ingoal swhic h has takenplace .Afte r thepublicatio n of the first "Report onphysica lplannin g inth eNetherlands " (1961), thispolic ywa s implemented inth elong-ter m planning of the IJsselmeer region "Astructur e plan for the Southern IJsselmeerpolders" (1961). Inthi spla nLelysta d "beingdesigne d as the regional centre of the , theMarkerwaar d and bothpart so fFlevolan d (intended number of inhabitants 30.000), itsfunctio n and sizeha dbee npu tmore ­ over inrelatio n to theurbanizatio n process invie w in thenorther n Randstad (new target:abou t 100.000 inn.)". The originalwidenin g trend inphysica l policy, turned intoa contract ­ ing trend inth e seventies and " recommended adequate housingpro ­ duction and urbanrenewal ,s oadvertise d more concentration ofal l urban functionswithi ncertai nareas ,th eagglomeration s and thenea r vicinity".Th epolder s did offer opportunities tomee t thischallenge s Lelystad (target: 100.000 inh.)an dAlmer e (target -a sbein g apur e satellite ofAmsterda m -:250.00 0 inh.)actuall y reflect the tremendous change inphysica lpolic y designating polders originallymean t for agricultural use toarea s asa habita t forabou t half amillio no f people. Spierings doespresen t -withou t stating soexplicitl y -th eabilit y of the southern IJsselmeerpolders tofi twithi n thechangin gphysica l planningpolic y -du e tothei rver y ownnatur eo f rather unrestricted opportunities.Wit hrespec t to the lastpolde r tob e reclaimed hecon ­ cludes "As fara s thereclaimin g of theMarkerwaar d isconcerned ,th e future developments onspatia l policy and practice will influence deeply the functions of this lastpolde r inth e IJssellake region,designe d in

393 the 19thcentury ,whe n itwil l be drained". * A * In"Th e IJsselmeer area:Th eprotectio n of anatura l freshwate r area of international importance"va nGrondell e calls attention toth e impor­ tance of theproces s of "reorientatio n on thenecessit y of reclaiming theMarkermeer" . Inhi svie w thereclamatio n scheme for this lake -a s proposed by theDutc h government-"i sa clea rviolatio n of theWetland s Convention (1972;ratifie d by theDutc h government)accordin g towhic h the conservation and carefulmanagemen t of thiswetlan d of international importance should prevail".Moreove r he states "Invie w of thisdevelop ­ ment- thechang eo fphysica lplannin gpolic y toa muc h strangercon ­ centration of urbandevelopmen t (see Spierings'papers )- on eca n understand that serious doubts arise about thenecessit y of theMarker ­ waard polder".Continuin g headd s "Tobuil d thene wpolde rwoul d bet o fightth esymptom s instead of the true reasons willmea n afre ehan d toth e space-wasting processwhic h increases theproblem s isthere ­ fore contrary toth e government policy onphysica l planning". Hismajo r point of critism concerning thedecision-makin g processi s the lack ofalternative s inth e government'sdra ftdecisio n forreclama ­ tion,especiall y "the lacko f anelaborate d alternative for thedevelop ­ ment of the IJsselmeer areawithou t theMarkerwaar d polder".H epresent s a short sketch for thisdevelopmen t defining "thevalue s ofecology , landscape and cultural history of this area as thebasi c values",com ­ bining thesewit h other functions of thearea . Concluding he states "inm yopinion ,i ti snecessar y togetherwit h every proposal forreclamatio n -wher e ever itma yb e inth eworl d -t o also seriously consider the alternative:developmen twithou t reclama­ tion".

A

* A Goverde in "Decision criteria:difference s and shiftsbetwee n insiders and outsiders inDutc hpolde r decisionmaking "attempts ,b y using the Markerwaard case,t o illustrate his theoretical proposition that "there isa stron g relationbetwee n the competition of individuals,group san d institutions forbette r power positions and thedecisio ncriteri awhic h willb euse d inth e finaldecisio n taking".

394 Inm yview ,withi n theMarkerwaar d decisionproces s during thelas t decade, thedecisio n criteriadi dno tchange ,bu t the seto f criteria used,ha sbee ncomplete d by outsiders and aconsiderabl e change of importancy level of the criteria considered has takenplace .Howeve r renouncing discussion onthi smatte r ofdefinitions ,I woul d liket o put forward some important features of thedecisio nprocess ,a spresen ­ tedb yGoverde . In 1972th eministe r of Traffic andWaterstaa t publishes adiscussio n nota concerning theMarkerwaard . Sixreclamatio n options (including the non-reclaiming onear epresented . Thesesi xoption s arepu t topubli c participation,whil e inth emeantim e one alternative iselaborate d by theDevelopmen t Authority andadde d into theparticipatio n process,alread y being on itsway . Partly due to the arguments addedb y thepubli cparticipatio n itappear s that someadvisor y boards are largely divided, largeminoritie sno t (yet)bein g convinced of thedesirabilit y of thene wpolder . TheCabine t decides toa mor e extensive and formally regulated public participation procedure.Onl y one (large scale)reclamatio n scheme (the oneelaborate d by theD.A. ) canb ediscusse d upon.Durin g thepartici ­ pationproces s a substantial amount of "new"alternative semerges . Actually theproble m setting asa whol e did change.Formall y thegovern ­ ment stillpose s oneoption ,bu tpressur e ispu t uponalternatives . Thisprofoun d change tookplac ebecause ,a sGoverd e states,th eaccessi ­ bility of thedecisio n takers toth e insiders of theMarkerwaar dopposi ­ tiondi d fairly increase,an d theonc e exclusive support for thepro - Markerwaard position (scientific research,plannin gprocedures ,symbols ) isno wals ouse db y the opponents."I n summary thepowe r balance sheet was slightly shifted toward theanti-Markerwaar d position Forth e decision takers,however ,th epresent-da y condition of thepowe r balance sheet isa nuncomfortabl e one.Therefor e themos t likelyprospec t for the futurewil lb e adeliberat epolic y ofnon-decisio nmaking" . *

* A Tocomplet e theMarkerwaar d picture -a sfa r aspossibl ewithi n this brief context - Iwil lpresen t somemai n features of the 1980govern ­ ment's draftdecision . Reclaiming theMarkerwaar d offers opportunities toa numbe r of space

395 consuming activities.Th evalu e of aMarkerwaar d with respect toth e spatial development of theNetherland s asa whol e however ismor e impor­ tant,tha n thevalu e to specific activities. (Corresponding with theabilit y ofadjustin g tochange s inphysica l policy as shownb y Spierings). Due to its geographical position and thenatur e of itsundergroun d the Markerwaard offers specific opportunities to several sectors likeurba ­ nization,agriculture ,forestry ,recreatio n (withexceptio n of large scale shipping)a secondnationa lairport ,a larg emilitar y training ground. An essential element inweighin g thenee d forreclamatio n isth eexpec ­ tation thatphysica lpressur e inth eNetherland s keeps increasing.A s first useo f apolde r canonl yb emad e 13-15year s after the starto f reclamation,i nvie wo f increasing spatial pressure reclamation hast o startprett y soon.Fo r the samereaso no f time-span detailed planning at themomen t isn'tpossible . The reclamation schemeproposed ,doe s giveenoug hremainin g opportunities to sectorswhic hwil l beaffecte d by thereclamatio na s fishery,natur e conservation, landscape and cultural history. *

It isdifficul t toextrac t general features of theMarkerwaar d issue, worth tob e discussed by aforeig n audience.Therefor e Iwoul d confine myself to some reflections,no tnecessaril y comprising theke y features of the issue,bu tmean t as incentives for discussion (andno t necessarily reflecting the author's opinion). Duringa long termreclamatio nproces s theDevelopmen t Authority involved,acquire s alo t of specific experience and knowledge. Ina continued planningproces s thisma y lead totechnocrati c planning principles forprestigeou s self invented objects,a sdecisio n takers aren o longer able todeman d aneutra l problem setting. Ina recla ­ mationproces s possiblyt ob eterminate dth eAuthorit y's nee dt osurviv e mayals oobscur eth eproblem ,setting .Th equestio narise swhethe r Development Authorities donee d aspecifi c democratic control,an d if soi nwhic hwa y this should be realised. The firstDutc hpolder swer ereclaimed ,withou t consideringalterna ­ tives.Usefulnes s oreve nnecessit y ofreclamation s wasobvious .

396 Nowadays inman y countries the same situation applies tomos t recla­ mation projects.Grondell e however actually doesplea d for aworld - wide considering of theno nreclamatio n option.Question s arise such as, fromwhic h scale alternatives have tob e considered or evenca n be considered and towhic h extent alternatives have tob e considered (e.g.withi n the totalnationa l physical policy). Uncertainty nowadays isa keywor d inDutc hpolde r decisionmaking . TheFlevopolder s afterward appeared tooffe r important opportunities inrealisin g thechangin gphysica l policy advocated. Timespan needed toreclai m theMarkerwaar d isabou t 15year s and uncertainty exists with respect to the future situation. Isi tresponsibl e torely-a s the government does -upo n theMarkerwaardpolde r playing acorres ­ ponding role in theyea r 2000.Eve n ifal lexistin g options fail toexist ,a t least alarg e natural areaha sbee n created?

5 Conclusion

From thepaper s presented itha s tob e concluded that the theme physical planning inpolder sdoe shav eman y facets.Mos t of these facets equally beingapplicabl e toreclamatio n projects ingeneral . Thisrepor t only dealswit hver y little of therelevan t facets.Man y reclamation/impolderingproject s throughout theworl d are on theirway , each undoubtedly confronting acomple x task inth e field ofplanning . Therefore appropriateway shav e tob e found to transfer the large amount ofexperience-base d knowledge and expertise fromwher e itha sbee n gathered, towher e itisneeded .

Reference

Constandse,A.K. , 1982.Fro m Spontaneous Settlement to Integrated Planning andDevelopment .Pape r tob e presented at "Polders inth e World",Octobe r 4-10-1982,Lelystad , TheNetherlands .

397 SUB-THEME: SOCIO-ECONOMIC ASPECTS D.B.W.M.van Dusseldorp Agricultural University,Wageninßen ,Th eNetherland s P.N.G.van Steekelenburg International Institute forLan d Reclamationan d Improvement,Wageningen ,Th eNetherland s

INTRODUCTION

For thediscussio n in theworksho p socio-economic aspects ofpolde r development, 14paper swer emad e available to thereporters .Te no fth e papers focus onth e IJsselmeerpolderso r at least onTh eNetherland s and fourar edealin gwit h settlement activities inothe r countries,b ei t notonl y polders. Iti sclea r that through thisse to fpaper s nota balanced picture ispresente d on thesocio-economi c problemswit h regard topolder s in theworld . Thepaper shav ebee ndivide d into twomai ncategories . 1 papers dealingwit h polders and settlements outside TheNetherland s (Awanan d Latif;Oyedipe ;Smit ;Steenwinkel) . 2 The IJsselmeerpolders (Netherlands) Papers in thiscategor y are rather arbitrarily organised infou r groups.: a sociological andhistorica l aspects (Constandse;Hoeve ;Schenk ) bmanagemen t and administration (DenHertog ;va nde r Spek) c roleo fne wcentre s and employment (Fels;Scherjo n andVerhoef ) d landuse and recreation (TerHaar ;Hengeveld ;Hoeve )

398 Ashor t abstract of the fourteenpaper s isi sgive nhereafter .

SHORTABSTRAC TO FTH EPAPER S

2.1 Paperso npolder s and settlements outside TheNetherland s

- Thepape r ofAwa nan d Latif dealswit h 'Socio-economic aspects of water management of salinity control and reclamation project no. 1 in Pakistan: a case study'. Theresult s of thepre -an d post-project evaluation and thesocio-economi c impact of theprojec t arediscussed . Inthi spilo tprojec t of0. 5 millionhectare s inth eIndus-plai ntube - wellsar e installed whoshoul d lower thever y high groundwatertable, decreasewate r logging,hel p toreclai m salt-affected soilsan d providemor e irrigationwater .Althoug h thehig h investment inth e tubewellswa s justified in terms ofhighe r cropping intensity and expected higheryields ,th eresult s showquit e adifferen tpicture . Due toth ehig h capacity of thetubewell s installed and theirpositio ­ ning,combine d with inadequate and irregular organizationo fwate r allocation,operatio nan dmaintenance ,irrigatio nwate r supply to thefarmer s isno t reliable and insufficient.A n increase incroppin g intensity isonl ydu e toth eadditiona l installationo fprivat e tubewells.I n 1981 theyield s areonl y 50-60%o f theexpec t ones.A result, thebenefi t cost ratio is less thanon e and theinterna l rate ofretur n isonl y5.7% .

399 The farmerswh o oftenhav e salt-affected lands,ar ehardl y able to pay theirwaterfees : loans and thesellin g of animalsmus t filli n thegaps . Oyedipedescribe s inhi spape r "Innovative potentials of Kainj'i Lake Basin for Fadama farming: a study of three settlements' the situation in three settlement villages.H eexplain s therol e and functionso f the 'chief farmers'i nrelatio n toth eWorl d Bankpromote d training andvisi t system for extension service.H e concludes 'thatmeaningful l change fordevelopmen t has tocom e from outside therura l areas',an d that innovations have tob eadministere d carefully. In thepape r 'The origin and early stages of the Herman Goring polder (Tümlauer Koog) in Schleswig-Holstein, Germany', Smit stresses the influence politics and ideology canhav eo npolde r development.I n the case discussed thenee d for aquick ,politica l success led toa hasty implementation of theempoldermen tan d theconstructio no f (farm)house swhic h resulted inman y technical problems. Conflicting political views and institutional interests canb eperceive d inth e layout of thene w land, the architectural designan d theselectio no f settlers.Du e to thefac t that thesettler sha d tostar tunde rpoo r natural and social conditions andha d todepen d heavily oneac h other in theearl y stages,a considerabl e amount ofsolidarit y andcommu ­ nity-spirit wasdeveloped . Even afterhandin g over their farms toth e second generation of farmers and often living outside thepolder , they stick together.Unde r the second generation the ideological character of thepolder ,bot h social and economic,ha s disappeared. Steenwinkel'spape r 'Policy and settlement aspects of tidal swamp land development in Indonesia', discusses someo f theproblem s con­ cernedwit h thereclamatio no f the last remaining land resourceso f thisnation .

Indicated are the concequences ofhig h and lowcost sdevelopmen t and thepossibilitie s tocombin e fourmai n policy options: 1)A fastand ' certain increase of rice production; 2)a maximu m income forfarme r from 2ha ;3 )maximizin g the transmigration from Java and Bali toth e Outer Islands;4 )keepin g development costpe r haa tminimu mlevel . Furtheron,criteri a are indicated for settlement planning,suc ha s the locationo f houses,th e services tob eprovide d onbasic ,primar y and secondary level,an d its location.

400 2.2 Papers on the IJsselmeerpolders (Netherlands) a. Sociological andhistorica l aspects -Constands ei n hispape r 'From spontaneous settlements to integra­ ted planning and development' indicatesth echange si ncharacte ro f landreclamatio n and its settlement inTh e Netherlands. Initially theai mo fpolder swa s toprotec t the land against flooding and occupy itpermanentl y and safely.Durin g thenex tphas e investment considerations of rich urbanmerchant swer e thereason s forpolde r construction. From the 19thcentur y on thestat e intervened in polder construction.Thi s state interventionwa s at thebeginnin g a veryminima l and purely technical assistance:settler swer ereall y pioneers. Gradually thestate-interventio nbecam emor e andmor e comprehensiveunti l itreache d itspresent-da y all-comprehensive character. Thecharacte r of thevariou s IJsselmeer-polders thatwer e construc­ ted during several decades,reflec t thechange s inDutc h society, through differences inlanduse ,agricultura l layout,settlemen t pattern,servic e centres and recreational facilities:eac hpolde r isa nexpressio no f the time justbefor e its construction. -Th epape ro fHoev e 'Allocation of land to agricultural uses in the Duteh IJsselmeerpolders'^ indicates that since 1910ther e isa tren d toallocat emor eo f the land that through reclamationbecome s avai­ lable, tourba nuse ,recreatio n and natural reserve.Furthero n the paper indicates thetren d of further specialization inagriculture , thegrea t increase infarmsiz e andplotsize ,th e criteria for settler selection and the two legal forms of land lease tosettler s and special agriculture-related enterprises. -I nhi spape r 'New structures in newly reclaimed land? The develop­ ment of social structures in Flevoland, (IJsseîmeerpolder) The Netherlands? Schonk pays attention toth e threemai n taskssocio ­ logists canhav e inhelpin g tobuil d ane w community, 1)mak ea thourough study of the intention and aims of thepolde r inconnec ­ tionwit h the social structure of thefutur epopulation ; 2)advi ­ sing in land use and service building inorde r to improve the quality of life;3 )evaluatio n of thequalit y of lifean d following and explaining, thesocia l changes thatoccur .

401 Hefocusse shi s attention on thetw omai ncitie s inth epolder : Lelystad andAlmere .Lelysta d was started by asmal l groupo f 'colonists'wh o inbot hworkin g and leisure timewer e strongly involved inbuildin g the townan d thecommunity . The atmosphere of 'participation' changes,whe n thecommuter so f Amsterdam settled,whos emai nreason s tomov ewer e tofin dbette r houses ina safe r surrounding andwit hmor e outdoor recreation facilities. InAlmer e Haven the sameproces s tookplac ebu ti n Almere stadn o 'colonists'mentalit y was developed. Thismad e the starto f community lifemuc hmor edifficult .Withou t specialan d guided efforts theimmateria l aspectso f thequalit y of lifeo fth e new settlerswil l notb e anybette r than thesituatio nwher e they are coming from:ne w andmor e integrative social structures dono t come autmatically intoexistenc e toreplac e the social luggage settlers tookwit h them tothei rne wenvironment . b.Managemen t and administration -De nHerto gi nhi spape r 'The Zuiderzee project in The Netherlands ' describes someo f theadministrativ e changes that tookplac ewit h regard tosevera lpolders .Onc e thedecisio nwa s taken thati t shouldb e thecentra l government tofinanc e and carry out the Zuiderzeepolders ,specialise d authoritieswer e created by lawt o carryou t thewor k and for thefurthe r development of thepolder s (IJsselmeer Polders Development Authority),bot h under theMinistr y ofTranspor t and PublicWorks .Afte r completiono f thepolder s and before thestar t of settlement,differen t organizational arrange­ mentswit h different degrees of autonomywer e founded forth e various polders to incorperate them (provisionally)int o thenorma l administrative structure.However ,i ti sonl y inth ecas eo f the Wieringermeerpolder authority that itgovern s settlement plus management andwate r control.I nth eNort h Eastpolder ,initiall y a commissionerwa s appointed as solemanage rwit h thepowe r ofa municipal council and itsexecutives .Wit h the increaseo f the numbero f inhabitants,fou rmunicipalitie swer e formed up tillnow . Conclusive arrangements forwatercontro l (volume),waterdefence s and theprovincia l structure for thepolder s are stillpending .

402 -Th epape ro fva nde rSpek . 'Management as a task, polder administra­ tion as a means for an integral management of rural areas 'make s thesuggestio n toexten d theresponsibilit y of thepresen tpolder - administrationunit .Qualit y andquantit y ofwate r and its level influence strongly certainvaluabl e ecosystems.Canal s andembank ­ ments are or canbecom e important recreation areaswit h onlymino r adaptions tob emad e (slightly higherbridge s for thepassin go f canoes,etc. ;simpl e pavement of inspection roads tomak e them attractive for fisherman,walker s and cyclers etc.)Du et oth e close interrelationship between control ofwate r for agricultural purposes,natur emanagement ,landscap emanagemen t and recreation in rural areas,a n integrated management via thepolde r administration units isadvocated . c.Rol eo fne w centres and employment -Fel si nhi spape r 'Employment planning in new towns in the IJssel- meerpolders' describes the influence changes inth e economy andne w insights*wit h regard to therol e ofne w towns canhav ea nemploy ­ ment forecasts andDronten ,planne d as agricultural centres showno wa nemploymen t structure where the service sector andmanufacturin g industrydominates . Lelystad changed itpositio n ofne w town,fro m regional economic centre tooverflo w townwit h employment growth laggingbehin d demand.Almer eha s reasonally fulfilled itsemploymen t targets in 1981 but thecompositio n of the labour force isdifferen t fromwha t was planned. Instead of themanufacturin g sector iti sespeciall y thewholesal e sectorwhic h showsparticula r interest inmovin g from theAmsterdam-regio n toAlmere .Employmen t planning is supported by attractive services, low-costs facilities and tax-stimulants to encourage enterprises tostar t theirbusines s there. - Scherjon andVerhoe f in theirpape r The regional economic policy in the new towns Almere and Lelystad' discussth efunction sthos e two towns have tofulfil l inth enationa l framework ofTh eNether ­ lands. Themai n functionwa s toreliev e theovercrowde d conditions, of theRandsta d by offeringhousin g facilities and tocreat e atth e same timea livin genvironmen t that couldmee tbot hhousin g and jobneeds.

40"? Due to twodevelopment s thispolic y had tob e reconsidered 1)Ther e was afailur e inmatchin g jobsan d skills.Thi s forcespolder s resi­ stent tocommut e to theRandsta d forjob s 2)Th epresen t recessioni n theeconomy ,make s firmshesistan t tomov e fromon eplac e toan ­ other. But theauthor s claim that these townshav e comparative advantages for small andmediu m sizedenterprises .

Land use and recreation -Te rHaar' spape r 'Recreation in new areas. The IJsselmeerpolders as a case-study', shows aconsiderabl e change inth eattentio ngive n toopen-ai r recreation since the firstpolder swer e started. Inth e planning of the firstpolder s attentionwa s only givent oopen-ai r recreationo f the 'following type1: small forests andparks , central open spaces invillages ,swimmin gpool s etc.wer e clearly meant for therecreatio n of theloca l residents.Wit h theconstruc ­ tiono f thesubsequen t polders,th eresponsabl e authoritieswer e surprised by theenormou s interest ofone-da y tourists for thene w borderlakeswit h their freshwater beaches andwaterspor tfacili ­ ties.Th epolde r area itself turned out tob ea touris t goala s well. Inrespons e to thisinteres t itwa s decided upon inth eearl y sixties toconside r open-air recreation asa stimulatin g factorfo r regional development:bot h 'following'an d 'stimulating' typeo f open-air recreation facilities were included in theregiona lphysi ­ calplanning .Area s around and close toborderlake s havebee n arranged insuc h awa y that theyno w attract and canabsor bman y tourists fromal love r thecountr y and even fromoutsid e thenatio ­ nalboundaries . -Hengeveld' spape ro n 'land evaluation for urban development in the Netherlands' indicates that applications of land evaluationproce ­ dures forurba ndevelopmen t canprovid e important informationfo r planning anddesig no furba nare adevelopment . Since soil-an dhydrologica l surveys are necessary for local urban development anyway,suc h alan d evaluation should bedon e atth e beginning of theplannin g process,whe n itca nb edon ewithou t extracosts .

404 Inhi spape r 'Cost benefit analysis for a planned part of the IJsselmeerpolders project' Hoeve shows first of all that therear e many practical and theoretical problems related to cost-benefit analysis,becaus e oneha s tod owit h direct and indirect -materia l and immaterial effects.Furthero n thepape rmake s clear thatcost - benefit analysis iswid eope n topolitica l and other typeso f manipulation.

3 SOMECOMMENT SAN D SUGGESTED THEMES FOR DISCUSSION

Itwa s laudable that theorganiser s of theinternationa l symposium on 'Polders in the World' havemad e room for thehuma n being inthes epol ­ ders. After all,polder s aremad e by people forpeopl e (Schonk). Howeverw e are faced nowwit h thequestio nwha t iti si npolder s that influenceshuma nbehaviou r insuc ha wa y that it isdifferen t fromothe r areas. Oneelemen t that clearly makesa differenc e is the influence of theeter ­ nal fightagains t thewate r onhuma n character and society.Withou t following all thewa y longHuntington' s opinion inhi sboo k 'The climatic factor' (1914) itcanno tb e denied that thehabitan t has aprofoun d influenceo n society (Forde;Habitat ,Econom y and Society, 1934). Ina polde r -environmen t acommunit y must necessarily find an internal organization form insuc h awa y that iteffectivel y canprotec t itself from thepotentia l calamity that inon e night could destroy the community (likewha t happended inTh eNetherland s in 1953). A fairly high degree of internal organizationo f thepolde rpopulatio n andpolde rmanagemen t isnecessar y not onlywit h avie w toeventua l calamities but alsot o copewit h thedail y operation andmaintenanc e of therathe r complex watersystem andwaterdefences . As compared tolarg e irrigationproject s there isa vita lnee d foradequat e maintenance andoperation . Another possible difference inpolder s compared toothe r areas istha t oncema nha s driven out thewater ,h eha s land that istabul a rasa,bot h physically and socially. This gives theopportunit y tocreat e aphysica l environment that iscompletel y man-made ata specifi c point intim ean d requires hardly any adaptation (Constandse;Steenwinkel) .

405 Polders therefore reflectver y clearly the social and even thepolitica l situation at the time theywer e created (Smit and other authors).How ­ ever,th e latter point isno t specific forpolders .On eha s only to think about theGeziria-schem e inSudan .Whic hmean s that infac t the socialproblem s encountered inpolder s during their initial stageso f settling the 'colonists'an d latero ndurin g thegrowt h of ane w society arebasicall y the same as thoseme t in (large)settlemen t schemes in empty areas allove r theworld . Our conclusion is that polders represent aspecia l formo fsettlement - scheme inempt y landwit h high requirements fordrainag e facilities (and irrigation eventually)an d for internal organization andmanagement .

Of thepaper s presented,severa l of them aredealin gwit h subjects that areno t specific at allfo r polders or even for settlements ingeneral . Most of thecontribution s to this section of thesymposiu m areo fa descriptive nature;the y supply uswit h interesting information butd o not compare their informationwit h experiences from elsewhere.Neithe r arew e suppliedwit h efforts towards amor e general or systematic approachbase d on information theauthor smigh thave ,a swa s for instance doneb yR .Chamber shi sboo k 'Settlement schemes in trop-iaal Africa' (Routledge andKega nPau l 1969),b y G.B.Palme r inhi s article 'The agricultural settlement scheme: a review of cases and theories' (in Antropology and SocialChang e inRura lAreas ,B .Berdichewsk y ed,Mouto n 1979)o rb yC .Take si n 'Land settlement and resettlement projects ', ILRI1975 . Nevertheless,i nman y papers directly or indirectly themes are indicated that are encountered allove r theworl d where largescal e polderso r settlement schemes areplanne d and implemented. Some of these themes willb ementione dhere . The influence ofpolitics ,ideolog y and thenationa l imageo nth e start,th e layout and thespee d of implemention ofpolder s and irri­ gationan d settlement schemes.I t isofte n related toa catastroph e or the threatening of it that thepolitica lwil l becomes strong enough todevot e considerable shares ofpubli c funds torealiz e schemes that have lingered often fora long timeo n thedrawin g boards ofth e civilengineers .Th eNetherland s isa cas e inpoint . Forpolitica l purposes polders and schemesmus tb e inaugurated ata

406 specific time.Sinc e this time inman y cases isearlie r thandesirable , thespeedin g upofte nha s adetrimenta l effect on thequalit y ofth e technicalwork s and affects the level of living and itsqualit y for thene w inhabitants forman y years ina nadvers eway . Smit'spape r presents aclea r example on thisitem .Th e samephenomen a ishappenin g ona muc h larger scale inth eMahawel i Ganga Scheme inSr iLanka . Anexampl eo fpolitica lmotive s torevis e thecivi l engineeringde ­ signi spresente d by theSyria nGovernmen twh o required acheape ran d higher designo f theEuphrate s dambecaus e itwante d tohav e the highest dam inth eregio n (higher thanEgypt' shig h dam).Consequent ­ ly,settlemen twa sdelayed . Iti sinterestin g tofin d outho w instrumental orho w dysfunctional political forceshav ebee n inth e start,desig n and speed ofdevelop ­ ment ofpolder s and other settlement schemes. Largepolder s and settlement schemes require aspecifi c typeo forga ­ nisation that ispowerful l and cancoordinat e theman y different typeso f activities that are involved insuc hworks .Th e 'authority' isa wel lknow n and preferred typeo f institution for theseactivities . Theyhav e considerable advantagesbu t alsodisadvantages .T o create anorganizatio n iseas ybu t once itstas k isove r ordeclinin g in size and importance,i t iss ofa rmor e difficult todiminis h iti n sizeo r to liquidateit . Could itb e that theslo w integration of thene warea s inth epoli ­ tical system of theNetherland s (municipal,provincia l system). (DenHertog )wa s alsopartl y due tosom ehesitanc e of theIJsselmee r Development Autority tolos e some of its influence? Oneo f themos t interesting sociological aspects ofpolder s and large settlement schemes inempt y areas is thecreatio no fne wcommunities . Several important issues canb e distinghuished. First their is theselectio no f settlerswit h suchproblem s asth e questionwhethe r togive nprefenc e tohighl y qualified settlers in order tomak e thepolder/settlemen t aneconomi c success or togiv e chance topoore r farmers from theol d land (Steenwinkel,Smit) . Should selectionb edon eo n an individual basis,ofte n resulting ina deformed demographic structurewit h serious concequences forth e school andhealt h systems,o rshoul d one takewhol e communities or parts of them inorde r tohav e at least somebasi s for thedevelop -

407 ment of 'new'community . Inth e latter casei t is likely that the 'social luggage' (Schonk)wil l survive longer and can retardmoder ­ nisation. Often,du e to the excisting social and political structure,selectio n of settlers isals obase d on certainquota' swit h regard to specific groups in thesociety .A specific distribution over religious groups has strongly influenced the society inth eNort h East Polder.Th e samekin d ofdistributio n tookplac e inSurinam ewit h regard to racial groups and inAfric awit h regard to tribalgroups . Another interesting aspect inho w far the settlement agency should takecar eo f all aspects:wha t efforts canb e expected from thesett ­ lers themselves.Apar t from the economic and financial aspects (ofteno f great importance indevelopin g countries) there areals o some interesting consequences that have tob e taken into accountb y making thisdecision . There isfo r example thecommunit y spirit. From several papers (amongother s Schonk, Smit,Scherjo n and Verhoef) one candra w the conclusion that asettlemen t agency preferably should r.ottak e care,o f everything but instead should leaveth e settlerswit hbuildin g and organizing apar t of theirne wenvironment . These common activities,ofte n tob e carried outunde r difficult conditions,enhance s acolonisers ' spirit thatmake s thebuildin go f ane w community and the integration of settlers in it,muc heasier . When the 'late'settle r arrivesmos t thingshav e already been organised and found itsplace ,an d communicationpattern s havebee n established, whichmak ehi s integration in theyoun g community muchmor edifficult . People aremakin g polders forpeopl e (Schonk)bu twha t isth e sayo f thesettler s inth ephysica l and social environment inwhic h theyan d their childrenhav e tolive ? Inothe rword s is therean y roomfo r participation (andwha tkin d ofparticipation )o f settlers inth e design and implementation ofpolder s and settlement schemes? It isquit enorma l that the governments'objective s leading toth e constructiono f apolder ,ar e revised during theconstructio nperio d which extends over anumbe r ofyears .Pressin g problems and newin ­ sightsmigh t lead torevise d wishes likehighe rdemand s forurba n development andindustria l facilities,o r for amodifie d typeo f agricultural exploitation and related settlement. The IJsselmeer- polderAuthority ,unde r sometimes heavypolitica lpressure ,ha sbee n

408 able toadap t itsplan s for thephysica l infrastructure toaccommo ­ date thene wwishes . Iti sa ninterestin g questionho wmuc h flexibility canb ebuil t into the initial plans for layout and physical infra­ structure thatmigh t comeu p during later stages ofplannin g and implementation.Ho w far in theplannin g procedure could flexibilities bemaintaine d atwha t extra cost? Thesequestion s areno t only relevant topolder s and settlement-schemes,bu t do apply toirrigatio n projects inne warea so r inalread y populated areas aswell . Giving roomfo r new insights inregiona l development,i nfar meconomic s and for settler-participation looksworthwil e tob e considered. - From theoretical point ofvie w it isinterestin g todiscus sunde r which social,economi c and ecological conditionspolder s are/were constructed.Unde r thesocia l conditions one could imagine ahig h populationpressure , the fear for acalamity ,a nadequat e levelo f technology,a fairl y high degree of internal organization anddif - ferentationplu s asufficientl y strong central government toallocat e thenecessar y funds and requiredmanpowe r for the construction and operation (Wittfogels'hydrauli c society?).Th eeconomi c conditions require a.o.suc h ahig h surplusproductio n that the investment capital canb e supplied and that future demands for thehig h cost agricultural and industrial goods or facilities tob eproduce d inth e polder,i shig henoug h tojustif y the investment as compared to investing it infurthe r intensificationo n theexistin g land.Ecolo ­ gical conditions could be thatth eprevailin g (agricultural)productio n system fits into thepolde r environment,an d that the creationo f the polder does not interfere toomuc hwit h thenatura l conditions necessary for foodproductio n andhealth y living conditions inothe rpart so f thecountry .

Iti sclea r that only some of the themesmentione d by thevariou s authors of thepaper shav ebee n indicated: theselectio n of thetheme s indicated above isstrongl y influenced by theexperience s and interests of thereporters .

409 THEMEB SUB-THEME BA:SOCIO-ECONOMI C ASPECTS ANDPHYSICA LPLANNIN G

General reportsby : Prof.dr.ir.D.B.W.M .va nDusseldor p Ir.H.J . Groenewegen

Conclusionsb yProf.dr .A .Constandse , chairman

Socio-economic aspectspertainin g topolder s andpolde r development were discussed without arriving atpertinen t conclusions:a wish , rather,wa s expressed tocontinu e todeepe n the insight intosocio ­ economicfactors . Amajo r issuewas :th eeconomi c andpolitica l aspects ofdecisio n making.Measurin g orweighin g thepro' s and con'so f imponderable values, inparticula rwit h regard toth e competition betweennatur ean d agriculture is,i nth eend ,no t ascientifi c but apolitica l problem. A secondmajo rpoin twa s also raised during this symposium: should thepoores tmember s of societyb e helped first,fo r instance by giving them land inpolders ,o r shouldpolder s serve toincreas e theproductio n of food and fibre,s o that therewil ln o longerb e anypoo r andhungr y people in the future? A third point thatkep t reappearingwa s theorde r ofpriorit y inth e attempts tosatisf y thewishe s and needs ofpeople .Th e oneextrem e is togiv epeopl e just land tosatisf y their first needs,foo d andincome . The other extreme isno t tostar t theoperation s before ensuring that everything is taken careof ,an dwel l organized,s o thatne wdisaster s areavoided . Other topicswer ediscusse d too,suc ha s theproble m ofuncertainty , the irreversibility of developments,th estatemen t "small isbeautiful" , the significance ofpeople' s participation and the levels inth e decisionmakin g process where thisparticipatio n takesplace .

410 THEME B 5: ENVIRONMENTAL ASPECTS

ENVIRONMENTALASPECT S A.va nde rBeke n Laboratoryo fHydrolog y VrijeUniversiteit ,Brussel ,Belgiu m

Abstract Eleven papers were presented to this theme. Nine of them are from The Netherlands, one is from Suriname and one deals with the protection of the city of Venice and its Lagoon. Three papers deal with general aspects of polder environment, its functions and influences. Developments in the Ysselmeer- polders and the Wadden Sea area are described. For part of the latter region, a project assessment study was discussed. The ecological effects of a proposed reclamation project we­ re quantified for use in a cost-benefit analysis. Another project assessment was related to a land consolidation pro­ ject. The methodology of these assessment studies should be given widespread use. Similarly, the use of modeling tech­ niques, as presented in a paper on eutrophication processes, can help to understand effect-cause relationships and to take the right decisions on safe-guarding or improving our environment.

1 Classification of papers

Eleven papers have been submitted to the theme B5 "Environ­ mental aspects". Nine papers are describing polder environ­ ments in the Netherlands,on e paper is from Suriname and one deals with the protection of the city of Venice and its la­ goon. All papers are listed in Table 1. If the title did not give full information about its subject or area, additional information has been given in the column "Remarks".

411 A classification of the papers was made as follows : A General aspects in the Netherlands Paper 1 by De Jong and Wiggers Paper 2 by Klein in Suriname Paper 3 by De Jong B Developments in the Ysselmeerpolders Paper 4 by Driebergen Paper 5 by Polman C Developments in the Wadden Sea area Paper 6 by Drijver Paper 7 by Joenje D Project assessment Paper 8 by Bankers Paper 9 by Asjes E Water quality Paper 10 by Bernardi et al. Paper 11 by Smits and De Rooij Paper 8coul d be also classified under the heading C. Each paper will be summarized and discussed according to the afo­ rementioned classification but cross-references will be made to the other papers whenever appropriate.

2 Summary and discussion of papers A General aspects Paper 1b y De Jong and Wiggers is mainly a descriptive re­ view of the historical development of the four main polder areas in The Netherlands :polder s in the downstream flat river catchment areas, polders in peat areas, polders on the bottom of drained lakes and polders created by coastal em­ bankments (Figure 2).Th e authors describe how the original habitat was changed in each of these areas and how land use and parcelling was affected by the type of reclamation (Fi­ gures 3, 4an d 5).Improvement of farming conditions has often resulted in a decrease of bird species and floreal va-

412 lue (see Paper 2).Th e land accreation areas along the coast are recognized as having a very high ecological value. New embankment constructions in the Wadden Sea are therefore un­ likely to be executed (see Papers 7an d 8). Bu t it is also noted that large parts of the new polders have been develo­ ped into nature sanctuaries and forests (see Papers 4 and5) . The authors briefly discuss the change in land use since 1900 (Figure 8) i.e. the decrease in agricultural land, esti­ mated nowadays at ca. 13000 ha per year, lost by urban ex­ pansion. They introduce so-called disturbancy zones around towns and villages in order to assess the effect of urbani­ zation upon the region (Figures 9an d 10).Pollutio n effects, such as eutrophication of canals and lakes and waste dumping, are mentioned (see also Papers 10 and11) . This paper gives the general reader an interesting overview on the subject of this session. It is in fact an introduc­ tion to many of the other papers of this session. Detailed information, e.g. about increase or decrease of number of bird species,etc . ...,ca n probably be found in the litera­ ture listed at the end of the paper. For easy reference,however , it would have been preferable, if the literature cited had been also quoted in the text. Maybe the authors could specify during the discussion how they define "disturbancy zones".

Paper 2b y Klein details about the ecological developments and relationships in new polder areas. The author discusses briefly the soil ripening, the influence of the hydrological conditions (leaching processes and capillary rise) and the microbial development. The vegetation development is affec­ ted by dispersal, spatial differentiation and prevailing wind direction. Management measures,e.g . the sowing of reed,hel p to establish favorable conditions. Human inter­ ference, by reclamation activities and road building, etc... • offer opportunities to study the spatial dynamics of vari­ ous species. It is surprising to note that plants spread more rapidly

413 than animals. Nature conservation and nature-engineering or habitat-buil­ ding is discussed (see also Papers 4, 5an d 7).Detaile d inventory prior to embankment and development and regular surveys are strongly recommended. The use of remote sensing techniques is suggested. This paper points rightly to the extraordinary possibilities for research on ecology in new polder areas. These studies form the base for environmental impact studies (see Paper 8). As most of the referenced literature is from Dutch ori­ gin, the author indicates the need for more research else­ where in the world. Would it be useful to draw minimum cri­ teria for this kind of research ? Finally, it is worthwhile to note that 53 references have been collected by means of an online search using computer­ ized literature data bases :a method to be promoted. Paper 3b y De Jong may be seen as an answer to the request of Klein,urgin g for more research on new polder areas else­ where in the world. The estuarine area of Suriname has a high natural fish productivity. Reclamation of the area for rice production will enhance very important effects on the ecology of the environment. Among these effects are decrea­ sed fresh water runoff,alteratio n of the forest habitat which is very important for fish populations, contamination of drainage water by pesticides. It is recommended that the whole estuarine zone should be­ come a Special Management Area and that planning assessment should be performed prior to development. The reference list includes local research on the ecological effects. The reporter missed ama p of the region involved and an in­ dication about its size.

B Developments in the Ysselmeerpolders Both papers 4an d 5,respectivel y by Driebergen and by Pol- man, deal with so-called shallow borderlakes of the Yssel­ meerpolders. These lakes have been designed for multiple

414 water management purposes. Drontermeer and , dis­ cussed by Driebergen,hav e a closed water management system since 1956. During the period 1957-1961 a rich and varied plant and animal life developed. During the sixties and the seventies the transparancy indicator decreased drastically from 1m to 0.2 m. The cause is the pollution by domestic and agricultural waste waters. The high contents of nitrates and phosphates increasealgae growth, especially Blue-green algae which limit severely development of other plants and animal life. The original rich environment deteriorated ra­ pidly. Several steps have been taken to limit the phosphate content of the waters discharged into the lakes from 0.5 to 1.5 grams per m2 per annum. The estimated load in 1975 was 3.7 grams per m2 per annum. These steps are often very costly. Therefore, results of this type are very useful.A reference list at the end of the paper would have improved the interest of this paper.

The Oostvaardersplassen (Paper 5b y Polman) in Southern Fle­ voland are just south of Lelystad and have been planned as a nature reserve of 550 0ha . The original area developed in a natural way into a very important resting, foraging and breeding area for numerous species of birds. Therefore,i t was decided to further develop the area as a nature reserve, especially for waterfowl. An artificial water level has to be maintained by embankment and by artificial water supply in dry years or water discharge in wet years. This extensive paper gives a detailed account about exper­ iences, discussions and targets of both the original area and the new development. A main technical point is the water level in winter and summer. My question is :wha t is the cost benefit relationship for developing and maintaining these artificial ecosystems.

C Developments in the Wadden Sea area Paper 6b y Drijver lists the recent reclamation projects in the Wadden Sea region, either completed, rejected or

415 planned in Denmark, Germany and The Netherlands. The author stresses the irreplaceable role of the existing salt marshes and mud flats for the biological life. Efforts are made to express this role both quantitatively and economically and to incorporate the total environment of the Wadden Sea area with its connection to the North Sea. The author's argu­ ments are impressive,bu t do they imply the rejection of all diking projects in the area ?

Paper 7b y Joenje,a t the other hand, discusses the ecologi­ cal developments in new embanked polder areas in the same area, which "... however,b y no means (compensate) the los­ ses of saltmarsh and wadden ecosystems ..." (quotation by the author). The case of the 9100 ha Lauwerszee-polder ,embanke d in 1969, is described.Th egenera l question,whethe r nature management should be a "laissez-faire" or some mode of nature exploita­ tion, is answered in favor for some "active"management.. But even then,differen t and conflicting options may exist.Mo ­ reover, some management methods may be limited by cost consi­ derations. The nature reserve in the Lauwerszee-polder has several management programmes side by side in different zo­ nes. They are still very much a matter of trial and error. This study holds a challenge for many years to come,a s sta­ ted by the author.

D Project assessment Paper 8b y Dankers gives an account about an ecological stu­ dy of the Balg-zand tidal flats made in such awa y that the information could be used in a cost-benefit analysis of a proposed reclamation project. The author lists 25 functions of the Wadden Sea area and discusses their interaction. I think that this list is a very useful one and should be an example for all studies on environmental impact assessment. The environmental effects are divided into primary, seconda­ ry and tertiary effects. They are called a "factor train".

416 The description of this factor train is again a very welcome step towards a more rational and methodological approach of this type of studies. The author recognizes that some func­ tions cannot readily be quantified. Could he explain how they have been introduced into the analysis ?

Paper 9b y Asjes treats the subject of land consolidation in an older polder area versus conservation of nature areas and landscape. The assessment method made a comparison between several variants of land consolidation schemes and their effects on agricultural development, nature value and land­ scape value. The conservation of nature value was measured by the number of meadow birds. The size of a bird sanctuary was taken variable. Likewise the number of farm resettlements was a variable versus theopennes so f the land scenery. The increase in renumeration for the farmers and the internal rate of returns were the base for comparison. It is clear that conflicting interests exist. Could the author discuss how the decisionmaking process will use the information resulting from this assessment method ?

E Water quality Since water is one of the main substances of the environment, it is not surprising that two papers are essentially related to water quality s.s. Paper 10 by Bernardi et al. presents the problem of monitoring water quality of the fresh water discharged into the Lagoon of Venice. The large number of inflow channels does not allow a full control. Moreover, the tidal flow with its salt wedge and changing water depth ne­ cessitates monitoring at several depths and different hours. Symptotic values of total water, salt and heat flow are de­ rived. An even more complex problem is the exchange of mat­ ter with the bottom sediments of the Lagoon. A circulation model is being developed. The authors could maybe give so­ me more details about present state of the project.

417 The last paper of this session (Paper 11 by Smits and de Rooij) is an extensive one about eutrophication processes and their modeling in the Westeinder Plassen, a lake of 9 km2 and average depth of 2.9 m, situated in the RijnlandPol ­ der system. The authors describe the model CHARON-BLOOM II where CHARON stands for the chemical part and BLOOM II for the phytoplankton part. Both models as well as the coupled version have been applied elsewhere in The Netherlands. Ca­ libration results for the years 1977/1978 are satisfying the authors. Iwoul d like to know somewhat more details a- bout the calibration method :ho w was the procedure to ad­ just equation coefficients ?Wa s a residue analysis applied systematically ?Th e literature cited will certainly give answers to these questions ? This modeling study resulted in an important conclusion: phosphate is far from limiting for phytoplankton growth. Therefore a decrease of phosphate load will be only effective if the reduction is very substan­ tial. This result is probably a very exemplary one in show­ ing the usefulness of careful modeling techniques.

2 Conclusions Reporting on theme B "Environmental aspects" has been a most profitable exercise for the reporter. All papers have arou­ sed my interest and widened my knowledge. Many introduced methods or definitions which, in my opinion, are most useful and should become standard procedures in these studies. One author reghtly concluded that new ponder areas are ex­ cellent opportunities to study developing ecosystems.An ­ other author pointed out that relatively few studies on pol­ der environments are known outside The Netherlands. May this session be a step towards increasing interest into these studies which should be the strong base for preserving orma ­ naging nature while serving humanity.

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A20 THEMEB SUB-THEME B5:ENVIRONMENTA L ASPECTS

General reportby : Prof.dr.ir.A .Va n der Beken

Conclusions byDr .M .Vannucci , chairman

Owing toth e subdivision of thebroa d subjecto fpolder s in themeso f an interdependent character participants faced aserie s ofchoices . Perhaps thediscussion swoul d havebee n enriched if thearra yo f possibilities had notbee n allsimultaneous . A good number ofauthor s ofpaper s onenvironmenta l aspectswa s present (9ou t of 15).Ye t therewa sn o representative of adevelopin g country inth e group.Thu s itwa s notpossibl e topursu e thever y far lines of thought established by thekeynot e speakersMeye r andBrammer . Thiswa s regretted since theirpaper sha d soprofoun d asens e ofmulti - objective planning,interdisciplinar y research and cooperative human effect. The sessiono nenvironmenta l aspects reviewed 11paper s dividedb y subjects asfollows : - General aspects (3papers ) - Developments inth eIJsselmeerpolder s (2papers ) - Developments inth eWadde n Sea area (2papers ) - Project assessment (Apapers ) All thepaper s except threewer eb y Dutch authors onDutc h conditions and problems.Tw ower eb y Italian authors dealingwit h the cityo f Venicean dVenic eLagoo nproblems .On epape rwa sb y aDutc h authoro n polder construction inSurinam . Theproblem s of theVenic eLagoo n arebein g solved bymethod s other thanpolde r construction.Fro m thepaper s itemerge d that the Netherlands systemo f planning andmakin g environmental impact assessmentsha sbee n tested inman y complex situations fromwhic h lessonswer e continuallybein g drawn.Th e tensionbetwee n the conservationo fnatur e and thejustifiabl e useo fnatura l resourceswa s well recognized.

421 It was the consensus of the group that: l. Polders give special opportunities for studying ecosystems. 2. New methods, new .criteria and new definitions for the study and monitoring of polders and waters should be developed and standardized. 3. Analysis of polder ecology should aim at establishing easily quantifiable factors in reclamation projects. 4. The use to which the information gained should be put should reflect different types of values for the cost-benefit analysis, some of the values being expressed in terms of money, others not. 5. An enV-ironmental impact assessment should be made before any lnpoldering is undertaken. 6. Pollution and ecological development should be monitored .for a long time after the completion of new polders. Furthermore there was a number of questions about environment, society and economies in regard to impoldering in developing countries and the group recognized that these questions needed a broader framework for their appraisal. Finally it was recognized that the political evalua_tion of the variables in the management of polders was a matter for fine judgment. The Dutch decision-making process_ appeared to cope satisfactorily with the need to balance factors in the perspective of the future.

422 CONCLUSIONS

FINAL CONCLUSIONS

Prof.dr.ir. J.C. van Dam Chairman of the Scientific Sub­ committee

Mr, Chairman, Ladies and Gentlemen,

After listening to so many excellent speakers- during the past three days it is a heavy task for me to speak as the last speaker but one. It is also difficult to summarize the findings of this symposium in a balanced way. W_e listened to a great number of interesting lectures and there were so many papers that even with the chosen system of presentation by means of general reports we had a full prograrmne, if not too full. It will still take us a long time to digest it and to have the full benefit of it. The printed lectures, papers and reports are valuable material for reference and study when back home, I will now try to summarize what, in my opinion, is at this moment the balance of our activities. during the past three days. There exist several definitions and interpretations of the word 11 polder". This is no wonder as indeed there is a great variety of polders in the world. I will not try to formulate a definition at the end of this symposium. I am only too happy that we did not stick to too strict a definition when accepting papers •. So we had not only a large number of papers, but these papers deal with many different conditions, aspects, and solutions. Much of the knowledge and know-how presented here .can also be used in and for other areas than polders. This symposium on polders has widened our outlook and insight into new possibilities, into all kinds of problems and into the ways they have been tried to solve.

423 Instead ofworryin g about adefinitio n onemigh t ask oneself:I n what respect differ polders from theres t of the land ?I n terms of the five sub-themes of this symposium it iscertainl y thewate rmanagemen t aspect,rathe r thewate r control ofpolder swhic hmake s them sospecial . This intur n canb e attributed to the topography of thearea swher e the polders are located. Closely related to the topography ofpolder so r prospective polder areas the soilpropertie smak e them suitable for agriculture inman ycases . The topographical features,i nmos t cases,necessitat e the construction ofdike s and embankments togetherwit h sluices and pumping stationsfo r the control ofwater . The construction of apolde rmean s aradica l transformationo f the original landscape,ofte n ina natura l state,int o anare a liable to serve therequirement s ofmankind . So it isclea r thatpolde r construc­ tion implies ahug e impact on the original environment.Thi s asksfo r due consideration. The great step fromnatura l environment toa develope d polder areaca n notb emad ewithou t physical planning,base d on theprevailin g socio­ economic conditions.

Almost at theen d of thissymposiu m onemigh t askonesel fwh y this uniquehappenin g washel d ina smal l country as theNetherlands . Several answers arepossible ,suc ha s - the initiativewa sbor nhere ; - theNetherland s have a long and impressive polder-history and newpolderlan d isan dwil lb ereclaime d here,no w and inth e nearfuture . In thiscontex t it isnic e tomentio n thatou rne wDfl .50, — banknote isprinte d with acolourfu lma p of the IJsselmeer polderso n itsback . - therati oo f thepolde r area to the total land areao f the country isextremel yhigh ,becaus e thiscountr y iss osmall . After these introductory remarks Ino wcom e to theformulatio n ofm y impressions of this symposium. We received awealt h ofpaper s dealingwit h polders allove r the world.Whe nprojectin g thepolder sdeal twit h inthes epaper s onth e world polderma p aspresente d during this symposiumw e canconclud e

424 that thepaper s give agoo d coverage ofal lcontinents . Thepaper swer ecertainl y also useful contributions toth epreparatio n of theworl d poldermap .However ,I a mconvince d thatdespit eal l research efforts thema pwill , sooner or later,nee d updating. Theexhibition ,consistin g of twoparts ,scientifi c and demonstrative, wasver y interesting.Lik eme ,yo umigh thav ewishe d tob eabl et o spendmor e timeo nthi s important itemo f our symposium. Thefilm san d Surinam session contributed evenmor e toth eexten t andvariet y of the information presented inthi s symposium. Thevalu eo fa symposiu m likethi s liespartl y inth eprinte dpapers , including thegenera l reports and the invited lectures,bu tperhap s evenmor e inth epersona l contacts.Thes e contacts are particularly important becausew eme ther eno t onlywit hpeopl e fromdifferen t parts of theworld .Th eparticipant s have different disciplines andwor ka t various levels,suc ha sdecisio nmakers, scientist s involved in investigations and study,engineer s involved indesig nan dexecution , university professors for theeducatio n of thenex t generationo f polder engineers.Ther e areals oparticipant swhos e interest arose from themer e fact that they live ina polder . Thegenera l reportswer edifferen t innature ,partl y due toth e freedomwhic hwa snecessaril y given toth ereporters ,partl ybecaus eo f thedifferen t degreeso fheterogeneit y of thepaper s tob edeal t withb y the individual reporters.Mos t of thereporter s provoked theauthor so fpaper s and theaudienc eb ymean s of interesting questions.Thi s gaveris e tolivel ydiscussions . During theafternoo n sessionsw ediscusse d thegenera l papersan d thepaper s inth efiv e sub-themeswel lknow n toal lo fus .Remarkabl y thenumbe ro fpaper so n the important sub-themes "agricultural aspects"an d "environmental aspects"wa s smaller thanth enumber si n theothe r themes.Nevertheles s therelevan t sessionswer eattende d bygoo d audiences.Fo r theagricultura l aspectshold s thatman yo f theseaspect s canb e interpreted as land-an dwate rmanagemen t aspects and indeed weha dman y papers and aver y great audience on thatsub - theme.Anothe r striking feature istha t several paperso n"environmental - aspects"wer ewritte nb y agrea tnumbe r of co-authors (upt o seven). Thisma yb ea n indicationo f the interdisciplinary character of some paperso nenvironmenta l aspects.Ther ewer e only fewpaper sdealin gwit h

425 '"environmental aspects"i ndevelopin gcountries . Thepaper s inbot h these sub-themes -"agricultura l aspects"an d "environmental aspects"- wer eals over y diverse innatur ean dcontents . Thismad e iteve nmor e difficult for thereporter s of these sub-themes topresen tu sa pictur e ofwha t isgoin g on in theseaspects . Like inman y symposia,an d also inliterature ,ther e ishardl y any paper dealingwit h failures.Thi s isunderstandable ,bu tals o regrettable ason eca nlear nmuc h from suchcase s and thuspreven t a repetition ofsuc h afailure .

Sofa rm y concluding remarkswer erelate d toth e symposiumwit hal l its sessions and theexhibition .Wha t conclusions canno wb edraw n andwha t lessons canno wb e learned from this symposium onpolder s? Many !Le tu s try toformulat e them: 1. Construction ofpolder s isa peacefu lmean s of enlarging thelan d areaand/o r tomak eproductiv e land.Mor eproductiv e landfo r thesam epopulation ,a sdistinc t frommakin gwar ,wher e inth e end,fewe rpeopl e live inth e same landarea .

2. Inconsequenc e of therapidl y growingpopulatio no f thisworl d there isa growin g need for landwher epeopl eca n livean dproduc e the food and fibre theyneed .Par to f thelan d tob ereclaime dwil lb e inpolders .

3. Besides thereclamatio n ofne w land the improvemento f existing land,whethe r inpolder s ornot ,ca nals o contribute toa greate r agricultural production.

4. People living inman y polders of theworl d dono t appear tob e afraid of flooding.The ymus t eitherhav egrea t confidence inth e skill of theengineer s or theyd ono t evenrealiz e thatthei r lives areprotecte d by dikes,becaus edikeburst shav eno t occurred there fora long time,du e to theconstructio no f safe dikes andembankments .

5. Thedesig nan d operation ofpolder s depend greatly on theclimate . Not only thedimensions ,bu t eventh econcep t canb e different indifferen tclimates .

6. Thegeologica l features ofpolder shav eha d relatively little

426 attention.Thi s ispossibl ebecaus e the importance of thegeologi c conditions issometime s underrated. Dueattentio n should alsob egive n tofutur e sea-levelrises .

7.Considerabl e progressha sbee nmad e inth epas t fewdecade sin : - scientificknowledge ; - practicalknow-how ; - development ofequipmen t needed forpolde r construction, development andmaintenance .

8.A s inman y other fields,moder nmethod s assyste manalysis , modelling and optimization techniqueshav e alsobee n applied -an d with success- inth edesig nan doperation ,o fpolde rprojects .

9. Inth e sub-theme "construction aspects"muc h attentionwa s givent o theconstructio n ofdike s and embankments and theman y recent developments therein.

10.Despit e theprogres smad e there are still limits toth epossibili ­ tieso fpolde r construction.Thes e limitsma y be andofte nar eo f a technical nature.Fo r example,th ehydrauli c capacity of tidal inlets is toogrea t toenabl e aclosur ewit h the technicalmean s locally available.Man y times therear eals oeconomi crestrictions . For example storm surgesca nb e sohig h that thecos t ofa saf e dikear eeve nprohibitive .

11.Afte r the sequence:investigatio n and study,planning ,decisio n making,desig nan d construction follows:operatio n andmaintenance . Theoperatio n andmaintenanc e aspects areofte nneglecte d in practice.Imprope roperatio n can lead toconsiderabl e reductiono f theprofit s of theinvestments .I t is true that thecos to f maintenance canb ehigh ,bu twhe nneglectin g itth e consequences canb edisastrous .No tonl y are these aspectsneglecte d in practice;als ofo r thepaper smaintenanc ewa s apparently nota n attractive aspect.Ther ewa sno t toomuc h information about maintenance inthem .

12. It istru e thatpolde r constructionan ddevelopmen t canhave ,an d inman y casesd ohave ,a tremendou s impact onth eorigina l environment.I nman y cases itmean s evena complet e transformation fromth eorigina l state intoa differen tne wstate .

427 This transformation isa n irreversibleprocess .Therefor e due considerationmus t begive n toal l foreseeable and possible consequences.Thi sha sbee ndon e since long,bu t inpresen t times the concern for our environment,bot h thenatura l environment and men's living environment isgreate r thaneve rbefore .A t present there isals omuc hmor eknowledg e and experience available thani n thepast . Practiceha s learned that tooofte nunforesee n consequences appear later. Newly created environments canals ob emos t valuable orattractive . When creating newpolder s there isofte ngrea t freedom inth e design and dueattentio n canb epai d tomeasure s tocompensat e orminimiz e damage to theorigina l environment. It ishighl y desirable that theenvironmenta l objectivesar e specified interm so f quantities rather thanbein g expressed ina descriptivewa y only; they could thenb ebette r incorporated in theplannin gprocess . There area fe wexample swher e theso-calle d irreversible transformationwa sno t for ever.I na fe wcase sme n gaveu p and abandoned apolde r for technical oreconomi c reasons.I n other casesnatur e took revenge,fo rexampl eb y inundationafte r theoccurrenc e ofdik ebursts .

13.Th erentabilit y ofne wwork s iscommonl y judged on thebasi so f the internal rateo freturn .Thi s figuredepend s onth e estimated life timeo f theworks .I nsuc ha calculatio n the lateryear s contribute less thanth e first.Th e life timeo fpolder si s almost for ever.Thi smean s that thebenefit s of such anenterpris e continue longafte r theperio d ofusuall y some tenso fyear swhic h count in thecalculatio n of the internal rate ofreturn .

14. Itappear s that inth epas tne wpolder swer e often constructed anddevelope d asa n investment intime so fprosperity .I ntime s ofeconomi c depression therewa s generally lessactivit y inth e creationo fne wpolders .

15.Histor y teaches thatofte n longtim espan s elapsebetwee nth e moment the first initiatives are launched and theirrealization . Aftermakin g thenecessar y studies,plannin g anddesig n it isofte n

42S a longwa ywit hup s anddown s inth epolitica lspheres .

16. Inrecen t timesne wmethod s havebee ndevelope d for theevaluatio n ofproject s andplans .Multi-criteri a analysismethod s areno w available for theevaluatio nwher e thebenefit s and drawbacks cannotb eexpresse d inon ecommo nuni t ase.g .money .Thes e newmethod s area might y toolfo rdecisio nmakers .Th e consequences ofvariou s decisions canno wb e looked over clearly inadvance . However,i nth een d thedecisio nmakers ,ofte n thepoliticians , stillhav e toassig nweight s to thevariou s elements inthei r choiceproblem .

17.Anothe r observation from thepas t istha tofte n somenatura l disasters as flooding are the impulses formakin g thedecisio n toperfor m thenecessar yworks .Thes e are thehar d lessons from naturewhic h are solightl y forgottenb ymankind .

After all these conclusions somerecommendation s canno wb e formulated.

1.Mor e landmus tb ereclaimed ,par to fwhic hwil lb e inth efor m ofpolders .Thi s is inorde r tocop ewit h thegrowin g demand for space to livean d for theproductio no f food andfibre .

2.Becaus eo f thelon gperiod s thatusuall y elapsebetwee n thefirs t initiative and thebeginnin g ofoperatio n thenecessar y studies should starta searl y aspossible . Thisma yb e rightnow .

3.Apar t from thenecessit y toundertak epolde r projects forou r near futureneed s it isals o recommendable toundertak e them rightno w inthi sperio d of economic depression asa contributio n toth e solution of theproble m ofunemployment .

There isstil lmuc hwor k tob edone .

Letu sbegi nI

429 LISTO FAUTHOR SAN DPAPER S fromContent sPaper sVolum e I,II ,II I aspublishe d by ILRI,Wageningen ,Th eNetherland s

Volume I.

POLDERPROJECT S C. Desplanque. Dykelands (polders)alon g theBa y ofFundy , Canada - A. P. Vernimmen and J. P. Hei.jligers. Protectingth eNorth - Holland Polder areaagains t flooding - H. de Bakker and M. J. Kooistra. Marinepolder si nTh e Netherlands - H. J. Groenewegen. Polders asa disposa l site fordredge d material fromRotterda m harbourare a - R. Eggelsmann. Peatland polders ofNorth-Wes t Germany - P. J. Kowalik, Polders ofVistul arive r - R. B. Rivera. Basic information about themarshe s at thelo w Guadalquivir River (Sevilla-Spain) - M, Sh. Diab. Polder areaso fnorther n localities of theNil e Delta - S. Ruanglek, Sh. Chaveesuh and M. Poolsup. Landreclamatio n inThailan d - E. Stamhuis. A experimental polder forresearc h onaci d sulphate soils inth eMekon g Delta - A. T. Chowhury. Polder development inBangladesh . PaperII : The land reclamation project - A. Quassem. Polder development inBangladesh . Paper III: The delta development project

431 J. Abi-Saab Sotot W.J. Heijnen, P. W.Roest and H. Velsink. Polders and dykeso f theBoliva r coast,Venezuel a R. J. Oostevbaan. Natural and social constraints topolde r development inGuiné-Bissa u S.H.C. de Silva, Reclamingmutura-jawel a- Sr iLank a Sh. Mong - Hsiung. Problems instratu m settlement due toground ­ water exhausted L. S. Pereira and M. G. Bos. Land reclamation and agricultural development of theLeziri a Grande (Portugal) P. D. Cook. Thereclamatio n of land on theeaster ncoas to f England J. H. Kop, K. Lukkien and J. B. Venema. The 'Pluit'urba npolde r A. K. Constandse, J. de. Jong and M.J.H.P. Pinkers, TheI.Tssel - meerpolders R, Brouwer. HadejiaValle y irrigation and drainageproject , Nigeria H. W. Appel and N. M. Vierhout. Irrigated ricepolder s inth e Delta of theTan a river,Keny a W.T. de Groot and M. Marchand. Kafue flats,Zambia :flood-plai n planning oncrossroad s Md. M. Uddin and Sh. Islam. Polder development inBangladesh . Paper I:Pas t and present development Sh. Haq. Delta development of Bangladesh I. Gil Sanchez and J. Martinez Beltrân- Drainage ofnea t soils in thepolde r ofPego-Oliv aAlicante ,Spai n L. Horst. Alternative development concepts inpotentia l polder areas

LANDAN DWATE RMANAGEMEN TASPECT S Y. Tohara. Water qualitymanagemen t ofa desalte d reservoir M, Okasaki. Accumulation and eluviation of salts insoil so f reclaimed land along easternpar t ofToky oBa y S.M.K. Donker. The influence of Soil Salinitv onric eyield s in theWageninge n polder,Surinam e L. T. Kadry. Soilwate r salinity relationship -environmenta l factorso f land reclamation

432 V. Gomez-Miguel, J, Perez Arias, F. Guerrero, and C. Roquero, The soils andwatertabl e properties of thepolde r area 'Castillod e DorîaBianca' ,puert od eSant aMaria ,Cadiz ,Spai n D. B. Vieira, A. E. Pissarra, J. rr. Ponbo and L. S, Pereira. Drainagean d desalinization studies and design inLezîri aOrande , Portugal G. Schrale and R. E. Desmier. Saline groundwater inflow into irrigated Dolders along theMurra y River,Sout h Australia K. Rijniersce. A simulation model forDhysica l soilriper.ingi n the Usselmeerpolders A. F. Al-Ani. Effect ofdifferen t salts onth ehydrauli c conductivity of soil R. S. Garzon. The influence of shallow groundwater onth e drainage problem,o f theKabaca nRive r irrigation system A. C. Armstrong. Thedesig no f in-field drainage systems in theEnglis h Fenlands E. Dahnen. Drainage and irrigation requirements:a n integrated approach K. KoaheV. Somemethod s for selecting and designingo fa prope r drainage system ina rive rpolde r R. K. Price and J. E. Slade. Amode l for thedesign , analysis and operation ofpumpe d drainage systems A. J. Hebbink. Drainage ofurba narea s inth e^levopolder s M. Dorai. Design considerations for thedrainag eo fpad ipolder s E. A. Korany and S. A. Hussein. Ceohydrologic status and control of land andwate rmanagemen t inth ereclaime d desert areas,wes t ofNil eValley ,Egyp t J, Dijkstra. Watermanagemen t inth eIJssellak epolder s J. G. Grysen and G. Miedema. Water supply to theMid-Wes to * The Netherlands R. Th. Wiersinga. Land andwate rmanagemen t intida l swamp land development projects inIndonesi a M. Kuroda. Watermanagemen t and operationo f irrigation systems in lowlyin gdelt a areawit h creeks I. E. Soe Agnie. Land andwate rmanagemen t inBanan a cultivation inSurinam e

433 - J. Wesseling. Hydrological conditions and their influenceo n surfacewate r quality inth et)utc hpolde rregio n - J. Bouwknegt and L.J.M. Kroon. Wind influenceo nth ewate r movement inope nchanne l networks - P.J.M. van Boheemen. Amode l for thecomputatio no fwate r requirement forleve l control ofpolde r areas - Z. I. Diankov, Groundwater flowdynamic s inBulgaria nriversid e polders -A numerica lmode l investigation - M. Szinay. Hydroamelioration ofagricultura l lands inHungar y - K. Tanaka. Application of theextende d Kalman filter for forecasting thechanne l flow - I. Mihnea. Someo f theDanub e floodplainpolde r project criteria - M. A. Beran. Aspects of flood hydrology of thepumpe d fenland catchments ofBritai n - J. Buys. Irrigation requirements ofrice ,retur n flowsan d their effect on the irrigation capacity of arive r - E. Schultz. A model todetermin e optimal sizes for thedrainag e system ina polde r - F.H.M. van de Ven and G. A. Ven. A comparison between therunof f froma rura l and anurba nbasi n inFlevolan d - F.B.J. Barends. Seepage induced surface leakagei nan d around polders - A. Svier, Present stateo fwate r resources development in North-West Suriname - A, lanes and M, F. Aaevedo. Tide-driven drainage networks:th e caseo f Guara Island

Volume II

- M, A. Viergever. Foundation on softmarin edeposit s ina recentl y reclaimed polder - D. Kirkham. Free surface potential theory fora gravit ywel l - A. Masumoto, Thepossibilit y ofusin gundergroun d damst o irrigatepolder s intropica l areas - 3. Kuwano. Effective protection ofpolde rdik e - L.W.A. van den Elzen and H. L. Jansen. Possibilitieso fdik e enlargements increased byus eo f thecolbon dvertica l drainage system.

434 G. J. Florian and H. J. Vinkers. Calculation of hydraulic head for river embankment design using anumerica l groundwater model D. L. Gudgeon and M. E. Hannah. The raising of the defences of Canvey Island to resist a 1i n 1,000 year tidal surge J. van Duivendijk and J. R. Pieters. Design and construction of the seadefence s of Guyana R. Dresnaak, E. B. Golub and J. R. Pfafflin. Statistical risk assessment of polderprotection structures A. V. Guzman. Construction aspects in thepolder s of the left bank at lowGuadalquivi r marches,Sevilla ,Spai n D. De.jas, A. Reinhard and W.Trseoiak. The control of pumping aggregatesan dth emeasuremen t of discharge in polder pumping station. P. H. Reiter. Test runs and acceptance tests of polder pumping stations W. Broeders, J. Huis in 't Veld and J. Stuin. Strategies and methods for closing dike breaches F. Smit. Management aspects of catch-water embankments in 'Deoud eVeenen ' drainage district G. P. Bourguignon. Reclamation indeltai c regions A. M. van Nispen tot Pannerden. TheZuiderzeercroiect ; construction of dikes G. W. Beetstra and P.V.F.S. Krajtcek. Reliability of Dutch polderdikes S. Bernardi, F. Costa, R. Santagelo and S. Vazzoler. Protection of the city ofVenic e and its lagoon:flo wo f freshwate r and pollutants into the lagoon B. Hajos. Use ofhydromechanizatio n for hydraulic earthworks in Hungary S. Wesseling and M. Madsalin. Labour - intensive nolder construction in Indonesia L. van 't Leven. Construction of polders in Suriname J.J.L.M. Enneking and M. M. Vierhout. Design and construction of flood control dikes around 43,00h a of irrigation areas in theRhar b Plain,Morocc o

435 AGRICULTURAL ASPECTS L.F.C. Lopez dos Rp.is and M.V.N.L. Pevdigao, Land evaluation foragricultura l development inLezifi aGrande ,Portuga l J. Westerhout. Agriculturaldevelopmen t of tidal lands inIndonesi a A, B. Chaudry. Drawdown agriculturea sa suitabl e substituteo f traditional fadama land cultivation in theKainj iLak e Basin J. Chs. da Costa. Agricultural aspects ofbanan a cultivation inpolder s inSurinam e A. D. van Dijk, J. W. Erdman and M. J. Idoe. Mechanized rice production inSurinam e H. Hoeve. Cost-benefit analysis for aplanne d part ofth e IJsselmeerpoldersprojec t (case studyMarkerwaard ) H. Hoeve. The significanceso f agriculture inth eDutc h IJsselmeerpolders H. Hoeve. Allocation of land toagricultura l uses inth e Dutch IJsselmeerpolders (farm settlement policy) H. HoéVe. Criteria for thedeterminatio n of themomen to f suitability forprivat e agricultural landuseo f clay and loamy clay soils inth eDutc h IJsselmeerpolders D. E. van der Zaag. Yield and quality ofpotatoe sproduce d in thene wpolder s inTh e Netherlands A. Moens. Agricultural machanization and plot dimensions in polder development projects P.J.M. van Boheemen, P. J. Kusse, C. Maas and J. W. Wesseling- Effects of fresh-water supply of Schouwen-Duiveland,Th eNetherland s C. van Wallenburg and G.J.W. Westerveld. ^eat polders inth e western part ofTh e Netherlands C. P. van Goor, B. Groenhuis and L. Jacobs, Forestry and foresty research

SOCIO-ECONOMIC ANDwvsiCA L PLANNINGASPECT S P. Bos. Dopolder s adapt to their environment? K.A.A. van der Spek. Management asa task ,polder-administratio n asa mean s fora n integralmanagemen to f therura lare a

436 W. J. van Grondelle. The IJsselmeer area:th eprotectio n ofa natural freshwater areao f international importance Ü.J.M. Govevde. Decision criteria:difference s and shiftsbetwee n insiders and outsiders inDutc h polder-decisionmaking M. Spierings. Urbanization inDutc h polders;th eevolutio n of theRandsta d conception E. ter Haar. Recreation inne w areas,th e I.Tsselmeerpoldersa s case study J. A. Wezenaar. Qualitative spatial planningmodel s forne w urban fringearea s J.F.W. Fels. Employment planningo fne w towns inth eIJsselmeer - polders M.K.A. Schonk. New structuresi nnewl y reclaimedland .Th edevelop ­ mento fsocia l structuresi nFlevolan d (IJsselmeerpolders),Th eNetherla n A.L.M. Rijpert. Shopsan d shopping centres inth e IJsselmeerpolders D. P. Saherjon and L.H.J. Verhoef. Theregiona l economic policy in thene w townsAlmer e and Lelystad A. K. Constandse. From spontaneous settlement to integrated planning and development E. P. den Hertog. The zuyderzee project inTh eNetherland s C. H. Steenwinkel. Policy and settlement aspects tidal swamp land development inIndonesi a F.P.A. Oyedipe. Innovative potentials atKainj iLak e Basin for fadama farming:a study of three settlements N. M. Awan and M. Latif. Socio-economic aspectso fwate r management of salinity control and reclamationprojec t no.I i n Pakistan:a cas e study J. G. Smit. Theorigi n and early stageso f theHermann - Göringpolder (TümlauerKoog )i nSchleswig-Holstein ,German y J. P. Braaksma. Polders and landfills asalternativ e sitesfo r major airports

ENVIRONMENTAL ASPECTS G.K.R. Potman. TheOostvaardersplassen , thedevelopin g ofmarshy , ecosystems especially forwaterfow l J. Klein. Flying or creeping: the immigation oforganism sbetwee n reclamationan d cultivation

437 - N. Dankers. Ouantifying thelos so ffunction so fa natura l area asa mean so fimpac t assessment forreclamatio n projects - C. A. drijver. Cumulative ecological consequenceso fdykin g projects inth eWaddense aare a - J. Driebergen. Environmental developments intw oo fth eborder - lakeso fth eIJsselmeerpolder s inTh eNetherland s - R. Santagelo and A. Tomasin. Highwate ri nVenic e - B.H.J. Jong. Ecological impactso fpolde r constructioni n Suriname - J.G.C. Smits and N. M. de Rooy. Modelingeutrophicatio n processes ina polde rare a - J. P. Asjes. xheassessmen to fth elan d consolidationprojec t Eemland - F. de Srnedt, H. Vanlishout and A. van der Beken, Awaterbalanc e model applied toth eproble mo fmaintainin gaswam pnatur e reserve ina nagricultura l area

VolumeII I

- J. J. Sallaber. Openpolde r inth edelt ao fth eprovinc eo f Entre Rios,Argentin a

LANDAN DWATE RMANACE»ŒN TASPECT S - V. V. Dhruva Narayana and S. K. Kamra. Subsurfacedrainag efo r saline soil reclamation

POLDERASPECT S - G. Heerten. Modern technique inban k protection - M. Th. Radu. Hydraulic problems related toplannin go fpolders , solvedb yusin gprogrammabl e pocket calculators

SOCIO-ECONOMICAN DPHYSICA L'LANNIN GASPECT S - H. Hengeveld. Land evaluationfo rurba ndevelopmen t inTh e Netherlands - W. J, Wolff and J. J. Zijlstra. Effects ofreclamatio no ftida l flatsan dmarshe s inTh eNetherland so nfishe san dfisherie s - W. Joenje. Nature inne wwadden-polder s conservationb yexploitatio n

438 LISTO FAUTHOR SAN DPAPER S ofpaper s received toolat e - M. Ardeleanu. Complexdevelopmen to f thePardin a Polder inth e DanubeDelt a - H. N. Kerkdijk and W.van Uriel. Heavymeta l pollution in polder areas - El Cazaou and M. Rosea. The lowerBrates h Polder landrecla ­ mationprojec t - R. K. Sivanappan. Management ofavailabl ewate r resources - M. Zaman. Polderso fBanglades h and their economic opportunities.

439 PUBLICATIONS

Papers of the Symposium 3volume s Price for 3volume s Dfl. 180.— English language. Available at: I.L.R.I. P.O.Box4 5 6700A A Wageningen TheNetherland s Tel.:0837 0- 19100

Compendium of polder projects.A reviewo f anumbe ro f polders and pilot polders allove r theworld . English language. PriceDfl .10, — Available at: DelftUniversit y ofTechnology , Department ofCivi lEngineering , Mr. J.H. Schuurmans, P.O. Box504 8 2600G ADelft , TheNetherlands . Tel.:01 5- 781727 .

The flatwetland s of theworld .A soilexploratio n topotentia l polder areas.Englis h language. PriceDfl .7,50 . Available at: I.S.M., Ir.C.A . vanDiepen , P.O.Bo x353 , 6700A JWageningen , TheNetherlands . Tel.:0837 0- 19063.

Polders.Polde r issue in theserie s quarterlies of 'Civielee nBouwkun ­ digeTechniek' ,a cooperatio nbetwee nKIV I- Misset . An issue in theDutc h language of theplenar yhel d lectures ofth e Symposium. PriceDfl . 28,--. Available at: Uitgeversmij.C .Misset , P.O. Box4 , 7000B ADoetinchem , TheNetherlands . Tel.:0834 0- 31031 .

441 Polder issueo f the 'Cultuurtechnisch Tijdschrift'.A revie wo fa numbero fpolde r projects,o nwhic h Dutch peopleworked ,sprea d all over theworld . English language. Price Dfl. 8,50 including dispatchcosts . Availableat : Cultuurtechnisch Tijdschrift, Ing.A.C .d eBirk , P.O.Bo x 20021, 3502L AUtrecht . TheNetherland s Tel.:03 0- 859111 .

Polder issueo f 'Polytechnisch Tijdschrift'edition :Civi lEngineering . Articles about thewate rmanagemen t ofpolder s ingenera l andTh e Netherlands asa whole . Dutchlanguage . PriceDfl . 12,—includin g dispatch costs andV.A.T . Available at: StamTijdschrifte nB.V. , Ing.A.W .va nde nThoorn , P.O. Box235 , 2280A ERijswijk , TheNetherlands . Tel.:07 0- 991516 .

Polders of theWorld .A brochur e published by the information department of theMinistr y of Transport and PublicWorks . In theEnglis h language aswel l as theDutc h language. PriceDfl .5, — (per issue).

Poster- Polder s of theWorld . Description: 'Existingandpotentia lpolders' . Marked ona stylize dworl dmap . Price of theposte r isDfl .2,50 . Available at: Informatiecentrum 'NieuwLand' , Oostvaardersdijk 01-13, 8242P ALelystad , TheNetherlands , Tel.:0320 0- 27799 .

Polderlands of theWorld . Article of Professor ir.A .Volke r ina n issueo fUnesco : 'Nature andResources 'Decembe r issue1982 . Single copies canb eordere dat : Dekker enNoordeman , P.O. Box197 , 1000A DAmsterdam , TheNetherlands . Tel.:02 0- 240885 .

442 Articles inWate r International.Volum eVII Inumbe r 2^ 1983. Internationally orientated Keynotes,th eplenar y held lectureso f the Symposium.Publishe d inth emagazin eo f theInternationa lWate rRe ­ sourcesAssociation . Magazine free formember s of theIWRA . More information at theeditoria laddress : Elsevier Sequoia S.A., P.O. Box851 , 1000Lausann e 1, Switzerland.

Mondaymorning lectures of theMiniste r ofTranspor t and Public Works:Mr .H.J . Zeevalking, thechairma n of theJoin tCivi l Engineering Organizations:Mr .J . vanOord ,an d theChairma no f theSymposium : Professor ir.W.A .Segeren . Articles in the issue:Lan d +Wate r International ofNedec o and the Ministry ofForeig nAffairs .Numbe r 48/82. English language. A limited number ofcopie s canb e requested at: Nedeco, P.O.Bo x 80508, 2508G MDe nHaag , TheNetherlands . Tel.:070 -469421 .

A limited numbero f reprints canb e requested at: DelftUniversit y of Technology, Department of CivilEngineering , Ir.J .Luijendijk . P.O.Bo x 5048. 2600G ADelft . TheNetherlands . Tel.:01 5- 784677 .

443