Proceedings of the International Symposium on Shal/ow Sea and Low Land/Saga/oct. 1988

Lessons from 1200 years' irnpoldering in the Netherlands

P. Ankurn, K. Koga and W. A. Segeren Faculty of Civil Engineering, Delft University of Technology, Delft, the Netherlands

J. Luijendijk International Institute for Hydraulic and Environmental Engineering,Delft, the Netherlands

ABSTRACT: Polder development faced many problems in the past, but most of these problems were solved by many studies and research activities during the recent reelamatien of the IJsselmeer polders, such as: design of the drainage system, "soil-ripening" of the soft mud, management of the land reclamat\on through state farms.

1. INTRODUCTION and an additional 10.00 m for wave run-up.

The Netherlands is a small country The geological profil• in the lower ~art (34,000 km2) located in the delta and the of the Netherlands is formed of a 20 m former flood plains of the Rhine (160,000 toplayer of clay and/or peat on a thick km2), Heuse (33,000 km2) and Scheldt ri­ sand layer. The groundwater is brackish or vers. saline, so seepage water is often brack­ A quarter of the land is situated below ish. Normally seepage amounts to less than the mean sea level, with elevations to 1 mm/day, but there are exceptions of upto about 5 m below mean sea level. In absence 20 mm/day. of dikes, 65\ of the country would be flooded at high sea and river levels.

The country bas almost 15 million in­ 2. HlSTORY OF POLDER DEVELOPMENT habitants (450 per km2), with most of the population in the low-lying western part 2.1 Early development (900 inhabitants per km2). Some two thousand years ago, the major The Netherlands bas a cool maritime eli­ part (20,000 km2) of the Netherlands con­ mate with a mean annual rainfall of 775 mm sisted of lagoon and delta type areas, and and a mean annual (open-water) evaporation flooded during high water levels of the of 700 mm. North Sea and of the rivers, see also. The rainfall is evenly distributed over Figure 1. the year, but the open-water evaporation Bebind the coastal dunes, large areas varies from 0 mm/day in the winter, upto 5 with peat-forming vegetations existed mm/day in the summer. Generally, there is together with reedmarshes and marsh fo­ a rainfall surplus of some 300 mm in the rests. Along the rivers, forests on nu­ winter, and an average deficit of 120 mm trient rich alluvial soils existed, as in the summer. well as marsh forests and reed marshes The average temperature in the summer downstream. months reaches upto 17 °C, in the winter The people, mainly fishermen and hun­ months around 2 °C. ters, lived on the natural levees of the rivers. The sea tide in the North Sea differs in amplitude along the coast, with the maxi­ Proteetion works against the water star­ mum average tide in the Southern part of ted around 300 BC by constructing artifi­ +2.00 m and -2.00 m around mean sea level. cial dwelling mounds. However, the maximum sea levels during Construction of small di es along rivers storms are much higher and the sea dikes was started around 100 · BC under influence are presently designed for sea levels of of the technica! and organizatorial power +5.00 m (return period of 1:10,000 years) of the Romans. - 95 - r

1532 and was foliowed by the empoldering ged to other land uses: in the Flevoland of many other lakes: 3,000 ha during the polders even good soils were allocated for 16th century, 28,000 ha during 17th cen­ recreation and urban development (Lelystad tury, 25,000 ha during the 18th century, and Almere for at least 100,000 inhabi­ North Sea North Sea 52,000 ha during 19th century, and 2,000 tants each). ha in the 20th century.

Vieringeneer polder The empoldering of the Haarlemmermeer (18,000 ha, see also Figure 2) in 1852 was 3. EXPERIENCES IN THE NETHERLANDS a break-through towards modern empoldering techniques to be used for the IJsselmeer 3.1 Introduetion polders. Here, the 4 m deep polder was reclaimed by using steam engine driven The polder development in the Nether­ pumping stations. lands started as private initiatives in the early days when no gavernaent ergani­ zation existed. Later in the 16th and 17th 2.5 Empoldering of IJsselmeer polders century, the polder development was under­ taken by merchants on a commercial basis. The IJssel lake ("IJsselmeer") polders are located in a shallow inlet of the The polder development of the Haarlem­ North Sea, and was formerly called "Zuider mermeer in 1852 was undertaken with the Sea", see also Figure 2. main purpose to proteet Amsterdam against First plans of closing the Zuider Sea bank erosion by waves. Its agricultural ~ tldal marshes - reclalmed lakes from the North Sea dates back to 1667. It development was not very successful during would eliminate stormtloods and saliniza­ the first generations, because was it done ~ peatland § cosstal lowlands · tion of the heart of the country. The by individual farmers without support on I22Z:J flood plalns first plan for reclaiming parts of the technica! know-how, research, finance and Zuider Sea dates from 1849 and was fol- organization by the govecnment. Figure 1. The Netherlands 2000 years ago Figu~e 2. The Netherlands at present lowed by many other plans. The polder development in the 20th cen­ The first IJsselmeer polder, Andijk tury was undertaken by the government, who polder of 30 ha, was constructed as an set up the IJsselmeer Development Autho­ 2.2 Empoldering of "old land" 2.3 Empoldering of coastal areas experimental polder to gain experience rity ("RIJP") in 1930. About one fourth of with the land reelamatien techniques on the employees of the IJsselmeer Develop­ It is estimated that the first polders The reelamatien of coastal areas started the Zuider Sea bed deposits. ment Authority are working in the research were constructed in the eighth century. around 1200 AD. Tidal forelands and is­ divisions. These polders were remnants of old land lands, silted up to about high tide level The Wieringermeer polder became dry in Initially, the research was limited to lost to the sea in bistorical times. were reclaimed from the sea. 1930 and its land development was com­ soils, water management and agriculture, The polders had elevations at around mean Generally, the soils are loamy and have pleted by 1940. The reelamatien of the but was gradually extended to a wider high-tide level and were originally used groundwatP.r levels of 1 - 2 m below sur­ 20,000 ha of salty saturated sediments scope, including research on biology, for the growth of cereals at a low ground­ face. The land use is predominantly ara­ learned much on the ripening process of environment, rural and urban development, water table. ble, with potatoes and sugarbeet as main soft muds. archeology, economy. However, the major part of the first erop. polders were "peat" polders, consisting of With the construction of a 30 km long Sub-surface drainage machines, such as peat soils overlaying mainly loamy or harrier dam with sluices in 1932, the trench cutters, trench ploughs, wheel and clayey soils. Reclaimed peat soils oxydate 2.4 Empoldering of lakes IJsselmeer was formed by closing off salt chain diggers for sub-surface drains were and shrink after the groundwater table was water entrance from the North Sea. Within developed during the reclaaation of the lowered. The terrain subsided gradually The Netherlands in its early days was a few years the IJsselmeer became a fresh IJsselmeer polders. and the water management conditions in the not only characterized by land of just water lake. The Wieringermeer polder was developed polders deteriorated. Therefore, the above sea level, but also by numerous by manual hand labour, which involved 200 groundwater table was kept as high as pos­ lakes. These lakes were some 4 m deep and The North-East polder (48,000 ha) was manhour per km for trenches and 180 man­ sible, thus allowing only grass cultiva­ extended gradually because the soft banks reclaimed from 1942 to 1962. hour per km for subsurface drains. This tion for cattle. of peat were either excavated by the po­ The Flevoland polder was split for deve­ was reduced for the Flevoland polders to 3 pulation for their fuel, or were eroded by lopment into two sub-polders: the Eastern manhour per km for trenches and 12 manhour These first polders drained their water the attack of the waves on the lakes. Flevoland polder (54,000 ha) was reclaimed per km for subsurface drains due to the by gravity through simple sluices into an from 1957 to 1976, and the Southern Flevo­ machines. internal channel system with a water level The application of the windmills made it land polder (43,000 ha) from 1968 to date. of ± 0.50 m below mean sea level. The possible to reclaim the land in these Besides the mechanization, there was channel system discharged also by gravity lakes and to use the fertile clay soils The Markerwaard (41,000 ha) is awaiting also a development in subsurface drainage into the sea during low tide. suitable for cereal production. financing of around one billion US dollars pipes: from clay pipes with straw enve­ in 1988-prices. lopes, to corrugated pvc pipes with cocos The first lake (Achtermeer, 35 ha, near envelopes or even without any envelopes. Alkmaar) was successfully empoldered in Agricultural development was of prime importance in the first polders, but chan- The scope of the IJsselmeer Development - 96 - - 97- .. \

Authority was extended from the original iv storage canals ("boezem") surrounding , 3.4 Field drainage system 3.5 Main drainage system area of the IJsselmeer polders only, to­ the polder. wards general polder development in the The tunetion of the field drainage sys­ The main drainage system of a polder whole of the Netherlands, and even to pol­ The water management in a polder is tem is two-fold: (i) during the reclama­ consistsof (see Figure 5 and Table 1): der development outside the Netherlands. mainly determined by "water level control" tion period is to speed up the soil-ripe­ and to a lesser extent by capacities or ning process, inwhich the very soft and i Canals, which are often navigable and "volume control". wet soils are transformed into normal have (stagnant) water deptbs of some 1.50 - 2.50 m. The gradient of the 3.2 Present approach on polder development Therefore, the determination of the soils, and (ii) to maintain adequate drai­ canal bed is normally horizontal; stagnant water level ("polder level") and nage conditions during after reclamation. ii Main ditches; and At present, the development of a new the amount of water storage in the polder, iii Ditches, which run polder in the Netherlands is more or less i.e. the percentage of open water in the Preparation of new clay-polders (see ri­ along the long sides of the plots, i.e. the rectan- fixed and follows specific steps: polder, is most important. gure 4) starts with the digging of tren­ gular fields of about 1. construct the enclosing dike with out­ ches of ± 0.60 m deep at intervals of some 500 111 x 1200 m. Iets (pumping stations, sluices); The "polder level" is the target level 50 m, to promote the de-watering process. 2. dredge main drainage canals when the of the open water to be maintained in a One year before cultivation, other tren­ polder is still submerged; polder. ches at intervals of some 10 m are dug 3. evacuate the water from the polder The polder level is established on the between the existing trenches. during 6 to 12 months; basis of mainly agricultural considera­ After a few years of farming, the tren­ slulce 4. sow reed-seeds on the (soft) mud sur­ tions, such as: che drainage system is replaced by sub­ face by airplanes. This is to promote - the functioning of the field drainage surface ~rainage pipes, e.g. 1.20 m depth the drying process ("soil-ripening") system, and at 1nterval of 50 m for a design dis­ and to prevent other weeds; - to prevent or reduce the (irreversible) charge of 10 mm/day. The interval of the 5. construct of the drainage network of subsidence of the soil, drainage pipes for sandy soils is usually main drainage canals, main ditches and to prevent the oxidation of wooden pile less (e.g. 10 m), because the permeability plot ditches, as well as the construc­ foundations, of ripened soft clays appears to be high­ tion of the road system; - to meet interests of navigation, recrea- er. 6. develop the land by (i) burning the tion and nature preservation. reed vegetation, (ii) construction of The actual determination of the polder the open field drains; level is based on an experimental basis: 7. farm the land for about 5 years with the optimum polder level gives the highest Figure 5. Relation Polder-Boezem-Sea level government funds, very often with oil­ erop yields. seed in 1st year, wheat in 2nd year, barley in 3rd year, oilseed in 4th Polders may be divided into sections ha­ The present design procedure of the main year, wheat in 5th year; drainage system is still rather empirica! ving different polder levels, depending on and based on steady flow. 8. replace the open field drains by a the topography as to limit the varfation subsurface drainage system (pipes) in groundwater deptb to e.g. 0.50 m. after the soil bas ripened and the Different polder levels are also applied The required capacity of the drainage land subsidence has halted, e.g. after when soil conditions differ, e.g. peat system depends not only on the rainfall but also on the seepage (often 0.7- 1.0 the 5th year; soils with high polder levels ± 0.50 m mm/day) and on water from polder shiplocks 9. construct farm buildings and villages, below terrain, clay soils with deep polder (1- 2 mm/day). and lay telephone and electricity sup­ levels at ± 1.50 m below terrain. This leads for the IJsselmeer polders to ply cables and the water mains; Very often a "summer" polder level and a discharges in the main drainage system in 10. allocate land to private individuals deeper "winter" polder level is applied, the order of 13 mm/day for the ditches and on the basis of one to four workers as to provide for more drainage in the of 11 mm/day for the canals. per farm-holding; winter season. For urban polder areas, values for the 11. landscape, afforest and construct re­ main system of 20 mm/day and more are creation areas; often applied. 12. when the polder is ready: transfer of the administration and maintenance pumplng station functions to e.g. a Polder Board. Table 1. Type of polders.

polder land open polder pumping 3.3 Drainage System of the Polder type use Figure 4. Drainage during reclamation water level capacity % The drainage system in a polder exists of m~terrain mm/day (see Figure 3): peat grass . The design. of the field drainage system 5 - 10 0.20 - 0.50 8 12 i field drainage system, to maintain the old-clay grass 3 10 0.40 groundwater table under the root zone; 1n a polder 1s now almost at its optimum. - 0.70 8 12 old-clay crops 5 - 10 0.80 - 1.00 8 12 ii main drainage system, to divert the Modern criteria for polders are related to new-clay crops the groundwater level, which may reach 1 - 2 1.40 1.50 11 14 drainage water from the field drainage urban 3 - 8 1.50 system to the outlet; upto e.g. 1.00 m below terrain level du­ 1.80 15 30 iii sluices and/or pumping stations, to ring 2 days with a frequency of once per year, and upto e.g. 0.75 m during one day evacuate the water from the main drai­ The above criteria depend nage system to the hordering canals; Figure 3. Drainage system in polder with a frequency once per 10 years. also on the percentage of open-water, which is kept -98- -99- low in the modern polders (1- 2%), but is during some 30 60 days of sufficient - Parallel with the physical ripening, va­ ning water control in their areas. much higher in older peat polders (5- wind. rious chemical and biologica! changes 15%). occur in the soil. The management of the Water Board is In the past, the estimation of the pum­ carried out by: (i) tbe general assembly, Water management in the polders is based ping capacities of windmills was rather At the beginning of the reclamation, the (ii) the council, and (iii) the dike- reeve on "water level" control to keep the pol­ experimental set at 8 mm/day, which refer­ clay soils have a very high pore volume ("dijkgraaf"). der level constant. However, a water gra­ red to the criterium that the rainfall · (70 - 80%) and are almost impermeable (K = The general assembly is composed on a dient will be needed during discharges. during five consecutive days (40 mm) 10-3 to 10-• m/day). Thus , subsurface functional basis and represent different During periods of discharge, actual should be discharged within the same pe­ drainage is not feasible and is done by interest groups, mainly land owners, on an canal levels in the upper part of the riod. the evapotranspiration of pioneer-vegeta­ election basis. The general assembly polder will generally exceed the polder tion such as by reed. elects the council, who does tbe day-to­ level (+0.10 to +0.20 m), while near the The steam engine for pumping was applied This drying of the mud is irreversible day management of tbe Water Board. outlet the water level may be lowered well from 1770. The application of diesel and and the rewetting of the ripened clay does The dike-reeve is tbe chai rman of tbe below the polder level (-0.30 to -0.40 m) electrical driven pumps foliowed in the not bring back the soft original mud . council and is employed by the assembl • beginning of the 20th century. The maximum velocity in the drainage The physical soil-ripening process cau­ The costs of the water management in a channels is maintained at low values of ses a considerable shri nkage of the soil. polder is paid by tbe interested parties, 0.25 m/s to limit the gradient and to 3.7 Surrounding Open-Water The vertical component leads to a sub­ mainly land owners and domesti c/ industrial prevent erosion. sidence of 0.5 to 1.5 m. The horizontal polluters. The polders evacuate the drainage water component causes soil cracks. These cracks The Water Boards have no fixed financial from the polder canals to the surrounding are irreversable and are very important relationship with the central government , 3.6 Sluices, Windmills and Pumps open-water, sse also Figure 3. for the drainage of the soils. unlike the provincial and the municipal This is a system of higher-lying canals, governments. If a polder is surrounded by open water lakes or former rivers, usually at some Predietien of subsidence is often calcu­ in which tides are active, evacuation of 0.50 m below mean sea level and serves as lated with Terzaghi formula. The disad­ the drainage water can be accomplished by a temporary water storage. vantage of the use of this formula is that 4.2 Water legislation opening a sluice in the dike during low the relative subsidence (öz/z) can reach tide. The starage system ("boezem") is actual­ impossible values above 1 for soft soils By public law, tbe Water Board and the ly not a part of the polder and is drained and for large values of the grain pres­ Municipalities belong to the lower (third In the early days, the discharge modulus independently into the sea by means of a sures after and before loading. level) administrative level. The Province was lower than presently applied. So was sluice or by a pumping station. A new set of formulae has been developed is the second management level, and the assumed that winter rainfall of 260 mm Often a maximum water level ("maal in the Netherlands. State is the first. should be evacuated between 1 February and peil") is set in the starage canals, at 15 April, when 50 - 70 days are available which it is not allowed to receive drai­ The Water Board is a form of functional for sluicing. This means a drainage capa­ nage water from the polder. 4. THE POLDER BOARD decentralisation within the Netherlands city of 3.7 to 5.2 mm/day. State and bas responsibilities on water Another old rule-of-thumb prescribed 2- An additional function of the surroun­ 4.1 Water Board system management mat t ers, such as: 4 m sluice width per 1000 ha polder. ding open-water was only understood after - operatien and maintenance of hydraulic the groundwater problems with the Morth­ The origin of polder development i n the structures along coast and rivers, However, gradually the polders subsided East Polder since 1940. The polder ap­ Netherlands is to be found in proteetion control of water quantities (mainly so that pumping became more and more peared to have a serious draining an ef­ of land against flooding. Initially, these drainage, but also supply of water), necessary. fect on the adjacent old-land, by lowering activfties were carried out by individual - control of water quality, The first windmills for water evacua­ the groundwater table in a vast area. farmers and by private corporations. Gra­ - control of polder dikes and roads. tion, were constructed around 1400. An This effect was prevented at the next dually, the maintenance of the embankments impravement of the efficiency of the wind­ IJsselmeer polders by constructing a wide and sluices was controlled by regulations. The Water Board, as a functional body, mil! foliowed in the sixteenth century lake of 1 - 5 km between the polder and is not responsible for public administra­ with the fnvention of the revolving cap of the old land. At that time, no central or regional go­ tive matters. This is left to the Munici­ the mill bywhich a changing wind direction vernment existed, so local communities had pality which is the general administrative could be followed. to play an important role. Thus, the Water body. 3.8 Soil-ripening of clayey soils Boards ("waterschap") were formed, being The first windmills used the paddle­ special corporations on polder management. The provincial government is responsible wheel for raising the water, to a maximum Kuch of the current knowledge about the for the organization and eperation of the head of 2 m. reelamatien of unripened soils have been The Water Boards are one of the earliest Water Boards in its Province, by giving The technique of placing several wind­ gained during the impoldering of the IJs­ forms of government administration in the them authority and controllino their du­ milis in a series to overcome more head selmeer polders and bas been applied in Netherlands. ties. was developed in the seventeenth century many other parts of the world. Since the 15th century, the Water Boards and could reach a head of a multiple of 2 have a clear management and juridical The central government and the Provinces m. The physical soil-ripening process identity. have also management responsibilities on The open "Archimedes" screw pump to lift starts as soon as a polder falls dry and water control in addition to their tasks •tpto 4 m was invented in 1634. is a process of de-watering. Full ripening Since the early 19th century the Water on Water Boards: (i) the central govern­ of a soil profile to 1.00 - 1.50 m depth Boards are supervised by the provincial ment manages the large waterways, such as Generally, one windmill could cover may take centuries. Good drainage is most governments, but they have retained a high IJsselmeer, river Rhine, and (ii) the around 600 ha polder, from where some 300 essential for ripening. degree of independenee with regard to Provinces manage certain rivers on e.g. mm per year was pumped at a head of 1 m, finance and to issuing regul ations concer- navigation and main dike system. - 100- -101- ()>() 2·1 ;, \

,. RIFERENCES ·- [1] Kley, J. van der, and H. J. Zuidweg, 1969. "Polders en dijken". Agon El­ sevier, Amsterdam (in Dutch). [2] RIJP, 1980. "50 jaar Onderzoek door de Rijksdienst voor IJsselmeerpolders". Flevobericht nr. 163, Rijksdienst voor IJsselmeerpolders, Lelystad, the Netherlands (in Dutch).

[3] Schulz, E., 1983. "From natural to reclaimed land". Polders of the World, final report. ILRI, Wageningen, the Nether lands. [4] Rijniersce, K., 1983. "Een model voor de simulatie van het fysische rij­ pingsproces van gronden in de IJssel­ meerpolders". Rijksdienst voor IJssel­ meerpolders, 's Gravenhage, the Netherlands (in Dutch). [5] RIJP, 1985. "De Waterstaatkundige hoofdstructuur van de Markerwaard".

Rijksdienst voor IJsselmeerpolders, / Lelystad, the Netherlands (in Dutch).

[6] Schulz, E., 1987. "Water management in newly reclaimed land". RIJP-rapport 9 cbw. Rijksdienst voor IJsselmeerpol­ ders, Lelystad, te Netherlands.

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