Strategic Directions for Integrated Flood Risk Management in Focal

THEMEKONGRIVERCOMMISSIONSECRETARIAT

Strategic Directions for Integrated Flood Risk ManagementinFocalAreas

The Flood Management and Mitigation Programme, Component2:StructuralMeasures&FloodProofing intheLowerMekongBasin December2009 DraftFinalReport,Volume2D

HASKONINGNEDERLANDB.V. UNESCOIHE

MRCFloodManagementandMitigationProgrammeComponent2:StrucuralMeasuresandFloodProofing

CONTENTS Page

1 INTRODUCTION 1 1.1 Guide to the reporting structure of the Flood Management and Mitigation ProgrammeͲComponent2,StructuralMeasuresandFloodProofing 1 1.2 Strategicdirectionsforintegratedfloodriskmanagementinfocalareas 1

2 STRATEGICDIRECTIONSFORFLOODRISKMANAGEMENTINTHELOWERSEBANG FAIFOCALAREA 1 2.1 Flooddamagesandrisks 1 2.2 Floodbenefits 1 2.3 Structuralfloodriskmanagementoptions 1 2.4 Impactsofstructuralfloodriskmanagementoptions 1 2.4.1 Floodriskreduction 1 2.4.2 Environmentalimpacts 1 2.5 Strategicdirections 1 2.5.1 Landusescenarios 1 2.5.2 Reductionoftheactualfloodrisk 1 2.5.3 Floodprotectionforagriculturaldevelopment. 1

3 STRATEGIC DIRECTIONS FOR FLOOD RISK MANAGEMENT IN THE UPPER SE SAN FOCALAREA 1 3.1 Flooddamagesandrisks 1 3.2 Floodriskmanagementoptions 1 3.3 Strategicdirection 1

4 STRATEGICDIRECTIONSFORFLOODRISKMANAGEMENTINTHEMEKONGDELTA TRANSBOUNDARYAREA 1 4.1 Floodmanagementlevels 1 4.2 Regionalfloodmanagementscenarios. 1

5 STRATEGICDIRECTIONSFORFLOODRISKMANAGEMENTINTHEWESTOFBASSAC REGIONINCAMBODIA(TAKEO) 1 5.1 Flooddamagesandrisks 1 5.2 Floodbenefits 1 5.3 Structuralfloodriskmanagementoptions 1 5.4 Impactsofstructuralfloodriskmanagementoptions 1 5.4.1 Floodriskreduction 1 5.4.2 Transboundaryimpacts 1 5.4.3 Environmentalimpacts 1 5.5 Strategicdirections 1 5.5.1 Landusescenarios 1 5.5.2 Floodmanagementstrategicdirections 1 5.5.3 Mitigationoftransboundaryeffects 1

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6 STRATEGICDIRECTIONSFORFLOODRISKMANAGEMENTINTHEEASTOFMEKONG AREAINCAMBODIA(PREYVENG) 1 6.1 Flooddamagesandrisks 1 6.2 Floodbenefits 1 6.3 Structuralfloodriskmanagementoptions 1 6.4 Impactsofstructuralfloodriskmanagementoptions 1 6.4.1 Floodriskreduction 1 6.4.2 Transboundaryimpacts 1 6.4.3 Environmentalimpacts 1 6.5 Strategicdirections 1 6.5.1 Landusescenarios 1 6.5.2 Floodmanagementstrategicdirections 1 6.5.3 Mitigationoftransboundaryeffects 1

7 STRATEGICDIRECTIONSFORFLOODRISKMANAGEMENTINTHEWESTOFBASSAC AREAINVIETNAM(LXQ) 1 7.1 Flooddamagesandrisks 1 7.2 Floodbenefits 1 7.3 Structuralfloodriskmanagementoptions 1 7.3.1 Options 1 7.3.2 Structuralmeasures 1 7.4 Impactsofstructuralfloodriskmanagementoptions 1 7.4.1 Floodriskreduction. 1 7.4.2 Transboundaryimpacts 1 7.4.3 Environmentalimpacts 1 7.5 Strategicdirections 1 7.5.1 Floodmanagementstrategicdirections 1 7.5.2 Mitigationoftransboundaryimpacts 1

8 STRATEGICDIRECTIONSFORFLOODRISKMANAGEMENTINTHEEASTOFMEKONG AREAINVIETNAM(POR) 1 8.1 Flooddamagesandrisks 1 8.2 Floodbenefits 1 8.3 FloodriskmanagementEastofMekongRegionVietnam(POR) 1 8.3.1 Options 1 8.3.2 Structuralmeasures 1 8.4 Impactsofstructuralfloodriskmanagementoptions 1 8.4.1 Floodriskreduction 1 8.4.2 Transboundaryimpacts 1 8.4.3 Environmentalimpacts 1 8.5 Strategicdirections 1 8.5.1 Floodmanagementstrategicdirections 1 8.5.2 Mitigationoftransboundaryimpacts 1

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9 STRATEGIC DIRECTIONS FOR MEKONG RIVER EROSION RISK MANAGEMENT IN BOKEOPROVINCE,LAOPDR,ANDKRATIE,CAMBODIA 1 9.1 Introduction 1 9.2 Background 1 9.3 TheRationale 1 9.4 Objective 1 9.5 Guidingprinciples 1 9.6 Maincomponentsofthejointproject: 1 9.7 Futuredirections 1 9.8 Implementation 1

10 STRATEGIC DIRECTIONS FOR MEKONG RIVER EROSION RISK MANAGEMENT IN KRATIEPROVINCE,CAMBODIA 1 10.1 Introduction 1 10.2 Background 1 10.3 TheRationale 1 10.4 Areasthatrequireattention 1 10.5 Objective 1 10.6 Maincomponentsofthejointproject: 1 10.7 AdditionalInformation 1 10.8 Activitiestoformulatebankerosionriskmanagementplansandmeasures 1 10.9 Futuredirections 1 10.10 Implementation 1

11 APPENDIX:ENVIRONMENTALBASELINESFOCALAREAS 1 11.1 EnvironmentalbaselineNamMaeKokFocalArea 1 11.2 EnvironmentalbaselineBokeoFocalArea 1 11.3 EnvironmentalbaselineSeBangFaiFocalArea 1 11.4 EnvironmentalBaselineKratieFocalArea 1 11.5 EnvironmentalbaselineCambodianDelta 1 11.6 EnvironmentalbaselineVietnamDelta 1 11.7 The Tonle Sap Great Lake ecosystem and its importance for ecology and LowerMekongfisheries 1

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CHAPTER1 INTRODUCTION

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1 INTRODUCTION

1.1 GuidetothereportingstructureoftheFloodManagementandMitigationProgrammeͲ Component2,StructuralMeasuresandFloodProofing

Component 2 on Structural Measures and Flood Proofing of the Mekong River Commission's Flood Management and Mitigation Programme was implemented from September 2007 till January 2010 under a consultancy services contract between MRCS and Royal Haskoning in association with Deltares and UnescoͲIHE. The Implementation was in three stages, an Inception Phase, and two Implementation Stages. During each stage a series of outputs was deliveredanddiscussedwiththeMRC,theNationalMekongCommitteesandlineagenciesof the four MRC member countries. A part of Component 2Ͳon 'Roads and Floods'Ͳwas implementedbytheDelftClusterunderaseparatecontractwithMRC.Component2prepared fiveDemonstrationProjectswhichhavebeenreportedseparatefromthemainproducts. TheconsultancyservicescontractforComponent2specifiesingeneraltermsthat,inaddition toaFinalReport,fourmainproductsaretobedelivered.Hence,thereportsproducedatthe endofComponent2arestructuredasfollows: Volume1 FinalReport Volume2 CharacteristicsofFloodingintheLowerMekongBasin Volume2A HydrologicalandFloodHazardsintheLowerMekongBasin; Volume2B HydrologicalandFloodHazardsinFocalAreas; Volume2C FloodDamages,BenefitsandFloodRiskinFocalAreas; Volume2D StrategicDirectionsforIntegratedFloodRiskManagementinFocalAreas. Volume3 BestPracticeGuidelinesforIntegratedFloodRiskManagement Volume3A BestPracticeGuidelinesforFloodRiskAssessment; Volume3B BestPracticeGuidelinesforIntegratedFloodRiskManagementPlanningand ImpactEvaluation; Volume3C BestPracticeGuidelinesforStructuralMeasuresandFloodProofing; Volume3D Best Practice Guidelines for Integrated Flood Risk Management in Basin DevelopmentPlanning; Volume3E BestPracticeGuidelinesfortheIntegratedPlanningandDesignofEconomically Sound and Environmentally Friendly Roads in the Mekong Floodplains of CambodiaandVietnam1. Volume4 ProjectdevelopmentandImplementationPlan Volume5 CapacityBuildingandTrainingPlan DemonstrationProjects Volume6A FloodRiskAssessmentintheNamMaeKokBasin,Thailand; Volume6B IntegratedFloodRiskManagementPlanfortheLowerXeBangfaiBasin,Lao PDR; Volume6C IntegratedFloodRiskManagementPlanfortheWestBassacArea,Cambodia; Volume6D FloodProtectionCriteriafortheMekongDelta,Vietnam; Volume6E FloodRiskManagementintheBorderZonebetweenCambodiaandVietnam. TheunderlyingreportisVolume3Aoftheaboveseries. 1 DevelopedbytheDelftCluster

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1.2 Strategicdirectionsforintegratedfloodriskmanagementinfocalareas

AttheendoftheInceptionPhaseoftheFMMPͲC2anumberoffocalareaswereselectedfor whichstrategicdirectionsforfloodriskmanagementweretobedevelopedduringtheStage1 ImplementationPhase. Thefocalareasthatwereselectedforthisplanningexerciseare: 1. ThelowerNamKokbasininThailand; 2. ThelowerSeBangFaibasinintheLaoPDR; 3. TheUpperSeSanbasininVietnam 4. ThetransboundaryMekongDeltaareaontherightbankoftheBassac 5. ThetransboundaryMekongDeltaareaontheleftbankoftheMekong. The analysis for the NamMae Kok basin was delayed and couldonly partly be completed in Stage2duetoissueswiththehydraulicmodelofthebasin. Twootherfocalareas(BokeoinLaoPDRandKratieinCambodia)refertoareaswherebank protectionisthemainissue,ratherthanflooding. FortheupperSeSanbasinitwasfoundthatthetargetarea(Kontum)isbarelyatriskandthat floodriskreductionshouldfocusonvulnerabilityreductioninareasupstreamofKontumrather thanonstructuralmeasurestoreducethefloodhazardsatKontum. For the formulation of the strategic directions for flood risk management in the above mentionedfocalareasthefollowingapproachwasdeveloped: 1. Assessmentofthefloodrisksfortheactualsituation; 2. Formulationoffloodriskmanagementmeasures; 3. Estimatesofimpactsofthefloodriskmanagementmeasures. For the assessment of the flood risks in these areas reference is made to Volume2B for the floodhazardpartandVolume2Cfortheflooddamageandriskanalysuspart. It is noted that the acceptability of the assessed flood risks in the focal areas has not been evaluated. Such evaluation would require an extensive consultation and political decision makingprocess,especiallywhenitcomestotheassessmentoftheacceptabilityoftheriskof loss of live and other intangible consequences of the floods. Such consultation and decision makingprocesscannotbecarriedoutintheframeworkoftheFMMPͲC2. Whathasbeenachieved,though,istoillustratetowhatextentfloodriskscanbereducedand whetherthemeasuresthatarerequiredtoachievetheriskreductioncanbejustifiedfroma socioͲeconomicandenvironmentalpointofview. Structuralfloodriskreductionmeasuresaimingatfloodprotectionmaycreatebenefitsthatgo beyondthereductionoftheexistingfloodrisk.Suchmeasuresmayallowforamoreattractive landusethantheactualone,generatingmorepotentialbenefits.Itisdeemedessentialtokeep thesepotentialdevelopmentsinmindwhenevaluatingthesocioͲeconomicimpactsoffloodrisk reductionmeasures. ItisnottheintentiontoassesundertheFMMPͲC2themostattractivelanduseintheflood prone focal areas. For the socioͲeconomic evaluation, though, of the flood risk management measures, assumptions are made regarding potential land use in the areas once protected againstfloods.TheselandusescenariosareindicativeonlyandshouldbereͲevaluatedinthe frameworkofintegratedlandandwaterresourcesmanagementintherespectiveareas.

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CHAPTER2 STRATEGICDIRECTIONSFORFLOODRISK MANAGEMENTINTHELOWERSEBANG FAIFOCALAREA

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2 STRATEGICDIRECTIONSFORFLOODRISKMANAGEMENTINTHELOWERSEBANGFAIFOCAL AREA

2.1 Flooddamagesandrisks

The Se Bang Fai floodplain, downstream of the crossing with Road 13, experiences flooding problemsduringtherainyseasonnearlyeveryyear. Four districts in the Khammouane Province, Thakhek, Nongbok, Mahaxay, Se Bang Fai, are pronetoflooding,aswellas1districtinSavannakhetProvince:Xaybouly.Morethan80%ofthe flooding is caused by overflow from the Se Bang Fai River. A second cause of flooding is improperdrainageoftheareaafterheavyrain.Drainagecanalsandotherinfrastructure(gates) todischargethewateroutoftheareaintotheSeBangFaiortheMekongRiverareabsentorin apoorcondition.Finally,backwateroftheMekongRiveroccasionallycausesindirectfloodingin thearea.WhenthewaterintheSeBangFaiRiverexceedsacertainwaterlevel,backwaterfrom high discharges in the Mekong River cause a reverse flow and flooding of up to 1.5 meters occursinthelowerareas.FloodinggenerallystartsbetweentheendofJulyandSeptember,and normally last between 15 and 30 days. Most of the area flooded is used for agricultural purposes.AcomprehensivedescriptionofthefloodhazardisgiventheVolume2B. On the basis of the results of the socioͲeconomic survey carried out in the Nongbok district flooddamageandfloodriskassessmentshavebeenmadeforthisdistrictaspresentedinthe Volume2C.Theriskinthisdistrictundertheactuallanduseconditionshasbeenestimatedat some USD 3 million per year.Extrapolating the results of the Nongbok district to the flood proneareadownstreamofthenationalRoad13,itisestimatedthatthefloodriskinthelower SeBangFaiareaisoftheorderofUSD6mlnperyear.90%ifthisriskisrelatedtoagricultural damages. Itisnotedthatthisestimatedriskreferstotheactuallanduseanddoesnottakeintoaccounta moreintensivelandusethatmaydevelopincasethefloodhazardintheareaisreduced. 2.2 Floodbenefits

Apart from the negative impacts of flooding as mentioned above, floods also have positive impactsonthesocialeconomysuchasnaturalfishingandsoilfertility.Resultsfromfocusgroup discussionsheldinfocalareas2showedthatbenefitsfromnaturalfishingforpeoplelivingflooded areasvaryfrom150Ͳ3,200US$/householdinnormalfloodyearstoUS$290Ͳ6,400forbigflood years.Thefishingismainlyfromriverandcreeks. AccordingtotheMRCͲTechnicalPaper3onfishyields,thedatafortypicalyieldsoffishinpaddy fieldsinLaoislimited.However,itisreasonabletoexpectthatthefishyieldinLaowouldbe lowerthanintheCambodianandVietnamesefloodplains.Thelowerlimitsofnaturalfishin CambodiaandVietnamwere55Ͳ80kg/ha.ThefloodplaininSeBangFaiisunderrainyseasonal paddy from JuneͲOctober, with much shorter flooding duration compared to flood plains in CambodiaandVietnam.Itisestimatedthatthefishyieldwouldbeabout20kg/ha,resultingin thevalueof6US$/ha.Farmersinthestudiedareasaidthattherearenofloodingbenefitto agricultureintermsofsedimentationandsoilfertility,acidityleachingandpestcontroltothe land.

2SeeVolume2Cfordetailedanalysisofthefocalgroupdiscussions 3MRCͲTechnicalPaper,No:16,October2007:Consumptionandtheyieldoffishandotheraquaticanimalsfrom theLowerMekongBasin

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2.3 Structuralfloodriskmanagementoptions

Thereductionofthefloodriskcanbeachievedbyeitherthereductionofthefloodhazardwith thehelpofstructuralmeasures,thereductionofthevulnerabilityoracombinationofboth. The flood risk in the lower Se Bang Fai is mostly due to agricultural damages. Reduction of vulnerability is therefore most effective if the vulnerability of the agricultural production is reduced. This can be done by adapting the cropping pattern to the flood regime and/or the introductionofmorefloodresistantcrops. Itisassumedthattheactualcroppingpatternisalreadyoptimallyadjustedtothefloodregime (traditionalcopingmechanism)andthatfurthervulnerabilityreductionistobesoughtinthe useand/ordevelopmentoflessvulnerablevarieties. ThereductionofthefloodhazardinthelowerSeBangFaiareacaninprinciplebeachievedby: 1. The creation of flood retention capacity in or upstream of the flood prone area. Such measureallowsforthereductionoftheSeBangFaipeakdischargesand,consequentlyof thepeakwaterlevelsintheriverandadjacentfloodplains. 2. Thecreationofadditionaldischargecapacityoftheriversystem.Suchmeasurewillreduce the peak water levels. The discharge capacity can be increased by deepening and or wideningoftheriveritselforbycreatingadditionalcapacityinadiversionand/orbyͲpass channel. 3. Theconstructionofdikingschemesthatprotectselectedareasagainsthighwaterlevels. 4. TheconstructionofgatestopreventortocontrolfloodwaterstoentertheSeBangFai floodplains; 5. Theimprovementofthedrainagesysteminthefloodplains,allowingforareductionofthe durationoftheflooding.Furtherreductionofthedurationoffloodingcanbeobtainedby theinstallationofgatedstructuresatthelocationswherethe(natural)drainagesystemof thefloodplainsdrainsintotheSeBangFaiortheMekongriver. 6. TheconstructionofadiiversionorbyͲpasscanalfromtheXebangfaitotheMekong. Regardingthecreationoffloodretentioncapacityupstreamofthefloodpronearea,aproject ideawasidentifiedconcerningtheconstructionofafloodstoragereservoirintheSeBangFaiat the confluence with the Xe Noy, just upstream of the Road 13 crossing, combined with construction of a flood gate in the Se Bang Fai mouth. This option has been discarded for reasonsoffarͲreachingresettlementneedsoftheimplementationofsuchoption. Under the actual conditions the floodplains have their own natural retention capacity. The creation/reservationofretentioncapacityinthefloodproneareais,therefore,onlyrelevantin combinationwiththeimplementationofdikingschemes.Inthatcase,partofthefloodplain canbeprotectedwhileanotherpartisreservedfortheretentionoffloodwaters. Forthecreationofadditionaldischargecapacity,referenceismadetopreviousstudiesonthe flooddiversionchannel"Xelat"fromBanneSokbotoBanne. Dikingschemesforfloodprotectioncanbeconsideredatseverallevels,fromthesoͲcalledminiͲ polderstoafullprotectionofthefloodplainsonbothsidesoftheriverdownstreamoftheNR 13.MiniͲpoldersrefertotheprotectionofisolatedareasintheorderof1,000haeach.Forthe rightbankofthelowerSebanfai(Nongbok)planshavebeendevelopedforpoldersfrom3,000 hatoalmost10,000ha.However,consultationofthestakeholdersrevealedthattheyprefer embankmentsthatprotectthewholearea.

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AttheNongbokdistrictlevel,ideashavedevelopedthatfocusondrainageimprovementrather than on flood protection. A number of 23 schemes have been identified for widening and deepening (natural) drains to be provided with gates at the confluence with Se Bang Fai or Mekong.Theseschemestrytoachieveareductionoftheinundationtimeoffloodedareato15 daysorless.Someoftheschemesalreadyexistbutneedrehabilitationand/orimprovement. FromtheDemonstartionProjectthedevelopanIntegratedFloodRiskManagementPlanforthe Lower Xe Bangfai area it is concluded that substantial reduction of the existing risk can be achieved by reduction of the duration of flooding. Hence, flooding would not be eliminated completelyinordertopreservetheimportantwetlandareasandfisheriesbenefits.Controlled floodingcanbeusedinthatapproach. The option of embankments along the river banks and controlled flooding with drainage improvementincombinationwithgatingofthesmallXeBangfaitributariescanbeattractiveto achievethisgoal. 2.4 Impactsofstructuralfloodriskmanagementoptions

2.4.1 Floodriskreduction

ThefloodriskintheNongbokdistrictwasestimatedwiththehelpoftheresultsoftheexisting ISISmodel,whichhasanumberofshortcomingsasexplainedinVolumes2Aand2B.Therisk assessmentwasdoneforthesituationinwhichbothsidesofthelowerSeBangFai(Nongbok andSavannakhet)areunprotected. DespitetheshortcomingsofthehydraulicISISmodel,anattempthasbeenmadetosimulate theimpactofthedikinganddiversionoptionsonthefloodhazardinthelowerSeBangFai.The resultsaregiveninappendix3toVolume2BandinVolume6B,ytheDemonstrationProjecton thepreparationofanIntegratedFloodRiskManagementPlanforthelowerpartofthebasin. New risk estimates have been made with the help of these simulation results for the diking optiononly.Fourscenarioshavebeenconsidered: 1. Scenario1:thebasecase,i.e.withoutfurtherembankmentconstruction; 2. Scenario2:LeftbankembankmenttoprotectareasinSavannakhetprovince; 3. Scenario3:EmbankmentonbothbanksoftheSeBangFairiver. 4. Scenario 4: a diversion canal from the Se bang fai, dowstream of ban Se Bangfai, to the Mekongriver. TheScenario2haslargelybeenimplementedsince2002butitislikelythattheembankment was designed for a probability of exceedance of 15% only. The flood assessment for this scenario indicates that diking of the Savannakhet bank has given a 0.1Ͳ0.2 m extra flooding depthintheNongbokarea.Thiscorrespondswithanincreaseofthefloodingriskintheorder of0.04millionUSDperyear. Under Scenario 3, a flood risk reduction of 3 million USD per year has been calculated for Nongbok.However,protectionoftheNongbokfloodplainswouldcreatealossofnaturalfishin thisareaintheorderof0.1millionUSDperyear.Furtherinvestigationsinthedemonstration project showed that also taking into account the risk at the Savannakhet side and for a probabilityofexceedanceof1%,totalriskreductionwouldbeUSD6mlnperyear. Scenario4,isveryeffectivefromahydraulicpointofview,anoptimalcanalbottomwidthof some125mhavebeenreseachedintheframeworkoftheDemonstrationProject.Ineconomic termsthediversionchanneltogetherwith(lower)embankmentsissome12%morecostly.

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2.4.2 Environmentalimpacts

TheseasonallyinundatedLowerSeBangFaifloodplainisasensitiveandvaluableecosystem.It consistsofamosaicoffreshwaterlakes,riverponds,ricepaddyandfreshwatermarshes.Close totheriverthereareseveraloldriverchannelswithoxbowlakes,thatsiltedupandformfairly largemarshes.Althoughnotmuchisknownaboutthefloraandfaunaspeciespresentinthe area,itistobeassumedthattheseareasareimportanthabitatsforfishandwaterbirds.The wetlandsarealsoimportantasrefugesforBlackfishinthedryseasonandasspawningand nursingareasforbothBlackandWhitefishinthefloodseason. NoofficiallyprotectedareasarelocatedinSeBangFaiplain,however,BirdLifeInternationalon itswebsitementionsanImportantBirdArea(IBA)locatedinthearea.Detailsarenotknownat present. Population in the project area is concentrated along the river and in villages located on the higheroldleveesinthefloodplain,wheredensitiesareconsiderable.Theriverisanimportant sourceofwaterfordomesticuse. Paddyriceisthemaincropinthearea,whilethebanksoftheSeBangFaiRiverareintensively usedfortheproductionoffruits,vegetablesandcashcropsliketobacco.Fisheriesisimportant inthefloodseason.Itisasourceoffoodandadditionalincomeforasubstantialpartofthe population. Potentialenvironmentalimpactsofstructuralfloodriskmanagementmeasuresare: 1 Destructionofnaturalhabitats,valuableresources 1.1 Provisionoffullfloodprotection,keepingoutthefloods,willhaveadetrimentaleffect onthewetlandhabitats,themoresowhencombinedwithimproveddrainage.Alarge proportion of the wetlands will dry outand the floral species composition will change drastically.Thiswillhaveanegativeimpactonthevalueoftheseecosystemsasahabitat forwetlanddependentfishandbirds,theywilldecreasegreatlyinnumbersordisappear completely.Whennotfloodedanymore,thefunctionofthefloodplainasadryseason refugeforBlackfishandawetseasonfishspawningandnursingarea(forbothBlack andWhitefish)willbelost. 1.2 Indirectimpactsofreducedfloodingwillalsobeconsiderable.Betterprotectionofthe areawillincreasethevalueofthelandforagriculturalproductionandhencewillincrease thepressureonthepresentlynotͲcultivatedareas. 1.3 Otherimportanthabitatsintheprojectareaarepoolsandslowwaterstretchesinthe river.Thesearenotexpectedtobeaffectedbytheproject. 2 Lossofbiodiversity,rareandendangeredspecies 2.1 Reducedfloodingwillhaveasignificantnegativeimpactonthebiodiversityinthearea. Speciescompositionoffloraandfaunawillchangeandthediversityandextentofwater bodies and swamps in the floodplain will decrease. SixtyͲseven fish species have been recordedinthelowerXeBangFai.Noendemicspecieswereamongthese.Mostofthe recordedspeciesarehighlymigratory.Adultsandjuvenilesspendthedryseasonindeep refugepoolsinthemainstreamMekong.Attheonsetofthewetseason,theymigrate upstream until they encounter a tributary, and then swim up the tributary until they reach a floodplain or another suitable spawning/nursing habitat. There are over thirty mediumandlargesizespeciesofcyprinidandpangasiidcatfishwhichexhibitthisgeneral migrationpattern. 2.2 Thefirstmajorfishmigrationoftheyearcommencesatthebeginningofthewetseason. Atthattime,accordingtovillagers,alargenumberoffishspeciesbeginmigratingupthe

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SeBangFai,anditslargertributaries,whileotherfishspeciesarebelievedtomovefrom deepͲwaterpoolstospawningareasintheSeBangFai. 2.3 These two migrating groups include the following taxa: Cyprinids (Labeo chrysophekadion, Labiobarbus sp., Sikukia gudgeri, Hypsibarbus sp., Puntioplites sp.), Catfish(Pangasiuslarnaudii,P.macronema,P.pleurotaenia,P.bocourti,Wallagoattu,W. leeri, Bagarius sp, Hemibagrus wyckioides, H. nemurus, Helicophagus waadersi, Laides sp., Mystus spp.), Mud perch (Pristiolepis fasciata), Glassfish (Parambassis siamensis), River loach (Schistura sp. or Nemacheilus sp.). During overbank flooding events fish migratelaterallytotemporallyinhabitadjacentfloodplainsforspawningandfeeding. 2.4 In the dry season Black fish species remain in lakes and swamps on the floodplain, wheretheyareabletosurviveharshconditions.Theopenwatersandwetlandsarevital inmaintainingabreedingstockofthesespecies.Adecreaseinnumberorareaofthe floodplainlakes,orevenalaterarrivalofthefloodwater,resultsindryingoutofthe floodplainlakesandpondsorthedevelopmentofverypoorwaterqualityconditionsand ultimately in a loss of species like snakehead, mud perch, spiny eels, climbing perch, walkingcatfish,andgouramies. 2.5 It will be clear that under Alternatives 1 and 2 the survival rate of Black fish in the floodplainwilldecreaseconsiderablyandthatlateralmigrationtospawningandfeeding areasinthefloodplainwillbeimpossibleforWhitefish.Underalternative3,upstream fish migration in the Se Bang Fai will be impossible and will ultimately lead to the disappearanceofmostofthesemigratoryspecies. 3 Lossofenvironmentalservices 3.1 Floodingandtherelatedsustenanceofwetlandsisknowntohaveanumberofbenefits, these benefits may disappear or decrease if flooding is prevented or diminished, as discussedbelow. 3.2 Higheragriculturalproduction:informationgathered duringFocal Groupdiscussionsin theareashowedthatpaddyyieldsafterayearwithahighfloodarenotdifferentfrom yieldsafterayearwithanormalflood.AlsotherewasnodifferenceinrequiredagroͲ chemicalinputs.Apparentlythesiltdepositionduringtheflooddoesnotimprovethesoil fertility and there are no positive impacts of flushing of contaminants or sanitation (killing pests and bugs) of the soil. Reduced flooding will reduce the replenishment of groundwaterandsurfacewaterbodieswithfloodwater.Asalreadydescribed,thiswill affectthewetlandecology,butprobablyalsotheamountofsurfaceandgroundwater availableinthenextseason.Ofimportanceisalsothatnotonlytheavailablequantity willbeaffected,butalsothequalityofthewater.Pollutantconcentrationsincreasein the course of the dry season and flooding flushes these pollutants out or reduces the concentrationstoharmlesslevels.Reducedfloodingwillresultinadeteriorationofthe waterqualityinthearea. 4 ImpactonProtectedAreas 4.1 Not applicable, there are no officially protected areas located in the area. BirdLife InternationalonitswebsitestatesthatthereisanImportantBirdArea(IBA)locatedin thearea.Detailsarenotgiven. 5 ImpactonFisheries 5.1 Afterrice,fishisthemostimportantitemonthedietforallethnicgroupsinthearea. Besides,thesaleoffishonlocalmarketsaddstotheincomeofmosthouseholds.Fishis caught all year round by men, women and children. The seasonal fish migrations betweentheMekongRiverandtheXeBangFaiareimportantperiodsforfisheries. 5.2 ThemainSeBangFaichannelisthemostimportantfishinggroundduringthedryseason (when fish concentrate in refuge habitats), while habitats on the floodplain (flooded forests,swamps,backyardponds,paddyfields)areimportantduringthewetseason.

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5.3 Asdescribedbeforereducedfloodingofthefloodplainswillhaveasignificantnegative impactonfishstocks,bothinthefloodplainitselfandintheriver. 6 Landacquisitionandresettlement 6.1 UnderAlternative1and2thedikesalongtheSeBangFai,andpartlytheMekongRiver, willbeheightened.Becauseoftheirrelativelyelevatedposition,theseriverbanksarethe areaswherepopulationisconcentrated.Landacquisitionandresettlementareimportant issues in this case. Of additional concern is the (temporary ?) impact of the dike constructionontheriverbankgardening.Thisisanimportantactivity,providingfoodand incometoalargenumberoffamilies.Femalesmaybeaffectedmorethanman,because theriverbankgardeningismainlydonebywomen.Constructionofadiversionchannel, underAlternative2,willentailadditionallandacquisitionandresettlement,aswellas lossofsomeagriculturalarea. 6.2 An alternative including the construction of a storage reservoir would require the acquisitionofalargearea:theimpoundmentareaofthereservoirisestimatedat10,500 ha.Thisareaincludesagriculturallandof18villages.Resettlementwouldbeatoobig issue.Forthisreasonsuchscenariohasbeendiscarded. 7 Humanhealthandsafetyimpacts 7.1 Overalltheprojectwillhaveapositiveimpactonhumanhealthandsafety.Peoplewillbe betterprotectedagainstflooding,floodswilllastshorterandfood(rice)production,and sofoodsecurity,willincrease.Thisisnotthecasefortheamountoffishavailableinthe floodseason,thatwillgreatlyreduce.Reducedflushinganddilutionofpollutedwaterat theendofthedryseasonmayposeathreattohumanhealth. 7.2 Constructionactivitiesareanotherthreattohealthandsafetyforavarietyofreasons: emissionofdust,fumes,noiseandvibrationfromconstructionsitesandaccessroads, increasedtrafficandworkersaccidents.Inflowofworkersfromotherareasincreasesthe riskofaspreadofHIV/AIDS. ReducedfloodingintheSeBangFaifloodplainwillhaveanumberofsignificantenvironmental impacts. The area is at present a fairly important wetland area, which sustains a high biodiversityoffloraandfauna,mainlywaterbirdsandfish.Reductionofthefloodingwillaffect thedryseasonrefugehabitats,smalllakes,pondsandmarshes,whichareimportantforthe survivaloffloodplainfish.Inthefloodseason,thefloodedwetlands,forestsandricepaddies areanimportantspawningandnursingareaforbothfloodplainresidentfishandmigratoryfish. Itwillbeclearthatfisheriesintheareawillreducegreatly.Evenmoresoiftheobjectiveofthe projectisreachedbyconstructionofadamacrosstheSebanfai.Suchadamwouldobstructthe fishmigrationupanddowntheriver. Otherimportantissuesaretheriverbankgardeningandlandacquisition/resettlement.River banksarecultivatedintensively,mainlybywomen.Thefruitsandvegetablesgrownthereare important for the diet, tobacco is important as cash generator. Land acquisition may be considerable,sincepopulationisconcentratedontheriverbanks. Fromanenvironmentalpointofviewcompletefloodprotection,keepingthefloodsout,does notseemtobeagoodidea.Afloodprotectionsystemthatwouldallowfloodingofthearea duringthemainfloodperiodoftheMekongRiverwouldsustainthepreciouswetlandecology andthefisheriespotential. The findings of the initial environmental evaluation are summarised in the "screening table" overleaf.

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Screening question Yes No Remark A. Project siting

Is the Project area adjacent to or within any of the following environmentally sensitive areas? in or near sensitive and valuable ecosystems X the area is an important wetland area, (e.g., protected areas, wetlands, wild lands, coral consisting of a mosaic of fresh water reefs, and habitats of endangered species) lakes, river ponds and fresh water marshes. No official protected areas are located in Xe Bang Fai plain in or near areas with cultural heritage sites (e.g. X - archaeological, historical sites or existing cultural or sacred sites) densely populated areas where resettlement may X population is concentrated along the river be required or pollution impacts and other bank and in villages on higher grounds. disturbances may be significant Alternative 3 of the project may require significant resettlement regions subject to heavy development activities or X - where there are conflicts in natural resource allocation watercourses, aquifer recharge areas, or reservoir X river water is an important source for catchments used for potable water supply domestic water for a large proportion of the population in the area lands or waters containing valuable resources X the area is an important rice producing (e.g. fisheries, minerals, medicinal plants, prime area. Besides fisheries provides agricultural soils) additional food and income to the rural population

B. Potential environmental impacts

Is the project likely to lead to: permanent conversion of potentially productive or X the wetlands in the project area are likely valuable resources (e.g. fisheries, natural forests, to be affected when flooding reduces. wild lands) Reduced access to, and flooding of, the floodplain reduces fisheries potential greatly destruction of natural habitat and loss of X a reduction of the flooded area will affect biodiversity or environmental services provided by the flora and fauna diversity (fish and a natural system water birds). Under alternative 3 upstream migration of fish will be hampered risk to human health and safety (e.g. from X limited, some construction activities generation, storage, or disposal of hazardous related health and safety risks are to be wastes, inappropriate occupational health and expected. Improved flood protection on safety measures, violation of ambient water or air the other hand reduces risks and quality standards) improves food security and thus health encroachment on lands or rights of indigenous X - peoples or other vulnerable minorities displacement of large numbers of people or X under Alternative 3 a considerable businesses number of people will have to be resettled absence of effective mitigation or compensation X - measures 2.5 Strategicdirections

2.5.1 Landusescenarios

Rice cropping and vegetables growing are the main agricultural activities in the project area. Agricultureistheareaslargestsectorofemployment,with92percentoftheinhabitantshaving riceproductionaspartoftheirlivelihoodsystems.Vegetablesand othercropsaregrownby residents on the somewhat elevated Se Bang Fai river banks, as well as in the flood plains aroundnaturallakesaswaterrecedes.Lowlandwetriceiscultivatedinthelowerlyingareas. TheSeBangFaiplainisoneofthefourmainriceproductionareasincentralLao.Successor failureoflowlandriceiscloselylinkedtothenaturalfloodcycleandeveryyearpartofthecrop

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isdamagebytheflood.Yieldsarehighest,2.0Ͳ2.8ton/ha,inareasthatarenotfloodedvery long.Thetotalpaddycroppedareais12,381ha/yr,or2.13haperhousehold. Intheprojectareatherearetwomaintypesofriceproduction:rainfedlowland(wetseason) paddyandirrigatedlowland(dryseason)paddy.Inthewetseason8,029haarecropped,inthe dryseasonthecroppingareais4,351ha.Althoughfoodsecurityappearsnottobeanissuein the area, the Government of Lao PDR has embarked on a major program of irrigation developmentalongtheSeBangFai;mostvillagesalongtherivernowhaveirrigationpumps, andanetworkofcanalswithwatercontrolstructureshasbeenconstructedtodeliverwaterto thefieldsinthedryseason. ThedevelopmentofastrategicdirectionforfloodriskmanagementinthelowerSeBangfaiarea is closely related with theenvisaged land use scenarios. The risk under the present land use conditionsisrelativelylow,essentiallybecausetheactualcroppingpatternsarefullytunedto thenaturalfloodcycle.Nevertheless,theriskundertheactualconditionsisstilloftheorderof USD2millionperyearintheNongbokdistrictalone. Astrategicdirectionforfloodriskmanagementcouldaimat: 1. riskreductionunderthepresentlanduseconditions; 2. floodprotectionmeasuresthataimatamoreintensivelanduse. 2.5.2 Reductionoftheactualfloodrisk

If no substantial development of the agricultural sector in the lower Sebanfai flood plain is envisaged,thereductionoffloodriskinthisareashouldfocusonthereductionoftheactual flood damage in this sector. Based on the risk assessment that was made for the Nongbok districtitcanbederivedthattheagriculturalfloodriskinthelowerSeBangFaifloodplainisof theorderofUSD150peryearperhectare.Aprotectionofthisareaagainstfloodslowerthan the1in10yearfloodwouldreducetheriskwithsomeUSD100peryearperhectare.Thisrisk reductiondoesnotjustifysubstantialinvestmentsinlargescaledikingschemes. Itisanticipatedthatsubstantialreductionoftheexistingriskcanbeachievedbyreductionofthe durationofflooding.TheoptionofdrainageimprovementincombinationwithgatingoftheSe BangFaitributariescouldbeanattractiveoptiontoachievethisgoal. The diversion option will reduce the peak levels along the Se Bang Fai downstream of the diversion canal. It will have no impact on the Mekong back waters. Further analysis of this optionisrequiredtoassessitsimpactsontheagriculturalrisk.Itisanticipatedthoughthatthe costofsuchmeasureisprohibitiveascomparedtothebenefits(riskreduction) AminiͲpoldermightbeattractiveifitprotectsanareawheretheactuallandusewouldjustify suchinvestment.FurtheranalysisisrequiredtoassesswhethersuchareaexistinthelowerSe BangFaifloodplain. 2.5.3 Floodprotectionforagriculturaldevelopment.

Floodprotectionforagriculturaldevelopment Khammouane and Savannakhet provinces have expressed desire to develop the agricultural sectorinthelowerXeBangfaifloodplainsbyhavingalargerirrigatedarea.However,irrigation schemesareatpresentusedforabout50%oftheirrigationschemeareas,thesesmallschemes are located on the river levees and are not seriously affected by flooding. Though there is a potential for new irrigation schemes, the focus should first be on the rehabilitation of the existingschemessothatthesecanbeusedtotheirfullextent.

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CHAPTER3 STRATEGICDIRECTIONSFORFLOODRISK MANAGEMENTINTHEUPPERSESAN FOCALAREA

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3 STRATEGICDIRECTIONSFORFLOODRISKMANAGEMENTINTHEUPPERSESANFOCALAREA

3.1 Flooddamagesandrisks

The upper Se San focal area corresponds essentially with the Kon Tum province in Vietnam. Reportedflooddamagesinthisprovinceovertheperiod2001Ͳ2005areoftheorderof0.9 millionUSDperyear(in2007adamageof1.9millionUSDwasreported).Thesedamagesare direct damages only. About half of the damage is related to irrigation and transport infrastructure,whiletheotherhalfisrelatedtohouseholdsandagriculture. Kontum town does not suffer from inundation, except under extreme flood conditions. Some damagewasreportedintheyear1996,whichwasanexceptionalyear(estimatedprobabilityof lessthan0.02%).DespitethefactthatKontumisrelativelysafeforflooding,itslocationonthe bankoftheDakBlatributarymakesbankprotectionnecessarytoavoiddamagesduetoerosion. Informationonerosiondamagesisnotavailable. MostfloodrelateddamagesintheintheprovinceoccurreportedlyintheareaupstreamofKon Tum town. In the framework of Community Based Disaster Risk Management programme, damageassessmentsweremadeintwocommunesintheTuMoRongDistrict.Theresultsare showninthetablesoverleaf.Fromthesetablesitappearsthatmostdisasterrelateddamageis due to land slides and not the direct impacts of floods. However, fatalities are essentially relatedtofloods. 3.2 Floodriskmanagementoptions

Floodriskmanagementintheprovincefocusesessentiallyonthereductionofthevulnerability ofthepeopleandinfrastructure.Ongoingfloodriskmanagementmeasuresinclude: 1. Softmeasuresforvulnerabilityreductionlike: a. Capacitybuildingatcommunelevel(UNDP) b. Earlywarning c. Emergencymanagement,preparednessplans 2. Hardmeasuresforvulnerabilityreduction: a. Floodproofing/upgradinginfrastructure(roads,bridges,culverts,irrigationworks) b. BankprotectionKonTum(2.6km) 3. Softmeasuresforhazardreduction: a. Reforestation(5millionhas) StructuralworkstoreducethefloodhazardsupstreamofKonTumtownarenotenvisaged.

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Hazardsimpactsduringthepast10Ͳ15yearsinMangRyCommune Year Hazards Affected Damagesonhuman,house,propertyandproduction areas Damageditems? Reasons? 1994 Fire Ng cLa Burntwholevillage (80houses) 1996 Fire Ng cLa Burnt7houses Landslide PuTá Filledup2ha Locatedatmountainsidecloseto productionlandand3 road.Landwasburiedbysoiland storehouses unabletoberecovered. 1997 Fire PakD n Burnt20houses Severalhouseholdsdidnot extinguishthefirewhentheyleft forfield;strongwindfannedthe restfireinkitchenandcaused houseburning. Landslide LongHy Killedmanycowsand Letwander buffaloes Landslide ChungTam Lost2haproduction Closetoroad,buriedbysoiland landofrice,cornand unabletoberecovered. noodle 2000 Drought whole Damaged0%ofSpring commune cropduetowater shortage 2002 Fire LongHyII Burnt3houses Firewasnotextinguishedbefore leavingforfield;strongwind fannedtherestfireinkitchen andcausedhouseburning. Typhoon whole Lost60Ͳ70%ofcrop, commune unabletobe harvested Typhoon LongHy Killedoneperson Crossingstreamwithoutbridge Driftedonecow Wandernearbystream Flood Ng cLa Driftedtwoelders Crossingstreamwithoutbridge Landslide Ng cLa Filledup3hafield,lost HillblowͲoffcausedfieldbury 100%Wintercrop 2004 Fire Ng cLa Burnt4houses Childrenstartedfirerecklessly causinghouseburning. 2005 Thunder Ng cLa Killedonepersonand Workinginforestandchildren injured5people camehomefromschool. 2006 Landslide LongHy Filledup2hafield Landbury Landslide PuTá Lost3hafield,unable Soilburiedchannelsystem toproduce. leadingtonowaterfor production. Landslide Ng cLa Lost500m2ricefield Soilfilledupfieldclosetostream 2007 Landslide LongHyII Lost200m2rice StreamͲnearbyfieldwasburied andunabletobeproduced TyphoonĉkD n RoofedͲoff5houses Corrugatedironroofwerenot reinforced LandslideĉkD n Filledup2haricecrop StreamͲnearbyfieldwasburied andunabletobeproduced Flood Ng cLa Killedoneperson Driftedwhilecrossingstream Whirlwind Ng cLa RoofedͲoff IronͲroofedhouseswerenot kindergartenand reinforced.

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Year Hazards Affected Damagesonhuman,house,propertyandproduction areas Damageditems? Reasons? primaryschool. Landslide Ng cLa Lost5haricefield Fieldwasclosetosloppy mountainside. Hazardsimpactsduringthepast10Ͳ15yearsinTumorongCommune Year Hazards Affected Damagesonhuman,house,propertyandproduction area Damages Reasonfordamage 1996 TyphoonĉkKaͲDamagedstored Storehouseistemporarilybuiltin sentryͲboxes field. Ͳ3rodsoffarm products Whirlwind TuC pͲRoofedͲoffmany ͲNomaterialsavailableforhouseͲ housesanddamaged8 enforcement; sentryͲboxesforrice ͲBamboosentryͲboxplacedin storinginfield. exposedmountain. Whirlwind TuM ͲRoofedͲoff ͲBamboohouses&ironͲroofed Rông ͲFarmloss housesarenotreͲenforced beforewhirlwind Hail TuC p Ͳ80%offarmlost; ͲHeavyhailinlargeareasburied TuM ͲBroketreesandfarms riceandfarmproductsintheir Rông growingperiod. ĉkka VĉngSĉng 1997 Landslide VĉngSĉngͲBuriedirrigational ͲFieldisclosetolandslidearea, ditch,transportation buriedwithrocksandsoil. roadandfarmfields Typhoon TuC p ͲRoofedͲoffhouses ͲHouseswerenotreͲenforced; withheavy VĉngSĉng anddamagedsentryͲ ͲTemporarilybuiltsentryͲboxes. rain boxesinfield. 1998 Flood TuM ͲDamagedirrigational ͲFloodfilledupirrigationwork Rông works; causingwatershortagefor ͲLost4hafieldofnonͲ production. productionsinceno water. 2002 TyphoonĉkNeang ͲDamagedcommunal ͲHeavystorm,temporary 2003 TyphoonĉkChum houseandroofedͲoff bamboohouseswerenotreͲ I residentialhouses; enforcedbeforefloodseason. ͲTotallydamagedfarm products 2004 Thunder TuC pͲDamagedelectronic ͲLocatedinthunderstruckareain appliances(TV,radio...) highmountain. andtelevisionstation. 2005 ThunderĉkkaͲDamaged5televisions ͲLocatedinthunderstruckareain andburntone highmountain communalhouse. 2006 WhirlwindĉkChum ͲRoofedͲoff3houses ͲTemporaryhousesnotbe II anddamaged enforcedyet; irrigationalchannel ͲEarthenirrigationalchannelnot systemandfarm concretizedyet. products.

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Year Hazards Affected Damagesonhuman,house,propertyandproduction area Damages Reasonfordamage Typhoon ĉkChum ͲDamagedmany ͲHeavystormwithsostrongwind Whirlwind I residentialhouses, thatresidentswereunreadyfor storehouses,and housereͲenforcement.Poultry communalhouse; wereletwanderwithoutkeeping ͲFarmproductswere facilities. hitbytyphooncausing noharvestandpoultry loss. 2007 Whirlwind LongLeoͲDamagedfarm productsand1.1ha rice. Typhoon VĉnSangͲRoofedͲoffmany ͲTemporarybamboohouses. housescollapsedone Woodenschoolwithmetal houseandoneschool. roofing. Yearly Drought Whole ͲLackofwaterfor ͲCluechannelsystemisblownoff commune production. byfloodandunabletostore enoughwaterforproduction field; ͲEarthenchannel. 3.3 Strategicdirection

TheSteeringCommitteeforFloodStormControlofthePeople'sCommitteeofKontumProvince has stipulated that a long term plan for flood risk management needs to be developed to minimisethelossestoreplacetheexistingreactiveapproach. In line with this recommendation CBDRM activities are initiated in which the communal Committee for Flood and Storm Control members together with villages representatives developplansforSaferCommunities.Theobjectiveoftheseplansistogivesupplementary measuresforannualfloodcontrolanddisastermitigationinthecommuneinconjunctionwith longͲterm prevention measures for 3 years with stable production development plan of the villagesoftherespectivecommunes.Theplanobjectivesinclude: 1. Improvingcommunitysawarenessandcapabilityonhazardspreventionandresponsein areasfrequentlyͲhitbydisasters; 2. Providingbasicfacilitieswhicharenotavailableincommunitytoserveemergencyrescue work,especiallyagainstlandslideandflood; 3. Upgradinginfrastructuretoensuresafertransportationinfloodseason; 4. Establishing early warning system, warning boards in highͲdanger areas as well as informationboardsondisasteratcommunity. The relatively low flood related damages (besides the human fatalities) and limited development potentials do not justify substantial investments in subͲbasin wide structural measuresforfloodhazardreduction.Floodproofingofinfrastructure,thoughseemsasound measure that could reduce substantially the existing flood risks in the area, including human fatalities. InaUNDP/CECIDIPECHO(2007)studylookedtowhatextentdisasterriskreductionhadbeen integrated into the implementation of Program 135 in Kontum. The study found that the planningofProgram135investmentsintheprovincedidnotspecificallylookatdisasterrisk reductionasafactorintheplanningprocess.Forexample,Program135fundswerebeingused intheprovincetodistributelivestockandagricultureinputstovillagersthathadsufferedlosses

StrategicDirectionsFloodRiskManagementͲ20Ͳ December2009 MRCFloodManagementandMitigationProgrammeComponent2:StrucuralMeasuresandFloodProofing afterdisasters.However,theinvestmentsinagricultureproductionandtransportationwerenot analyzed in the context of how trends in disaster impacts in the local area might have an adverseimpactoneffortstoimprovelivelihoods.Theprojectrecommendsthatguidelinesneed to be developed that link the implementation of the Action Plan of the NSDPRM (National Strategy for Natural Disaster Prevention, Response and Mitigation) with major national investmentssuchasProgram135andthesocioͲeconomicdevelopmentprocess.Theguidelines would need to have legal bearing on local officials and include measures such as disaster proofing of infrastructure works and other assessments prior to implementing poverty reductionactivities. Anessentialelementinsuchguidelineswouldbetheassessmentoffloodhazardsintheareaor localityatstake.TheproposedmethodologyforsuchassessmentintheUpperSesanbasinhas beendescribedinAppendix4ofVolume2A.

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CHAPTER4 STRATEGICDIRECTIONSFORFLOODRISK MANAGEMENTINTHEMEKONGDELTA TRANSBOUNDARYAREA

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4 STRATEGIC DIRECTIONS FOR FLOOD RISK MANAGEMENT IN THE MEKONG DELTA TRANSBOUNDARYAREA

4.1 Floodmanagementlevels

ThefocalareasinMekongDeltacannotbeconsideredinisolationfromtheentireDelta.Forthe managementoffloodsandtherelatedrisksintheMekongDeltathefollowing basicoptions havebeenlookedinto: 1. Flood management by structural measures at the Delta level. This option looks into the possibilitytomakeuseofthestoragecapacityoftheTonleSaptoreducefloodrisksinthe MekongDelta. 2. Floodmanagementbystructuralmeasuresataregionallevel.IntheDeltafocalareasthe followingregionsaredistinguished: a. FloodplainsontherightbankoftheBassacRiverinCambodiaandsouthofthePhnom PenhMunicipality. b. FloodplainsontheleftbankoftheMekongRiverinCambodiaandsouthoftheNational RoadNo.1. c. DeepfloodedplainsonrightbankoftheBassacRiverintheLongXuyenQuadranglein Vietnam. d. Deep flooded plains on the left bank of the Mekong River in the Plain of Reeds in Vietnam. 3. Flood risk management at a subͲregional or local level. This option considers flood risk management at tertiary level and the protection and/or flood proofing of human settlementsandinfrastructureintheDeltafocalareas. FloodmanagementoptionsatDeltalevelthataimatthereductionofthefloodhazardsDelta wide are very limited. Such options would have to consider the reduction of the flood discharges and volumes that enter the Delta or the creation of diversion and/or retention optionsintheDelta. ThemanagementofflooddischargesthatentertheDeltabyupstreamretentionwouldnotonly requireenormousstoragecapacitiesinthebasinbutalsoanoperationofthesestoragesaiming at flood control. Effects of hydropower developments on floods have been investigated by BeechamandCross(2005)andAdamson(2007).ResultsofthesestudiesshowthattheChinese dams have a high potential to reduce flood peaks in the upper part of the LMB. The effect, however, rapidly reduces further downstream. Together with a high development of hydropowerintheLMBreductionsoftheannualfloodpeakof4to5dmcanbeachieved.Inthe deltatheeffectislimited,onaverage,to1to2dm,butfortheextremefloodoftheyear2000 only5cm.Thoughtheeffectissmallonthefloodlevelsandinundatedareaasignificanteffect wasfoundonthedurationofflooding,whichreducedsubstantiallyforsome40%oftheflooded area. It is noted, however, that these effects required an active storage capacity equal to roughly the annual amount of Mekong flood volume stored temporarily in the Tonle Sap. Hence, upstream retention as a flood mitigating measure for the delta is not considered a realisticoption. The option of Delta wide diversion schemes have been investigated in the Flood Control Planning for Development of the Mekong Delta (BasinͲwide,2007). Results of these studies showthatdifferentdiversionoptionshaveregionalimpactsonlyandnoneofthemhaveDelta wideimpacts. TheonlysubstantialretentionoptionwithintheDeltaareaisrelatedtotheuseofthestorage capacity of the Tonle Sap Great Lake. Preliminary investigations show that an uncontrolled diversionofearlyfloodwater(JulyͲAugust)totheGreatLakehasaverylimitedimpactonthe

StrategicDirectionsFloodRiskManagementͲ25Ͳ December2009 MRCFloodManagementandMitigationProgrammeComponent2:StrucuralMeasuresandFloodProofing flood hydrograph in the Delta. A controlled diversion of early flood waters could, however, delaytheearlyfloodingdownstreamofPhnomPenhbysomethreeweeksontheaverage.(See Appendix11toVolume2a).Suchdiversion,though,providesnoriskreductionforinfrastructure andhousinginthefloodplains,sincetheflooddamagetothesestructuresisdrivenbypeakof flood. A diversion scheme for flood risk management can be supplemented with works that regulatetheoutflowoftheTonleSaplakeandtheadjacentfloodplains.Suchregulationwould provide additional benefits since it improves the low flow conditions in the delta. Such comprehensiveregulationschemeaimingatanintegratedwaterresourcesmanagementinthe DeltaisbeyondthescopeofthisFMMPͲC2. FloodmanagementatregionallevelistheapproachthatisbeingfollowedintheVietnamese partofthedelta.ThisapproachwassuggestedintheMekongDeltaMasterPlanandisbeing appliedeversince.ThisapproachreferstothedifferentregionsintheDeltawithdifferentlevels of flooding (deep, shallow) and distinct boundary conditions requiring different flood control solutions. ThisregionalapproachisalsosuggestedfortheCambodianpartoftheDelta.Thedevelopment of cross boundary strategic directions is not considered appropriate, in view of the great differencebetweenthedevelopmentlevelandpaceatthetwosidesoftheborder.Emphasisis tobegiventothepotentialimpactsthattheseparateregionalstrategicdirectionsmayhaveon neighbouringregions,ratherthantotrytocometocommonstrategicdirections. ThesubͲregionalfloodriskmanagementrefersto: 1. The"floodproofing"ofsettlementsandinfrastructurewithintheregions. 2. Differentiationoffloodprotectionlevelswithinregionalprotectionschemes. 3. Thezoningofregionalprotectionschemes. Thefloodproofingofsettlementsandinfrastructureisessentiallypartofthe"livingwithfloods" approachinthefocalareas. Regionalprotectionschemeshaveinprinciplearegionalprotectionlevel.Itispossiblethough to differentiate within a region the protection levels without loosening the living with flood principle.Ingeneralsuchdifferentiationwouldrequiredifferentdikelevelsfordifferentland uses,ormoreregulationworks. SubͲregional flood risk management could be attractive from a financing and/or implementationpointofview.Zoningofregionalschemesallowsforaphasedimplementation andalsoforadifferentiationofprotectionlevels. ForthefloodriskmanagementintheDeltafocalareasalsoothermeasuresthanstructuralones can be taken. In the framework of the Integrated Flood Risk Management other relevant measuresforfloodriskreductionreferto:(i)landuse/cropplanning,(ii)awarenessraisingand (iii)earlywarning.Thesemeasuresaimatthereductionofthevulnerability.Forthefocalareas intheMekongDeltaitisassumedthatthesesoftmeasuresarealreadyinplace.Whenlanduse changes occur as a result of structural flood protection measures, then the need for enhancementofthesoftmeasuresshouldbeassessed.

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4.2 Regionalfloodmanagementscenarios.

ForthemanagementoffloodsandtherelatedrisksintheMekongDeltathefollowingbasic optionshavebeenlookedinto: 1. Scenario0:ExistingconditionoflanduseandfloodcontrollevelsinCambodia(Takeoand PreyVeng)andinVietnam(LongXuyenQuadrangleandPlainofReeds); 2. Scenario1:Vietnameseareasprovidedwithfullfloodcontrol,Cambodianareasunchanged; 3. Scenario 2: Cambodian areas provided with early flood control and Vietnamese areas unchanged; 4. Scenario3:Vietnameseareasprovidedwithfullfloodcontrol,Cambodianareasprovided withearlyfloodcontrol;

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CHAPTER5 STRATEGICDIRECTIONSFORFLOODRISK MANAGEMENTINTHEWESTOFBASSAC REGIONINCAMBODIA(TAKEO)

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5 STRATEGICDIRECTIONSFORFLOODRISKMANAGEMENTINTHEWESTOFBASSACREGIONIN CAMBODIA(TAKEO)

5.1 Flooddamagesandrisks

TheWestofBassacregionislocatedontheprovincesofKandalandTakeoalongthewestside of the Bassac. This area has an extension of 2,113 km2. In this area two districts have been surveyed for damage and risk assessment. The following risk have been estimated for these districts(seeVolume2Cforthedetails). Cambodia KohAndetDistrict USD0.7mlnperyear KohThomDistrict USD0.7mlnperyear Furtheranalysisisneededtoassesstheflooddamageriskatthelevelofthefocalarea.From thefloodhazardmapsitispreliminaryestimatedthatthefloodriskisoftheorderofsomeUSD 3millionperyear.Abouthalfofthisriskcorrespondstoagriculturalrisks. 5.2 Floodbenefits

Apart from the negative impacts of flooding as mentioned above, floods also have positive impactsonthesocialeconomysuchasnaturalfishingandsoilfertility.Resultsfromfocusgroup discussionsheldinfocalareasshowed thatbenefitsfromnaturalfishingforpeoplelivingin deeplyfloodedareawouldvaryfrom80Ͳ945US$/household.AccordingtotheMRCͲTechnical Paperonfishyields,averageamountoffishcatchfromricefieldinMekongDeltaFloodPlain (deepwaterfloodedareas)wouldbe80Ͳ119kg/haresultinginthevalueof30Ͳ40US$/ha.The amountoffishcatchfromricefield(inPreyVengprovince)wouldbe55Ͳ92kg/haresultingin thevalueof20Ͳ30US$/ha.Farmersalsomentionedthatfloodshavesignificantbenefitforcrop cultivation. After big a flood, WinterͲSpring Paddy (Planting in November and harvesting in March)hasahigheryieldthannormalfloodyearsby1.5Ͳ2.0ton/ha.Itwouldresultinflood benefitforagricultureofabout150Ͳ230US$/haafterabigflood.Assumingbigfloodfrequency ofonethird,theannualfloodbenefitforagriculturewouldbe50Ͳ77US$/ha. 5.3 Structuralfloodriskmanagementoptions

Threefloodriskmanagementzoneswereidentifiedbasedonpresentfloodconditions,existing road and flood embankments, human settlements and land use. Subsequently, the type of structural components required for each area has been preliminarily designed as a result of flooddamageandbenefitsduetotheriskreduction. Thethreezonesandtheirstructuralcomponentsaredescribedasfollow(seeError!Reference sourcenotfound.): Zone1 Thezone1islocatedintheKandalProvinceandispartoftheBassacfloodplain.RoadNational 21 (RN21 )is constructed as a road/flood embankment aligned along the west bank of the Bassac.TheRN21wasdesignedasfloodfreeroad.AlongtheRN21therealargenumberof connectionstocolmatagecanalslinkingtheBassacwiththefloodplaininthewesternsideof theBassac.ThefloodplaindrainsinthedirectionofthePrekAmbelriver. ThePrekAmbelisthebiggestnaturalofftakechanneloftheBassacwiththefloodplainandit hasthefunctionofabypasschannelduringthehighflood.Furthersouth,thePrekAmbeldrains intotheBassacriverthroughtheMaotChroukcanal.ThePrekAmbeloftakewillbecontrolled.

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Zone1hasatotalareaof208.6km2andhasbeensubͲdividedintofivelargepolders.Zone1 couldbedevelopedasfloodfreezone.Inordertomakethezone1floodfree,thefollowing structuralmeasuresareplanned: x ClosureofallthecolmatagecanalsalongRN21andkeepingonlyfourmaincanalslinkedto eachoneofthefourlargepoldersproposed.FlowfromtheBassacintothepolderswillbe controlledbyregulatorswithgates. x In order to create the 4 polders a flood protection dike along the left bank of the Prek Ambelhastobeconstructed. x Amaindrainagecanalalongthedikeandcontrolgatesfordrainagearealsorequired. x The system of existing colmatage canals inside the polders will be connected to a main drainagecanalconnectedtothePrekAmbelriver. x The Prek Ambel river has two functions: (i) drainage during the receding period and (ii) workingasabypasstodivertexcesswaterfromtheBassacduringthefloodperiodwhich willpreventincreasingwaterlevelalongtheBassacthatwouldthreatentheareaEastof the Bassac. The required conveyance capacity of the Prek Ambel as bypass will be determinedfrommodellingsimulations. x To control flows at the offtake of the Prek Ambel, a regulator with control gates will be constructedattheofftake. x Atsomeplacesinthepolderspumpingstationsoraccumulationareasarerequiredtodrain thearea x Polder number 4 at the southern side of zone 1 needs a full protection dike from Chrey ThomonRN21totheMoatChhroukcanal. Zone2 Thezone2hasatotalextensionof1,311.4km2.Thenortherneastcornerofthisareaislocated intheKandalProvinceandtherestoftheareaislocatedinTakeoprovince.Thisareaisdeep flooded during the high flood season. This zone could be protected against early floods to secureearlyricecrop(MayͲJuly).Becausetheneighbouringzone1,attheBassacwestsideis envisagedtobemadefloodfree,thenfloodinginzone2ofthisareacanonlycomefromthe southernsideduetohigherwaterlevelintheBassac. Thestructuralcomponentsforthiszoneare: x OnedikefromMoatChhroukcanaltoKampongKrasaing(attheborder,meetingpointwith theStungTakeo)forearlyfloodprevention.Thisdikeneedstobeconstructedfloodproof. x A flood proof dike from Kampong Krasaing to Sangkom Meanchey running along the southernborderfromSangkumMeanCheytoPhnomDen(meetingpointwiththeRN2) x Onemaindrainagecanalalongthesouthernborder(betweenCambodiaandVietnam) x OneregulatorwithcontrolgatesattheMoatChhroukcanalexit x OneregulatorwithcontrolgatesontheStungTakeoattheexit x At the northern border of the zone 2, construction of a dike and a drainage canal is required. x OnewatercontrolstructureatthejunctionofStungTakeoandTakeocanal x Floodfreesettlementareasatfourlocationsindeepfloodedareas.Eachsettlementareais plannedtoaccommodatearound500families.Eachfloodfreeareawillhaveanextension of15,000m2andconnectiontoruralroad(s). x Improvementofruralroadsinthesouthernpart(deepfloodedarea)toconnectwithflood freesettlementareas.

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Zone3 ThezoneisentirelylocatedinTakeoProvinceandhasatotalextensionof593.0km2.Thiszone isashallowfloodareathatisnotinundatedunderearlyfloodconditionswithprobabilitymore than10%.Thisareacouldbegivenprotectionagainsthighfloodstomakemoreintensiveland usepossible,providedthatirrigationisavailable.

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Thecomponentsofthisareaare: x Alowdikealongtheeasternsideofthezone3. x Amaincanaltointerceptexcessflowfromthewesterncatchmentarea.Thiscanalwillalso servethepurposetodivertwaterfromtheBassacforirrigation,duringthedryseason.This canalwillbeconstructedparalleltotheRN2fromTaKhmaotoTakeo; x RegulatorwithcontrolgatesattherightbankoftheBassacatTaKhmao. x InterceptorcanalfromTakeotoKampongChhrey 5.4 Impactsofstructuralfloodriskmanagementoptions

5.4.1 Floodriskreduction

Incaseearlyfloodprotectionisprovidedtothedeepfloodedareasandyeararoundprotection totheshallowfloodedareas4theriskreductionhasbeenestimatedat0.430MUS$/yearinKoh Andet,thiscorrespondswithsome55%oftheactualrisk.Thisestimatedriskreductionismainly relatedtothereductionoftheagriculturalriskintheshallowfloodedarea. Thebenefitsoftheprotectionofthedeepfloodedareasagainsttheearlyfloodscomefroma secondcropthatcanbeplantedoncealsoirrigationwaterwillbeavailable.Accordingto2006 statistics,thedryseasonpaddyareawas10,800hainKohAndetdistrict,13,000hainKohThom district.Itisanticipatedthatthesecondpaddycropinthesefocalareaswouldbethesameas dryseasoncrop.Assumingthatthenetbenefitsfrompaddyis500US$/ha,itwouldresultin5.4 MUS$/yearinKohAndetdistrict,6.5MUS$/yearinKohThomdistrict. 5.4.2 Transboundaryimpacts

The flood risk management options that consider protection of agricultural areas go automaticallytogetherwiththereductionofthestorageoffloodwatersintheseareasuntilthe designlevelofprotectionworkshavebeenreached.Thisreductionoffloodplainstorageresults in the increase of the river discharges at and downstream of the protected area and, consequentlyintheincreaseoftheriverwaterlevels. RunswiththeISISmodelhavebeenmadetosimulatetheimpactofthepreviouslydescribed protectionworksonthewaterlevelsinthedownstreamareainVietnam.Theresultsofthese simulationsareshownanddescribedintheAppendix6ofVolume2B.Ithastobetakeninto accountthatthemodelallowsforarelativeassessmentoftheseimpactsonly.Thatistosay that the presented absolute values are to be given due care. More accurate modelling is requiredtoassesstheabsolutevaluesoftheseimpactsandtheeventualimpactsontheflood risksinVietnam. FromthemodellingresultsitislearnedthattheprotectionworksinCambodiahaveamarginal (<0.1m) impact on the early flood levels in Long Xuyen Quadrangle. The impact on the maximumfloodlevelsintheLXQisnegligible.However,duetotheembankmentsinCambodia, themaximumwaterlevelinfocalareasofVietnambeinglowerthantheactualones.Itwould resultinreductionofriskforVietnamat0.1millionUS$/yearinChauPhudistrict. IntheBassacriver,though,themaximumfloodlevelsmayincrease1Ͳ3decimetresatChauDoc andabout1decimetreunderearlyfloodconditions.

4protectionlevelsaresetat10%,thatistosaythatprotectionisgivenfor9out10yearsontheaverage

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5.4.3 Environmentalimpacts

SensitiveandvaluableecosystemsthatareencounteredintheCambodianDeltaareseasonallyͲ inundated riparian forests; seasonal wetlands, including marshes, small pools and pools; and seasonallyinundatedgrasslands.Theseecosystemsareimportantasahabitatofavarietyoffish andwaterbirdsandforthesustenanceoftheinlandfisheries. Noofficiallyprotectedareasarelocatedintheprojectarea,however,BirdLifeInternationalhas declared Boeung Prek Lapouv in the south eastern part of the West Bassac Focal Area an ImportantBirdArea(IBA).TheareasouthofAngkorBoreiisanareawitharcheologicalvalue. RemainsofpreͲAnkorancanalscrossingthefloodplain,havebeenfoundhere. Population density in the project area is fairly low. Locally, densities in the more protected, higherareasalongriverbanksanddikes,arefairlyhigh.Therearenoregionssubjecttoheavy developmentwhereconflictsoverresourceusearetobeexpected.Watercoursesinthearea, rivers and canals, but also ponds and lakes are used as a source for drinking water by the majorityoftheruralpopulation. Asfarasresourcesareconcerned,theareaisprimarilyanagricultural,riceproducingarea.Of importanceasasourceforfoodandincomefortheruralpopulationisalsotheinlandfisheries. Thefollowingpotentialenvironmentalimpactshavebeenidentified: 1. Destructionofnaturalhabitats,valuableresources 1.1. The sensitive and valuable ecosystems encountered in the Cambodian Delta are all dependent on the seasonal flood. Protection against early flooding will mean an averagedelayoftheonsetofthefloodingwithaboutonemonth.Areaanddepthof flooding during the main flood are not expected to change. Direct impacts on the riparianforests,seasonalwetlandsandseasonallyinundatedgrasslandsareprobably limited, although species composition may change: some species will simply not be able to survive the prolonged drought (see 2.2). When also provisions for quicker drainageafterthefloodaremade,thetotalperiodoffloodingmaybecomesoshort thatwetlandsdryoutorchangesomuchinspeciescompositionthattheyloosetheir ecologicalvalue. 1.2. The indirect impact of the project on the natural areas may be significant as well. Increased protection against the early flood will encourage people to extent their agricultural activities to areas that are presently not used for rice growing. Encroachment into forest/scrublands, wetlands and natural grasslands will be the result. 2. Lossofbiodiversity,rareandendangeredspecies 2.1. As stated above prolonged drought may have an impact on the biodiversity in the area.Speciescompositionofaquaticfloramaychangeandthediversityandextentof marshes may reduce.In the dry season Black fish species remain in lakes and swamps on the floodplain, where they are able to tolerate acidic and low oxygen conditions.Thewetlandsarevitalinmaintainingbreedingstock.Prolongeddroughten morefloodplainlakesandpondsdryingoutcompletelycouldresultinadecreasein numbers of for example climbing perch (Anabas testudineus), clarias catfishes (e.g. Clariasbatrachus)andstripedsnakehead(Channastriata). 2.2. EightyͲfive to 95% of the freshwater fish populations in the Mekong basin have an inundationspawningpatternandundertakelateralmigrationsfromthemainstream andtributariesintotheinundationzonestospawnandrearyoungbetweenJulyand September. Representatives of this group are some of the cyprinids, such as Cyclocheilichthys enoplos (Soldier river barb or Chhkok) and Cirrhinus microlepis

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(Small mud carp or Prul/Kralang). Late access to the floodplain or blockage of migrationrouteswillhaveanimpactonthestandingstocksofthesemigratingspecies. 2.3. Apart from fish, the wetland areas support a high diversity of other aquatic animals includingvertebratesͲreptiles,birds,mammalsandamphibians,andinvertebrates,such asinsects,crustaceansandmollusks,allofwhichdependuponmaintenanceofaquatic ecosystems and could be affected if the total area of the wetlands reduces or when wetlandsdryoutcompletelyduringpartoftheyear. 2.4. DesiccationcouldalsoleadtolossofseasonallyͲinundatedriparianforestalongthe banksoflakesandriversandthelossofsomeoftheover200speciesofplantsthat areknowntooccurintheseforests.Thewoodyspeciesofthisforestarebearingfruits andseedsatthetimeofinundation,providingfoodforthe34speciesoffruitͲeating fish of the Lower Mekong Basin. Delay of the flooding could imply that the fruit is alreadyfallenanddecomposedbeforethefisharrive. 2.5. Loss of wetland areas could also affect the number and diversity of waterbirds, particularly cormorants, Oriental Darter, SpotͲbilled Pelican, Greater and Lesser Adjutants, Milky Stork, WoollyͲnecked Stork Ciconia episcopus, BlackͲnecked Stork Ephippiorhynchusasiaticus,PaintedStork,TheGloballyEndangeredWhiteͲshouldered Ibis Plegadis davisoni, Glossy Ibis P. falcinellus, BlackͲheaded Ibis Threskiornis melanocephalus,WhiteͲwingedDuck,PallassFishEagleHaliaeetusleucoryphus,GreyͲ headedFishEagle,theGloballyVulnerableMaskedFinfootHeliopaispersonata,and theGloballyNearͲthreatenedSarusCraneGrusantigone. 2.6. Lateinundationoftheseasonallyinundatedgrasslandsmightreducethefeedingareas of a number of birds, including the Sarus Crane, WhiteͲshouldered Ibis and Greater andLesserAdjutants.TheyarealsoofcrucialimportancefortheGloballyEndangered BengalFloricanHoubaropsisbengalensis. 3. Lossofenvironmentalservices. 3.1. Flooding and the related sustenance of wetlands are known to have a number of benefits, some of these benefits will be affected by later and shorter flooding as discussedbelow. 3.2. Theimportanceofdepositionoffertilizingsedimentisillustratedbytheresultsof theFocalGroupdiscussions.Itturnedoutthatafterayearwithagoodfloodrice yieldsareabout1ton/hahigherthaninyearsafterayearwithabadflood.Insome areasanincreaseof1.5ton/hawasmentioned.Productioncostswereestimatedto bethesameinyearsafterayearwithagoodfloodascomparedtoyearsafterayear with a normal flood. Overall benefit of the flood for agricultural production is estimated at 620,000 to 920,000 Riel/ha. Not only the fertilizing of the soil with sediments is important, also the flushing of toxic materials and pollutants by the floodwaters,thesanitationofthesoil(killingofpestsandbugs)andpossiblythegod replenishmentofgroundandsurfacewaters.Impactsofdelayingthefloodonthis benefitarenotthoughttobeverysignificant,thehighestsedimentconcentrations areobservedduringthemainflood.Thedelayedreplenishmentofgroundwaterand surface water bodies will not affect the quantities of water available in the next season. However, shortages for human and ecosystem use (flora and fauna) will increase, since the dry season is prolonged. Water quality at the end of the dry seasonwilldeterioratewithdelayedflooding.Notonlytheavailablequantitymaybe affected,butalsothequalityofthewater.Pollutantconcentrationsbecomehigher and the flushing/diluting effect of the flood is delayed. Finally the flow regulation effectofthefloodingwillbeless,meaningthatearlyfloodlevelsdownstreamwill increase.

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4. ImpactonProtectedAreas 4.1. TheBoeungPrekLapouvIBA(ImportantBirdArea)formsoneofthelargestareasof adjoiningnaturalhabitatsremainingintheMekongDelta.Althoughnot(yet)officially aprotectedarea,theareahasahighconservationvalue.Changingfloodpatternsor canal/dike construction could have a negative impact on the area and reduce the numberofaquaticvegetationspeciesandtheareasimportanceinprovidingcritical wetland habitat to 25% of the worlds population of endangered, nonͲbreeding Eastern Sarus Cranes (Grus antigone sharpii). In total 58 bird species including 34 waterbirdhavebeenobservedinthearea,6speciesaregloballythreatened:Sarus Crane(Grusantigone),BengalFlorican(Houbaropsisbengalensis),SpotͲbilledPelican (Pelecanus philippensis), Painted Stork (Mycteria leucocephala), Darter (Anhinga elanogaster)andBlackͲheadedIbis(Threskiornismelanocephalus). 5. ImpactonFisheries 5.1. Peopleinruralareasrelyheavilyonfisheriesfortheirsubsistence.Withanaverageof 76 kg of fish is consumed per person/year, fish provide from 40Ͳ60% of animal proteinintake.TheproductivityoftheLowerMekongFloodplainsrangesbetween139 and230fishkg/ha/year,whichisveryhighcomparedwithotherriversystemsinthe world.Fishproductivitydependsamongstothersonaccessibilityofthefloodplainfor fish, the availability of food and the length of the period that the fish stay on the floodplain to grow. All these three factors could be influenced negatively by the project.DispersalofWhitefishfryoverthefloodplainwiththefloodwaterwillbe delayed. At the time of flooding the amount of fry in the floodwater may have diminishedsomewhatresultinginlesserstocks.Atthesametimethesurvivalrateof Blackfishinthefloodplainhabitatswillbereduced. 5.2. Deteriorationofthefloodplainvegetationresultsinalowerfoodavailabilityandthe growth period of the fish during their stay on the floodplain is reduced with one month. These impact may have an effect on an area larger than the project area, downstreamriverfisheriesmightbeeffectedaswell. 6. Landacquisitionandresettlement 6.1. Projectimplementationwillentailquitealengthofcanalsanddikestobeconstructed. Partlythesecanalsanddikeswillfollowexistingalignments.Inotherwords,afairly large percentage of the works will be carried out at places where the population is concentratedandlandacquisitionandresettlementmaybeunavoidable. 7. Humanhealthandsafetyimpacts 7.1. Overalltheprojectwillhaveapositiveimpactonhumanhealthandsafety.Peoplewill bebetterprotectedagainstflooding,floodswilllastshorterandfood(rice)production, andsofoodsecurity,willincrease.Thisisnotnecessarilythecasefortheamountof fishavailableinthefloodseason.Reducedwateravailabilityandpoorwaterqualityat theendofthe(prolonged)floodfreeperiodmayposeathreattohumanhealth. 7.2. Constructionactivitiesareanotherthreattohealthandsafetyforavarietyofreasons: emissionofdust,fumes,noiseandvibrationfromconstructionsitesandaccessroads, increasedtrafficandworkersaccidents.Inflowofworkersfromotherareasincreases theriskofaspreadofHIV/AIDS. 8. Impactoncultural,historicandarchaeologicalsites 8.1. LargescaleconstructionofcanalsanddikeswillpartlydestroytheremainsofthepreͲ AngkoriancanalsthathavebeenfoundintheareaaroundAngkorBorei.

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Protection against the early flood, which means delaying of the flood and shortening of the floodperiod,mayhaveanumberofenvironmentalimpacts.Mostsignificantareprobablythe impactsontheinlandfisheriesandthewetlandvegetationandassociatedfauna. ProlongationofthedryperiodmayresultinlowersurvivalratesofBlackfishandsoareduced restocking during the flood season. Also White fish migration into the floodplain might be effected,becausethetimingofthefloodingmaynotcoincideanymorewiththepresenceoffish fryandlarvaeinthefloodwater.Adeteriorationoffloodplainecosystemslikeriparianforests andfloodedgrasslandscouldresultinreducedfoodavailabilityforthefish.

Screening question Yes No Remark A. Project siting

Is the Project area adjacent to or within any of the following environmentally sensitive areas? in or near sensitive and valuable ecosystems X the area consists for a large proportion of (e.g., protected areas, wetlands, wild lands, coral wetlands harboring a number of protected reefs, and habitats of endangered species) species and of vital importance for maintaining the Lower Mekong fisheries. Boeung Prek Lapouv has been identified as an Important Bird Area (IBA) by BirdLife International. in or near areas with cultural heritage sites (e.g. X in the area pre Angkorian canals have archaeological, historical sites or existing cultural been identified or sacred sites) densely populated areas where resettlement may X population is concentrated along canals be required or pollution impacts and other and dikes, works will concentrate on disturbances may be significant these areas regions subject to heavy development activities or X development in the region is limited where there are conflicts in natural resource allocation watercourses, aquifer recharge areas, or reservoir X canal and river water is used as a source catchments used for potable water supply for domestic water by the majority of the population in the area. lands or waters containing valuable resources X the area is an important fisheries area, (e.g. fisheries, minerals, medicinal plants, prime both for ‘black fish’ (floodplain residents) agricultural soils) and ‘white fish’ (migratory) species, and as such has more than regional importance

B. Potential environmental impacts

Is the project likely to lead to: permanent conversion of potentially productive or X the yearly flooded grasslands, paddy valuable resources (e.g. fisheries, natural forests, fields and natural areas are important wild lands) fish spawning and rearing areas destruction of natural habitat and loss of X a reduction of the flooded area might biodiversity or environmental services provided by affect the flora and fauna diversity (fish a natural system and water birds) and could have a negative impact on the fisheries resource risk to human health and safety (e.g. from X limited, some construction activities generation, storage, or disposal of hazardous related health and safety risks are to be wastes, inappropriate occupational health and expected safety measures, violation of ambient water or air quality standards) encroachment on lands or rights of indigenous X - peoples or other vulnerable minorities displacement of large numbers of people or X - businesses absence of effective mitigation or compensation X - measures Naturalvegetationcoulddeterioratebecausedelayedfloodingwillleadtoafurtherdesiccation of the floodplain at the end of the dry season. Important ecosystems/habitats like riparian forests, seasonally flooded grasslands and marshes may be effected, resulting in a change in

StrategicDirectionsFloodRiskManagementͲ38Ͳ December2009 MRCFloodManagementandMitigationProgrammeComponent2:StrucuralMeasuresandFloodProofing

speciescomposition.Asaresulttheymaylosetheirimportanceasahabitatforalargenumber of(rareandendangered)speciesoffishandwaterbirds.Ofspecialconservationimportanceis theBoeungPrekLapouvwetland.Itisimportantthatmeasuresaredesignedthatthiswetland willbeprovidedwithsufficientwateryearround,andfurtherdrainageoftheareashouldnot beallowed. The findings of the initial environmental evaluation are summarised in the "screening table" above. 5.5 Strategicdirections

5.5.1 Landusescenarios

IntheCambodianWestofBassacregion"livingwithflood"istheleadingconcept.Landuseis merely restricted to single rice cropping in the absence of adequate structural measures for flood management and irrigation. The formulation of a strategic direction for flood risk managementinthedeepfloodedareasisbasedonthelivingwithfloodconceptincombination withthefollowinglandusescenarios: 1. singlecroppinginthedeepfloodedarea(actuallanduse) 2. doublecroppinginthedeepfloodedarea 3. doubleortriplecroppingintheshallowfloodedareas The direct relation between the different land use scenarios and flood risk management strategiesisasfollows: x Single cropping can be done without protection of the agricultural land. Structural measurescanberestrictedtoprotectionand/orfloodproofingofhumansettlementsand publicinfrastructure. x Double cropping in the deep flooded areas requires flood management to secure that sufficientfloodfreetimeisavailablebetweentwofloods.Inpractice,thiscomesdownto earlyfloodprotectionoftheagriculturallandand/oradequatedrainageoffloodedareas after the flood. Additional protection and/or flood proofing will be required for infrastructureandhumansettlements. x Doubleortriplecroppingintheshallowfloodedareasrequiresafullprotectionofthese areas.Adifferentiationoftheprotectionlevelsintheseareasistobeconsidered,inwhich humansettlementsandessentialinfrastructureisprovidedwithahigherlevelofprotection thentheagriculturalareas. 5.5.2 Floodmanagementstrategicdirections

TheexistingfloodrisksintheWestofBassacareadonotjustifysubstantialinvestmentsinflood protectionworkstoreduceagriculturerelatedrisks.Incasenofurtheragriculturaldevelopment in this area is envisaged, flood risk management measures should focus on the reduction of floodrisksrelatedtobusiness,housingandinfrastructure.Theseriskscanbereducedby: x earlywarning x relocationofhousesandbusinesses x floodproofingand/orprotectionofresidentialareasandinfrastructure. An early warning system for the inhabitants of the flood prone areas is already in place. Relocationofhousesandorbusinessmaybeconsiderediftherelatedcostsarelessthanflood

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proofingand/orprotection.Thisisnotlikelytobethecase.Forthatreasonitissuggestedto focusonfloodproofingandprotectionoftheobjectsthatareatriskinthefloodproneareas. Agriculturaldevelopmentcanbestrivedatintheshallowflooded areas(zones 1and3),the deepfloodedarea(zone2)orinboth.AsocioͲeconomicevaluationisrequiredtodeterminethe mostattractiveapproachand/orphasingforsuchdevelopment. Floodrisksintheshallowfloodedareasarerelatedtothepeakfloodlevelsratherthantoearly floods. Risk reduction measures in these areas should therefore aim at protection against the mainflood.ThelevelofprotectionoftheagriculturallandsistobederivedfromasocioͲeconomic evaluation.Itisanticipatedthata10%protectionlevelwillbeadequate(thismeansthatflooding isacceptedonceinthetenyearsontheaverage).Fortheresidentialandbusinessareasandthe infrastructurewithintheseprotectedzonesahigherlevelofprotectionmaybemoreappropriate, forinstance4or5%. (Itisnotedthatlivinginaprotectedzonemaybringadditionalrisks.Floodingofaprotected zonemaybecausedbyadikebreach.Adikebreachcreatesmorehazardousconditionsthan normalflooding.Earlywarningisoftennotpossibleandhighflowvelocitiesmaylocallyoccur.) Agriculturaldevelopmentinthedeepfloodedarearequiresprotectionagainstearlyfloodsin ordertohavesufficienttimeavailableforthesafeharvestingofasecondcrop.Thisprotection canbeprovidedindifferentways: x by providing protection to the early flood level only (once this level is exceeded the protectionworkswillbeoverflownandtheprotectedareawillinundateautomatically; x by providing controllable protection works that allow the flooding to take place when suitable(ThistypeofprotectionispracticedinthedeepfloodedareasinVietnam) Itissuggestedtofollowthefirst(lesscostly)approach.Inalaterstageofdevelopmentofthe areaitcanthanbeconsideredtoupgradetheprotectionworksto"floodmanagement"works. Protection of the deep flooded areas against early floods is supposed to go together with protectionand/orfloodproofingofresidentialandbusinessareasandessentialinfrastructure fornotonlytheearlybutalsothemainflood. 5.5.3 Mitigationoftransboundaryeffects

The preliminary results show that the early flood protection in the West of Bassac area in Cambodia may have marginal impacts, if any, on the flood risk in Vietnam. More detailed modellingisrequiredtomakeamoreaccurateassessment.Incasetheincrease,ifany,ofthe floodrisksinVietnamisnotconsideredacceptable,mitigatingmeasuresaretobefoundthat compensate for the loss of storage during the early floods. It is suggested to investigate the possibilitytocompensateforthislossbyprovidingadditionaldischargecapacityoffloodwaters intheborderareatowardstheGulfofThailand(WestChinaSea).

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CHAPTER6 STRATEGICDIRECTIONSFORFLOODRISK MANAGEMENTINTHEEASTOFMEKONG AREAINCAMBODIA(PREYVENG)

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6 STRATEGICDIRECTIONSFORFLOODRISKMANAGEMENTINTHEEASTOFMEKONGAREAIN CAMBODIA(PREYVENG)

6.1 Flooddamagesandrisks

The flood risk in this region has been estimated for the Kampong Trabek District only (see Volume 2C). This risk has been estimated at 0.7 million USD per year. Flood hazards in this districtarelessseverethanthoseinthedistrictsPreahSdachandPeamChorthatarelocated between Kampong Trabek and the Mekong. Further analysis is needed to assess the flood damageriskatthelevelofthefocalarea.Fromthefloodhazardmapitispreliminaryestimated thatthefloodriskinthisregionisoftheorderofsomeUSD2mlnperyear.Over60%ofthis riskisrelatedtoagriculturaldamage. Flooddamagetoagricultureismainlyforthewetseasonpaddyinthesurveyeddistrict..Inthe absenceofAugustͲfloodprotectionaspractisedinVietnam,theflooddamagestoagriculture (mainlypaddycultivation)dependsmoreonthemaximumannuallevelofthefloodthanonits timing.Therefore,alsoforAgriculturethemaximumannualfloodlevelhasbeenusedtoanalyse theflooddamages. 6.2 Floodbenefits

Results from focus group discussions held in focal areas showed that benefits from natural fishing for people living in deeply flooded area would vary from 80Ͳ945 US$/household. According to the above mentioned MRCͲTechnical Paper, average amount of fish catch from rice field in Mekong Delta Flood Plain (deep water flooded areas) would be 80Ͳ119 kg/ha resultinginthevalueof30Ͳ40US$/ha.TheamountoffishcatchfromricefieldinPreyVeng provincewouldbe55Ͳ92kg/haresultinginthevalueof20Ͳ30US$/ha.Farmersalsomentioned thatfloodshavesignificantbenefitforcropcultivation.Afterbigaflood,WinterͲSpringPaddy (PlantinginNovemberandharvestinginMarch)hasahigheryieldthannormalfloodyearsby 1.5Ͳ2.0ton/ha.Itwouldresultinfloodbenefitforagricultureofabout150Ͳ230US$/haaftera bigflood.Assumingbigfloodfrequencyofonethird,theannualfloodbenefitforagriculture wouldbe50Ͳ77US$/ha. 6.3 Structuralfloodriskmanagementoptions

TothesouthoftheRN1,thefloodplainisdrainedbythetwomajorriverstheStungSlotand the Prek Kampong Trabek. Flood water expands to both sides of these two rivers in their respectivefloodplains,Lowlyingarea(elevation3Ͳ4mamsl)extendsfromthefloodplainof thetworiversfurthersouthleavingthemiddlepartwithhigherelevation(above5.0mamsl) where is concentrating settlement of subsistence rice farmers communities. Towards the Cambodian/Viet Nam border, low lying areas practically joint together to form a vast deep floodedarea. Thefocalareahasatotalextensionof1,194.7km2(119,469ha).ThetotalareahasbeensubͲ dividedintofourfloodprotectedzones,seeError!Referencesourcenotfound.

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StrategicDirectionsFloodRiskManagementͲ44Ͳ December2009 MRCFloodManagementandMitigationProgrammeComponent2:StrucuralMeasuresandFloodProofing x Zone1betweentheMekongandtheStungSlotriver(deepfloodedzone364.91km2).The zone1hasanextensionof364.91km2andbelongstothedeepfloodedareawithlongest flooddurationascomparedtootherareas.PeopleliveonlyalongtheMekongriverbank andsparselyalongtheStungSlotriverbankinthenorthernpart.Mostofthemdependon fisheries,dryseasoncashcropanddryseasonricecropfromMaytoJuly(generallyone cropperyearduetolackofwatermanagement).Thebeginningofthecropseasondepends onthespeedsofthefloodrecession,generally(DecemberͲJanuary). x Zone2betweentheStungSlotandthePrekKampongTrabekriver(408.64km2).Thiszoneis dominatedbysubsistencerainfedwetseasonrice.ThezoneislocatedinbetweentheStung SlotandPrekKampongTrabekrivers.MostofthearealocatedintheStungSlotandPrek KampongTrabekriversissubjecttofrequentfloods,whileotherpartsofthezone,athigher groundelevationssuffersfromdrought. x Zone3betweenthePrekKampongTrabekandthePrekKampongChhreyriver(242.08km2). Thewesternpartofthiszoneisconsideredasdeeptoshallowfloodedareas,whereasthe southernpartslopesdowntothezone4deepfloodedarea. x Zone4islocatedwithinthedeepfloodedareainthesouthernpartofthethreeotherzones (179.06km2).Inthiszoneonlydryseasonrecessionricecropsarepossibleduetohighflood depthandduration.Thiszonecouldbesubdividedintotwopartsi)betweentheStungSlot and the Prek Kampong Trabek, ii) between the Prek Kampong Trabek and the Stung Kampong Chhrey. This zone is not easily accessible by roads during the flood season. Currentlytwodryseasoncropsarepossible,whenwateristakenfromtheSohaCaicocanal attheborderandsufficienttimeisavailablebetweentwofloods. Structuralfloodriskmanagementoptionshavebeenoutlinedthatwouldaimatsecuringand stabilizingriceproductionofatleasttwocropsperyearasfollows: The zone 1 would be protected against early flood, zones 2 and 3 would have a protection againstthe1:10yearsfloodandzone4zoneswouldhavenoprotection. Zone1: Thisdeepfloodedareawouldbeprotectedagainstearlyfloodsuntilthe1stofAugust.Afterend ofJulytheareawouldbeleftfloodeduntilNovemberͲDecember.Thefloodrecessioncropwill start from November until April depending on the ground elevation and speed of the flood recession.AlimitedearlycropseasonstartsfromMayanditisharvestedinJuly.Watersupply forMayͲJulycropseasonwouldbesuppliedbylowheadpumping. Thezonewouldbeprotectedbythefollowingcomponents: 1. OnedikealongtheleftbankoftheMekongtoprotectagainstearlyfloodspilluntilendof July.ThisdikestartsatPrekKhsayanditisconnectedtotheRN1andextendstothesouth, alongtheMekongbank,uptotheborderwithVietnamnearKohKok. 2. Rehabilitation of seven controlled colmatage canals that would remain connected to the dike along the left bank of the Mekong and the Stung Slot River. The canals have the functionofdrainageandwatersupplyinthiszone; 3. Afloodproofdike/roadembankmentfromRusseySroktotheborderwithVietnamatKoh Sampouv.Thisdike/roadembankmentisdesignedwithcrestleveltoprotectagainstearly floodonly. 4. Until end of July the discharge capacity of the opening under the RN1 bridge would be controlledtoprotectagainstearlyfloodcausedbytheStungSlotriverflow.

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Zone2: Thiszonehasanextensionof408.64km2andisconsideredasshallowfloodedareaandwould beprotectedagainstthe1:10yearshighflood.Thiszonecouldallowforthreecropsperyear. Thefollowingstructuralmeasuresareproposed: 1. One flood protection dike bordering the left floodplain of the Stung Slot river. The crest levelofthisdikeisdesignedtoprotectagainstthehighfloodwithreturnperiod1:10years. ThisdikestartsaroundKampongSoeungandendsatRusseySroksouthatKampongPrasat. Thisdikeisthewestboundaryofzone2. 2. OnedikealongtherightbankoftheStungKampongTrabekriverstartingfromKampong TrabektoChemnangTea.Thisdikewouldbedesignedwithcrestlevelrequiredtoprotect against1:10yearsflood. 3. OnedischargecontrolstructureatKampongTrabekbridgeonRN1. 4. AnirrigationcanalparalleltoRN1fromKampongSeungtoKampongTrabek. 5. ApumpingstationanddrainagecanalrunningfromKaSoutoChemnangTea. 6. Insidethiszone2thereisalsoproposedanirrigationanddrainagecanalnetwork. 7. A flood proof dike/road in the southern part (between zone 4 and zone 2) Ka Sou to ChemnangTea.Thecrestlevelofthisdike/roadwouldbedesignedtoprotectagainst1:10 yearsflood. Zone3: Thiszonecouldbealsoconsideredfordoublericecropping(wetseasonandrecessioncrops)by pumping from the Prek kampong Trabek. To secure two full crops per year, the following measuresareenvisaged: 1. FloodprotectiondikealongtheleftbankofthePrekKampongTrabekriver,fromKampong TrabektoChemnangTea.Thedikeisdesignedforprotectionagainstthe1:10yearsflood. 2. FloodprotectiondikealongbothsidesoftheStungKampongChhreyriver.Thecrestlevelof thisdikeisalsodesignedtoprotectagainstfloodwith1:10yearsreturnperiod.Thedike startsatKrolKotoPrasatKraing. 3. Irrigation/drainagecanalsforirrigationandwatersupplyinsidezone3; 4. Lateraldrainagecanalattheborderwiththezone4withpumpingstationatChemnangTea todrainoutexcessfloodwatercausedbylocalrainfall. 5. Afloodproofdike/roadembankmentinthesouthernpart(betweenzone3andzone4) fromChemnangTeatoPrasatKraing.Thecrestlevelofthisdike/roadwouldbedesignedto protectagainst1:10yearsflood. Zone4: To address the problem of flood and people living far away from their lands, the following structuralmeasureisproposed: 1. Construction of flood proof settlement areas along the border with Vietnam, including connectiontoroadembankments.Eachsettlementareawouldallowaccommodating200 families.Thetotalareaeachsettlementis60,000m2.

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6.4 Impactsofstructuralfloodriskmanagementoptions

6.4.1 Floodriskreduction

Incaseearlyfloodprotectionisprovidedtothedeepfloodedareasandyeararoundprotection totheshallowfloodedareas5theriskreductionhasbeenestimatedat0.5millionUS$/yearin KampongTrabaek,orabouttwothirdoftheactualrisk.Thisestimatedriskreductionismainly relatedtothereductionoftheagriculturalriskintheshallowfloodedarea. Thebenefitsoftheprotectionofthedeepfloodedareasagainsttheearlyfloodscomefroma secondcropthatcanbeplantedoncealsoirrigationwaterwillbeavailable.Accordingto2006 statistics,thedryseasonpaddyareawas6,900hainKampongTrabaekdistrict.Itisexpected that the second paddy crop in these focal areas would be the same as dry season crop. Assumingthatthenetbenefitsfrompaddyis500US$/ha,itwouldresultin3.45MUS$/yearin KampongTrabaekdistrict. 6.4.2 Transboundaryimpacts

The flood risk management options that consider protection of agricultural areas go automaticallytogetherwiththereductionofthestorageoffloodwatersintheseareasuntilthe designlevelofprotectionworkshavebeenreached.Thisreductionoffloodplainstorageresults in the increase of the river discharges at and downstream of the protected area and, consequentlyintheincreaseoftheriverwaterlevels. TheresultsofthesesimulationsareshownanddescribedintheAppendix6ofVolume2B.Ithas tobetakenintoaccountthatthemodelallowsforarelativeassessmentoftheseimpactsonly. That is to say that the presented absolute values are to be given due care. More accurate modellingisrequiredtoassesstheabsolutevaluesoftheseimpactsandtheeventualimpacts onthefloodrisksinVietnam. FromthemodellingresultsitislearnedthattheprotectionworksinthePreyVengareasouthof NationalRoadno1inCambodiatendtohaveapositiveimpactonthefloodrisksinthePlainof ReedsinVietnam.ThisisduetothefactthattheprotectionworksinCambodiablock,partially, theactualfloodplainflowontheleftbankfloodplainsoftheMekong.Thisholdsforboththe earlyfloodandthepeakflood.ThiswouldresultinreductionofriskforVietnamof1.4million US$/yearinTanHongdistrict,and0.5millionUS$/yearinTamNongdistrict. IntheBassacriver,though,themaximumfloodlevelsmayincrease1Ͳ3decimetresatChauDoc andabout1decimetreunderearlyfloodconditions. 6.4.3 Environmentalimpacts

Sensitive and valuable ecosystems that are encountered in this region, such as seasonallyͲ inundated riparian forests; seasonal wetlands, including marshes, small pools and pools; and seasonallyinundatedgrasslandsareessentiallythesameasthosefortheWestofBassacarea describedinChapter5..Noofficiallyprotectedareasarelocatedintheprojectarea. The potential environmental impacts of flood risk management in this area correspond, therefore,withthosedescribedinthepreviouschapter.

5protectionlevelsaresetat10%,thatistosaythatprotectionisgivenfor9out10yearsontheaverage

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6.5 Strategicdirections

6.5.1 Landusescenarios

AlsointheCambodianEastofMekongregion"livingwithflood"istheleadingconcept.Land useismerelyrestrictedtosinglericecroppingintheabsenceofadequatestructuralmeasures for flood management and irrigation. The formulation of a strategic direction for flood risk managementinthedeepfloodedareasisbasedonthelivingwithfloodconceptincombination withthefollowinglandusescenarios: 1. singlecroppinginthedeepfloodedareas(actuallanduse) 2. doublecroppinginthedeepfloodedarea 3. doubleortriplecroppingintheshallowfloodedareas The direct relation between the different land use scenarios and flood risk management strategiesisasfollowsisasdescribedinthepreviouschapter. x Single cropping can be done without protection of the agricultural land. Structural measurescanberestrictedtoprotectionand/orfloodproofingofhumansettlementsand publicinfrastructure. x Double cropping in the deep flooded areas requires flood management to secure that sufficientfloodfreetimeisavailablebetweentwofloods.Inpractice,thiscomesdownto earlyfloodprotectionoftheagriculturallandand/oradequatedrainageoffloodedareas after the flood. Additional protection and/or flood proofing will be required for infrastructureandhumansettlements. x Doubleortriplecroppingintheshallowfloodedareasrequiresafullprotectionofthese areas.Adifferentiationoftheprotectionlevelsintheseareasistobeconsidered,inwhich humansettlementsandessentialinfrastructureisprovidedwithahigherlevelofprotection thentheagriculturalareas. 6.5.2 Floodmanagementstrategicdirections

ForthefloodmanagementinEastofMekongareathesamestrategicdirectionisproposedas fortheWestofBassacareadescribedinsection5.5.2.Anessentialdifference,though,wouldbe tokeepasubstantialzoneunprotectedneartheVietnameseborder.Floodprotectioninthis areaiscloselyrelatedtotheoperationofthefloodmanagementinfrastructureinVietnamand floodmanagement,ifany,inthisareaistobedonejointlywithVietnam. 6.5.3 Mitigationoftransboundaryeffects

ThepreliminaryresultsshowthatthefloodprotectionintheEastofMekongareainCambodia wouldhavepositiveimpactsonthefloodriskinthePlainofReedsinVietnam.Moredetailed modellingisrequiredtomakeamoreaccurateassessment. AslightincreaseinthefloodwaterlevelsintheMekongisanticipatedthough.Thisincrease couldbecompensatedforbycreatingadditionaldischargecapacityintheborderzone,either towardstheVamCoriver,theGulfofThailandorboth.

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CHAPTER7 STRATEGICDIRECTIONSFORFLOODRISK MANAGEMENTINTHEWESTOFBASSAC AREAINVIETNAM(LXQ)

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7 STRATEGICDIRECTIONSFORFLOODRISKMANAGEMENTINTHE WESTOFBASSACAREAIN VIETNAM(LXQ)

7.1 Flooddamagesandrisks

FortheestimateofthefloodrisksintheLXQreferenceismadetotheVolume2C.Theaverage annualdamageintheAnGiangProvincealonehasbeenestimatedatsome23millionUSDper year.ThefloodriskinthesurveyedChauPhuDistricthasbeenassessedat1.9millionUSDper year.ItisnotedthatasubstantialpartoftheriskintheAnGiangprovinceisrelatedtobank erosion.ThisphenomenonisnotreflectedinthefloodriskoftheChauPhudistrict. Furtheranalysisisneededtoassesstheflooddamageriskatthelevelofthefocalarea.From thefloodhazardmapsitispreliminaryestimatedthatthefloodriskintheVietnamesepartof thefocalarea(LongXuyenQuadrangle)couldbetwotimesthefloodriskofAnGiangProvince only. Itisnotedthatunderthepresentlanduseandfloodprotectionconditionstheriskrelatedto agricultureisrelativelylowascomparedtothetotalrisk.Theshareofagriculturalriskisonly1% ofthetotalrisk.Byfarmostoftherisk(about85%)isrelatedtoinfrastructureandrelief. Itismoreovernotedthatunderaveragefloodconditionshardlyanydamageoccursandthat mostriskisrelatedtoextremefloodconditions.Apparently,adequateprotectionisalreadyin placeforthelowerfloods. 7.2 Floodbenefits

Apart from the negative impacts of flooding as mentioned above, floods also have positive impactsonthesocialeconomysuchasnaturalfishingandsoilfertility.Resultsfromfocusgroup discussions held in the Vietnamese focal areas showed that:benefits from natural fishing for peoplelivingindeeplyfloodedareavaryfrom100Ͳ300US$/householdinnormalfloodyears andfrom120Ͳ750US$/householdinbigfloodyears. AccordingtotheMRCͲTechnicalPaperNo16onfishyields,theaverageamountoffishcatch from rice fields in the Mekong Delta Flood Plain (deep flooded areas) are 80Ͳ119 kg/ha, resulting in a value of 30Ͳ40 US$/ha. Farmers also mentioned that floods have significant benefitforcropcultivation.Afterbigaflood,applicationoffertilizersandpesticidestoWinterͲ SpringPaddy(PlantinginNovemberandharvestinginMarch)islessthaninanormalfloodyear, andtheyieldishigherby0.5Ͳ1.0ton/ha.Itwouldresultinfloodbenefitforagricultureofabout 200Ͳ300US$/haafterabigflood.Assumingbigfloodfrequencyofonethird,theannualflood benefitforagriculturewouldbe60Ͳ100US$/ha. 7.3 Structuralfloodriskmanagementoptions

7.3.1 Options

The transboundary focal areas correspond with the soͲcalled deep inundation areas. The Vietnamese long term planning for these areas is essentially based on the "living with floods" conceptandmanagementoffloodstoallowforasafeproductionofdoublericeWinterͲSpring andSummerͲAutumncrops. ThefollowingobjectiveshavebeenformulatedbyVietnamforthefloodmanagementinthe deepinundationareas:

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1. Agriculture:DoublericecultivationofwinterͲspringandsummerͲautumnhastobeproduced reliablyandstably;itisrecommendednottoencouragetoproducethethirdcropseason; fruittreesaretobereasonablydevelopedinfavourableareas;creatingfavourablecondition forchangingcropseasons;developagriculturemechanization. 2. Transportation: a. Nationalroads,interͲprovincialroadsandprovincialroads:roadsarereliableand safely constructed over flood level of 1961 for transportation during the whole floodseason. b. Districtroads:constructedaccordingtoprobabilityofroadscalesofnonͲinundated withlowandmediumfloodsandinundatedwithhighfoods c. Ruralroads:willbeconstructedoverwaterlevelsoflow,mediumandhighfloods of the early and late season. These roads might be inundated by large floods. Althoughhavingfavourablecondition,constructionofhigherroadsshouldnotbe donebecauseofblockingfloodwayscausingincreasesofwaterlevelsandlonger inundation. 3. Navigationlines: a. InterͲprovincelines:Itshouldbeoperatingfullyinthefloodseasonhenceithasto haveshipͲtransferfacilitiesincaseoffloodcontrolworksblockfreepassageofthe waterway; b. InnerͲregion: Full transport only in innerͲregion is needed hence vessell transfer facilitiesarenotneeded. 4. Residentialareas: a. Towns and inhabitant centres , schools, infirmaries have to be ensured of no inundationinthefloodseason,includinghighfloods b. Inhabited lines along large roads and big canals have to be ensured not to be inundatedinthefloodseason c. Scatteredinhabitantareasneedtobeprotectedinthefloodseason FortheLongXuyenQuadrangletheseobjectivesarespecifiedasfollows: 1. Safelyprotectallinhabitedandurbanareas; 2. FulltransportationinthewholeyearforNationalRoad80,NationalRoad91,NationalRoad N1,NationalRoadN2andtheprovincialRoadLongXuyenHueDuc,LongXuyenͲTriTon; 3. ReducewaterlevelsforearlyandendͲofͲseasoninordertosafelyproducedoublerice: WinterͲSpringandSummerͲAutumn; 4. ReduceleveloffloodͲpeaksformainͲfloodͲseasonintheeasternsubͲareaandareasalong theNationalRoad80; 5. ReclaimlandoftheHaTienQuadrantinordertoputintoagriculturalproduction; 6. Combine with other hydraulic works in order to complete water resources system for developmentofsocioͲeconomy.Simultaneously,combinewithtransportationconstruction and inhabited areas in order to develop rural areas in a trend of civilization and modernization. 7.3.2 Structuralmeasures

Thestructuralmeasuresthathavebeenidentifiedto realizeabovementionedobjectivesare shownintheError!Referencesourcenotfound.overleafandreferto: 1. ControlfloodsfromthebordertotheLongXuyenQuadrantanddrainfloodstotheGulfof Thailand 2. BuildupflooddrainageconstructiontotheGulfofThailand 3. Buildupsalinitypreventionconstruction,andkeepfreshwaterinthecoastalareasofthe GulfofThailand 4. BuildupfloodcontrolconstructionfromtheBassacrivertotheLongXuyenQuadrant.

StrategicDirectionsFloodRiskManagementͲ52Ͳ December2009 MRCFloodManagementandMitigationProgrammeComponent2:StrucuralMeasuresandFloodProofing

Thesestructuralmeasuresallowinprinciplenotonlyforaprotectionagainstearlyfloodsbut alsoforfullcontroloffloodsthatarelowerthanthedesignfloodoftheworks. t

Group work#4: Flood controlwork along Bassac River Bassac along sluices 8 - Build

-Enlarge 18 main canals for draining flood to Wes to flood draining for canals main 18 workGroup #3: system canalDischarge -Enlarge sea

Group work#1: Systemalong coastal of West sea discharging flood for canals 20 Dig - large protection, forsaline 20 sluices - Build bridges on the National road number80 tide high preventing for dyke Implement -

Group work#2: Over boundaryflood Flowcontrol system: of Southern the in located line Dyke - Vinh Te canal. Dam. Rubber La Tha Su, Tra - sluices. protection Flood -

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7.4 Impactsofstructuralfloodriskmanagementoptions

7.4.1 Floodriskreduction.

If the flood risk management works as described above would be operated to provide full protection to the LXQ, then most of the flood risks, apart from the bank erosion, would be eliminated. This would give a risk reduction of some USD 1.9 million/yearfor the Chau Phu Districtonly. Iftheseworks,however,wouldbeoperatedtoprotecttheLXQagainsttheearlyfloodsonly (untilhalfofAugust)thenonlytheveryminoragriculturalriskwouldbeeliminated. Full protection would enable a third paddy crop. Currently, there are 1,913 ha in Chau Phu districtcoveredbythethirdcropduringthefloodseason.Theseareasareboundedbynational roadsandembankmentsdevelopedbylocalauthorities.Theexistingthirdpaddycropoccupies about5%paddylandinChauPhudistrict.Sincethethirdcropgrowsduringtherainyseason withhighfloodwaterinriverandcanal,drainageofexcesswateronthefieldbypumpingwould be critical. It is assumed that additional 70% of paddy land could be used for a third crop, consideringtheexistingthirdpaddyandthatdepressionareasmaynoteconomicallyforthis crop.Netbenefitofadditionalpaddywouldbeattherateof900US$/ha,resultinginexpected additionalbenefitfromcultivationofthirdpaddyasUSD24millionintheChauPhudistrict. FullfloodprotectioninLXQwouldreducenaturalfishonpaddyfieldattherateof of30Ͳ40 US$/ha.Takenintoaccounttheremainingfloodedpaddyarea,thefishlosswouldbesomeUSD 1.3million/yearinChauPhudistrict. Floodingbringssedimentationtothedelta,leachesacidsulphatesubstancesandtoxicityfrom thesoil,andcontrolspests.Thisbenefitwasevaluatedas60Ͳ100US$/haforWͲSpaddy.Full floodprotectionwouldcreatethelossofthesebenefitstoanestimatedamountofsomeUSD 2.6million/yearforChauPhudistrict. 7.4.2 Transboundaryimpacts

The flood risk management options that are described in the previous section allow for the managementofnotonlytheearlyfloods,butalsothefloodsarrivingafterAugust.Operationof the flood management infrastructure beyond the early flood (or half of August) will create increasedwaterlevelsintheriversbothdownstreamandupstreamoftheprotectedarea.In principlethefloodmanagementinfrastructurecouldbekeptcloseduntilafterthepassageof thefloodpeak.Inthatcase,thepeaklevelsupstreamoftheprotectedareawillincreaseand affectdirectlythefloodriskinCambodia. RunswiththeISISmodelhavebeenmadetosimulatetheimpactofthescenariowhichimplies thatfortheVietnameseFocalAreasfloodwaterwillenterneitherLongXuyenQuadranglenor thePlainofReedsunlessthemanagementdecidesforcontrolledinlet.Theconditionsinthe CambodianFocalAreasareasinthepresentconditions. TheresultsofthesesimulationsareshownanddescribedintheAppendix6ofVolume2B.Ithas tobetakenintoaccountthatthemodelallowsforarelativeassessmentoftheseimpactsonly. That is to say that the presented absolute values are to be given due care. More accurate modellingisrequiredtoassesstheabsolutevaluesoftheseimpactsandtheeventualimpacts onthefloodrisksinVietnam. The results of these runs indicate that full flood control for the Focal Areas Long Xuyen QuadrangleandPlainofReedswouldaggravatethefloodingconditionsinCambodia:from1.5

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to 1.7 m in Prey Veng to 0.5 to 0.8 m in Takeo. Corresponding increment of risk have been calculatedatsomeUSD1millionUS$/yearinKohAndetdistrictandUSD0.3MUUS$/yearin Koh Thom district. It is repeated again that these calculations are based on ISIS simulation results,andshouldbeconsideredwithduecare. 7.4.3 Environmentalimpacts

SensitiveandvaluableecosystemsthatareencounteredintheVietnameseMekongDeltaare MelaleucaswampforestsandseasonallyͲinundatedgrasslands.Theseremainingnaturalareas areimportantasahabitatforalargenumberofbirdspecies.Seasonallyinundatedgrasslands, togetherwithinundatedpaddyfieldsareimportantfishspawningandrearingareas. No officially protected areas are located in Long Xuyen Quadrangle, however, Bird Life Internationalidentified10prioritywetlandareasforconservationatthenationalorprovincial level. Populationintheprojectareaisconcentratedalongtheriverandcanalbanks,wheredensities areconsiderable.Thereisashortageofagriculturallandandpressureontheresourceishigh. Watercoursesinthearea,riversandcanals,areusedasasourcefordrinkingwaterbyalarge proportionoftheruralpopulation. Theareaisintensivelycultivated,withriceasthemaincrop.Fisheriesisimportantintheflood season.Itisasourceoffoodandincomeforasubstantialpartofthepopulation. ThepotentialenvironmentalimpactsofimplementationoffullprotectionoftheLongXuyen Quadranglearedescribedbrieflyinthefollowing.Ithastoberemarkedthatfullprotectiononly meansthatfloodscanbekeptoutoftheareacompletely,butthatthiswillprobablynotbethe case. Controlled flooding of certain areas during certain parts of the year will be allowed, possiblyinarotationalscheme. 1. Destructionofnaturalhabitats,valuableresources 1.1. NaturalandsemiͲnaturalvegetationcommunitiesintheareaarelimitedinextentand are under heavy pressure. Both the Melaleuca swamp forests and the seasonally flooded grasslands are dependent on regular, annual flooding. Keeping the floods completely out will result in a deterioration of these ecosystems and have a very negativeimpactonthespeciesdiversityofthefloraandfauna.Especiallywaterfowl (73species)andwetlanddependentbirds(another27species)willreduceinnumbers ordisappearcompletely.However,keepingoutthefloodscompletelyisnotlikelyto happen and measures to provide the remaining natural swamp and grassland areas withsufficientwatercouldbedesigned. 1.2. Indirectimpactsontheremainingnaturalareasareprobablyasimportantasreduced flooding. Better protection of the area will increase the value of the land for agricultural production and hence will increase the pressure on the presently notͲ cultivatedareas.Alreadynowthereisashortageoflandandencroachmentinnatural areas. 2. Lossofbiodiversity,rareandendangeredspecies 2.1. Reduced flooding will have an impact on the biodiversity in the area. Species compositionoffloraandfaunawillchangeandthediversityandextentofswampsand grasslandswillreduce. 2.2. DisappearanceoftheswampforestwouldmeanlossofplantspecieslikeMelaleuca leucodendron, Syzgium sp., Elaeocarpus hygrophilus, Ficus microcarpa and Cassia grandis,aswellasanumberoffish,amphibians,reptilesandbirds.Theforestsareof primeimportantforbreedingcoloniesoflargewaterbirds.

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2.3. Lossoftheseasonallyinundatedgrasslandswouldmeanthelossofplantspecieslike Eleocharis dulcis, Oryza rufipogon, Phragmites vallatoria, Eleocharis ochrostachys, Ischaemum rugosum, Lepironia articulata, Eragrostis atrovirens, Setaria viridis, Mnesithea laevis and Panicum repens. Globally threatened birds like the Bengal FloricanHoubaropsisbengalensisandWhiteͲshoulderedIbisPseudibisdavisoni,would loseanimportanthabitat,aswouldtheSarusCraneGrusantigone. 2.4. Atotalof194birdsspecieshavebeenidentifiedina1999survey,fourteenofwhich aregloballythreatenedornearͲthreatened.Ofthese,threeareclassedasendangered, twoasvulnerableandnineasnearͲthreatened. 2.5. The Mekong Delta provides habitat for a significant proportion of the regional or global population of several bird species. Most notably, the Glossy Ibis legadis falcinellus, Little Egret Egretta garzetta and Cattle Egret Bubulcus ibis, Indian CormorantPhalacrocoraxfuscicollisandPurpleHeronArdeapurpurea. 2.6. Bird species richness is highest in seasonally inundated grassland and swamps (100 species),whileanthropogenichabitats(includingpaddyfields,aquaculturalpondsand villages) have the lowest richness (83 species). Melaleuca forest also holds a large numberofspecies(97). 2.7. Ofthe14globallythreatenedornearͲthreatenedspeciesrecordedinthearea,nine wererecordedinseasonallyinundatedgrasslandsandswamps,andonlythreewere recorded in anthropogenic habitats (Greyheaded Lapwing, SpotͲbilled Pelican and PaintedStork). 2.8. Thereare260speciesoffishknowntooccurinthearea,200ofthesecontributeto the commercial fishery. A large proportion of these has an inundation spawning pattern and undertakes lateral migrations from the mainstream and tributaries into theinundationzonestospawnandrearyoungbetweenJulyandSeptember.Lateor noaccesstothefloodplainorblockageofmigrationrouteswillhaveanimpactonthe standing stocks of these migrating species and may ultimately lead to the disappearanceofcertainspecies. 3. Lossofenvironmentalservices 3.1. Flooding and the related sustenance of wetlands is known to have a number of benefits, these benefits may disappear or decrease if flooding is prevented or diminished,asdiscussedbelow. 3.2. Higheragriculturalproduction:informationgatheredduringFocalGroupdiscussionsin the area showed that paddy yields after a year with a high flood are substantially higherthaninayearafterayearwithanormalflood.Afterahighfloodtheyieldis0.3 to1.5ton/ha(4to20%,onaverage0.7ton/ha)higher.Notonlytheyieldsarehigher, butalsotherelatedproductioncostsarelower(15to20%),resultinginanetbenefit of the flooding for agriculture of between 2.35 and 5.50 million VND/ha. The differencecanbeattributedtoanumberofpositiveeffectsoftheflooding:thefloods bringfertilesediments,acidity,toxicmaterialsandsaltsareflushedfromthelandand harmful insects and pests get killed. In flood free areas the replenishment of groundwaterandsurfacewaterbodieswithfloodwaterwillnottakeplace.Thiswill affectthequantitiesofwateravailableinthenextseason.Thisisprobablynotabig problem, because water can be brought to the area via the canal system. Of more importanceisthatnotonlytheavailablequantitywillbeaffected,butalsothequality of the water. Pollutant concentrations increase in the course of the dry season and floodingflushesthesepollutantsoutorreducestheconcentrationstoharmlesslevels. Reduced flooding will result in a deterioration of the water quality in the area. The Melaleucaforestsprovideanumberofvaluableproductstolocalpeople.Thetimberis valuedforconstructionofhousing,andisalsousedasfuelwood.Theproductionof honey is practiced in Melaleuca forest, and honey harvested from wild bees is particularly highly valued. Other forest products are taken to provide a source of income. These include aquatic fauna for food, Melaleuca oil (a valuable medicine),

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chaoi Stenochlaena palustris (a plant used for making rope and fish nets), mop Alstoniaspathulata(awoodyplantusedformakingfishingfloats)andMelaleucabark (usedforthermalinsulation). 4. ImpactonProtectedAreas 4.1. IntheLongXuyenQuadrangleFocalArea,10prioritywetlandsitesforconservation havebeenidentified.Highestpriorityisgiventotheseasonallyinundatedgrasslands oftheHaTienplainandtheTinhDoiandTraSuwetlandareas. 4.2. TheHaTienplaincontainssignificantpopulationsofseveralgloballythreatenedand nearͲthreatenedbirds(SarusCranesandtheendangeredWhiteͲshoulderedIbis).The area also has a high diversity in flora, including unique gradients from brackish to freshwaterandfromacidtoalluvialvegetationcommunities. 5. ImpactonFisheries 5.1. Fisheriesisimportantfortheruralpopulationinthearea.Amuchas200differentfish speciescontributetothefisheries inthearea,inadditionshellfish,mainlyMollusca andCrustacea,arecollected.Some70%ofthehouseholdsintheareaisinvolvedin fishing.Allfishinghouseholdsusepartofthefishcatchforconsumption.Mostfamilies sellpartofthecatchtoincreasefamilyincome.Intotalsome50%ofthecapturefish productionissoldtomarkets. 5.2. Themainhabitatsusedforfishing,inorderofimportance,arefloodedirrigatedrice lands and riverine floodplains, perennial rivers, perennial canals and rainfed rice paddies.Floodedricefieldsarethemainfishinggroundduringthefloodseason. 5.3. The importance of the flooding for fisheries is illustrated by the results of the Focal Groupdiscussionsheldinthearea.Itappearedthatduringahighfloodcatchesare50to 100%higherthaninyearswithanormalflood.Averagevalueofthecatchperhousehold duringanormalfloodwasreportedtobe3.6millionVND,inahighfloodyearthisis6.2 millionVND,oranincreasewithabout75%. 5.4. Makingtheareacompletelyfloodfree,willbasicallydestroytheinlandfisheries.Fish will not be able to migrate to the flooded wetlands and rice field and the area of feedingandspawninggroundswillreduce,aswilltheareawherefishcanbecaught. Asaruleofthumbitisestimatedthatforeveryhathatdoesnotflood,fishproduction lowerswithabout100to200kg. 6. Landacquisitionandresettlement 6.1. Projectimplementationwillentailcanalanddikeconstructionorenlarged.Thesecanals anddikeswillmainlyfollowexistingalignments.Inotherwords,afairlylargepercentage oftheworkswillbecarriedoutatplaceswherethepopulationisconcentratedandland acquisitionandresettlementmaybeunavoidable. 7. Humanhealthandsafetyimpacts 7.1. Overalltheprojectwillhaveapositiveimpactonhumanhealthandsafety.Peoplewill bebetterprotectedagainstflooding,floodswilllastshorterandfood(rice)production, andsofoodsecurity,willincrease.Thisisnotnecessarilythecasefortheamountof fishavailableinthefloodseason.Reducedflushinganddilutionofpollutedwaterat theendofthedryseasonmayposeathreattohumanhealth. 7.2. Constructionactivitiesareanotherthreattohealthandsafetyforavarietyofreasons: emissionofdust,fumes,noiseandvibrationfromconstructionsitesandaccessroads, increasedtrafficandworkersaccidents.Inflowofworkersfromotherareasincreases theriskofaspreadofHIV/AIDS.

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Reduced flooding in the Vietnamese Delta will have a number of significant environmental impacts. Probably most important is the negative impact on inland fisheries. Reduction of accesstothefloodplainformigratoryfishandreductionoftheareawherethefishcanspawn andfeed,willreducethepossibilitiesofruralpeopletobeengagedinfisheriesasameansto improvehouseholdnutritionalconditionsandhouseholdincome. Alsoimportantistheverylikelyfurtherdeclineofthefewremainingnaturalareas(seasonally flooded grasslands and Melaleuca swamps). These areas are important habitats for a large varietyoffloraandfaunaspecies,amongwhichanumberofrareandendangeredspecies. Finally, a number of environmental benefits of flooding will be lost. Important are the decreasedsupplyoffertilizingsediments,thereducedflushingofacidandtoxicmaterialsfrom the soil and the reduced sanitation of the area (pest control). Also the reduced flushing and dilutingofpollutedwaterattheendofthedryseasonwillresultindeterioratingwaterquality conditions. Itisrecommendednottomake(partsof)theareacompletelyfloodfree.Asystemofcontrolled floodingshouldbedesigned,whichreducesthedamages,butatthesametimeconservesthe benefitsofthefloodingasmuchaspossible.Specialattentionshouldbegiventotheremaining naturalareas,theyarenotonlythreatenedbychangesinthefloodingregime,butalso,and probablyevenmoreso,byencroachmentoflocalpeople. ThepotentialenvironmentalimpactsofimplementationoffullprotectionoftheLongXuyen Quadranglearesummarizedinthefollowingscreeningtable. 7.5 Strategicdirections

7.5.1 Floodmanagementstrategicdirections

StrategicdirectionsforfloodriskmanagementintheLXQareclearlydefinedinthelongterm floodcontrolplanning1998,asapprovedbytheVietnameseGovernmentin1999.Objectives and guiding principles for the flood management in the Long Xuyen Quadrangle have been mentionedaboveundersection7.3.1. 7.5.2 Mitigationoftransboundaryimpacts

FromthemodelsimulationsasdescribedinVolume2Bitisclearthatanyfloodmanagement that goes beyond the early flood (half of August) protection, will have impact on the flood hazardandeventuallythefloodriskinCambodia. Retention options to compensate for lost storage capacity are hardly available in the VietnamesepartoftheMekongDelta.Itisthereforesuggestedthatcompensatingmeasures aresoughtinthediversionoffloodwatersjustupstreamoftheprotectedLXQareatowardsthe SouthChinaSea(GulfofThailand).

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Screening question Yes No Remark A. Project siting

Is the Project area adjacent to or within any of the following environmentally sensitive areas? in or near sensitive and valuable ecosystems X remaining areas of Malaleuca forest and (e.g., protected areas, wetlands, wild lands, coral seasonally inundated grasslands are reefs, and habitats of endangered species) important bird habitats. No official protected areas are located in the Long Xuyen Quadrangle, but 10 priority sites have been identified for conservation. In the Plain of Reeds Focal Area there are two protected areas. Tram Chim National Park and the Lang Sen Wetland Reserve. in or near areas with cultural heritage sites (e.g. X archaeological, historical sites or existing cultural or sacred sites) densely populated areas where resettlement may X population is concentrated along canals be required or pollution impacts and other and dikes, works will concentrate on disturbances may be significant these areas regions subject to heavy development activities or X in the project area agricultural land is in where there are conflicts in natural resource demand, putting pressure on the land as allocation a resource watercourses, aquifer recharge areas, or reservoir X canal and river water is used as a source catchments used for potable water supply for domestic water by a large proportion of the population in the area. lands or waters containing valuable resources X the area is a very important rice (e.g. fisheries, minerals, medicinal plants, prime producing area. Besides fisheries agricultural soils) provides additional food and income to the rural population

B. Potential environmental impacts

Is the project likely to lead to: permanent conversion of potentially productive or X the seasonally flooded grasslands and valuable resources (e.g. fisheries, natural forests, Melaleuca forests have high conservation wild lands) value, flooded paddy fields are important as fish rearing areas. destruction of natural habitat and loss of X a reduction of the flooded area will affect biodiversity or environmental services provided by the flora and fauna diversity (fish and a natural system water birds) and will have a negative impact on the fisheries resource. risk to human health and safety (e.g. from X limited, some construction activities generation, storage, or disposal of hazardous related health and safety risks are to be wastes, inappropriate occupational health and expected. Improved flood protection on safety measures, violation of ambient water or air the other hand reduces risks and quality standards) improves food security and thus health encroachment on lands or rights of indigenous X - peoples or other vulnerable minorities displacement of large numbers of people or X - businesses absence of effective mitigation or compensation X - measures

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CHAPTER8 STRATEGICDIRECTIONSFORFLOODRISK MANAGEMENTINTHEEASTOFMEKONG AREAINVIETNAM(POR)

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8 STRATEGICDIRECTIONSFORFLOODRISKMANAGEMENTINTHEEASTOFMEKONGAREAIN VIETNAM(POR)

8.1 Flooddamagesandrisks

FortheestimateofthefloodrisksinthePORreferenceismadetotheVolume2C.Theaverage annualdamageintheDongThapProvincealonehasbeenestimatedatsomeUSD44millionper year.Furtheranalysisisneededtoassesstheflooddamageriskatthelevelofthefocalarea. The share of agricultural risk is some 10% of the total risk. Most of the risk (about 55%) is relatedtoinfrastructureandrelief,andonethirdisrelatedtohousing.ItisclearthatDongThap ismoreatriskthantheAnGiang.Also undermoderatefloodconditionsthedamagecanbe substantial(someUSD20millionduringtheaverageflooduptosomeUSD90millionunderthe oncein5yearflood) The flood risk in the surveyed Tan Hong and Tam Nong districts has been assessed at respectivelyUSD2.2millionandUSD2.5millionperyear.Itisnotedthatasubstantialpartof theriskintheDongThapprovinceisrelatedtobankerosion.Thisphenomenonisnotreflected inthefloodriskofthesurveyeddistricts. 8.2 Floodbenefits

Resultsfromfocusgroupdiscussionsheldinthreedistrictsinthedeepfloodedareasshowed thatbenefitsfromnaturalfishingvaryfrom100Ͳ300US$/householdinnormalfloodyearsand from120Ͳ750US$/householdinbigfloodyears. AccordingtotheMRCͲTechnicalPaperNo16onfishyields,theaverageamountoffishcatch from rice fields in the Mekong Delta Flood Plain (deep flooded areas) are 80Ͳ119 kg/ha, resulting in a value of 30Ͳ40 US$/ha. Farmers also mentioned that floods have significant benefitforcropcultivation.Afterbigaflood,applicationoffertilizersandpesticidestoWinterͲ SpringPaddy(PlantinginNovemberandharvestinginMarch)islessthaninanormalfloodyear, andtheyieldishigherby0.5Ͳ1.0ton/ha.Itwouldresultinfloodbenefitforagricultureofabout 200Ͳ300US$/haafterabigflood.Assumingbigfloodfrequencyofonethird,theannualflood benefitforagriculturewouldbe60Ͳ100US$/ha. 8.3 FloodriskmanagementEastofMekongRegionVietnam(POR)

8.3.1 Options

Similar to the approach for the LXQ, the strategy proposed to achieve the flood control objectives for the POR relies on isolating areas from flood waters using dikes, and utilizing embankmentsystemsatdifferentscalesandlevelstocontrolthetransportoffloodwaters.The correspondingtechnicaloptionsaimat: 1. Influenceandcontrolfloodingusingthe principleoflivingwithfloods;anddistributing floodflowinthemostefficientway. 2. ReducefloodpressuretothePORcentralareabyimprovingflooddrainagecapacityatTu ThuongandatlowpartsofMekongandVamCorivers. 3. Control early flood, for harvesting Summer Autumn crop and accelerate drainage for WinterͲSpringcrop;concurrentlyincreasehorizontalflowtoimprovesedimentaccretion fromMekongriver. 4. Improvedrainagecanalsystemforreducingdepth,durationofinundation;increasingdry seasondischargeforirrigationandimpedingsalinityintrusion.

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5. Useadvantagesanddisadvantagesoftidalexcursiontoenhanceeffectivenessofdrainage andirrigationmeasures. 6. Control flooding and redistribute flood flow by reasonable operation regime of floodͲ controlworks. 7. Raisecrestlevelsforresidentialareasandroadnetworks 8. Dig new canals and enlarge existing canal system to help reduce depth and duration of inundation,particularlytoaccelerateflooddrainageforearlyseedingWinterSpringcrop. 8.3.2 Structuralmeasures

Thestructuralmeasuresthathavebeenidentifiedto realizeabovementionedobjectivesare shownintheError!Referencesourcenotfound.overleafandreferto: 1. Definiteframeofcanalsystems(main,primary,secondary)toensuretheymeettheneeds ofintegrateduse. 2. TanThanhͲLoGachfloodcontrollineincludes;dyke,sluices,overflows.Thissystemhas function of controlling over flow from inundated area of Cambodia and diverting flood dischargetoMekongandVamCorivers.Itisoperatedprimarilytoprotectagainstflooding inAugust. 3. FlooddrainageworkgroupatTuThuongincludingroadͲoverflow.Itsfunctionistoreduce floodpressureforPORcentralarea. 4. Sluices located along upstream reaches of the Mekong River within Vietnames territory (fromHongNgutoAnPhongMyHoacanal).Thesesluiceshavethefunctionofreducing earlyfloodingfromMekongandincreasingdischargetoremoteareaofthePORduringthe dryseason. 5. SluiceslocatedalongdownstreamreachesoftheMekongRiver(fromMyThotoCaiBe). Thesesluicesareoperatedbytidalenergyandcanimprovenotonlydrainagebutirrigation capacitiesalso. 6. Sluice + navigation lock Vam Co, built at the confluence of two Vam Co rivers with automaticoperationcontrolledbytheenergyoftide. 8.4 Impactsofstructuralfloodriskmanagementoptions

8.4.1 Floodriskreduction

If the flood risk management works as described above would be operated to provide full protection to the POR, then most of the flood risks, apart from the bank erosion, would be eliminated. This would give a risk reduction of some USD 2.2 and USD 2.5 million/year for respectivelytheTanHongandTamNongdistricts. Iftheseworks,however,wouldbeoperatedtoprotectthePORagainsttheearlyfloodsonly (untilhalfofAugust)thenonlytheagriculturalriskwouldbelargelyeliminatedinthesurveyed districts. These risk reductions are estimated at USD 0.2 million for Tan Hong and USD 0.4 millionforTamNong

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Full protection would enable a third paddy crop. Currently, there are 2,088 ha in Tan Hong districtcoveredbythethirdcropduringthefloodseason.Theseareasareboundedbynational roadsandembankmentsdevelopedbylocalauthorities.Theexistingthirdpaddycropoccupies about8%paddylandinTanHongdistrict.Sincethethirdcropgrowsduringtherainyseason withhighfloodwaterinriverandcanal,drainageofexcesswateronthefieldbypumpingwould be critical. It is assumed that additional 70% of paddy land could be used for a third crop, consideringtheexistingthirdpaddyandthatdepressionareasmaynoteconomicallyforthis crop.Netbenefitofadditionalpaddywouldbeattherateof900US$/ha,resultinginexpected additionalbenefitfromcultivationofthirdpaddyasUSD16millionintheTanHongandUSD21 millioninTamNongdistrict. FullfloodprotectioninLXQwouldreducenaturalfishonpaddyfieldattherateof of30Ͳ40 US$/ha.Takenintoaccounttheremainingfloodedpaddyarea,thefishlosswouldbesomeUSD 0.8million/yearinTanHongandUSD1.1millioninTamNongdistrict. Floodingbringssedimentationtothedelta,leachesacidsulphatesubstancesandtoxicityfrom thesoil,andcontrolspests.Thisbenefitwasevaluatedas60Ͳ100US$/haforWͲSpaddy.Full floodprotectionwouldcreatethelossofthesebenefitstoanestimatedamountofsomeUSD 1.6million/yearforTanHongandUSD2.3millionforTamNongdistrict. 8.4.2 Transboundaryimpacts

AsisthecasefortheregionalLXQfloodprotectionscheme,alsothePORschemeallowsforthe managementofnotonlytheearlyfloods,butalsothefloodsarrivingafterAugust.Operationof the flood management infrastructure beyond the early flood (or half of August) will create increased water levels in the rivers both downstream and upstream of the protected area. Moreover, the blockage of the floodplain flow will affect directly the floodplain flood levels upstreamofthisblockage. Inprinciplethefloodmanagementinfrastructurecouldbekeptcloseduntilafterthepassageof thefloodpeak.Inthatcase,thepeaklevelsupstreamoftheprotectedareawillincreaseand affectdirectlythefloodriskinCambodia. RunswiththeISISmodelhavebeenmadetosimulatetheimpactofthescenarioinwhichflood waterwillenterneitherLongXuyenQuadranglenorthePlainofReedsunlessthemanagement decidesforcontrolledinlet. TheresultsofthesesimulationsareshownanddescribedintheAppendix6ofVolume2B.Ithas tobetakenintoaccountthatthemodelallowsforarelativeassessmentoftheseimpactsonly. That is to say that the presented absolute values are to be given due care. More accurate modellingisrequiredtoassesstheabsolutevaluesoftheseimpactsandtheeventualimpacts onthefloodrisksinVietnam. The results of these runs indicate that full flood control for the Focal Areas Long Xuyen QuadrangleandPlainofReedswouldaggravatethefloodingconditionsinCambodia:from1.5 to1.7minPreyVeng.Theseresultsdonottakeintoaccountthoughthemitigatingimpactof theplannedTuThuongfloodreleaseworks. Corresponding increment of risk have been calculated at some USD 1.4 million US$/year in Kampong Trabek district. It is repeated again that these calculations are based on ISIS simulationresults,andshouldbeconsideredwithduecare.

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8.4.3 Environmentalimpacts

ThepotentialenvironmentalimpactsofimplementationoffullprotectionofthePlainofReeds are very similar to those described in the previous sections regarding the Long Xuyen Quadrangle.Ithastoberemarkedthatfullprotectiononlymeansthatfloodscanbekeptoutof theareacompletely,butthatthiswillprobablynotbethecase.Controlledfloodingofcertain areasduringcertainpartsoftheyearwillbeallowed,possiblyinarotationalscheme. InthePlainofReedsFocalAreatherearetwoprotectedareas.TramChimNationalParkand the Lang Sen Wetland Reserve. Tram Chim is a lowͲlying wetland with seasonally inundated grasslandsandnaturalMelaleucaforests,anabundanceoffreshwaterfish,andconsequently manybirds. BirdLifeInternationalrankedTramChimNationalParkasoneofthemostimportantsitesfor conservation in the Mekong Delta. The park receives international recognition as seasonal habitatforthegloballyendangeredSarusCrane.Itisalsoanimportantbreedingsiteforwater birds. LangSenisanotherremnantoftheoriginalwetlandlandscapeofthePlainofReeds.TheLang SenWetlandReservecoversanareaofsome5,030ha,amongwhich1,500haisswampland providing habitats for a variety of wetland fauna and fish. Substantial areas of natural lotus swamparepreservedatLangSen.ThisvegetationtypeischaracteristicofthePlainofReedsbut isnowseldomfoundanywheretoanygreatextent.Itisoneofthefewremainingsiteswhere semiͲnaturalMelaleucaforestoccursalonganaturalriverchannel,and,assuch,isofnotable biodiversityvalue.ThesiteislistedasanImportantBirdArea(IBA)becauseasignificantnumber oflargewaterbirds,includingtheEasternSarusCraneandthePaintedStork,useLangSenasa stopͲover area en route between their breeding areas in Cambodia and their nonͲbreeding areasintheMekongDeltaofVietNam. Biodiversityisveryhigh,156plantspeciesand149vertebratespecies(ofwhich13speciesare listedintheVietNamRedBookofendangeredspecies)arefound.Theimportantandunique vegetation types/habitats are all flood dependent: riparian forests along rivers and canals, seasonallyfloodedgrasslands,swampsandMelaleucaforests. The above described protected areas are depending on regular flooding for their survival. Reducedornofloodingwillreducetheirecologicalimportancesignificantly. Alsohereitisstronglyrecommendednottomake(partsof)theareacompletelyfloodfree.A systemofcontrolledfloodingshouldbedesigned,whichreducesthedamages,butatthesame time conserves the benefits of the flooding as much as possible. Special attention should be giventotheremainingnaturalareas,theyarenotonlythreatenedbychangesintheflooding regime,butalso,andprobablyevenmoreso,byencroachmentoflocalpeople. 8.5 Strategicdirections

8.5.1 Floodmanagementstrategicdirections

StrategicdirectionsforfloodriskmanagementinthePORareclearlydefinedinthelongterm floodcontrolplanning1998,asapprovedbytheVietnameseGovernmentin1999(DcisionNo 144/1999/QDͲTTg)andtheMasterPlanStudyonwaterWorksoftheMekongDeltaasapproved bytheVietnameseGovernmentin2006(DcisionNo84/2006/QDͲTTg.Objectivesandguiding principles for the flood management in the Long Xuyen Quadrangle have been mentioned aboveundersection8.3.1.

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8.5.2 Mitigationoftransboundaryimpacts

FromthemodelsimulationsasdescribedinVolume2B,itisclearthatanyfloodmanagement that goes beyond the early flood (half of August) protection, will have impact on the flood hazardandeventuallythefloodriskinCambodia.EspeciallytheprotectionoftheVietnamese POR has substantial impact on the flood hazards in the East of Mekong flood plains in Cambodia. Retention options to compensate for lost storage capacity are hardly available in the Vietnamese part of the Mekong Delta. Consequently, additional discharge capacity is to be providedatanddownstreamoftheborderareatomitigatethecrossͲboundaryimpacts.Such additionalcapacitycouldbeprovidedinthedirectionoftheMekongRiver(KOICAalternative), towardstheVaiCoRiverortowardstheGulfofThailand. TransboundaryimpactsdonotonlyrefertotheimpactofriskreductioninVietnamontheflood risksinCambodia,butalsotheotherwayaround,asdescribedinthepreviouschaptersrelated to the flood risk management in Cambodia. It is therefore recommended to investigate the optionsofdiversionintheborderzonebetweenCambodiaandVietnam.

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CHAPTER9 STRATEGICDIRECTIONSFORMEKONG RIVEREROSIONRISKMANAGEMENTIN BOKEOPROVINCE,LAOPDR,ANDKRATIE, CAMBODIA

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9 STRATEGIC DIRECTIONS FOR MEKONG RIVER EROSION RISK MANAGEMENT IN BOKEO PROVINCE,LAOPDR,ANDKRATIE,CAMBODIA

9.1 Introduction

TheTermsofReferenceoftheFMMPC2callforthepreparationofaFMMProjectDevelopment and Implementation Plan (ProDIP) based on a limited number of Flood Management and Mitigation (FMM) projects nominated by the four riparian countries In the Stage 1 ImplementationPhasethelistofprojectshasbeenpreparedandendorsedbythecountries. DuringtheStage2ImplementationPhasethelistwillbeprioritisedandthePIN'sprepared. Theconsultantdevelopedinconsultationwiththerelevantlineagencies,ProjectIdeasinthe frameworkoftheIFRMstudiesinthefocalareas. TheTermsofReferencealsocallfor4Ͳ6demonstrationprojectstobeselectedfromthelistof projects that eventually will make up the ProDIP. The most important criterion in selecting thesedemonstrationprojectsistheircontributiontoachievingtheprincipalobjectivesofthe FMMPͲC2,thatistosay,totheestablishmentofsustainablefloodriskmanagementcapacityin theMRC,MRCS,NMCsandnationallineagencies. During the second stage of the Implementation phase these demonstration projects will be further developed in preparation of an application by the respective member countries for fundingoftheimplementationoftheseprojects. This document on strategic directions outlines a strategy for developing a joint project that makesbringstheerosionriskmanagementvisioninthesubͲareas2Tand1L,showninError! Referencesourcenotfound.,toreality.Itwillhelpbringingtogetherthemostcriticalareasof joint work for improving the knowledge on development of the river channel (international border between Laos and Thailand) and sustainable options for reducing erosion risk and minimizingtransboundaryimpacts. It shall provide a framework for planning, implementing and evaluating erosion control measures, efficient, and effective interventions, whose impacts can be managed in joint coordination.Themajorcomponentsare: x Rationale, the needs that require an integrated and comprehensive study on river bank erosion mechanisms to improve stabilization of the international border and to reduce damagetoinfrastructureandagriculturallandensuringsustainabledevelopment. x Guidingprinciplestoguidethisjointproject. x Future directions for major areas of river bank erosion work to share and extend river engineering and river training techniques for achieving costͲeffective as well as environmentallyfriendlyriverbankprotections. x Implementation of the strategic directions with Member Countries and partners. The strategyshallalsoprovidearoadmapforthejointopportunitiestocontrolandformidable challengesahead 9.2 Background

ThemostcriticalimpactalongtheMekongRiverontherightbankinLaoͲPDRisriverbankerosion thattakesplacealongseveralareasbetweenTonPheungdistrictandHouayxaydistrict.Because river bank erosion is considered as a critical problem in Bokeo, the Government of LaoͲPDR allocatesannualbudgetforriverbankprotectionatsomecriticallocations;however,thebudgetis not sufficient to undertake works to stop the extend of the erosion along the Province and thereforepartialprotectionsconsistingoftemporaryworksareonlypossibleeveryyear.

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TheseongoingerosionprocessesalongtheleftbankoftheMekongRiverinBokeoProvince(subͲ area2L),HouayXayandTonPheungDistrictsandtherightbankinThailandhaspromptedthe need to undertake a joint technical evaluation of the present situation and the forecast of potentialscenariosofdevelopmentinthecomingfloodseasons. Duringthemonsoon2007,additionalareasofagriculturallandwerewashedawaybytheriver andthepotentialscenariooferodingTonPheung,BKhouan,BSimouangngamandBDonSavan is of great concern for the LaoͲPDR Government. The present critical situation, the lack of enoughfundstoconstructpermanentrivertrainingworksandtheneedtodevelopaplanfor theprotectionofcriticalareasrequiresofurgentsupportfromMRCanddonors. ApartfromgeoͲmorphologicalcharacteristicsoftheriverthegeneralviewofthepeopleinthe province is that erosion has increased over the last years due to the impact of river bank protectionworksimplementedalongtherightbankoftheMekonginThailand. ThisjointprojecthasbeennominatedintheframeoftheProDIPanddealswithrelatedtobank protectionalongtheMekongMainstream.Thiscategoryofprojectsisconsideredas"erosion riskmanagement"measuresandreferstoerosionriskmanagementaswell. Besidesthedifferentprojectcategories,adistinctionhasbeenmadebetweenprojectsthataim atthepreparationoffloodriskmanagementplansandprojectsthataimattheimplementation offlood/erosionriskmanagementmeasures.Thisjointriverbankprotectionstudyisclassified asaprojectforpreparationoferosionmanagementplans. 9.3 TheRationale

Likemanyotherrivers,theMekongerodesitsbanksinmanypoints.ErosionattheMekonghas not reached alarming proportions but the considerations on: (i) international border, (ii) sustained socioͲeconomic development of the region, (iii) flood and protection of existing infrastructure and cultural heritage could require prompt attention at critical locations along thewaterfront. AlongthesubͲareas2Tand1L(Figure9.1)requiringaction,theMekongRiverhasavariable width and it is geologically controlled almost along the whole length and local geology and related rock outcrops are very important. In the Upper Mekong reach the floodplain is only marginally developed, and often the river reaches the flood plain levels only during extreme floods. ThereareseveralprovincesanddistrictsalongtheMekongRiverand,urbanandinfraͲstructural development will become much more important than in the past, adding significantly to the investmentvalueofpropertyandservicesneedingprotectionfromfloodsandshiftingofthe riverbankduetoerosion. ContrarytoFloodriskmanagement,which,thathasreceivedaboostfromtheexecutionofthe FMMP, erosion risk management up till now has not got the attention it should have. River erosioncreatespovertybymakingpeoplehomelessovernight.Thepoorareaffectedmost.

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Figure9.1 AlignmentoftheMekongriverinBokeoProvince,controlledbygeology,from theGoldenTriangletoChiangKhongProvinceinThailand Theproblems,which,untilnow,havepreventedasystematicandstrategicapproachtoerosion managementinparticularinLaosareofamorphological,economicandtechnicalnature: Theincreaseinpopulation,theinvestmentininfrastructureintownsandruralareas(irrigation anddrainageprojects),therivertrainingworksalreadycarriedoutintherecentpastforvarious as well as costͲeffective improved techniques (JMREMP) in arresting bank erosion, are all reasonsforaformulatingaprojectwithabroaderviewintothetechnical,economicandsocioͲ economicfeasibilityofprotectionworksagainstbankerosion. The strategic directions shall be aimed to jointly study and formulate of an overall erosion managementstrategyforthesesubͲareas.Itisfeltthatsuchajointstudyisafirststeptowards afuturecontroloferosionofthebanksofthismajorinternationalriver. Therefore,theMRCFMMPComponent2shallpromoteandprovideastrategicdirectionsfor studyingtheriverbankerosionproblemsandalternativesolutionsandstrategiesfortheriver bankprotectionworksalongtherightandleftbankoftheMekongRiverinThailandandLaoͲ PDR.Focuswillbeplacedonthoseriverstretcheswereriverbankerosionposesahigherthreat toinfrastructure,roads,agriculturallandandurbancentres. Areasthatrequireattention WiththiscomponentoftheFMMP,MRCwillprovideaframeworkforarangeofinvestigations into the technical, environmental and social issues to be faced in formulating demonstration projectsincludingstructuralmeasuresandriverbankprotectionworksalongtheMekongRiver. Furthermore it will increase knowledge of Line Agencies on river morphological changes, erosionriskareasandlowcost(adaptivemethods)riverbankerosionworks.Althoughoverthe lastdecadetherehasbeenprogressinsurveying,datacollectionanddevelopingofdesigntools it is still required to look into advanced techniques needed to pursue a multiͲdisciplinary approachinwhichamultiͲcriteriaanalysiscanbeusedforevaluatingalternativedemonstration projectstoalleviateriverbankerosionproblemscausedintheMekongRiver. ForthepurposeofestimatingriverbankerosioninthesesubͲareasanddesigningriverbank protection works as well as for the planning of future programmes of erosion risk reduction measuresisnecessarytobeawareofthegeomorphologyoftheriver,asitmayhaveinfluence on the plans for river bank stabilization. Therefore an important consideration in predicting futuredevelopmentsandriverbehaviourandresponseis"thesensitivityofthechannel.This meanshowcloseisittoundergoingachangewithoutanexternalinfluence".

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Knowledgeonthegeologyandgeomorphologyoftheriveralsoallowstheidentificationofthe majorandsecondarygeologicalcontrolsalongtheriver.Thesecontrolswillhavetobeanalyzed regardingtheircorrelationwiththealignmentoftheriverandfuturedevelopmentsduetoriver bankerosionormajorgeologicalevents(i.e,shiftinginwestdirection). The potential for using satellite images to monitor and document recent and contemporary rivermorphologyhasbeendemonstratedthroughrecentstudiesinothermajorrivers.Methods forpredictingmorphologicalchangesoftheMekongRiveronashortͲterm(annual)basiscan alsobedevelopedusingdryseasonsatelliteimages. Furthermoreadditionalfieldinvestigationsshallbeplannedandcarriedoutandtheiroutputs integrated with the geoͲmorphological study. Additionally, the characterization of the river stretchesneedstobepreparedforpreparingthedesignofsustainableriverbankprotection worksforsiteͲspecificriverstretches. The differences between river stretches along the Mekong are reflected in their channel patternsandthesearecontrolledbythestabilityofthebanksandtheriverslope. BetweenLaoͲPDRandThailand,riverBankProtection(RBP)demonstrationprojectsalongthe Mekong River main objectives are twofold: (i) to prevent the erosion along the international borderbetweenLaoͲPDRandThailandand(ii)topreventbankerosionthataffectsurbanand semiͲurbanareas,transportandfloodinfrastructurefromdamageduringfloodsthatwillalso likelymayincreaseregionalflooding. 9.4 Objective

The main objective is the formulation of an overall joint integrated erosion management strategy project for Laos and Thailand in the MekongRiver aiming at a future control of the erosionofthebanksofthismajorriver.ThestrategyshouldbeaimedatsustainablelongͲterm planningofrivertraining(includingbankprotectionatvulnerablereaches)tostabilizethewidth oftheriverandthussafeguardvaluablelandandinfrastructureaswellastoreducetheriskof conflictsresultingfromtransboundarycrosscuttingissues. Technicallyandeconomicallyfeasibleriverbankmanagement,shortͲtermprotectionworksand rivertrainingworksonasustainablescaleforamajorriverlikeMekongcannot,ingeneral,be successfully developed unless they are incorporated within an integrated overall strategic programme. Accordingly, when designing river bank erosion protection measures it is agreed that they shouldfitintoacoherentplan(rivertraining)toharnessinoptimumwaytheriversystemwith thepossibilityofnewconceptsbeingappliedinrecentprojectsorinnovativedifferentconcepts incombinationwithtemporaryprotectionworksatkeylocations. The overall objective of the joint project is to provide a framework in which the technical, economic, social, environmental and other effects of various alternatives for river training works of the Mekong river along subͲareas 1L and 2T, can be assessed and evaluated at differentlevelsofdetail.Thejointprojectwillmoreover,provideasystematicapproachofthe rivertrainingworksinregardoftheirvariousaspectsasdesigncriteria,construction,sequenceof implementation, monitoring and maintenance, and the institutional and organizational managementrequirementsrelatedtotheseaspects. The respective Line Agencies in both countries will involve hydrologic, hydraulic, hydraulic engineering studies, geotechnical, morphological and geoͲmorphological studies. It will also

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requiremathematicalandphysicalmodellingstudiestosupportthepreparationofthedesignof rivertrainingworksandimplementationplan.AgroͲsocioͲeconomicandenvironmentaleffects oftheproposedschemesaretobeincluded.TheJointprojectshouldbeconsistentwiththe LineAgenciespolicies. 9.5 Guidingprinciples

Fourprinciplesguideformthebasisfortheimplementationofthestrategicdirectionsoutlined forthisjointproject: 1. Jointly addressing erosion risk management and implementing a joint strategic plan for riverbankerosioncontrol,developingeffectiveplansforprotectionofthepriorityareas. 2. Taking into account the social and environmental benefits obtained by reduction of risk erosioninthesubͲareas1L&2Tbyfocusingonpriorityareas. 3. Mitigationofpotentialtransboundaryissues. 4. Applicationofbestpracticeguidelinesandtrainingandcapacitybuildingwhichwillleadto preparecostͲeffectiveinterventionstoprotectinfrastructure,urbanandagriculturalareas. Startingpointsfordevelopingtheguidingprinciplescanbelistedas: Startingpoints: x Basedonexistingknowledgeandexperience(Thailand,Laos,andotherstudiescarriedout withintheframeofMRCorbilateralpartners) x Additionaldataongeotechnical,socioͲeconomicandenvironmentalconditionstobe collected, x Experiencefromelsewhere(i.e,Europe,China,USA)tobeused x TogetherwithMRCselectthemostsuitablemathematicalmodelstobeused.Similarly selectmostsuitableagenciesforcollectingandprocessingsatelliteimages. x ContinuousinteractionwithMRCandLineAgenciesandotherrelevantagencies x Extensiveuseofsatelliteimagesfordevelopmentofriverbankerosionhazardmaps x Ultimatelylearningbydoing,soaflexibleplanforimplementation

The 9.6 Maincomponentsofthejointproject:

In order to strategically address the erosion problems and formulate cost effective bank protectionprojects,insubͲareas1L&2Trequiresansweringthefollowingquestions:Where, WhenandWhattoprotectandHow. • WHEREisrelatedtothreatinshortͲtimebycurrentsorwaves, • WHENisamatterofmorphologicalpredictionsofriverchannels,makinggooduseoflow riverstagesandtheurgencytostopthethreat, • WHAT,isamatterofeconomicsandstrategicconsiderations, • HOWtoprotectwhichisfirstatechnicalproblemtobesolved The approach of the joint bank protection study focuses on the engineering analysis of all reasonable options and strategies for protecting the river banks against erosion, with special emphasisonfloods,environmental,socialandpoliticalconsiderations.Themaincomponentsof thejointprojectcanbesummarizedasfollows:

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(1) Rivertrainingcomponent.Consistingof: x Divisionofmainriversystemintodifferentstretches x Reviewofearlierstudies x Selectionofmoststableriverplanformforeachofthedifferentriverstretches. x Interactionwithotherprojects(navigation)andeffectofdevelopmentsupstream, x identifytheinfluencesofbankmaterialsandchangesintheplanformontherateofbank erosion, x Develop bank erosion prediction methods using satellite images. The potential of such prediction methods for erosion monitoring and vulnerability assessment has been recognized, x Preparingerosionhazardmaps, x DevelopmentofshortͲterm(upto5years)andmediumtermstrategy(5Ͳ15years),forriver bankprotection,basedalsoonsocioͲeconomicandenvironmentalimpactsandeconomic analysis, x ReviewofrecentbankerosionprotectionexperiencesinThailandandLaos x StudyoffailuresandsuccesseswithriverbankprotectionworksinThailandandLaosand elsewhereandrecommendationsonbestpracticerelatedtotypeofprotectionworks x Developmentofstrategyforimplementingriverbankerosionworksandhowtoreachmost stableriverplanform x Recommendationsforlearningbydoing (2)Environmentalimpactcomponent.Consistingof: x StudyofbaseͲlineconditionsalongtheriverinsubͲareas1Land2T x Morphologicalimpactstudyofproposedstrategiesonthealignmentoftheriverbanks x Environmental impact study of proposed strategy and alternative approaches (when needed) (3)Economicanalysiscomponent,consistingof: x C/Banalysisofproposedriverbankerosionstrategy(ies) x EconomicanalysistohelpformulatingshortͲtermandmediumͲtermstrategy(ies) (4)Institutionalcomponent,consistingof: x AdviseonpresentsettingofriverbankerosionmanagementunitsinLaosandThailand, x Adviceonfutureinstitutionalneedsinrelevantagencies, x TrainingofprofessionalstaffresponsibleforriverbankerosionworksinthecountriesLine Agencies,and x Adviceonmonitoringandmaintenance(how,who?) 9.7 Futuredirections

Thefuturedirectionslieincontinuingandexpandingthosecomponentsofthejointprojectand learningfromtheimplementationofinterventionswithproveneffectiveness,andinmonitoring prediction of erosion where evidence has demonstrated that the need is for river bank protectionisgreatest.Whatneedstobedoneineachofthepriorityareasforactioncanbe approachedinasystematicmannergoingthroughthemaincomponentsandactivitieslisted above.GovernmentLineAgenciesandconcernedpartieswillcontinuetoidentifyprioritiesfor joint implementation of erosion control measures based on erosion risk the socioͲeconomic benefitsandotherfactorsrelevanttospecificcontexts. Oneimportantfutureoutputofthejointprojectactivitieswillbedefinitionofhazardareasand preparationoferosionhazardmapsbymeansofmodellingresultsandbymeansofhistorical records(ratesofaverageerosionm/year),whichwillallowtodelineatehazardareasonand establishsetbackrequirements.Consequently,itwillbealsopossibletoprioritizerivererosion

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problems.Itshallbeasystematicprocessthatleadstorankingofriverstretchesbasedonthe significanceofbankerosionandaffectedinfrastructureandstructures. 9.8 Implementation

Thegreatest challengeto promotethis strategicdirectionsanddevelopmentofjointerosion protectionplansinthefuturewillbetransformingknowledgeintoaction. As an example, in order to develop a costͲeffective plan and secure funds in time for demonstration projects inBokeo Province, it is urgently needed to review themorphological processesandthepresentandpotentiallyfutureplanformchangesintheMekongRiveralong theProvince.Thishastobeaccompaniedbyatechnicalestimateofpresentbankstability.The understanding of the aforementioned morphological processes will allow determining which areasneedtobeprotectedfirstandwhattypeofmeasurestocontroltheongoingerosionare required. Withintherangeofpotentialareasforaction,MemberCountrieswillidentifyprioritiesbearing inmindthenationalcontext,andtakingintoaccountinteraliathecostofthemeasuresand impacts on socioͲeconomic development of their Provinces. This joint project will provide guidance to Member Countries and partners to identify priorities and develop strategic operationalresponses. Working with MRC, partners and in Joint Initiatives will be very important in view of the importanceofinvestinginsustainableerosionriskreductionmeasures.

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CHAPTER10 STRATEGICDIRECTIONSFORMEKONG RIVEREROSIONRISKMANAGEMENTIN KRATIE,CAMBODIA

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10 STRATEGIC DIRECTIONS FOR MEKONG RIVER EROSION RISK MANAGEMENT IN KRATIE PROVINCE,CAMBODIA

10.1 Introduction

TheTermsofReferenceoftheFMMPC2callforthepreparationofaFMMProjectDevelopment and Implementation Plan (ProDIP) based on a limited number of Flood Management and Mitigation (FMM) projects nominated by the four riparian countries In the Stage 1 ImplementationPhasethelistofprojectshasbeenpreparedandendorsedbythecountries. DuringtheStage2ImplementationPhasethelistwillbeprioritisedandthePIN'sprepared. Theconsultantdevelopedinconsultationwiththerelevantlineagencies,ProjectIdeasinthe frameworkoftheIFRMstudiesinthefocalareas. TheTermsofReferencealsocallfor4Ͳ6demonstrationprojectstobeselectedfromthelistof projects that eventually will make up the ProDIP. The most important criterion in selecting thesedemonstrationprojectsistheircontributiontoachievingtheprincipalobjectivesofthe FMMPͲC2,thatistosay,totheestablishmentofsustainablefloodriskmanagementcapacityin theMRC,MRCS,NMCsandnationallineagencies. During the second stage of the Implementation phase these demonstration projects will be further developed in preparation of an application by the respective member countries for fundingoftheimplementationoftheseprojects. Thestrategicdirectionsshallprovideaframeworkforplanning,implementingandevaluating erosioncontrolmeasures,efficient,andeffectiveinterventions,whoseimpactscanbemanaged injointcoordination.Themajorcomponentsofthestrategicdirectionsare: x Rationale, the needs that require an integrated and comprehensive study on river bank erosion mechanisms to improve stabilization of the left bank and reducing damage to infrastructureandurbanlandensuringsustainabledevelopment. x Guidingprinciplestoguidethisproject. x Future directions for other priority location of river bank erosion and extending river engineering and river training techniques for achieving costͲeffective as well as environmentallyfriendlyriverbankprotections. x Implementation of the strategic directions with Line Agencies and partners. The strategy shallalsoprovidearoadmapfortheopportunitiestocontrolandformidablechallenges ahead This document on strategic directions outlines a strategy for developing an erosion risk managementplanandmeasuresthatbringstheerosionriskmanagementapproachtorealityin subͲarea8C,KratieProvince. 10.2 Background

TheProvinceofKratieislocatedwithinsubͲarea8Canditwasselectedasoneofthefocalareas forthepreparationofdemonstrationprojectsinCambodia.Themainobjectiveinthisfocalareais tocarryoutariskassessmentofbankerosionandformulateplansandmeasuresformitigating theerosionrisk. KratieProvinceislocatedinthenortheastpartofCambodia.TheProvincesharesthefrontierwith Mondulkiri province in the east, Kampong Cham province and Vietnam in the south, Kampong Thomprovinceinthewest,andStungTrengprovinceinthenorth.

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Kratieprovinceconsistsoffivedistricts,46communesand250villages.ThepopulationofKratie isapproximately290,000andthepopulationdensityis26peoplepersq.km.Roughly70%ofthe peoplelivealongtheriver,whereas30%liveinthemountainsareas. KratieProvincecoversanareaof11,094squarekilometerswhichiscategorizedintoseveralareas suchas83%forest,agriculturalland8%andredland0.5%inSnouldistrict. The Mekong River, the natural water resource, flows over about 140 km long across Kratie province.Theerosionoftheleftbankoccursover6kmfromSambokatkm572toPhThmar KraeKraonandPhRusseiCha(km566)andover15kmfromKratie(km572)toPrekTe(km 557). 10.3 TheRationale

AMajorriverliketheMekongischaracterisedbyhavinglargevariationinwaterlevels,shifting riverchannelswithlargesandbarsandcreatingdeepscourholesalongouterbendsduringthe flood season. The left bank of the Mekong along Kratie Province consists of steep slopes of brownsiltrisingabout14to20mabovethelowwaterlevel.Thetopoftheriverbankshowsa naturalleveeandthegroundsurfacegetslowerinthefirsthundredmetersawayfromtheriver bank. Theleftriverbankcanbeundersevereattackinagivenyearandorbenotaffectedbycurrents inthenextyearorevenforanumberofyears. ThegeneralgeologycharacteristicsoftheMekongRiveralongtheDistrictofKratieasdescribed intheOTCAReport6,consistoftwogeologicalformationsintheareaofSambok: x TheTmorMoykbykbedonrightbankand, x TheSambokgroupontheleftbank Thebedrockintheriverconsistsofsandstoneanditiscoveredwithdepositsofseveralmeters thick. The surface deposits are compacted and mainly consist of silty clay and clay and the underlyingmaterialismorecohesiveandstrongbondedtocompletelyweatheredrock. Therivervalleyingeneraliswideandslightlyundulatingwhichextendssome5to10kmfrom eachbank.Itisalsoobservedthatnaturalvegetationgrowthsatelevationcorrespondingtothe maximumelevationofyearlyfloods. Riverbankerosionratehasnotreachedalarmingproportionsbutitrequiresattentionatsome locationsinviewofinfrastructure,urbanareasandeconomicgrowthoftheDistrict. As shown in Figure 9.2, the total length of the river threaten by erosion is 21 km in Kratie ProvinceandtheyarealllocatedalongtheKratieDistrictthathasapprox40mofwaterfront alongtheMekong.Consequentlyitcanbeconcludedthataround50%oftheDistrictboundary isaffectedbyriverbankerosion. MostoftheareaswhereerosionoccursarelocatedalongtheKratieDistrictinKratieDistrict TownandupstreamofKratieTownatkm560,PhThmarKraeKramandatkm566PhRussei Cha.Theroad/floodembankment(oldalignmentofroadN7)isparalleltotheriverbankandat somelocationstheoldroadhasbeenerodedalready. 6SamborProjectReport,LowerMekongRiverBasin,VolumeVIIBasicData.OverseasTechnicalCooperation Agency(OTCA),Japan

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ThetotalprioritylengthaffectedbyerosionatKratieDistrictTownisestimatedtobe5km.Most oftheerosionproneareaislocatedbetweenkm557startingatPrekTeandkm563PrekAndang Pring,whichincludestheKratietownareaandportarea.Atpresentatotallengthof370mof bankhasbeenprotectedandtheworkswereimplementedintwophases,thefirstoneof130m andthesecondone240m.Thelowerleveloftheprotectionworksislocatedat+17.3m.Thetop leveloftheprotection is+23.3mwhich 0.05mhigher thantheleveloftheexistingroadalong KratieTownwaterfront. There is not a long experience in Cambodia of design and implementation of river bank protection works based on morphological analysis or erosion risk management plans. Those attempts to stop locally bank erosion have been carried out at short river reaches near infrastructure(roadsandriverports).Failureoftheriverbankisduetophysicalfactorslikehigh currents,shipwaves,scouringandgeotechnicalinstabilityofthebanks,butalsoitcanbedueto poor design, construction and maintenance. In other cases the structures applied does not appeartofulfilsomefunctionalrequirementsandtheymightnotyetbeenexposedtothefull environmentaldesignloads.

Sambor Rapids

Sambok

Thmar Krae Kraom

Kratie

Peam Te

Figure9.2. LayoutofbankerosionandbankprotectionsitesonMekongKratieDistrict 10.4 Areasthatrequireattention

WiththiscomponentoftheFMMP,MRCwillprovideaframeworkforarangeofinvestigations into the technical, environmental and social issues to be faced in formulating demonstration projectsincludingerosionriskmanagementplansandriverbankprotectionmeasuresalongthe KratieDistrict. Furthermore it will increase knowledge of Line Agencies on river morphological changes, erosionriskareasanddesignofcostͲeffective(adaptivemethods)riverbankerosionmeasures. For the purpose of estimating river bank erosion in this subͲarea and designing river bank protection works as well as for the planning of future programmes of erosion risk reduction measures is necessary to be aware of the geomorphology and morphological changes of the river.

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Knowledge on the geology and morphology of the river also allows the identification of the majorandsecondarygeologicalcontrolsalongtheriver.Thesecontrolswillhavetobeanalyzed regarding their correlation with the alignment of the left bank of the river and future developmentsduetoriverbankerosionandsandbarformation. Thepotentialforusingsatelliteimagestomonitoranddocumentrecentandcontemporaryriver morphologyhasbeendemonstratedthroughrecentstudiesinothermajorrivers.Methodsfor predictingmorphologicalchangesoftheMekongRiveronashortͲterm(annual)basiscanalsobe developedusingdryseasonsatelliteimages. Furthermoreadditionalfieldinvestigationsshallbeplannedandcarriedoutandtheiroutputs integrated with the geoͲmorphological study. Additionally, the characterization of the river stretchesneedstobepreparedforpreparingthedesignofsustainableriverbankprotection worksforsiteͲspecificriverstretches. AlongthesubͲarea8C,riverBankProtection(RBP)demonstrationprojectsmainobjectiveisto preventtheerosionalongtheKratieDistricttownpreventingbankerosionthataffectsurban andsemiͲurbanareas,transportinfrastructurefromdamageduringfloodsthatwillalsolikely mayincreaseregionalflooding. 10.5 Objective

Themainobjectiveofthestrategicdirectionsistheformulationofanerosionriskmanagement plananderosioncontrolmeasuresinSubͲarea8Caimsatafuturecontroloftheerosionofthe left bank of this major river along Kratie District town. The strategy should be aimed at sustainablelongͲtermplanningofrivertraining(includingbankprotectionatprioritylocations) andthussafeguardvaluablelandandinfrastructure. Throughoutthedesignprocess,itisimportanttounderstandandevaluatethemanytypesand levelsofriskassociatedwithabankprotectionproject.Ariskassessmentshouldconsiderboth theriskofcontinuedbankerosionandtheriskassociatedwiththebankprotectionprojectwith respecttoproperty,habitat,andpublicsafety.Allbankprotectionprojectscontainsomelevel ofrisk Thestrategicdirectionswillalsoprovideforpreparingariverbankerosiondamageassessment considering damages to contents and structures. This means that the riverbank erosion vulnerabilityvaluescanbedeterminedandcombinedwiththetotalcostoftheelementsatrisk. Acriteriashallbedeterminedfortheriverbankerosionvulnerabilityassessmentanddamageto infrastructure, buildings etc. Finally, a damage map of the subͲarea 8C will be prepared. Proposedparameterscanbe: x Nodamage x Lowdamage x Moderatedamage x Highdamage Considering hazards alone may lead to a skewed set of priorities for action. It is equally importanttoconsidertheseverityofpossibleimpactsfromthehazardaswellasthefrequency orlikelihoodofahazardeventoccurring.Thecombinationofseverity/damageandlikelihoodis termedthelevelofrisk. AriskassessmentforriverbankerosionisnotpossibleatthisstageinsubͲarea8C,duetolackof informationonprobabilityforthistypeofevent.

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Accordingly, when designing river bank erosion protection measures it is agreed that those measuresshouldfitintoacoherentriskerosionmanagementplan. Theoverallobjectiveoftheprojectistoprovideaframeworkinwhichthetechnical,economic, social, environmental and other effects of various alternatives for river training works of the MekongriveralongsubͲarea8C,canbeassessedandevaluatedatdifferentlevelsofdetail.The projectwillmoreover,provideasystematicapproachoftherivertrainingworksinregardof theirvariousaspectsasdesigncriteria,construction,sequenceofimplementation,monitoring andmaintenance,andtheinstitutionalandorganizationalmanagementrequirementsrelated totheseaspects. The respective Line Agencies7 will be involved in hydrologic, hydraulic, hydraulic engineering studies, geotechnical, morphological and geoͲmorphological studies. It will also require mathematicalandphysicalmodellingstudiestosupportthepreparationofthedesignofriver training works and implementation plan. SocioͲeconomic and environmental effects of the proposedschemesaretobeincluded. 10.6 Maincomponentsofthejointproject:

Inordertostrategicallyaddresstheerosionproblem,prepareanerosionriskmanagementplan and formulate cost effective bank protection projects, in subͲareas 8C requires answering the followingquestions:Where,WhenandWhattoprotectandHow. x WHEREisrelatedtothreat/erosionriskinshortͲtimebycurrentsorwaves, x WHENisamatterofmorphologicalpredictionsofriverchannels,makinggooduseoflow riverstagesandtheurgencytostopthethreat, x WHAT,isamatterofeconomicsandstrategicconsiderations, x HOWtoprotectwhichisfirstatechnicalproblemtobesolved Oneofthemostdifficultbutimportantaspectsofthedesignprocessismovingfromthesite andreachassessmentstotheselectionofanappropriateandcostͲeffectivesolution. Inordertobridgeobjectiveswithselectionoftechniques,itisimportantthatdesigncriteriaare established.Thesecriteria,consideringriskandcost,andstratifiedaccordingtorelativepriority, outline the objectives of the project and provide the foundation for making design decisions aboutthespecificsizesandcomponentsofbankprotectionalternatives. The approach of study focuses on the engineering analysis of all reasonable options and strategies for protecting the river banks against erosion, with special emphasis on floods, erosion risk, and environmental, social and political considerations. The main components of thejointprojectcanbesummarizedasfollows:

7ProvincialDepartmentofWaterResourcesandMeteorology

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Startingpointsfordevelopingthestrategicdirectionscanbelistedasinthetextbox Startingpoints: x Basedonexistingknowledgeandexperience (Cambodiaandotherstudiescarriedoutwithin theframeofMRCorbilateralpartners)

x Additionaldataongeotechnical,socioͲ economicandenvironmentalconditionstobe collected, x Experiencefromelsewhere(i.e,Europe,China, USA)tobeused x TogetherwithMRCselectthemostsuitable mathematicalmodelstobeused.Similarly selectmostsuitableagenciesforcollectingand processingsatelliteimages. x ContinuousinteractionwithMRCandLine Agenciesandotherrelevantagencies x Extensiveuseofsatelliteimagesandaerial photographsfordevelopmentofriverbank erosionhazardmapsandriskassessment. x Ultimatelylearningbydoing,soaflexible planforimplementation 10.7 AdditionalInformation

Itisenvisagedtocollectsomeadditionalinformation(secondarydataandfromsurveys),forthe formulationofthisproject.Theinformationrequiredisasfollow: x Aerialphotographsof1992(availablewithLNMC) x Aerial photos of 2005 (new ones). It may be required to buy them from the relevant organizationinPhnomPenh. x CollectReportspreparedfortheSombakhydroͲproject(feasibilitystudy) x Collectexistingbestpracticeguidelinesforriverbankerosioncontrolworks x Informationongeologyofthearea(crossͲsections) x HydrographicAtlas(bathymetricmaps) x Collecting specific data on river bank protection and urban planning for Kratie in future (shortandmediumterm) x SocioͲeconomicassessmentforpreparingerosionriskmanagementplan 10.8 Activitiestoformulatebankerosionriskmanagementplansandmeasures

Asperthestrategicdirectionsitisintendedtoprepareerosionriskmanagementplansandriver bankerosionprojects.Therefore,theactivitiesproposedare: x Analysisofbanklinesandhistoricalmaps,aerialphotos, x Analysisofsatelliteimagesandfieldinvestigation, x Determinerecentplanformdevelopment, x Determineplanformcharacteristics, x Developmentofpastbankerosionratesanderosionprediction(shortͲtermandmedium termprediction), x Erosionhazardmap, x Channeldeclining,

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x ImpactofmigrationofbifurcationatKratie, x Impact of migration of the curved channel without rock controls, downstream and upstreamofKratieTown, x Bankstabilizationdesignconsiderations, x AnalysisofmostsuitableBankErosionprotectionworks(cost/effective),includingnewlow costprotectiontechniques. 10.9 Futuredirections

The future directions lie in continuing and expanding those components of the project and learningfromtheimplementationofinterventionswithproveneffectiveness,andinmonitoring prediction of erosion where evidence has demonstrated that the need is for river bank protectionisgreatest.Whatneedstobedoneineachoftheprioritylocationsforactioncanbe approachedinasystematicmannergoingthroughthemaincomponentsandactivitieslisted above. Government Line Agencies and concerned parties will continue to identify priorities for implementationoferosioncontrolmeasuresbasedonerosionriskthesocioͲeconomicbenefits andotherfactorsrelevanttospecificcontexts. One important future output of the project activities will be definition of hazard areas and preparationoferosionhazardmapsbymeansofmodellingresultsandbymeansofhistorical records(ratesofaverageerosionm/year),whichwillallowtodelineatehazardareasonand establishsetbackrequirements.Consequently,itwillbealsopossibletoprioritizerivererosion problems.Itshallbeasystematicprocessthatleadstorankingofriverstretchesbasedonthe significanceofbankerosionandaffectedinfrastructureandstructures. 10.10 Implementation

Thegreatestchallengetopromotethisstrategicdirectionsanddevelopmentofnationalerosion protectionplansinthefuturewillbetransformingknowledgeintoaction. As an example, in order to develop a costͲeffective plan and secure funds in time for demonstration projects in Kratie Province, it is urgently needed to review the morphological processesandthepresentandpotentiallyfutureplanformchangesintheMekongRiveralong theKratieDistrict.Thishastobeaccompaniedbyatechnicalestimateofpresentbankstability. The understanding of the aforementioned morphological processes will allow determining which areas need to be protected first and what type of measures to control the ongoing erosionarerequired. Within the range of potential areas for action, Cambodian Line Agencies and Provincial Authoritieswillidentifyprioritiesbearinginmindthenationalcontext,andtakingintoaccount interaliathecostofthemeasuresandimpactsonsocioͲeconomicdevelopment.Thisproject willprovideguidancetoNationalLineAgenciesandpartnerstoidentifyprioritiesanddevelop strategicoperationalresponses.

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CHAPTER11 APPENDICES

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11 APPENDIX:ENVIRONMENTALBASELINESFOCALAREAS

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11.1 EnvironmentalbaselineNamMaeKokFocalArea

1 GeneralCharacteristics TheNamMaeKokBasincoversanareaof10,730km2,3,336km2or31%ofwhicharelocated inMyanmar.ThefirstmayortributaryinThailand,theNamMaeFang,drainsanareaof1,732 km2,whereasdownstreamofChiangRaitheNamMaeLao,withadrainageareaof2,932km2 joinsthemainriver.Thelengthoftheriverfromsourcetomouthis360km.ItcrossestheThai borderafter160km.TheriveremptiesintotheMekongatSopKok,justdownstreamofChiang Saen at an elevation of 355 masl. The Focal Area covers the Lower Nam Mae Kok Basin, downstreamofChiangRai. Thebasinismountainouswithelevationsupto2,000m,thevalleysoftheFang,theLaoandthe Kokriversdownstreamof ChiangRaiareflatandfloodprone. Upperslopesin thebasinare steepanddenselyforested,theflatter,lower,slopesareusedforintensiveagriculture. Six different soil types can be distinguished in the project area. Directly along the river Cambisolshavedevelopedinthenaturallevees.Thesesoilshaveagoodstructureandfavorable chemical properties. They have a high fertility, and are only moderately sensitive to yield decline. Further from the river, in the floodplain, Acrisols are found, acidic, strongly leached tropical soils with a low fertility which are prone to degradation. On the floodplain around Chiang Mai Luvisols and Gleysols are found. Luvisols are thetropical soil most used by small farmersbecauseoftheireaseofcultivation.Nutrientsareconcentratedinthetopsoilandthey havelowlevelsoforganicmatter.TheGleysolsareencounteredinwaterloggedareaswithpoor drainage.Theymaysupportricecultivation,butarenotsuitableforothercrops.Onthehilland mountainslopesthesocalledSlopeComplexisencounteredwithsmallspotsofLixisols. Thenaturalregimeoftheriversintheprojectareahasbeenmodifiedbyirrigationwateruse andwaterstorageforhydropowerproduction.AccordingtotheBasinDevelopmentPan(2006) about150,000halandwasirrigatedinthewetseasonandsome15,000hainthedryseasonin 1998 in the basins of the Nam Mae Kok and adjacent Nam Mae Ing together. Chiang Rai is locatedattheconfluenceoftheNamMaeKokandNamMaeLao.Thecityisfloodpronewhen theriversconveylargedischarges.Thelastmayorfloodof2006camefromtheNamMaeLao andasmallcreeknamedNamMaeKorn. Thewaterqualityand,consequentlytheaquaticecosysteminthelowerbasin,isunderpressure fortworeasons.Firstlyreducedstreamflowinthedryseason,causedbytheincreaseduseof waterforirrigatedagricultureanddomestic/industrialuse,reducesthedilutionofwastewater dischargedintotheriver.Secondly,pollutionloadsareincreasing,duetopopulationgrowth, changedlifestyles,intensifiedtourism,andintensifiedagriculturalandindustrialproduction. In2000therewerenoseweragesystemsandtreatmentplantsoperationalintheprojectarea. SewagestabilizationpondswereunderconstructionfortreatmentofthewastewaterofChiang RaiTown.Thesewillbeoperationalbynow.Industriesaremostlyprocessingplantsforfruits andvegetables,ornoodlefactories.Theyproducemainlyorganicsewage.Mostindustriesare locatedaroundChiangRai,andintheFangandUpperLaosubͲbasins. AccordingtotheRiverBasinstudyof2000,theassimilativecapacitiesoftheriversintermsof BOD,nutrientsorbacteriaarebigenoughtodealwiththepollutantinflowandkeepthewater qualityandthediversityoffishes,vegetation,planktonandinvertebratesatacceptablelevels. However,pressureonthesystemcertainlyhasincreasedinthelastdecadeandthesituation mayhavedeterioratedsince2000.

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AccordingtoarecentMRCreport(MRC,2007)thewaterqualityofboththeMekongatChiang SaenandtheNamMaeKokinChiangRaiisgoodtoverygood. Groundwaterisextractedfordomesticandindustrialsupplies.Handpumpwellsfordomestic suppliesinruralareashavebeenestablishedinmanyplaces.Groundwateryieldsaregenerally characterized as 'high', and no shortages have been reported. Groundwater quality is threatened by pollution with agrochemicals (pesticides and fertilizers) and the uncontrolled disposalofsolidwaste,whatmayresultincontaminationbyinfiltration. Thefollowinglandcovertypesarefoundinthearea:paddyfieldsonthefloodplainandonlow terracesalongtherivers;uplandcrops,cultivatedonmiddleandhighterracesandinthehilly areas;fruittrees,grownbothonlowandhighlands;wetlands:lowͲlyingareasthatareflooded partoftheyearoryearͲround;andforests,disturbedforestsandforestplantations.Seventy percentoftheareaoftheLowerKokBasinisinuseforagriculture.Nearlyhalfofthis,34%,is irrigated paddy. The rainfed areas produce one crop per year, while the irrigated areas can produce one or two crops per year. Typical crop intensities on irrigated lands are 110Ͳ130 percentonly.Thisisbecausemanyfarmersseekemploymentelsewhereinthedryseason. 2 Riverineandterrestrialhabitats For the Mekong River system and its tributaries a number of important habitats for conservationhavebeenidentified,theyare: - riverchannels; - smallislandsandriverinesandͲbars; - marshes,smallpoolsandseasonallyͲinundatedfloodplainwetlands; - seasonallyͲinundatedriparianforest;and - inundatedgrasslands. LittleinformationisavailableonthepresenceofthesehabitatsintheLowerandUpperNam MaeKok. 3 Fauna AccordingtotheKokRiverBasinstudyof2000,surveysindicatethepresenceof115fishspecies in the Basin, belonging to 22 families. One family of freshwater prawn was registered. They includeseveraleconomicspecies,likeforexamplebarb,catfish,andsnakeheadfish.Thereare alsoseveralexoticspecies,likeloachandcarp.SomespeciesmigratebetweentheMekongand the Kok River Basin, where they breed. Rare or endangered species were not reported. The standingstockisestimatedat20Ͳ25kg/ha,whichiswellbelowthenearly100kg/hafoundin productiveriversandreservoirselsewhereinThailand. IUCNinformationonredlistspecies,reportsthattheNamMaeKokisprobablyaspawningsite forthenearlyextinctGiantCatfish(Pangasianodongigas),oneoftheworld'slargestfreshwater fish,measuringuptothreemetersinlengthandweighinginexcessof300kilograms.TheThai DepartmentofFisheriescollaborateswithlocalfishermenintheNongBongKaiNonͲHunting Area(seeSectiononProtectedAreasbelow)inobtainingeggsandspermfromtheGiantCatfish in order to rear fry for release. The fish was bred in captivity for the first time in 2001. IndividualsartificiallyspawnedfromwildͲcaughtparentshavebeenreleasedintotheMekong since1985. ThetotalnumberofaquaticbirdspeciesdocumentedalongtheupperMekongstretchincludes about100species,comprisingrareandendangeredspecies.Nearly40percentoftheaquatic birdsdocumentedfromtheregionareannualmigrants,whereassome30%ofthespeciesis associatedwithwetlandecosystems.SpecificinformationfortheNamMaeKokbasinislimited.

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ThatinformationthatisavailablepertainstotheNongBongKhaiNonͲHuntingAreaandwillbe presentedinthesectiononprotectedareasandrareandendangeredspeciesbelow. 4 Protectedareasandrareandendangeredspecies According to ICEM, 2003 (Thailand National Report on Protected Areas and Development. ReviewofProtectedAreasandDevelopmentintheLowerMekongRiverRegion)noprotected areasarelocatedintheprojectarea. IntheInventoryofWetlandsofInternationalandNationalImportanceinThailandoftheOffice of Natural Resources and Environmental Policy and Planning (ONEPP) of the Thai Ministry of Natural Resources and Environment (2002), the Kok River is listed as a wetland of national importance in Thailand. The river is considered a valuable water resource both for transportationandtourism.Raftingispopularwithtouristsandtherearemanyresorts,hotels andrestaurantsalongthebanks.Gravelminingisasourceofincomeforlocalpeople. In the report 8 fish species are reported to be found in the river: Climbing perch (Anabas testudineus),Niletilapia(Oreochromisniloticus),TheeͲspotgourami(Trichogastertrichopterus), Stripedcroakinggourami(Trichopsisvittatus),Stripedsnakehead(Channastriata),Yellowmystus (Mystusnomunus)andWalkingcatfish(Chariasbatrachus). TheNongBongKaiNonͲHuntingAreaintheLowerKokBasin,closetotheconfluencewiththe Mekong River, was designated a Ramsar Site in 2001. ONEPP prepared the Nong Bong Kai StrategicWetlandManagementPlanin2004.Theinformationgivenbelowismainlytakenfrom thisdescriptionandfromtheWetlandsInternationalwebsite.Thefloraandfaunaencountered intheareaisprobablyrepresentativeforotherwetlandareasintheLowerNamMaeKokBasin. TheStrategicNongBongKaiWetlandManagementPlancovers100km2,thisareausedtobe an intermittent floodplain surrounded by low mountains and hills. Villagers constructed an earthen dam on the Lua River to store water for agricultural uses and a 40 ha big lake was created:ChiangSaenLakelocallycalledNongBongKaiLake.NongBongKaiNonͲHuntingArea wasformallydeclaredonthe4thofApril1985. NongBongKaiisanaturaldepressionsurroundedbylowhills,360Ͳ500mhigh.Eightypercent oftheareaisflattoundulating,360Ͳ380mhigh,andhasslopesnotover2percent.TheLakeis 0Ͳ4.5metersdeepwithanaveragedepthof2meters.Maximumwaterstorageis4.9million m3.Thewaterlevellowerswith1Ͳ1.5mduringthedryseason.ThelakedrainstotheLuaRiver asmalltributaryoftheLowerNamMaeKok.Figurebelowshowsthelocationoftheareainthe LowerKokBasin. Flora Mostofplantspeciesthatarefoundintheopenwaterareaarefloatingplants,Waterhyacinth (Eichhornia crassipes) and Water fern (Azolla pinnata). These often clot together to form floating mats. Another typical aquatic plant is Cogon grass (Imperata cylindrica). In the submergedzonethereareonlyafewspecies:Commonhornwort(Ceratophyllumdemersum), Hydrilla(Hydrillaverticillata),Duckweed(Lemnaperpusilla),andBlyxajaponica(Blyxajaponica). Plants in the emergent zone include Water primrose (Jussiaea repens), and Lotus (Nelumbo nucifera). On the shores 3 zones are distinguished, a herb subͲzone, where species such as Giant reed (Arundodonax),Commonreed(Phragmiteskarka),Cogongrass(Imperatacylindrica),Swamp Millet (Isachne globosa), and Lindernia anagallis (Lindernia anagallis), a shrub subͲzone with speciesliketheGiantmimosa(Mimosapigra),Pagodaflower(Clerodendrumbuchanani),and Bitterbush(Chromolaenaodorata)occurandathirdsubͲzoneconsistingofBamboo(Bambusa sp.),shrubandtrees.

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LocationoftheNongBongKaisiteintheLowerKokBasin Fish Atleast46speciesoffishfrom17families,with17specieshavingeconomicvalue,arefoundin thewetland.ThemostabundantspeciesistheBandedshark.Thereare9exoticspeciesthathave been introduced including the Hybrid walking catfish, Indian barb, Mekong giant catfish (Pangasianodon gigas), Iridescent catfish (Mystus reghna), and Giant snakehead (Channa micropeltes). Five threatened species are important for conservation: BigͲhead walking catfish (Clarias macrocephalus), Walking catfish (Charias batrachus), Siamese fighting fish (Betta splendens),Barb,andBadis(Badisbadis). Thereare15speciesthatmigrateintherainyseasonbetweenNongBongKai,LauRiverand Nam Mae Kok River, for example the Banded shark, Black striped barb and Tawes from the KhongRiverandThaiminnowandWalkingcatfishfromtheLuaRiver. Mammalsandbirds Wildlife habitats in Nong Bong Kai and nearby areas have been mostly destroyed. This has causedadecreaseinthenumberofwildlifespeciesandnowonlysmallanimalsthatcanadapt tothechangedhabitatsremain.However,waterresourcesinNongBongKaiLakeandadjacent wetlandsareanappropriatehabitatformigratorybirdsarrivingheretoavoidcoldanddrought insouthernChinaandSiberia.FromNovembertoFebruaryeveryyear,largenumbersofwater birdsstayandbreedinthecatchmentareaandoftenfindfoodinthepaddyfields. From literature reviews and a bird surveys at Nong Bong Kai Lake and adjacent areas it was foundthatthereareatleast225birdspecies.Thesedivideinto79migratoryspeciessuchas

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Garganey(Anasquerquedula),23residentbreederspeciessuchasChinesefranolin(Francolinus pintadeanus) and 23 migratory/resident breeder species such as the Common Moorhen (Gallinulachloropus). The status of 219 of these species (97%) is protected and 19 species are threatened. Five speciesarerecognizedtobeofinternationalimportance:Whiteeyedpouchard(Aythyanyroca), Baers pochard (Aythya baeri), Grey headed lapwing (Vanellus cinereus), Schrencks bittern (Ixobrychuseurhythmus)ͲandPaintedstork(Mycterialeucocephala). BirdLife International, on their website, considers the Nong Bong Kai lake an Important Bird Area(IBA),onthebasisoftheoccurrenceofBaerspochard(Aythyabaeri),Spottedredshank (TringaErythropus)andSmallpratincole(GlareolaLactea). 5 Fisheries Intermsofoccupation,fisheriesplaysaminorroleonly.IntheKokBasin,only0.8percentof thehouseholdsindicatefisheriesastheirmainsourceofincome.However,itisbelievedthat thisfiguresunderestimatesthesignificanceofthefisheries.Fromaneconomicpointofview, manypeopleengageinfishingasasideoccupation,whereasexperiencefromelsewhereinthe Mekong Basin indicates that fisheries for own consumption contributes a large part of the proteintothediet. Althoughfishingismainlypracticedforownconsumption,thereissomecommercialcapture fishery,whichistypicallydoneasasideoccupation.Fishinggearsaresimple,likecastnets,pole andline,and,inthewetseason,bambootraps.Someillegalmethodshavebeenreported,like electrofishing,poison,andnetswithsmallmeshsizes.Atypicalcommercialcatchis2Ͳ6kg/day inthedryseasonand10Ͳ15kg/dayinthewetseason. Inadditiontothecapturefisheries,therearewidespreadsmallͲscalehatcheriesandfishponds, forexampleinconnectionwithintegratedfarming. 6 Tourism The provinces of Chiang Mai and Chiang Rai offer a large variety of tourist attractions. They coverbothculturalsites,adventures(boatingandtrekking),naturalattractions,shopping,and museums.Therearenumeroustemples,landscapesandnaturalattractions,aswellasactivities likeculturalshowsandfestivals.Thereisalargeandsteadilygrowingnumberofvisitorstothe provincesandtourismcontributesconsiderablytotheeconomy,bothintermsofnationaland foreigncurrency.Already,touristsincludeasmallproportionofbirdͲwatchers.

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References BirdLifeInternational(www.birdlifeindochina.org). ICEM,2003,ThailandNationalReportonProtectedAreasandDevelopment.Reviewof ProtectedAreasandDevelopmentintheLowerMekongRiverRegion. Kok River BasinͲPilot Study for Water Resources and Environment Management (Basinwide),7.1.25/97/UKM,FinalReport,October2000. MRC,2006,BasinDevelopmentPlanforSubͲArea2T. MRC, 2007, Diagnostic study of water quality in the Lower Mekong Basin. MRC TechnicalPaperNo.15). Office of Environmental Policy and Planning, Thailand and the Mekong River Commission,2000. OfficeofNaturalResourcesandEnvironmentalPolicyandPlanning(ONEPP)oftheThai Ministry of Natural Resources and Environment, 2002, Inventory of Wetlands of InternationalandNationalImportanceinThailand. OfficeofNaturalResourcesandEnvironmentalPolicyandPlanning,2004,NongBong KaiStrategicWetlandManagementPlan. Ogink,H.,FloodhazardmappingfortheNamMaeKok,June2008,FMMPͲ2report. Mekong Wetlands Biodiversity Conservation and Sustainable Use Programme (www.mekongwetlands.org). WetlandsInternational(www.wetlands.org). WorldWideFundforNature(WWF)(www.panda.org).

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11.2 EnvironmentalbaselineBokeoFocalArea

1 Generalcharacteristics The Mekong River channel upstream of the Bokeo Focal Area is characterized by a series of massiverockyoutcrops,bothabovewaterandsubmerged,formingrapids.Waterflowsinthis stretcharefastandturbulent.Manyrapidshaveassociateddeeppoolsandsandbanks.The widthoftheriverchannelvariesbetweenlessthan50mtoover150m.Becauseoftherocky substrateofthissection,bankerosionisnotconsideredmuchofaproblem,exceptinthewider areas, such as at Ban Don Moon. Here the banks consist of deposited sand, on which the villagerscultivatecropssuchassoybeansandgroundnuts. FromtheGoldenTriangletoBanNamKeungMai,theprojectarea,theriveriswider,upto500 minplaces.Theriverisslowermoving,withwidemeanders.Rockyareasandrapidsareabsent andthewaterflowinthisareaisnotturbulent.Theriverbanksconsistofsteep,erodedmud/silt (4Ͳ10mhigh)interspersedwithextensivewidesandandpebblebeaches.Islandsarepresent inafewsections.Theriverhasbeenheavilymodifiedthroughembankmentsalongasignificant portionofthisstretchofriverwhichisheavilyurbanized,especiallyontheThailandside.The floodplainiswideandtheadjacentcountrysideisrelativelyflat.Naturalforestisalmostabsent andhasbeenreplacedbycultivationonbothbanks.Anarrowstripofreedsisoftenpresenton bothsidesoftheriver.ThereisanextensiveareaofreedsatthejunctionbetweentheNam MaeKokriverandtheMekongontheThailandsidebelowChiangSaen.Manytributariesand streamsflowintotheMekongRiverinthisarea,includingtheNamRuak,NamKam,NamKok, andNamYon. DownstreamoftheprojectareatheMekongflowsagainthroughanarrowchannelandover theKhonPiLuangrapidsjustupstreamofBanHouayXay.Thissystemofrapidsconsistsofrock outcrops (not as massive as further upstream), mudflats and sand bars created by sedimentation,lowlyingislands(oftenwithshrubsfloodedduringhighflows)andlongdeep poolsandwhirlpools.Thedeeppoolsmaybeseveralhundredmeterslongandvaryindepthup to100m,butaremoreusually,30Ͳ60mdeep. ThesurroundingareaconsistsofsteephillsandforestcoverispresentinpatchesontheLao side.TheThailandsideoftheriverislargelyclearedandcultivated.Therearefewvillagesinthis stretch. ThebanksoftheMekongRiverintheBokeoProvincecompriseofresidualsoilofweathered rocks(mainlyshaleandsandstone)andoldandrecentalluvialdeposits,rangingintexturefrom clayeysiltandsiltyclay,tosiltyfinesandofbothrecentandoldleveedeposits,togravel. Waterqualityinthevicinityoftheprojectareaisreportedtobegoodtoverygood,butmay deteriorate in future (MRC, 2007). Two hydropower stations have been built on the on the mainstreamintheUpperMekongBasin(ManwanandDachaoshan)andsixmorehydropower stationsareplannedfordevelopmentinthenext20years.AlthoughChinesesourcesclaimthat thesedamswillhavenoimpactonwaterqualityintheLowerMekongBasin,thereisthedanger ofreleaseofanoxicbottomwatersfromthereservoirs.Also,a2.7oCreductionintemperature ofwaterisanticipatedattheXiaowandamsite. Industrial pollution is another threat to the water quality in the project area. In 2000, the provincial government of Yunnan Province in China (located immediately upstream of the China/Lao PDR border) inspected 1042 industrial enterprises. This resulted in the forced closures of four plants. Rapid development of the Lancang basin in China and increasing pollutioninChineseriversraiseconcernsaboutadeteriorationqualityofthewaterarrivingin theLowerMekongbasinfromChinainthefuture.

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Rapiddemographicgrowth,socioeconomicdevelopmentandurbanizationalsoaffectthewater quality. According to Meynell (2003) the water of the Mekong water downstream of Chiang Saen,waslesscleanandclearthanintheupstreamreaches,duetourbanpollution,rivertraffic andportconstruction.Dissolvedoxygenandorganiccontentoftheriverwaterwasreportedto be above the water quality standard, ammonia, oil and total coliͲform bacteria counts were belowstandard. ThelivelihoodsofthepeoplewholiveontheMekongriverbanksinthevicinityoftheproject area(bothonLaoandThaisides)aremixedbetweenlandͲbasedandriverͲbased.Theyfarmrice intheuplandarea,fishinsmallstreamsandtheMekongRiverandgrowvegetablesingardens onsandbarsandriverbankswhenthewaterlevelislowinwinterandsummer.Localpeople collectMekongseaweed(Kai),whichgrowsonpebblesinfastͲflowingshallowwatersfortheir income and food. Although Kai products are sometimes marketed, collecting is usually for householdconsumption. In some areas, villagers pan gold, digging up sand and gravel with favorable appearance, panningittoisolategoldparticles,andextractingthegoldwithmercury.Villagershavesmall quantitiesofmercuryforthispurpose. 2 Ecologicalresources Riverineandterrestrialhabitats For the Mekong River system a number of important habitats for conservation have been identified,theyare: - riverchannels; - smallislandsandriverinesandͲbars; - marshes,smallpoolsandseasonallyͲinundatedfloodplainwetlands; - seasonallyͲinundatedriparianforest;and - inundatedgrasslands. Theriverchannelintheprojectareaisvitallyimportantfortheseasonallongitudinalmigration offishspecies.TheMekongRiverhostsoneoftherichestfreshwaterfishfaunasintheworld. Morethan1,000specieshavebeenformallydescribedandthisdiversitysupportsthelargest inlandfisheryintheworld,notonlyintermsoftonnagebutalsointermsofthenumberof peopleinvolved. Two of the main factors that explain the high diversity and productivity of the Mekong fish faunaaretheextremehabitatdiversityoftheriverecosystemandthestateofhealthofthe river.Notonlyishabitatdiversityhigh,buttheecosystemfunctioningandconnectivitybetween habitatsislargelyintact.Fishesarestillabletoexploitdifferenthabitatsaccordingtonatural seasonal changes and can, for instance, migrate between upstream spawning habitats and downstreamrearinghabitats,andbetweenriverrefugesandfloodplainfeedinghabitats. Keyfishhabitatsarefeedinghabitats,spawninghabitatsandrefugehabitats.Mostfishesofthe Mekongfeedintheproductiveseasonallyinundatedfloodplains.Attheendofthefloodseason, whenthesehabitatsdryout,fishesmovetorefugehabitatswithinriverchannelswherethey waitforthenextfloodcycle.Mostfishspawnattheonsetoffloodseason.Themainhabitats usedforspawningarerapidsanddeeppoolsinriverchannelsaswellascertainfloodplains. Most migratory fishes, which account for a significant proportion of the fish catch of the Mekong, spawn within river channels at rapids/pools upstream from feeding and rearing habitats.

StrategicDirectionsFloodRiskManagementͲ99Ͳ December2009 MRCFloodManagementandMitigationProgrammeComponent2:StrucuralMeasuresandFloodProofing

AlargeproportionofMekongfishspeciesismigratory.Manyspeciesmovefromonehabitatto anothertocompletetheirlifecycle.Forinstance,severalimportantspeciesmigrateupstream tobreedatthebeginningoftherainyseason.Then,asthewaterrises,theyoungfishareswept downstreamtofloodedareas. TheMekongRiveranditstributaries,liketheNamMaeKok,arealsoanimportanthabitatfora distinctiveguildofriverinebirdspecies.SmallislandsandriverinesandͲbarsformahabitatfor pioneerplantcommunitiesandbreedingsitesforwaterbirds.Seasonalwetlandsinundateinthe wet season when water levels of the Mekong are high. Wetlands provide some of the most productivehabitatsintheBasinandincludereedandsedgebeds,swamps,andlotusponds. Another important habitat is the seasonallyͲinundated riparian forest found on the gentlyͲ sloping plains adjacent to the river. Fish use this habitat as a feeding, breeding, and nursery groundanditisimportantforbreedingcoloniesoflargewaterbirds. IntheriverchannelupstreamofheFocalAreadeepwaterpoolsareencountered.Thishabitat isimportanttomanyfishspecies,particularlyaslowwaterrefugeareaandasspawningground. Thehighlevelofwaterturbulenceinhisstretchprovidesgoodoxygenationofwaterattimesof lowflows. IntheFocalAreatheriverbroadensoutandtheflowratereduces.Rockyareasandrapidsare absent and the riverbank is predominantly steep. These steep river banks provide a nesting habitatforavarietybirds,seeTablebelowExtensivewidemud,sandandpebblebeachesand islandsarepresent,forminganexcellentfeeding,restingandnestinghabitatforwadingbirds andducks.Thefloodplainisfairlywideandtheadjacentcountrysideisrelativelyflat.Natural forestisalmostabsentandhasbeenreplacedbyshruboragriculturalareasonbothbanks.A narrowstripofreedsisoftenpresentonbothsidesoftheriver.Thereisanextensiveareaof reedsatthejunctionbetweentheMaeNamKokriverandtheMekongontheThailandside below Chiang Saen. The reed mashes are an important nesting habitat for birds and small mammals. DownstreamoftheFocalArea,therivernarrowsdownagaintoincludefrequentrapids.Sand andsiltbeachesarelessfrequentandmidͲstreamrocksareevident.Theriverbankisbordered bysteeplyrisinghills.ForestcoverispresentinpatchesontheLaoside,theThailandsideofthe riverislargelyclearedandcultivated. ThevarietyofaquaticandterrestrialhabitatsintheupperMekonghascontributedtoahigh levelofbiodiversity.EcosystemsandhabitatsinthevicinityoftheFocalAreathatareimportant fortheconservationofthishighbiodiversityarerapids,deeppools,longpoolsandwhirlpools, sandbars(withandwithoutpebbles)andislands,wetlandsandseasonallyfloodedshrubareas onthefloodplainandtheriparianforest.Thesehabitatsareveryimportantasasourceoffish foodandasspawninggroundforfishes. Wildlifeandrareandendangeredspecies ThetotalnumberofaquaticbirdspeciesdocumentedalongtheupperMekongstretchincludes about100species,comprisingrareandnationallyendangeredspecies.Nearly40percentofthe aquatic birds documented from this region are annual migrants, whereas some 30% of the species is associated with wetland ecosystems. Lazarus et al. (2006), identified in total 29 species that are dependent on either the riverbanks, the sandbars, the mudflats of a combinationofthesehabitats.TheyarelistedinTable .

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For 17 bird species observed during the survey, the riverbanks are an important habitat. Of these 17 species 4 were only rarely observed. Of the observed mammals, the Fishing Cat (Prionailurusviverrinus)isdependentontheriverbanks. The herpetofauna include 15 species of amphibians and 19 species of reptiles, including six globally threatened freshwater turtles. There are several globally significant sites for biodiversity conservation. Segments of the upper Mekong form part of the IndoͲChina BiodiversityHotspot. Althoughfishdiversityisgenerallyconsideredtobelowerinupperreachesofriverscompared tothelowerreaches,anIUCNinventory(Meynell(2003)andDubeau(2004))confirmedthata large number of fish species inhabit the upper Mekong. During interviews, sampling of fish catchesandobservationsonmarkets86fishspecieswereidentified. Habitatdependenceandrelativeabundanceofbirdsobservedduringthe2005IUCN survey(Lazarusetal.,2006) Family Common&ScientificName Habitat*) Abundance* *) R SB MF C UC R B Anatidae RuddyShelduckTadornaferrugineaX X X SpotͲbilledDuckAnaspoecilorhynchaX X X Scolopacidae CommonSandpiperActitishypoleucosX X X Burhinidae GreatThickͲkneeEsacusrecurvirostrisX X X Charadriidae LittleͲringedPloverCharadriusdubius X X X X LongͲbilledPloverCharadriusplacidusX X X KentishPloverCharadriusalexandrianus X XX RiverLapwingVanellusduvaucelii X X XX GreyͲheadedLapwingVanelluscinereus X X XX RedͲwattledLapwingVanellusindicus X X XX TemmincksStintCalidristemminckiiX XX Glareolidae SmallPratincoleGlareolalactea X X X X Ardeidae LittleEgretEgrettagarzetta X X X X IntermediateEgretMesophoyx X X XX intermedia GreatEgretCasmerodiusalbusX X X ChinesePondHeronArdeolabacchus X X X X GreyHeronArdeacinereaX XX LittleHeronButoridesstriatus X X Alcedinidae CommonKingfisherAlcedoatthis X X BlythsKingfisherAlcedohercules X X Halcyonidae WhiteͲthroatedKingfisherHalcyon X X Smyrnensis Motacillidae WhiteWagtailMotacillaalba X X X X GreyWagtailMotacillacinerea X X X PaddyfieldPipitAnthusrufulusXX Hirundinidae BarnSwallowHirundorusticaXX RedͲrumpedSwallowHirundodauricaXX WireͲtailedSwallowHirundosmithii X X PlainMartinRipariapaludicola X XX Apodidae AsianPalmSwiftCypsiurusbalasiensis X X Total 1 21 20 1 10 9 7 0

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*)RB=Riverbank,SB=Sandbar,MF=Mudflat **) C = Common, UC = Uncommon, R = Rare. Note: Relative abundance is given, as observedduringalimitedfieldsurveyofIUCNin2005reportedbyLazarusetal.(2006) However,itwasalsonotedthatmanyofthespecies,particularlythelargespeciessuchasthe MekongGiantCatfish(Pangasianodongigas)andPangasiussanitwongsei,haveexperienced quitedrasticdeclinesinrecentyears. Aquaticvertebratessuchasfish,amphibians,reptilesandwaterfowlareimportantindicators oftheoverallecologicalintegrityoftheMekongregion.Whilefreshwaterfishformamajor sourceofproteinforlocalcommunities,otheraquaticvertebratessuchasamphibians,reptiles andwaterfowlprovidesupplementaryfoodresourcesforlocalcommunities.Theinsectivorous and carnivorous vertebrate species (e.g., amphibians and reptiles) function as important biologicalcontrolagentsofagriculturalpestssuchasinsectsandrodentpests,especially in paddycultivation.Thespeciesrichnessandabundanceofavifaunaalongtherivercouldplaya keyroleinpromotingecoͲtourismintheregion. 2.3 Protectedareas AccordingtoICEM(2003)noprotectedorproposedprotectedareasarelocatedintheproject area. BirdlifeInternationalidentifiedtheMekongRiverinnorthernLaoPDR,asanimportantbird area(IBA).Itcomprisesa377kmsectionoftheMekongchannel,fromBanXiangkhokonthe LaoͲMyanmar border to Ban Bo on the boundary between the Oudomxai and Xaignabouli Provinces.Theprojectareafallswithinthisreach. Thesectionsupportsthreebasichabitattypes:stretcheswithawelldefinedchannelbutno, or negligible, exposed bed; stretches with many sandbars and stretches of channel mosaic habitat, comprising sand and gravel bars and islands, rock outcrops, bushland and braided streams. The stretches of channel mosaic habitat support a relatively rich riverine bird community, including River Lapwing Vanellus duvaucelii and Jerdon's Bushchat Saxicola jerdoni.ThestretcheswithmanysandbarsareimportantforSmallPratincoleGlareolalactea; theIBAsupports5%oftheestimatedworldpopulationofthisspecies.TheIBAalsosupports large numbers of Plain Martin Riparia paludicola and significant numbers of GreyͲheaded Lapwing V cinereus, and is the site of the only recent Lao records of Great Cormorant Phalacrocoraxcarbo.Finally,therearesinglerecordsofbothSwanGooseAnsercygnoidesand BlackͲbellied Tern Sterna acuticauda from the IBA, although it is unlikely that it regularly supportssignificantnumbersofeitherspecies. Key bird species for the IBA status are the River Lapwing Vanellus duvaucelii and Small Pratincole Glareola lacteal. The area holds on a regular base more than 1% of the Asean biographicalpopulationofthesespecies.TheRiverLapwingpopulationattheIBAisofhigh national(Lao)significancebutmoderatetolowglobalsignificance.TheIBApopulationofSmall Pratincoleisofmoderatenationalandglobalsignificance. MostoftheIBAiseasilyaccessiblefromalongthebanksoftheMekongRiver,andlevelsof humanactivityarehigh.MajorthreatstobiodiversityattheIBAareactivepersecution,inthe form of hunting and egg collection, and incidental disturbance, including boat traffic and accidentalnestdestruction. ClosetotheprojectareainthelowerNamMaeKokBasin,anotherprotectedareaislocated, the Nong Bong Khai, or Chiang Saen lake which is a Ramsar site (Wetlands International

StrategicDirectionsFloodRiskManagementͲ102Ͳ December2009 MRCFloodManagementandMitigationProgrammeComponent2:StrucuralMeasuresandFloodProofing website).Itisapermanentfreshwaterlakewithanareaof2km2atthecentreoftheChiang SaenBasin,knownforitsextraordinarybirdlifeanddiversityoffreshwaterfish. The Chiang Saen Basin is located on a plateau surrounded by low hills at the border of northernThailand'sChiangRaiprovince.Thenortheastofthebasin,whichisalmost18km wideand10kmlong,opensoutontotheMekongRivertowhichthebasinultimatelydrains. Atthesouthofthebasinisapermanentswampwhiletothenorthliesthelake. Thesiteisanimportantareaforlocalandmigratorybirds,particularlywaterbirds,including globally vulnerable species of duck.A total of 225 species of bird have been recorded at Chiang Saen Lake. In addition to the birdlife, some 21 fish species have found in the area, manyofwhichareattractedbytherichaquaticplantlifewhichincludesatleast24speciesof aquaticplants. 3 Fisheries Fisheries is practiced mainly for subsistence rather than for income. Deep pools, whirlpools and sand bars are the most important fishing grounds. The 2005 IUCN (Lazarus, 2006) assessmentmadeclearthatmorethan106fishspeciescontributetothefoodsecurityoflocal peopleintheregion.Thisincludesbothsmallandlargespecies,suchasgroupsofcyprinids (Morulius chrysophekadion, Puntioplites protozyscron, Cosmocheilus harmandi and Henicorhynchusspp.),Bagrids(MystusnemurusandMystuswyckoides),Silurids(Hemisilurius erythrospila),andPangasids(Pangasiusbocourti).Fishingactivitiesinruralcommunitiesrely onmigratoryfishspeciesandutiliseseasonallyͲspecifictypesoftraditionalfishinggear.The fishinggearusedintheareaduringthewetseasonisdominatedbybambootraps(60%),gill nets(20%),longlines(15)andbagnets(5%).Driftinggillnetsandcastnetsaremorecommonly usedduringthedryseason.Theuseofthedifferenttypesofgearalsodependsonhabitats. Thesurveymadealsoclearthatfishingisawayoflifeforthecommunitieslivingalongthe MekongRiver.Wheretherearepeople,thereisfishing. 4 Tourism The ancient town of Chiang Saen was originally called Wiang Hiran Nakhon Ngoen Yang. It servedasthecapitaloftheLannaThaiKingdomuntilKingMengraiestablishedChiangRaias thecapitalin1262.Ruinsoftheolddoublecitywallsandmanyotherantiquitiesremainboth insideandoutsidethetown.MostnotableisthedistinctivestyleofBuddhistsculpturewhich evolved in Chiang Saen during the late thirteenth century providing proof of the city's historical importance. Rich cultural heritage, coupled with natural tourist attractions, has madeChiangSaenauniquetouristdestination.Tourismisrapidlyexpandingintheareaand generallyattractstheyounger,lowerͲbudgetforeigntravellersaswellasagreatmanyThai nationals.Incomefromthissourceatpresentgoesdirectlyintothepocketsoflocalpeople sincetherearenooutside,largeͲscaletouristdevelopments.Already,suchtouristsincludea smallproportionofbirdͲwatchers.

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References Dubeau,P.,2004,FollowͲupSurveyforBiodiversityAssessmentoftheMekongRiverin NorthernLaoPDR,IUCNWaterandNatureInitiativeandMekongWetlandsBiodiversity ConservationandSustainableUseProgramme,Bangkok. ICEM,2003,LaoPDRNationalReportonProtectedAreasandDevelopment,Reviewof ProtectedAreasandDevelopmentintheLowerMekongRiverRegion. Lazarus,K.,P.Dubeau,C.Bambaradeniya,R.Friend,L.Sylavong,2006,AnUncertain Future: Biodiversity and Livelihoods along the Mekong River in Northern Lao PDR, IUCN,Bangkok,ThailandandGland,Switzerland.49pp. Meynell,P.J.,2003,ScopingStudyforBiodiversityAssessmentoftheMekongRiverin NorthernLaosandThailand,IUCNMekongWaterandNatureInitiativeandMekong WetlandsBiodiversityConservationandSustainableUseProgramme,Bangkok. MRC,2006,BasinDevelopmentPlan,SubͲArea1L. MRC, 2007, Diagnostic study of water quality in the Lower Mekong Basin. MRC TechnicalPaperNo.15,MekongRiverCommission,Vientiane.57pp. Wetlands International Website, Description of Nong Bong Khai NonͲHunting Area: ChiangSaenLake.

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11.3 EnvironmentalbaselineSeBangFaiFocalArea

1 Generalcharacteristics The Xe Bang Fai has a catchment area of about 10,240 km2. The river takes its rise in the Annamite mountain range near to the border with Viet Nam, west of Thakhek and joins the Mekongatkm1,166,oppositeofthecityofThatPhanominThailand.TheXeBangFaihasa numberoftributaries,thelargestofthese,theXeNoy,joinstheXeBangFaijustupstreamof theFocalArea.TheXeBangFaicatchmentdownstreamofthisjunctioniscalledtheXeBangFai Plain.Theplainisabout15kmwide,boundedbytheMekongRivertothewestandupland forest on an old alluvial terrace to the east. The length of the river in this stretch is approximately70km.Theareaisfairlydenselypopulatedwithsome60villagesandabout400 km2ofricepaddyfields.ItisamajorareaofriceproductionfortheKhammouaneProvince. The Xe Bang Fai plain is rather flat. Along the river narrow natural levees have developed, furtherfromtherivertheareaconsistsoflowlyingbasins,oldriverchannelswithoxbowlakes thathavesiltedup,separatedfromeachotherbyrelativelyhighlyingoldriverlevees.Mostof the flood plain has an elevation of less than 140 m amsl, and floods frequently. The natural levees along the river and in the floodplain have a somewhat higher elevation and are less frequentlyandlessdeeplyinundated. IntheperiodJulytillearlyOctoberhighdischargesoftheSeBangFaicoincidewithhighwater levels on the Mekong. When the water surface in the Xe Bang Fai exceeds a certain level, usuallylateintherainyseason,backwaterfromhighMekongRiverdischargescausestheflow in the river channel to be reversed and flooding takes place through the tributaries and by overtoppingoftheriverbanks.Floodingmaylastforseveralmonthsintheareasbelow140m amsl. Rice cropping and vegetables growing are the main agricultural activities in the project area.Agricultureistheareaslargestsectorofemployment,with92percentoftheinhabitants havingriceproductionaspartoftheirlivelihoodsystems.Vegetablesandothercropsaregrown byresidentsontheXeBangFairiverbanks,aswellasinthefloodplainsaroundnaturallakesas waterrecedes.Lowlandwetriceiscultivatedinthelowerlyingareas. Dryseasonriverbankvegetablecultivationisdonemainlybywomen,itisanimportantactivity whichprovidesfoodandincometolocalfamilies.Cropsgrownincludecorn,yam,watermelon, long bean, vegetables (cucumber, lettuce, garlic, and eggplants) and tobacco. Part of the produceissoldonlocalmarketsandtobaccoformsanimportantsourceofcashincome. Intheprojectarea,whereirrigationsystemsarefairlywelldeveloped,focusischangingfrom riverbankgardenstogardenswateredfromtheirrigationsystems,andthuslocatednexttoor inthevicinityofirrigatedpaddyfields. Ingeneral,pestattackonricecropsislowinLaoPDR.Consequently,alsothepesticideuseis low. Rice diseases are rarely treated with chemicals (e.g. fungicides), and weed control with herbicidesisalsoveryrare.Pesticideuseforvegetablegrowingisbelievedtobesignificant.The number of treatments applied is apparently not excessive, but every farmer treats his vegetableswithinsecticides. Inorganicfertilizersareusedpredominatelyonthedryseasonricecrop,butincreasinglyalsoin the wet season. Some inorganic compound fertilizers appear to be used on the basis of availabilityfromdonorsratherthanonneed.

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InthedryseasontheSeBangFaiisthemostimportantwatersourceforthevillagersinthe area,althoughforcookinganddrinkingothersources,mainlydeep(bore)andshallowwells,are alsoimportant.Inthewetseason,rainwaterandtheSeBangFaiareequallyimportantasa sourcefordomesticwater. ThewaterqualityofriverswithintheLaoPDRisconsideredtobegood.Thelevelofoxygenis highandthenutrientconcentrationislow.Duetorapiddemographicgrowth,socioeconomic developmentandurbanization,however,waterqualityisdeteriorating.Itiscommonpracticeto disposelitterandsewagetowatercoursesanddrainagechannels.Asaresult,thesurfacewater is invariably contaminated with faecal matter from latrines and coliforms from septic tank effluents. ThereislittleinformationavailableongroundwaterqualityinLaoPDR,eventhoughitisthe mainsourceofruralwatersupply.ArseniccontaminationisnotconsideredahighriskinLao PDR. 2 Ecologicalresources 2.1 Aquatichabitatsandfish AsurveyforthewholeofLaoPDRyielded203fishspeciesin1974,thelisthadgrownto481 speciesby2001(Kottelat,2001).EvenwithKottelatssignificantcontributiontotheincreasein knowledgeoffishdistributioninLaoPDR,informationonfishdistribution,biologyandecology remainsbasic. ThemaindryseasonfishhabitattypesinthelowerXeBangFairiverandfloodplainarepools andslowwaterstretchesintheriverandswampsandstagnantpoolsonthefloodplain.The river bed is characterised by a muddy to sandy bottom, with occasional rocky outcrops and rapids.Thewateristurbid,althoughcomparedtomostotherlowlandstreamsintheMekong basinitisstillclear,withavisibilityofabout50cm.Thedepthisvariable,fromseveralmetres toafewcentimetresonsomesandbars. Duringthewetseason,mostofthesehabitatschangecompletelyandsomearedisplacedto otherareas.Inthisperiodfishpopulationsfrequentlyusehabitatsthatarenotavailableduring thedryseasonforspawning,incubationofeggs,andrearingoffry.InthelowerXeBangFai basin,floodedareasareimportantasnurserygroundsandrefugesforjuvenilefish. OnehundredandthirtyͲonefishspecieshavebeenobservedintheXeBangFai,sixtyͲseven(67) oftheseinthelowerXeBangFai.Noendemicspecieswererecorderinthelatterstretch.The fish fauna of the lower and middle Xe Bang Fai fauna can clearly be described as a middle Mekongfauna.AccordingtoKottelat(2001),thestandingstockrangesbetween6and23kgper hectare. This is considerably less than what can be expected considering the high nutrient concentrations. This could be the result of fishing activities by local fishermen and because samplesweretakenduringthedryseasonwhenfewfishfromtheMekongwereintheriverto spawn. Abundance was lowest at Dan Pakse at the confluence with the Mekong. Monthly variations in abundance along the river channel reflect seasonal migratory behaviour of fish. Most of the catch consists of medium size cyprinids (Puntioplites spp, Hypsibarbus spp, Barbodes spp, Labeo chrysophekadion, Puntius orphoides). Catfishes (Pangasius siamensis, Clarias batrachus, Mystus wyckioides, Hemibagrus nemurus) and snakehead (Channa striata) arelessimportant. ThreegeographicallyͲdefinedfishmigrationsystemsexistintheMekongBasin:lower,middle and upper Mekong migration systems, the Xe Bang Fai basin fall within the middle Mekong migration system. Within this river section floodplain spawning and nursery habitats are

StrategicDirectionsFloodRiskManagementͲ106Ͳ December2009 MRCFloodManagementandMitigationProgrammeComponent2:StrucuralMeasuresandFloodProofing associatedwiththetributaries.Adultsandjuvenilesspendthedryseasonindeeprefugepools inthemainstreamchannel.Attheonsetofthewetseason,theymigrateupstreamalongthe Mekong until they encounter a tributary, and then swim up the tributary until they reach a floodplainoranotherpossiblysuitablespawninghabitat.Manyspeciesspawnonlyonce,soon afterarrivingonthefloodplain,whileothersspawnseveraltimesduringthefloodseason,anda fewothersspawnonlyonceattheendofthewetseasonorbeginningofthedryseason.Thefry growoutonthefloodplainwhichactsasanurseryandcontainsrichforage.Asthefloodwater beginstorecedefromthefloodplain,adultsandjuvenilesmigratebackinthetributariesand move downstream to the Mekong. There are over thirty medium and large size species of cyprinidandpangasiidcatfishwhichexhibitthisgeneralmigrationpattern.Thefirstmajorfish migrationoftheyearcommencesatthebeginningofthewetseason.Atthattime,accordingto villagers, a large number of fish species begin migrating up the Xe Bang Fai, and its larger tributaries,whileotherfishspeciesarebelievedtomovefromdeepͲwaterpoolstospawning areasintheXeBangFai. These two migrating groups include the following taxa: Cyprinids (Labeo chrysophekadion, Labiobarbussp.,Sikukiagudgeri,Hypsibarbussp.,Puntioplitessp.),Catfish(Pangasiuslarnaudii, P. macronema, P. pleurotaenia, P. bocourti, Wallago attu, W. leeri, Bagarius sp, Hemibagrus wyckioides, H. nemurus, Helicophagus waadersi, Laides sp., Mystus spp.), Mud perch (Pristiolepis fasciata), Glassfish (Parambassis siamensis), River loach (Schistura sp. or Nemacheilussp.).Duringoverbankfloodingeventsfishmigratelaterallytotemporallyinhabit adjacentfloodplainsforspawningandfeeding. 2.2 Wetlandsandterrestrialhabitats FortheLowerMekongRiversystemanumberofImportanthabitatsforconservationcanbe distinguished,theyare: - riverchannels; - smallislandsandriverinesandͲbars; - marshes,smallpoolsandseasonallyͲinundatedfloodplainwetlands; - seasonallyͲinundatedriparianforest;and - inundatedgrasslands. Theriverchannelsarevitallyimportantfortheseasonallongitudinalmigrationoffishspecies. TheMekongRiveranditslowgradienttributaries,liketheSebangFai,arealsoanimportant habitatforadistinctiveguildofriverinebirdspecies. SmallislandsandriverinesandͲbarsareformedbynaturaldepositionduringseasonalhighriver flow.Theyformahabitatforpioneerplantcommunitiesandbreedingsitesforwaterbirds. Seasonal wetlands inundate in the wet season when water levels of the Mekong are high. Groundwater and seasonal monsoonal rains maintain other wetlands yearͲround. Wetlands providesomeofthemostproductivehabitatsintheLowerMekongBasinandincludereedand sedge beds, swamps, lotus ponds, and inundated forest. They are usually shallow, filled by seasonalrainfallandtypicallyareconnectedtotheriversystemwhichinthewetseasonform the inundated plain of the Lower Mekong Basin. Submerged communities are dominated by Ceratophyllum demersum and Utricularia aurea. The seasonal changes in water level of the Mekonginundatedplaindrivesaseasonalmigrationoflargewaterbirdsbetweenwetlands.In thedryseason,manyspeciesmovetopermanentwetlandsandgrassyplainsaroundLakeTonle SapandtheDelta,whileinthewetseasontheyretreattohigherseasonalwetlandsinnorthern CambodiaandLao.

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In the dry season, these wetlands are vital in maintaining breeding stocks of floodplain fish, includingairͲbreathingspecies(e.g.gouramies,walkingcatfish),whileinthewetseasonthey functionasbreedingandnurserygroundsformanyfishspecies,theblackfish.Thesewetlands are important for almost all waterbirds in the Lower Mekong Basin, particularly cormorants, OrientalDarter,SpotͲbilledPelican,GreaterandLesserAdjutants,MilkyStork,WoollyͲnecked Stork Ciconia episcopus, BlackͲnecked Stork Ephippiorhynchus asiaticus, Painted Stork, The Globally Endangered WhiteͲshouldered Ibis Plegadis davisoni, Glossy Ibis P. falcinellus, BlackͲ headed Ibis Threskiornis melanocephalus, WhiteͲwinged Duck, Pallass Fish Eagle Haliaeetus leucoryphus, GreyͲheaded Fish Eagle, and the Globally Vulnerable Masked Finfoot Heliopais personata. One of the most important wetland habitats of the Lower Mekong Basin is the seasonallyͲ inundated riparian forest found on the gentlyͲsloping plains adjacent to lakes, rivers and tributariesandsubmergedbytheseasonalfloodofthewetseason.Fishusethishabitatasa feeding, breeding, and nursery ground and it is important for breeding colonies of large waterbirds. SeasonallyinundatedgrasslandsarecommononthefloodplainsoftheLowerMekongBasin. Closetothewateredge,floatingoremergentvegetationformsdensemats.Aswaterlevelsrise, densematsmaydislodgeandfloat,propelledbycurrentsorthewind.Themainspeciesinclude Achyranthes aquatica, Brachiaria mutica, Eichornia crassipes, Polygonium barbatum and Sesbania javanica. Other plant species found on the upper reaches of the inundated plain include several grasses, including Echinochloa stagina, sedges including Cyperus pilosis, Rhynchospora sp., and dicotyledons such as Aeschynomene indica, Impatiens sp., Ludwigia hyssopifoliaandNelumbonucifera(lotus).Theyareofcrucialimportanceforanumberofrare andendangeredbirdspecies. AccordingtotheInventoryofWetlandsinLaoPDR(Claridge,1996),theprojectareaisafairly importantwetlandarea,consistingofamosaicoffreshwaterlakes,riverponds,ricepaddyand freshwatermarshes.MostofthewetlandislocatednorthoftheXeBangFaiandisassociated with the Houay Vay and the Houay Sayphay. Close to the river there are several old river channels with oxbow lakes, that silted up and form fairly large marshes. Bung Xuak on the southernsideoftheriver,justwestofBungVeunNua,isthebestexample.Itispossiblythe onlywetlandintheareathatretainedasignificantproportionofitsoriginalvegetation.Itisalso thelargest,about3km2,andhasopenwaterattheendofthedryseason. Nearly 9% (2,726 ha) of the Nongbok District, the district covering most of the project area) consistsofwetlands.Some30%ofthedistrict(9,400ha)isunderforest.

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WetlandsintheLowerSeBangFaiarea 2.3 Wildlifeandrareandendangeredspecies Noinformationisavailableaboutthefaunaintheprojectarea.However,itisknownthatthe wetlandsoftheLowerMekongBasinsupportsome15globallyͲthreatenedbirdspecies,namely the Critically Endangered Giant lbis Pseudibis gigantea, the globally Endangered Sarus Crane Grus Antigone, Greater Adjutant Leptotilos dubius, WhiteͲshouldered lbis Pseudibis davisoni, WhiteͲwinged Duck Cairina scutulata, Bengal Florican Eupodotis bengalensis and Nordmann's Greenshak Tringer guttifer, the globally Vulnerable SpotͲbilled Pelican Pelican Pelecanus Philippensis, Lesser Adjutant Leptoptilos javanicus, Milky Stork Mycteria cinerea, Greater Spotted Eagle Aquila clangula, Green Peafowl Pavo muticus, Masked finfoot Heliopais personatus,BlackͲbelliedTermSternaacuticauda,andIndianSkimmerRynchopsalbicollis. Of the reptiles the Siamese Crocodile Crocodilius Siamensis is Critically Endangered. It was formerly widespread thoughout the Lower Mekong Basin but has declined drastically due to excessive hunting and habitat destruction. It is reported to be present in the vicinity of the projectarea.AlsoovertwentyspeciesofturtlesoccurintheLowerMekongBasin,tenofwhich arelistedintheRedDatabookincludingtheChinesethreeͲstripedboxturtleCuoratrifasciata thatisCriticallyEndangered. Possiblythewetlandsintheprojectareaareofimportanceforoneormoreoftheserareor endangeredspecies.

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2.4 Protectedareas According to ICEM, 2003, Lao PDR National Report on Protected Areas and Development. ReviewofProtectedAreasandDevelopmentintheLowerMekongRiverRegion,noprotected orproposedprotectedareasarelocatedintheprojectarea. BirdLifeInternationalinIndochina,onitswebsite,indicatesthatthereisanimportantbirdareas (IBA)locatedintheprojectarea.Detailsarenotavailable. 2.5 Fisheries Afterrice,fishisthemostimportantitemonthedietforallethnicgroupsinthearea.Besides, thesaleoffishonlocalmarketsaddsconsiderablytotheincomeofmosthouseholds.Fishis caught with a variety of gear and equipment including explosives, poisonous plants, nylon monofilamentgillnets,spears,hookandline,castnets,scoopnetsandmanytypesoftrap.Drift and fixed gillnets are the most important gear in terms of the size of fish landings made by fishermanfromtheXeBangFai.Fishiscaughtallyearroundbymen,womenandchildren.The seasonalfishmigrationsbetweentheMekongRiverandtheXeBangFaiareimportantperiods forfisheries. ThemainXeBangFaichannelisthemostimportantfishinggroundduringthedryseason(when fishconcentrateinrefugehabitats),whilehabitatsonthefloodplain(floodedforests,swamps, backyardponds,paddyfields)areimportantduringthewetseason.Catchesconsistmainlyof cyprinidsandcatfishes,manyofwhichinͲmigratefromtheMekongmainstream.Catchesinthe floodplains also include resident species such as snakehead, mud perch, spiny eels, climbing perch,walkingcatfish,andgouramies. FamiliesinthelowerreachofXeBangFaicatchonaverage168kgfish/fam/year,sufficientfor daily consumption and the production of 2Ͳ8 jars (= 22 kg) of Padek /family/year Padek, salted fermented fish, is the second staple food in Laos, after rice. The remaining catch, on average20%orsome35kg/household/y,issoldonthemarket.Anecdotalinformationsuggests that production has declined over the last 10Ͳ15 years. Average fish size and the number of speciescaughthavealsodeclined.Thereasonforthedeclineisthoughttobeoverfishingand useofsmallmeshmonofilamentgillnets. References Claridge, G.F.,1996, An Inventory of Wetlands of the Lao PDR. IUCNͲThe World Conservation Union,Bangkok. ICEM,2003.LaoPDRNationalReportonProtectedAreasandDevelopment.Reviewof Protected Areas and Development in the Lower Mekong River Region, Indooroopilly, Queensland. KhammouanRuralLivelihoodProjectImplementationUnitoftheProvincialDepartment of Planning and Investment of the Khammouane Provincial Government, 2008, Initial EnvironmentalExaminationoftheKhammouanRuralLivelihoodProject(KRLP). Kottelat,M,2001,FishesofLaos.WildlifeHeritageTrust,Colombo,SriLanka. MekongSecretariat,1981,FeasibiltyStudyofFloodwayandsmallstructures. NamTheunͲ2PowerCompany,2005,SocialDevelopmentPlan,Volume3,Downstream Areas. NamTheunͲ2PowerCompany,2005,EnvironmentalAssessmentandManagementPlan oftheNamTheun2HydropowerDevelopmentProject.

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11.4 EnvironmentalBaselineKratieFocalArea

1 Generalcharacteristics The Kratie Province is located in the northeastern part of Cambodia. Most of the province consistsoftheMekongfloodplain,whichhaselevationsbelow100m.Themainstreamofthe Mekong River runs through the central part of the province in a general north to south direction, before sharply turning to the west at Chhlong near the southern boundary of the province.Intheprojectarea,thewidthofthemainriverrangesbetween1.2and3.5km.The riverbed,atlowwaterlevels,ischaracterizedbynumeroussandandgravelbanksandislands. Justupstreamoftheprojectarea,aseriesofrapidshasdeveloped. Theriverdepositsintheprojectareaconsistoffinesand,siltandclaywithlayersofcoarsesand androundedquartzitepebbles.IntheriverbedfromSamboktoKratieandfurtherdownstream to Chhlong the underlying bedrock (sandstone) is almost totally submerged even in the dry season. Theriverbanksaresteepandrise14to20mabovethelowwaterlevel.Onthetopoftheriver banks natural levees have developed. Further from the river, after some 100 m, the surface slopes away to form depressions in which swamps have developed. Examples are the Boeng Long Leach, southͲeast of Kratie Town, and Phum Russei Char, between Sambok and Kratie town. A number of tributaries flow into the Mekong River, like the Prek Te that joins the Mekong some5kmdownstreamofKratie.Thesetributarieshavenaturalleveesatalowerlevelthanthe Mekongandfalldryforseveralmonthsduringthedryseason.Inthefloodseason,waterflows intothelowlyingareasbehindtheMekongleveesthroughtheseriverchannels. TheMekongfloodplainisslightlyundulatingandextendssome5to10kmfromeachbank. 2 Ecologicalresources 2.1 Riverineandterrestrialhabitats FortheLowerMekongRiversystemanumberofimportanthabitatsforconservationhavebeen identified,theyare: - riverchannels; - smallislandsandriverinesandͲbars; - marshes,smallpoolsandseasonallyͲinundatedfloodplainwetlands; - seasonallyͲinundatedriparianforest;and - inundatedgrasslands. Theriverchannelintheprojectareaisvitallyimportantfortheseasonallongitudinalmigration offish species.Key fishhabitatsarefeedinghabitats,spawninghabitatsandrefugehabitats. MostfishesoftheMekongfeedintheproductiveseasonallyinundatedfloodplains.Attheend ofthefloodseason,whenthesehabitatsdryout,fishesmovetorefugehabitatswithinriver channelswheretheywaitforthenextfloodcycle.Mostfishspawnattheonsetoffloodseason. The main habitats used for spawning are rapids and deep pools in river channels as well as certainfloodplains.Mostmigratoryfishes,whichaccountforasignificantproportionofthefish catchoftheMekong,spawnwithinriverchannelsatrapids/poolsupstreamfromfeedingand rearinghabitats. AlargeproportionofMekongfishspeciesismigratory.Manyspeciesmovefromonehabitatto anothertocompletetheirlifecycle.Forinstance,severalimportantspeciesmigrateupstream

StrategicDirectionsFloodRiskManagementͲ111Ͳ December2009 MRCFloodManagementandMitigationProgrammeComponent2:StrucuralMeasuresandFloodProofing tobreedatthebeginningoftherainyseason.Then,asthewaterrises,theyoungfishareswept downstreamtofloodedareas. TheMekongRiveranditstributariesarealsoanimportanthabitatforwaterbirdspecies.Small islandsandsandͲbarsformahabitatforpioneerplantcommunitiesandbreedingsitesforbirds. Seasonal wetlands inundate in the wet season when water levels of the Mekong are high. Wetlandsincludereedandsedgebeds,swamps,andlotusponds.Anotherimportanthabitatis theseasonallyͲinundatedriparianforestfoundadjacenttotheriver.Itisanimportanthabitat for breeding colonies of large waterbirds. Fish use this habitat as a feeding, breeding, and nurseryground. IntheriverchannelupstreamofheFocalAreadeepwaterpoolsareencountered.Thishabitat isimportanttomanyfishspecies,particularlyaslowwaterrefugeandasspawningground. In the Focal Area, rocky areas and rapids are absent and the riverbanks are predominantly steep.Thesesteepriverbanksprovideanestinghabitatforavarietyofbirds.Extensivewide sand and pebble beaches and islands are present, forming an excellent feeding, resting and nestinghabitatforwadingbirdsandducks. ThevarietyofaquaticandterrestrialhabitatsintheMekonghascontributedtoahighlevelof biodiversity.EcosystemsandhabitatsinthevicinityoftheFocalAreathatareimportantforthe conservation of this high biodiversity are deep pools, sand bars and islands, wetlands and seasonallyfloodedshrubareasandgrasslandsonthefloodplain. 2.2 Fishandotheraquaticfauna TheMekonghasaveryhighfishdiversity,morethan1,000speciesoffishareknown.Alarge percentageofthesefish,over80%,followtheinundationspawningpattern:lateralmigrations from the mainstream and tributaries into the inundation zones to spawn and rear young betweenJulyandSeptember. Twogroupsoffisharedistinguished:whitefishandblackfish.Fishthatmigratebetweenthe river and the floodplain are referred to as white fishes, whereas the species of fish which remaininlakesandswampsonthefloodplainareknownasblackfishes.TheKratiesubareais considered a vital corridor for the seasonal longitudinal migration of white fish species, including the commercially important cyprinids, Henicorhynchus lobatus (locally called trey reil)andH.siamensis,whichmigrateover800kmfromTonleSapLakeintoLaos.Otherhighly migratory groups are catfish species, including the endangered Giant Catfish Pangasianodon gigas,Pangasiussanitwongsei,P.sutchi,P.larnaudiandJulliensBarbProbarbusjullieni. NumerousdeeppoolsarelocatedinthemainstreamoftheMekongRivernearKratie.Theyare widely acknowledged as important dry season refuges for fish. In Kratie and Stung Treng provinces,58deeppoolsareidentifiedtobeprimaryrearinganddryseasonrefugesforlarge catfishandcarp.Someoftheseareasareimportantfeedinggroundsanddryseasonrefugesfor theIrrawaddydolphinaswellasaspawningareaforGiantcarp.Theprotectionofthesepoolsis considered imperative to maintain fishing productivity and some endangered species. The region of Kratie, where most deep pools are located, has high fish populations and surveys indicatedthatanywherealongthestretchbetween6and25differentspeciesoccur(Poulsenet al.,2002).

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MainfishmigrationroutesintheLowerMekongBasin 2.3 Protectedareasandrareandendangeredspecies BirdLife International identified the Mekong River channel and associated riverine vegetation fromKratietotheborderwithLaoPDR,asanimportantbirdarea(IBA). Alongthisriversection,theMekongisveryvaried;somesectionsformasinglechannelwitha vast expanse of water, in other sections the river is braided into a number of islands and channels. Several types of river channel vegetation occur: small periodically flooded, predominantlygrasscoveredislandsandshrubsandtreesthatbecomepartlysubmergedfor mostofthewetseason.However,muchoftheriverinefringingforestisdegraded. The IBA supports a large proportion of the global population of the Mekong Wagtail, Motacillasamveasnae,arecentlydescribedspecies,whichisthoughttobeendemictothe Mekong River and its tributaries. In addition, the IBA supports a number of riverine bird speciesthathavedeclinedseverelythroughoutmainlandSouthͲeastAsia,includingtheRiver Lapwing Vanellus duvaucelii, Great Thick Knee Esacus recurvirostris and River Tern Sterna aurantia. Furthermore, a number of globally threatened and nearͲthreatened species have been recorded in the IBA in small numbers, including White Rumped Vulture Gyps bengalensis,RedͲheadedVultureSarcogypscalvusandDarter Anhinga melanogaster. Small but significant numbers of WhiteͲshouldered Ibis, Pseudibis davisoni have been recorded along forested parts of the river. Finally the IBA may be one of the last remaining sites in IndochinatosupportBlackͲbelliedTernSternaacuticauda. KeybirdspeciesintheIBAaregiveninTablebelow.

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Keybirdspecies Commonname Scientificname IBA criteri a* SmallPratincole Glareolalactea A4i BlackͲbelliedTern Sternaacuticauda A1 WhitedRumpedVulture Gypsbengalensis A1 RedͲheadedVulture Sarcogypscalvus A1 Darter Anhingamelanogaster A1 WhiteͲshoulderedIbis Pseudibisdavisoni A1 MekongWagtail Motacillasamveasnae A1,A2 *A1:Globallythreatenedspecies,thesiteregularlyholdssignificantnumbersofaglobally threatenedbirdspecies. A2:Restrictedrangespecies,thesiteisknownorthoughttoholdasignificantcomponent oftherestrictedrangebirdspecieswhosebreedingdistributionsdefineanEndemicBird Area(EBA)orSecondaryArea(SA) A4i:Congregations:thesiteisknownorthoughttohold,onaregularbasis>1%ofa biogeographicalpopulationofacongregatorywaterbirdspecies Themostimportantthreatstotheriverinebirdcommunitiesarehunting,eggcollectionand disturbanceduetohumanactivitiesonthesandbanksduringthebreedingseason,aswellas cuttingoftreesandclearanceforagricultureontheriverbanks.Birdspeciesthatoccurinthe areaandaredependentoneitherriverbanksorsandbarsaregiveninthetablebelow. Habitatdependenceofbirdsobservedintheprojectarea Commonname ScientificName Habitat* RB SB SmallPratincole Glareolalactea X X BlackͲbelliedTern SternaacuticaudaX RiverTern SternaaurantiaX Darter AnhingamelanogasterX MekongWagtail Motacillasamveasnae X RiverLapwing Vanellusduvaucelii X X GreatThickKnee Esacusrecurvirostris X *RB=Riverbank,SB=Sandbank The IBA also supports one globally threatened primate species, the LongͲtailed Macaque, Macaca fascicularis, one globally threatened crocodile, the Siamesa Crocodile, Crocodylus siamensisandagloballythreatenedturtle,theAsianGiantSoftshellTurtle,Pelochelyscantorii. Of special importance are also the Irrawaddy Dolphins, Orcaella brevirostris. Smith, B.D. and Beasley(2004)estimatedtheirabundanceinthestretchfromKratietotheKhoneFallsat69 individuals.ThisnumberisprobablyclosetotheactualsizeoftheMekongsubͲpopulation. TheeffectiverangeofIrrawaddydolphinsintheMekongRiverisa190kmsegmentfromKratie to slightly upstream of the Laos/Cambodia border at Khone Falls, which physically obstructs furtherupstreammovement.Basedonvisualsurveys,dolphinsarefrequentlyfoundduringthe lowͲwaterseasoninninedeeppoolsintheKratietoKhoneFallssegment.Kampipool,located 15 km north of Kratie, is currently considered the most important dolphin habitat in the Mekong. No quantitative estimates of population trends are available, but significant range declines implythatthenumberofdolphinsintheMekongRiverhasdeclinedsubstantiallyoverthepast severaldecades.

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ThreemainendangeredfishspeciesarefoundintheMekongRiveranditstributarieswithinSub Area8,namelyJullien'sGoldenCarp,DwarfBotia,andLaotianshad. AccordingtotheWWFwebsite(Bezuijen,2008),a55ͲkmsectionoftheMekongRiverinKratie and Stung Treng provinces has recently (February 2008) been proposed as a special managementsitebecauseofitshighbiodiversityvalues.Thesitewasnominatedbyagencies fromtheprovincesandtheMinistryofAgriculture,ForestryandFisheries(MAFF). In2006Ͳ2007MAFFandWWFconductedbiodiversitysurveysalongtheMekongRiverbetween KratieandStungTreng,adistanceof125km.Thisregionwasalreadyknowntosupportthe critically endangered Irrawaddy Dolphin, but during the survey many new discoveries were made,ofwhichthemostimportantwaslocatingasectionofMekongofabout55kmlongwith veryhighbiodiversityvalues.Thisparticularpartoftheriver,thesoͲcalledcentralsection,has remainedrelativelyuntouchedbyhumanactivities.Atleast8endangeredmammals,including theregionslastremainingHogDeer,SilveredLeafͲmonkey,LongͲtailedMacaqueandOtters, were documented. It also it the home of the endangered WhiteͲshouldered Ibis, River Tern, WoollyͲneckedStork,LesserandGreaterAdjutant,andtherareCantorsGiantSoftͲshellTurtle, whichmayalreadybeextinctinmanyotherpartsoftheMekongBasin. 3 Fisheries Fish in the Mekong and its tributaries provide an especially important food source to local people.Anestimated90%ofthepopulationreliesonfishingforpartoftheirnutrition.Fishare estimatedtoprovide40Ͳ60%ofanimalproteinintakeforpeopleinruralareasinCambodia.An averageof25kgoffishisconsumedperpersonperyear,intheKratieprovince.Thisestimateis fairlylowascomparedtothenationalaverage. Aquacultureintheareaislowdeveloped,duetohighlevelsofcapturefisheriesandlowprices, aquaculture development has been very slow throughout most of Cambodia. Increasing aquacultureforthisregionisoneofthegovernmentsaimsforreducingpovertyandincreasing fishproduction. 4 Tourism Kratie Province is considered a new destination for tourism with a high growth potential. However, poor infrastructure and a limited number of tourism sites are still constraints to investmentintheregion. TheendangeredIrrawaddyDolphinsaretheregionsmostpopularattraction.Asfewas70of these dolphins survive in the Mekong after years of overͲfishing and hunting, and tourism is consideredimportanttotheirconservation,aslocalcommunitiesdependhighlyontheincome fromvisitors.AnimportantDolphinsightingsiteislocatejustupstreamofSambok. Phnom Sambok, a low hill along the river near the Thmor Kre Commune, 11 km north of Kratieisaculturalandhistoricsiteswhichattractsmanyvisitors.Accordingtoalegendaking named Cha Krey Sara Varman, son of Preah Bat Hathak Athi Reach Varman, ordered his officialstofindaplacewheregoldcouldbemined.TheyfoundaplacecalledKanLengSam BoMeasmeaningaplaceveryrichingold.LaterthenameofthesitechangedtoPhnom SambokMeastofinallybecomePhnomSambok.Thesiteispresentlyatouristresort. Anothertouristresortislocatedsome15kmupstreamofKratie,nearthePrekKampybridge. The area has a sandy riverbank and the scenic Mekong channel consists of thousands of islands. Services to visitors include crossing bridges, floating cottages, softͲdrink shops, restaurants,emergencyandsecurityprovisions.

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References Bezuijen,M,2008,AnotherareaintheCambodianMekongregionunderenvironmental protection(WWFWebsite). MRC,2006,BasinDevelopmentPlan,SubArea8. Poulsen, Anders, Ouch Poeu, Sintavong Viravong, Ubolratana Suntornratana & Nguyen Thanh Tung, 2002, Deep pools as dry season fish habitats in the Mekong Basin. MRC TechnicalPaperNo.4,MekongRiverCommission,PhnomPenh.22pp.ISSN:1683Ͳ1489. Smith, B.D. and Beasley, I. 2004. Orcaella brevirostris (Mekong River subpopulation). In: IUCN2007.2007IUCNRedListofThreatenedSpecies.

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11.5 EnvironmentalbaselineCambodianDelta

1Generalcharacteristics TheenvironmentalconditionsintheEastMekongandWestBassacFocalAreasaretoalarge extentcomparable,thereforetheseareasaredescribedhereinconjunction. FloodplainsintheCambodianDeltaareessentiallyflat.Theelevationrangesfromabout1to10 meters above mean sea level in the West Bassac area and from about 2 to 5 meters above meansealevelintheWestMekongarea.Atsomelocationstheplainsareborderedbylowhills. TheBassacandMekongRiversandthesmallertributariesareborderedbynaturalleveesthat are formed through silt depositing. The levees are intensively used for housing and transportationsincetheyarethelasttoflood.Theleveesseparatetheriversfromdepressions thatfloodduringthefloodseason.Asystemofcolmatagecanalshasbeendevelopedoverthe centuries to (partially) control the water flow in and out of the floodplain depressions to supportthecultivationofrice.Allsoilsintheprojectareaareofalluvialorigin.Thesoilsonthe natural levees have favorable properties for agriculture, the soils in the lower parts of the floodplainsarecharacterizedbyfrequentwaterloggingandlowfertility. Duringthefloodseason(JulyͲSeptember)thewaterlevelsintheMekongandBassacRiversrise sharply. In the West Bassac area part of the Bassac flood flow is diverted to the flood plain throughcolmatagecanals.Therelativelyhighlyingnaturalleveesdirectlyborderingtherivers are only affected by shallow flooding during relatively short periods. Deep flooded areas are located directly west of this shallow flooded area and in the area extending from Takeo in southeasterndirection,coveringmostoftheCambodia/VietNamborderarea. In the East Mekong area, flooding starts when the Mekong at Kampong Cham reaches a dischargeofabout30,000m3/sorawaterlevelofabout13.0m.TheRiverstartstooverflowits banks and in the vicinity of the project area the flood waters are forced to follow two river branches,thePrekVealRobang(StungSlot)andthePrekTrabek.Withrisinglevels,theflood waters start to spread over the lowͲlying (3Ͳ4 m amsl) floodplains of these two rivers. The centralareabetweentherivershasasomewhathigherelevation(above5.0mamsl)andfloods lessdeeply.Thisareaismoredenselypopulatedwithcommunitiesofsubsistencericefarmers. Towards the Cambodian/Viet Nam border, the low lying areas bordering the two rivers practicallyjointogethertoformavast,deepfloodedarea. Agricultureintheareaiscloselylinkedwiththeannualcycleofflooding.Normalfloodsimprove soilmoistureandfertility,restoregroundandsurfacewaterresources,andreplenishfisheries andforests.Normalfloodslikewisehavenoadversephysicalimpactonvillagesettlementsand onlyalimitedeffectonwetseasonrainͲfedricefields.Annualfloodsbecomedisastersforrice farmingonlywhentheycometooearlyorwhentheyaretoohighorlasttoolong. Exceptforthesmallleveezonesalongtherivers,wherecashcropsaregrown,riceisthemain crop in the area. Depending on soil type, elevation, flood frequency, flood depth and flood duration,differentricefarmingsystemsandricevarietiesareused. AstudybyChamroeunetal.(2001)indicatedthatmorefarmers(60toover90%)usechemical fertilizers inthedry seasonthaninthe wet season(lessthan10%).Most farmers(15to50%) applychemicalfertilizersinamountsfarexceedingtherecommendedlevels.Alsopesticideuseis morecommonduringdryseason(70to100%ofthefarmers)thaninthewetseason(about50%). Most farmers spray pesticides when they notice their crops damaged by pests or see a large numberofinsects intheirrice field.Sinceveryfew farmerscandistinguishbetweenbeneficial insectsandactualpests,theymaybesprayingpesticidesunnecessarily.Regardingthedisposalof

StrategicDirectionsFloodRiskManagementͲ117Ͳ December2009 MRCFloodManagementandMitigationProgrammeComponent2:StrucuralMeasuresandFloodProofing pesticideresieduals,over90%offarmersinPreySvaandPreyTamaodisposecans,bottlesand washsprayersintheirricefieldsand/orirrigatedcanals. AscomparedtoVietnam,thefloodplainsinCambodiaarelargelyundeveloped.Thefloodplains ofCambodiacanbecharacterizedasinTablebelowafterDouven(2008). GeneralcharacteristicsoftheEastMekongFloodplain Floodplain stillquitenatural Infrastructure fewroads,colmatageirrigationsystems, afewsmallͲscaleirrigationschemes Housinganddevelopment mainlyalongleveesborderingrivers Economy extensiveagricultureandfisheries Landuseandecology nonationalparks,butfloodplainsand floodingessentialforbiodiversityinthe region Hydraulics largelynaturalflooding,onlyobstructed byroadsandtosomeextentlevees 2 Ecologicalresources 2.1 Fishandotheraquaticfauna AccordingtoBaran(2005)theMekonghostsover1,000speciesoffish,oneofthehighestspecies countsofanyriversystemintheworld.Thelargevariationinhydrologyandthevarietyofhabitats allowthepersistenceofmanyspecies,whichallrequiredifferentconditions.Somespeciesare abundant on the floodplain and its wetlands, some favor lowland rivers and some are found mainlyintributaries.Nearlyallmigratewithinorbetweenhabitatstocompletetheirlifecycles. ForCambodia477freshwaterfishspeciesarerecordedofwhich40%isendemic.Tenspeciesare endangered(FishBase2004). ThefishfaunaoftheMekongRiverisdominatedbyspeciesofcarp(Cyprinidae;54%),catfish (Siluridae,Clariidae,Schilbeidae,Bagridae,SisoridaeandAkysidae;19%)andmurrels(Chanidae and Ophicephalidae; 8%). The remaining 19% consist of featherbacks (Notopteridae), herring (Clupeidae),climbingperchandgouramis(Anabantidae)andothermiscellaneousgroups.Some 85Ͳ95%ofthefreshwaterfishpopulationsintheMekongbasinfollowtheinundationspawning pattern,undertakinglateralmigrationsfromthemainstreamandtributariesintotheinundation zonestospawnandrearyoungbetweenJulyandSeptember. Basicallytwogroupsoffisharedistinguished:whitefishandblackfish.Whenfloodplainsdrain attheendofthewetseason,waterremainsinlakesandscattereddepressions,whichcontinue to shrink in size and number during the dry season. Floodplain water bodies become hot, oxygenisdepletedandfoodandshelterdiminish,withmanypondsdryingͲoutcompletely.So thefish,whichfeedandgrowonfloodedareasmusteitherreturntotheriverasthewaters recede,orremainandendurethepoorconditionsonthefloodplain. Specieswhichleavefloodedareasandreturntoriversarereferredtoaswhitefishes,asthey spend most of their lives in turbid (white) river water. Most whiteͲfish species migrate into flooded areas during the monsoon season and migrate over long distances to dryͲseason refugesattheendofthefloodseason.Representativesofthisgrouparesomeofthecyprinids, suchasCyclocheilichthysenoplos(SoldierriverbarborChhkok)andCirrhinusmicrolepis(Small mud carp or Prul/Kralang), as well as the river catfishes of the family Pangasiidae. The main migrationroutesintheLowerMekongBasinaredisplayedinFigurebelow.

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MainfishmigrationroutesintheLowerMekongBasin Thespeciesoffishwhichremaininlakesandswampsonthefloodplainareknownasblack fishes, as they spend their lives in relatively clear water that is teaͲcolored by chemicals dissolvedfromfloodplainvegetation.Decompositionofvegetationcausesfloodplainwaterto beacidicanddepletedinoxygen,stresseswhichblackfishescantolerate.Mostblackfishescan breatheair,whilemany speciescan surviveoutofthewaterfor longperiods, andmostcan moveoverlandinsearchofnewwaterbodies.Afewspeciescanburythemselvesdeepinthe mud and wait until the next flood. Many black fishes are used in aquaculture and are transportedalivetomarkets. They are normally referred to as nonͲmigratory, although they perform short seasonal movementsbetweenpermanentandseasonalwaterbodies.ExamplesofblackͲfishspeciesin the Mekong are the climbing perch (Anabas testudineus), the clarias catfishes (e.g. Clarias batrachus)andthestripedsnakehead(Channastriata). Apart from fish, inland waters support a high diversity of other aquatic animals including vertebratesͲreptiles, birds, mammals and amphibians, and invertebrates, such as insects, crustaceansandmollusks,allofwhichdependuponmaintenanceofaquaticecosystems. 2.2 Wetlandsandterrestrialvegetation ImportanthabitatsforconservationaredescribedbyBirdLifeInternationalinIndochina(2005). Theyare: Mainriverchannels Waterheightinthemainriverchannelsvariesbyupto10metresbetweenthewetanddry seasons.Thesechannelsarevitallyimportantfortheseasonallongitudinalmigrationofwhite fish species. Although the main channels support a rich assemblage of aquatic species, they exhibitlittleendemism. TheMekongRiveranditswiderlowgradienttributariesareimportantforadistinctiveguildof riverine bird species. The Globally Vulnerable Indian Skimmer Rynchops albicollis may have alreadydisappearedfromthishabitatinCambodia.andtheGloballyVulnerableBlackͲbellied TernSternaacuticaudaandLittleTernSternaalbifronsappeartobeonthevergeofdoingso. OthersignificantspeciesinthishabitatincludetheGloballyNearͲThreatenedGreyͲheadedFish

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Eagle,andGreatThickͲkneeEsacusrecurvirostris,RiverLapwingVanellusduvaucelii,andSmall PratincoleGlareolalactea. SmallislandsandriverinesandͲbars SmallislandsandriverinesandͲbarsarecommononstretchesoftheMekonganditstributaries. They are formed by natural deposition during seasonal high river flow. The plant Anogeissus rivularisdominatesthepioneercommunityoflowͲlyingvegetatedsandbars.Theolder,larger sandbars,builtupintoislandsovermanyyears,havemoresubstantialvegetationsimilartothe neighbouringgalleryforest. Thesmallersandbarsandislandsprovidesafebreedingsitesformanyspeciesofwaterbirds, someofwhicharegloballyrareandendangered.TheonlyrecentconfirmationinIndochinafor thebreedingoftheGloballyVulnerableBlackͲbelliedTernwasrecordedonsuchislands.They alsosupportthelargestnumbersofGreatThickͲknee,RiverLapwing,andSmallPratincolein SouthEastAsia. PermanentandSeasonallyͲinundatedFloodplainWetlands AnumberofpermanentandseasonalloticandlenticwetlandsarefoundintheLowerMekong Basin. The high wet season water levels of the Mekong inundate many of these wetlands seasonally;groundwaterandseasonalmonsoonalrainsmaintainothers.Theseprovidesomeof the most productive habitats in the Lower Mekong Basin and include reed and sedge beds, swamps,lotusponds,inundatedgrasslandsandinundatedforest. TheseasonalchangesinwaterleveloftheMekonginundatedplaindrivesaseasonalmigration of large waterbirds between wetlands. In the dry season, many species move to permanent wetlandsandgrassyplainsaroundLakeTonleSapandintheDelta,whileinthewetseasonthey retreattohigherseasonalwetlandsinnorthernCambodiaandsouthernLao. Thefollowingwetlandtypesaredistinguished: SeasonallyͲinundatedriparianforest One of the most important wetland habitats of the Lower Mekong Basin is the seasonallyͲ inundated riparian forest found on the gentlyͲsloping plains adjacent to lakes, rivers and tributariesandsubmergedbytheseasonal8Ͳ10metrefloodlevelsofthewetseason. The composition of this forest type shares little with swamp forests and mangrove systems. Over 200 species of plants have been found in these inundated forests. Major communities includeBarringtoniaacutangula,ElaeocarpusmadopetalusandDiospyroscambodiana;floating andemergentherbsincludingBrachiariamutica,Eichorniacrassipes,Polygoniumbarbatum,P. tomentosumandSesbaniajavanica,andadiversemixedscrublandcontainingover60species. Thewoodyspeciesofthisforestareoftenladenwithfruitsandseedsatthetimeofinundation, providing food for the 34 species of fruitͲeating fish of the Lower Mekong Basin. Over 200 species of fish use this habitat as a feeding, breeding, and nursery ground and it is vitally importantforbreedingcoloniesoflargewaterbirds. Marshes,smallpoolsandseasonalwetlandsinthelowlandplain Extensiveseasonalandpermanentmarshes,smalllakes,andotherwetlandsoccurthroughout theLowerMekongBasin.Theyareusuallyshallow,filledbyseasonalrainfallandtypicallyare connected to river systems which in the wet season form the inundated plain of the Lower MekongBasin.Theycontainamosaicofwetlandhabitatsincludingreeds,sedge,lotusbedsand open water. Submerged communities are dominated by Ceratophyllum demersum and Utriculariaaurea.

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Locationofimportantwetlandhabitatsintheprojectarea(SourceBirdLifeInternational) 2.3 Wildlifeandrareandendangeredspecies Wetland mammals known to occur in the project area include the SmoothͲcoated Otter Lutra perspicillata(quiterare)andFishingCatFelisviverrina. According to Baran (2005) the main endangered large fish species in Cambodia are the Giant Mekongcatfish(Pangasionodongigas),theGiantMekongcarp(Catlocarpiosiamensis)andthe sevenͲlinebarb(Probarbusjullieni).OtherendangeredspeciesareBalantiocheilosmelanopterus, Botiasidthimunki,Chelacaeruleostigmata,Dasyatislaosensis,Himanturachaophraya,Himantura oxyrhyncha,ScleropagesformosusandTenualosathibaudeaui. ThenumberofbirdspeciesfoundinCambodiais435(MinistryofEnvironment,2000).Ofthese 106 species are water birds. The wetland of the Lower Mekong Basin support 15 globallyͲ threatened bird species, namely the Critically Endangered Giant lbis Pseudibis gigantea, the

StrategicDirectionsFloodRiskManagementͲ121Ͳ December2009 MRCFloodManagementandMitigationProgrammeComponent2:StrucuralMeasuresandFloodProofing globally Endangered Sarus Crane Grus Antigone, Greater Adjutant Leptotilos dubius, WhiteͲ shouldered lbis Pseudibis davisoni, WhiteͲwinged Duck Cairina scutulata, Bengal Florican EupodotisbengalensisandNordmann'sGreenshakTringerguttifer,thegloballyVulnerableSpotͲ billed Pelican Pelican Pelecanus Philippensis, Lesser Adjutant Leptoptilos javanicus, Milky Stork Mycteriacinerea,Greater Spotted Eagle Aquilaclangula,Green PeafowlPavo muticus,Masked finfootHeliopaispersonatus,BlackͲbelliedTermSternaacuticauda,andIndianSkimmerRynchops albicollis. Of the reptiles the Siamese Crocodile Crocodilius Siamensis is Critically Endangered. It was formerlywidespreadthroughouttheLowerMekongBasinbuthasdeclineddrasticallydueto excessivehuntingandhabitatdestruction.Thesepopulations,areofextremeglobalimportance asthelastwildpopulations.OvertwentyspeciesofturtlesoccurintheLowerMekongBasin, ten of which are listed in the Red Data book including the Chinese threeͲstriped box turtle CuoratrifasciatathatisCriticallyEndangered. NotcleariswhichofthesespeciesthatareendangeredinCambodiaareactuallypresentinthe projectarea. 2.4 Protectedareas AccordingtoICEM(2003)noprotectedorproposedprotectedareasarelocatedintheWest Bassac Focal Area nor in the East Mekong Focal Area. BirdLife International (Bauld, 2005) declaredtheBoeungPrekLapouvinthesoutheasternpartoftheTakeoProvinceanImportant BirdArea(IBA). TheBoeungPrekLapouvareaconsistsofseasonallyinundatedgrasslandsandislocatedinthe BoreyChulsarandKohAndethdistricts.Thesiteisanimportantdryseasonrefugeforfishand birds and is inundated for about four months each year, during which some 30 species of aquaticvegetationcanbefound.Itformspartofoneofthelargestareasofadjoiningnatural habitatsremainingintheMekongDelta.Moreimportantly,theareaprovidescriticalwetland habitat to 25% of the worlds population of endangered, nonͲbreeding Eastern Sarus Cranes (Grusantigonesharpii),aswellasnumerousothergloballythreatenedbirdspecies. The Eastern Sarus Crane (the tallest flying bird in the world) is present in the area from December to April. After Ang Tropeang Thmor, this area supports the largest nonͲbreeding populationinCambodia.InthedryseasonfromlateNovembertoApril,thesiteprovidesan abundanceoffoodforavarietyofbirds,includingtheSarusCrane.Duringthistimeasmanyas 350cranesmaybepresentinthearea.PopulationsofEgret,PondHeron,CormorantandSpotͲ billed Duck are present from JulyͲMarch, with populations of the Painted Stork and Asian OpenbillfromNovemberͲMarch.

LocationoftheBoeungPrekLapouvImportantBirdArea

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Surveysconductedintheareahaverecorded58birdspeciesincluding34waterbirdspecies.In additiontobirddiversity,thesitealsosupportsotherwildlifeandplantsincludingspeciesof reptiles,amphibians,mollusks,fish,aquaticvegetation,andinundatedforestvegetation.Ofthe 58birdspeciespresent,6aregloballythreatened:SarusCrane(Grusantigone),BengalFlorican (Houbaropsisbengalensis),SpotͲbilledPelican(Pelecanusphilippensis),PaintedStork(Mycteria leucocephala), Darter (Anhinga elanogaster) and BlackͲheaded Ibis (Threskiornis melanocephalus). Because of the importance of the area, the Forestry Administration proposed Boeung Prek Lapouv(10.787ha)asaSarusCraneconservationareatotheMinistryofAgriculture,Forestry and Fisheries in August 2002. The site has not yet been officially approved by the Royal GovernmentofCambodia. 2.5 Fisheries TheproductivityoftheLowerMekongFloodplainsisthehighestworldwideandrangesbetween 139 and 230 kg/ha/year. This is the result of 3 uniquely interconnected factors: high biodiversity,largeaccessiblefloodplains,andaveryhighexploitationrate. Cambodianpeopleinruralareasrelyheavilyonfisheriesfortheirsubsistence.Fishprovidefrom 40Ͳ60%ofanimalproteinintakeforpeopleinruralareas,eventhoselivingfarfromwater.An averageof76kgoffishisconsumedperperson/year(Baran,2005).Thetotalvalueoffishcatches inSA10CisestimatedatapproximatelyUS$45million. Duringtheflood,fisharedispersedinalargevolumeofwater.Whenwaterlevelslower,fish areforcedoffthefloodplainandbecomeconcentratedinchannels,streamsandrivers.Various kindsoftrapsandlargestationarytrawls(dais)setacrossflowingwatersinthefloodrecession seasoncatchmanyfishandotheraquaticorganisms.Mosthouseholdsintheprojectareafish for some time each year on land they own, or in nearby water bodies, flooded forest and floodplainareas.Productionfromricefieldsfisheriesisveryimportanttomostruralfamilies.In theTakeoProvince17,535familiesin62communities(49%ofallcommunities)areinvolvedin fisheries,inKandalprovincethesefiguresare3,190and17respectively.Largecompaniesare not operating in the area. Fish production in the Takeo province is reported to be 11,182 ton/year,inKandalProvince32,769ton/year.InthePreyVengProvince43,450familiesin22 communities(17%ofallcommunities)areinvolvedinfisheries.Capturefishproductioninthe provinceisreportedtobe2,082ton/y(McKenny&Tola,2002). 3 Cultural,historicandarcheologicalvalues IntheareaaroundAngkorBoreiremainsofpreͲAngkoriancanalshavebeenfound(Bishopaet al., 2003). The archeological evidence indicates a flourishing local economy early in the first millennium AD. It is also suggested that the area experienced major reͲorganization or reͲ structuringintheearlyfifthtoearlysixthcentury.Thisrestructuringprobablydidnotinvolve major deͲpopulation, but a change from rice cultivation in bunded fields with dry season burning,tofloodrecessioncultivationofrice.

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ArcheologicalsitesandancientcanalsintheCambodianDelta References Baran(2005),Cambodianinlandfisheries,Facts,FiguresandContext.WorldFishCenter andInlandFisheriesResearchandDevelopmentInstitute. Bauld,S,2005,EcotourismFeasibilityStudyofBoeungPrekLapouvImportantBirdArea, TakeoProvince.ReportbyBirdLifeInternational. BirdLife International in Indochina, 2005, Annual report on Important Bird Area (IBA) managementandconservationinCambodia,July2004August2005. Bishopa,P.,D.C.W.Sandersonb,andM.T.Starkc,2003,OSLandradiocarbondatingof apreͲAngkoriancanalintheMekongdelta,SouthernCambodia. Chamroeun, M., Vann Kiet, and Sun Votthy, 2001, A survey on environmental and healtheffectsofagrochemicaluseinriceproduction. Douven,W,2008,RoadsandFloods,recommendationsforthePlanningandDesignof EconomicallySoundandEnvironmentallyFriendlyRoadsintheMekongFloodplainsof CambodiaandVietnam,SynthesisReport. FishBase,2004,GlobalFishInformationsystem. ICEM,2003,CambodiaNationalReportonProtectedAreasandDevelopment.Reviewof ProtectedAreasandDevelopmentintheLowerMekongRiverRegion. McKenny,B.andP.Tola(2002),NaturalResourcesandRuralLivelihoodsinCambodia:A BaselineAssessment.WorkingPaperNo.23,CambodiaDevelopmentResourceInstitute, PhnomPenh. MinistryofEnvironment,2000,WetlandbiodiversityofCambodia,Workshopon NationalWetlandsPlanning,October2000. MRC,2006,BasinDevelopmentPlan,SubArea10C.

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11.6 EnvironmentalbaselineVietnamDelta

1Generalcharacteristics Two Focal Areas are located in the upper Vietnamese Mekong Delta, the Long Xuyen Qaudrangle, west of the Bassac River and the Plain of Reeds, east of the Mekong River. Characteristicsofthesetwoareasarelargelycomparableandtheyaredescribedheretogether. TheMekongfloodplainsofVietNamrangesinelevationbetweenabout1and5metersabove meansealevel.IntheLongXuyenQuadranglethereareafewverysmallhillsinanotherwise flatlandscape.TheMekongriver(SongTieninVietnamese)entersthefloodplainattheborder withCambodiaandbrachesintoseveralriversinitslowerreaches.SongHauisthecontinuation oftheBassacriverfromCambodiaandrunsmoreorlessparalleltotheMekongriver.Thetwo riversareinterconnectedintheupperreachesoftheVietnameseMekongfloodplain.Therivers are bordered by low natural levees and manͲmade dikes. The levees and dikes are used for housingandroads. In Viet Nam the Mekong delta is intensively developed, especially if compared to the Cambodian Mekong floodplain. Agriculture and an extensive system of canals has been developedsincethe1700sfornavigation,irrigation,floodmanagementandmanagementof salinewaterintrusion.ThefloodplainsofVietNamcanbecharacterizedasinTablebelowafter Douven(2008). GeneralcharacteristicsoftheVietNamMekongFloodplain Floodplain highlydeveloped Infrastructure densenetworkofcanals,leveesandroads; irrigationandfloodmanagementsystems Housinganddevelopment mainlyalongroads,rivers,leveesandcanals Economy intensiveagriculture,fisheriesandaquaculture Landuseandecology TramChinnationalpark,otherwisemostofthe landinuseforagriculture Hydraulics Floodspartlycontrolledbysluicesandother waterinfrastructure InmostprovincesoftheVietnameseMekongdeltaagriculturallandusecoversmorethan80% oftheavailableland.Farmingandfisheriesarethemajoreconomicactivitiesandarestrongly linkedtothefloodplain.Theoriginallandusecoverincludedwetlands,inundatedforestsand mangrovesalongthecoast. The floodplain in the northern part of the deltaconsists of natural levees, sandbars, and backswamps. The eastern, closed section of the upper floodplain is known as the Plain of Reeds,wheredrainageoffloodwatersisslowanddifficult,andfloodingtoadepthofupto3m occursforpartoftheyear.Thewestern,openfloodplainsectioniscalledsobecauseitslopes gentlytowardstheGulfofThailandsothatfloodwatercaneasilydrainaway,andfloodingis only1.5Ͳ2mdeep.ThisregionisknownastheLongXuyenQuadrangle,andincludestheHa Tienplain. Acidsulphatesoilsoccupymorethan40%oftheMekongDelta,waterdrainingfromthesesoils isusuallyhighlyacidic,apHoflessthan3isnotuncommon.ThelowpHinitselfisnotamajor problem.Themainimpactcomesfromhighlytoxiclevelsofaluminumandferrousironandthe unavailabilityofphosphorusforplantuptake.

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Annually, a large part of the northern area of the Vietnamese Mekong Delta is inundated by floodsfromtheMekongriver.Theinundationareaisabout1.4millionhectaresinlowͲflood yearsandabout1.9millionhectaresinhighͲfloodyears.Inundationdepthvariesbetween0.5 and4.0m,thefloodingmaylastbetween3and6months. Inundation of the Long Xuyen Quadrangle is caused by flood waters coming from the Bassac RiverandfromacrosstheVietnamͲCambodiaborder.Inundationsintheareagenerallylastfrom 3.5to4.5monthsdependingonthefloodlevelandthelocationThehighestinundateddepthis about4,0m.Dredgingandconstructionofnewcanals,primaryandsecondary,hasimproved irrigationanddrainageinthepasttwodecades.Ontheotherhandthecanalsalsoconveyfloods tothefarmareas,especiallyfloodsfromCambodia,whereasconstructionandembankmentof roadswithnarrowculvertslimitsthedrainagetotheGulfofThailand. Inundation of the Plain of Reeds is mainly caused by floods from the Mekong River. Flood watersflowtothePlainofReedsfromtwomaindirections:fromtheMekongRiver,andfrom acrosstheVietnamͲCambodiaborder.Inyearswithhighfloodssuchas1996and2000,flood watersreachtheareafromacrosstheborderattheendofSeptember.FloodsinthePlainof ReedsdraintotheMekongRiverthroughbridgesunderNationalRoadNo.30andsluicesunder NationalRoadNo.AsmallerportionofthefloodwaterdrainstotheVamCoRiver.Floodsofthe PlainofReedscauselonginundations,lasting3.5Ͳ5.0months.Theinundationdepthsrange between0.5Ͳ4.0m. Water quality in the Mekong Delta varies over the seasons. Surface water has high concentrationsofdissolvedsubstancesinthedryseason,andlowconcentrationsofdissolved substancesinthefloodseason.Forsuspendedsolidsareverserelationshipisvalid. IntheDeltaareaanumberofwaterqualityrelatedissuesareofimportance:highacidity,high salinity, microbiological pollution, and pesticide and herbicide pollution. Acid water has an impactontheagriculturalproductionandthelivingconditionofthelocalpeople.IntheLong XuyenQuadrangleandthePlainofReedsacidwaterisobservedattheendofthefloodseason, normallyfromDecembertoJanuary.Salnityintrusiondependsonavarietyoffactors,likethe sizeofthepreviousfloods,theamountoffreshwaterinflowfromupstream,andthegeneral weather at the beginning of the rainy season. In the Plain of Reeds, the salinity intrusion is reportedtohaveincreasedinrecentyears,bothinareaandduration. Generally microbiological pollution of the surface waters in the Mekong Delta is high. The observed average coliform concentration is about 300,000Ͳ1,500,000/100 ml. Discharge of untreated waste water and solid wastes from humans and livestock explains the poor water qualitysituation.The few studiesonpesticideandherbicidepollutionavailablefortheDelta reportthatnosignificantpollutioncanbedemonstrated. Ground water is widely used as a source for drinking water. Ground water is exploited and pumpedfromshallowwellsforhouseholduseandfromdeeperwellsforalimitednumberof groundwater plants. Although a lot of the wells have experienced quality problems of some kind,pH,highironcontent,salinityandbadsmellbeingmostcommon,almostallplansforthe futurearebasedonincreasedgroundwaterwithdrawal.

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2 Fishandotheraquaticfauna Forageneraldescriptionofthefishesandaquaticfaunaoftheareareferenceismadetothe description given for the Lower Mekong River in section 2.5 Environmental baseline for the CambodianDelta. Additional information is available from a somewhat outdated publication by Le Dien Duc (1989).AccordingtoLeDienDuc(1989)260speciesoffishareknownfromtheVietnamesepart oftheMekongDelta.Manyspeciesaremigratory,showingseasonalupstreammovementsto spawn.ThebrackishandcoastalzonefaunaisdominatedbyspeciesinthefamiliesClupeidae, Scombridae, Sciaenidae, Tachysauridae and Cynoglossidae. In freshwater, the fish fauna is dominated by Cyprinidae, Siluridae, Clariidae, Schilbeidae, Bagridae, Sisoridae, Akysidae, ChanidaeandOphicephalidae. 3 Wetlandsandterrestrialvegetation Although there is evidence from tree stump remains that the Vietnamese Delta was once heavily forested, the character of the delta has changed to such an extent during its long occupationbyhumansthatlittleisknownoftheoriginalvegetation.NaturalandsemiͲnatural vegetation communities found in the area can be divided into freshwaterͲ and saline communities. Freshwater communities can be further divided into swampͲforest vegetation, herbaceous vegetation, riverbank vegetation, and aquatic vegetation in waterways and waterbodies.Salinecommunitiesconsistlargelyofmangroveforest. ThedominanttreespeciesinMekongDeltaswampͲforestisMelaleucacajuputi.Thisspecies forms semiͲnatural forest in some small remaining areas, though the majority is plantation. Species forming the ground layer in swampͲforests vary according to local conditions, but usuallyincludePhragmitesvallatoriaandEleocharisspp.grasslands. Melaleuca forests are encountered particularly in areas with acid sulphate soils. A high proportion of them are of relatively recent origin, and many are within wood production reserves. In Lang Sen, Plain of Reeds, there are patches of the former riverine delta forest comprisingMelaleucaleucodendronassociatedwithSyzgiumsp.,Elaeocarpushygrophilus,Ficus microcarpaandCassiagrandis.PeatswampsareassociatedwithMelaleucaforestinUMinh, southoftheFocalArea.Theremaining,scatteredpatchesofforestareanimpoverishedrelicof amoreextensiveandvariableforestcover. AlthoughtodaysMelaleucaforestsarelowinplantbiodiversity,theyformanimportanthabitat forfish,amphibians,reptilesandbirds.TheseMelaleucaforestsareofprimeimportantfortheir breedingcoloniesoflargewaterbirdsandareoneofthefewrefugesintheDeltaforfreshwater speciessuchasturtles. Formerly, extensive grasslands occurred throughout the Mekong Delta, today, much of this habitatisunderricecultivation.Herbaceousvegetationincludesareasofseasonallyinundated grasslandwhichcanbesubͲdividedintofourmaingroups:

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- grasslandinareasofdeepandprolongedfreshwaterinundationthataredominatedby Eleocharisdulcis,OryzarufipogonandPhragmitesvallatoria,occurringonpotentialor lightactiveacidͲsulphatesoils; - grasslandonactiveacidsulphatesoilsthataredominatedbyE.dulcis,E.ochrostachys, Ischaemum rugosum and Lepironia articulata, and inundated with freshwater to a moderatedepthandforamoderateduration; - grassland on sandy and old alluvial soils that are dominated by Eragrostis atrovirens, Setariaviridis,MnesithealaevisandPanicumrepens,andinundatedonlytoashallow depthandforashorttime;and - grasslands affected by brackish water that are dominated by Paspalum vaginatum, Scirpuslittoralis,Zoysiamatrella,EleocharisdulcisandE.spiralis.Theyareaffectedby brackishwaterandcanbeinundatedonadailybasisbythetide. In the Mekong Delta seasonally inundated grasslands provide habitat for globally threatened birds, including Bengal Florican Houbaropsis bengalensis and WhiteͲshouldered Ibis Pseudibis davisoni.Thehabitatalsosupportsatleast60%ofthepopulationoftheeasternsubspeciesof Sarus Crane Grus antigone sharpii in the dry season. These grasslands also contain unique vegetationcommunities,someofwhicharenotlikelytobefoundelsewhereinIndochina.The salineinfluenceandpredominanceofacidͲsulphatesoilsinthedeltahaveastronginfluenceon the species composition of plant communities found here. Seasonally inundated grassland in theMekongDeltaarenowmainlyconfinedtotheHaTienplainandthePlainofReeds.Inthe Ha Tien plain, substantial areas still exist, but none has any form of protection and is in imminentdangerofbeinglosttoricecultivation.AlmostallthegrasslandofthePlainofReeds has been converted to rice agriculture, with only a small fragment under conservation protectioninTramChimNationalPark.

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LocationofimportantwetlandhabitatsintheLongXuyenQuadrangle

LocationofimportantwetlandhabitatsinthePlainofReeds 4 Wildlifeandrareandendangeredspecies MuchofthefaunaoftheMekongDeltaremainslittlestudiedanddeltaͲwidedescriptionsof faunaarelargelylacking.Mostinformationpresentedherehasbeentakenfromapublication by Le Dien Duc (1989). More recent information was compiled during a survey of BirdLife Internationalin1999. ThemammalfaunaoftheMekongDeltaispoorlydocumented,anditislikelythatithasbeen severelydepletedasaresultofconversionoflandtoagricultureandexpansionofthehuman population. LeDienDuc(1989)listed23speciesofmammalasoccurringinthedelta,includingfivespecies of dolphin, CrabͲeating Macaque Macaca fascicularis, SmoothͲcoated Otter Lutragale perspicillataandFishingCatPrionailurusviverrina.Recentlyevidencehasbeenprovidedforthe

StrategicDirectionsFloodRiskManagementͲ129Ͳ December2009 MRCFloodManagementandMitigationProgrammeComponent2:StrucuralMeasuresandFloodProofing continuing occurrence of the latter three species, as well as Sunda Pangolin Manis javanica, Cambodian Striped Squirrel Tamiops rodolphii, an unidentified Callosciurus squirrel, an unidentified otter Lutra sp., Common Palm Civet Paradoxurus hermaphroditus, Small Asian MongooseHerpestesjavanicus,LeopardCatPrionailurusbengalensis,WildBoarSusscrofaand SambarCervusunicolorintheUMinhwetlands,southoftheLongXuyenQuadrangle.Itislikely that other otter species once occurred in the delta, and some may remain, including HairyͲ nosedOtterLutrasumatranaandOrientalSmallͲclawedOtterAonyxcinerea. LeDienDuc(1989)listed92speciesofwaterfowlinthedelta,andnotedimportantcoloniesof cormorants,herons,egrets,storksandibises.InthegrasslandsofHaTien74specieshavebeen recorded,includingthegloballyendangeredBengalFloricanHoubaropsisbengalensis. BirdLifeInternational,duringtheirsurveyworkin1999,recordedatotalof194speciesofbirds. Of these, 73 were waterfowl under the definition given by the Ramsar Convention, but a further 27 species could be described as wetlandͲdependent (including several kingfisher speciesandwetlandͲdependentpasserinessuchasreedwarblersAcrocephalusspp.).Thus,over half(100species)werestronglyassociatedwithwetlands.Almostonethird(61species)were strictlymigrantstothedelta,includingmostoftheshorebirdsrecorded.Mostofthesewere nonͲbreeding visitors that breed outside of Viet Nam. Fourteen globally threatened or nearͲ threatened species were recorded during the survey work, of which three are classed as endangered,twoasvulnerableandnineasnearͲthreatened. The Mekong Delta provides habitat for a significant proportion of the regional or global populationofseveralspecies.Mostnotably,over10%oftheSouthͲEastAsianpopulationsof GlossyIbislegadisfalcinellus,LittleEgretEgrettagarzettaandCattleEgretBubulcusibis,3%of theworldpopulationofIndianCormorantPhalacrocoraxfuscicollis,and6%oftheSouthͲEast AsianpopulationofPurpleHeronArdeapurpureawererecorded.AtBaiBoiandDatMuiupto 0.8% of the world population of endangered Chinese Egret and up to 1.1% of the nearͲ threatenedAsianDowitcherwererecorded.Likelytheseareunderestimatesandprobablythe sitessupport>1%oftheglobalpopulationofbothspecies. ForseveralwidespreadspeciesitislikelythattheMekongDeltaprovidesimportanthabitatfor significant proportions of their regional populations. For example, the minimum estimates of the SouthͲEast Asian populations of SpotͲbilled Duck Anas poecilorhyncha (subspecies poecilorhyncha), Chinese Pond Heron Ardeola bacchus, Black Bittern Dupetor flavicollis and OrientalPratincoleGlareolamaldivarumareeachlessthan70,000,andeachspeciesiscommon outsidethenaturalandsemiͲnaturalsitesinthearea.TheMekongDeltapopulationsofeach speciesisthereforelikelytoconstitute>1%ofitsSouthͲEastAsianregionalpopulation. The passerine avifauna of the delta is species poor. Most species recorded are common and widespreadthroughoutmuchofAsia,andonlytwospeciesofconservationinterestoccur,the globallynearͲthreatenedAsianGoldenWeaver,andLargeͲbilledCrowCorvusmacrorhynchos, whichisbelievedtobevulnerabletohumanpressureandisveryscarceintheMekongDelta. Particularly common and widespread resident species included GoldenͲbellied Gerygone Gerygone sulphurea, Pied Fantail Rhipidura javanica, Common Iora Aegithina tiphia, Oriental MagpieRobinCopsychussaularis,OrientalWhiteͲeyeZosteropspalpebrosusandOliveͲbacked SunbirdNectariniajugularis.Severalwintervisitorsusethearea,thecommonestbeingBrown Shrike Lanius cristatus, Black Drongo Dicrurus macrocercus and Oriental Reed Warbler Acrocephalusorientalis.WetlanddependentpasserinesincludedOrientalReedWarbler,BlackͲ browedReedWarblerAcrocephalusbistrigiceps,RustyͲrumpedWarblerLocustellacerthiolaand ZittingCisticolaCisticolajuncidis.Veryfewspeciestypicalofterrestrialforestwerefound:those recorded(e.g.ScarletMinivetPericrocotusflammeusandIndochineseCuckooͲshrikeCoracina polioptera)wererestrictedtomatureMelaleucaforest.

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Thenumberofspeciesrecordedineachofthefourmainhabitatcategoriesgivesanindication of the relative importance of each to biodiversity conservation. Bird species richness was highest in seasonally inundated grassland and swamps (100 species), while anthropogenic habitats(includingpaddy fields,aquaculturalpondsandvillages)hadthelowestrichness(83 species).Melaleucaforestalsoheldalargenumberofspecies,almostasmanyasgrasslandand swamp(97species). Of the 14 globally threatened or nearͲthreatened species recorded, nine were recorded in seasonallyinundatedgrasslandsandswamps,andonlythreewererecordedinanthropogenic habitats (Greyheaded Lapwing, SpotͲbilled Pelican and Painted Stork). The high number of threatenedspeciesrecordedinmangrovesandmudflatsemphasizestheimportanceofthese sitesformigratorywaterbirds. Numberofspeciesassociatedwitheachoffourhabitatsfromsurveyscarriedoutinthe MekongDelta,byBirdLifeInternational,1999. Agricultur Mangroveand Seasonallyinundated Melaleuca aland mudflats grasslandandswamp forest urban Numberofspeciesrecorded 83 92 100 97 Numberofglobally 3 7 9 4 threatenedspecies Mammals, reptiles and amphibians were infrequently recorded during the survey of BirdLife International.Noevidencewasfoundofthecontinuingexistenceofdolphinsorcrocodilesin thewaterwaysoftheMekongDelta.Althoughnospecificeffortwasmadetosearchforthese, therewasnoanecdotalevidencetosuggestotherwise.Anecdotalreportsdidsuggest,however, thatottersLutra,Lutragale,Aonyxspp.remainatafewsites. Historical information is available on some species known to exist in the past. Most notable amongstreptilesareEstuarineCrocodileCrocodylusporosus,BatagurTerrapinBatagurbaska, four species of water snake Enhydris spp., Water Monitor Varanus salvator and Reticulated PythonPythonreticulatus. 5 Protectedareas NoprotectedareasarelocatedwithintheLongXuyenQuadrangleFocalArea.However,BirdLife International (1999) identified 10 priority wetland sites for conservation in the Vietnamese MekongDelta.HighestprioritywasgiventotheseasonallyinundatedgrasslandsoftheHaTien plaininthewesternpartoftheFocalArea.ThisareameetsthecriteriaadoptedbytheRamsar ConventiononWetlandstoidentifywetlandsofinternationalimportance.Recommendedfor conservationwerealsotheTinhDoiandTraSuareas. HaTienplaincontainsuniqueaspectsofbiodiversity,includingsignificantpopulationsofseveral globallythreatenedandnearͲthreatenedbirds.OfparticularimportanceareSarusCranesand theendangeredWhiteͲshoulderedIbisPseudibisdavisoni.Theareaalsoshowshighdiversityin flora, including unique gradients from brackish to freshwater and from acid to alluvial vegetationcommunities.Thereisanurgentneedforestablishmentoftwoprotectedareasin theHaTienplain,asthegrasslandhereisunderseriousthreatfromconversiontoagricultural land.Currently,grasslandisregardedasunusedland,anditsconservationwillbedependent onchangingattitudestothisirreplaceablehabitat. TheTraSuandTinhDoiareasarenotsuitableforgazettementasnaturereservesatnational level due to their small size and/or severe management obstacles to overcome. However, establishing these as provincial level nature reserves would be a first step in improving the

StrategicDirectionsFloodRiskManagementͲ131Ͳ December2009 MRCFloodManagementandMitigationProgrammeComponent2:StrucuralMeasuresandFloodProofing conservationimportanceandpotentialofthesesites.Thelocationoftheproposedprotected areasisgiveninFigurebelow

LocationofproposedprotectionareasintheLongXuyenQuadrangleFocalArea InthePlainofReedsFocalAreatherearetwoprotectedareas.TramChimNationalParkand the Lang Sen Wetland Reserve. They are described here briefly, based on a description by NguyenandWyatt(2006).

LocationofthetwoprotectedareasinthePlainofReedsFocalArea TramChimNationalPark TramChimNationalParkislocatedinTamNongDistrict,DongThapprovince,rightintheheart ofthePlainofReeds,38kmtothenorthofCaoLanh,thecapitalofDongThapProvince,19km totheeastoftheMekongRiver,and200kmtothesouthwestofHoChiMinhCity.Bordering theparkarethecommunesofPhuHiep,PhuDuc,PhuTho,PhuThanhB,PhuCuong,TanCong SinhandtheTramChimTownlet. ThenameTramChimhasbeeninexistenceforalongtime.TramChimisadepressedwetland area within the Plain of Reeds with natural Melaleuca forests (Tram in the Vietnamese language), an abundance of freshwater fish, and consequently many birds (Chim). The park topographyisquiteflat,andslopesslightlytotheeast.Inthepast,severalnaturalstreamsand riversflowedfromwesttoeast,distributingwaterfromtheMekongRivertothePlainofReeds. Nowthesestreamsandrivershavebeenreplacedbyasystemofcanals,someofwhichflow throughthenationalpark. Presently,TramChimNationalParkcoversatotalareaof7,588hectares,comprisingamixture ofseasonallyinundatedgrassland,regeneratingMelaleucaforestscoveringapproximately30% of the park, and open swamp. The park is surrounded by a 52 km perimeter dyke system interspersed by sluice gates, which control water flow in and out of the different zones. A

StrategicDirectionsFloodRiskManagementͲ132Ͳ December2009 MRCFloodManagementandMitigationProgrammeComponent2:StrucuralMeasuresandFloodProofing systemofcanalsanddykesdissectstheparkintosixpiecesseeFigure .ZoneA1,A2,A3andA4 arestrictlyprotectedareas;zoneA5isanecologicalrehabilitationarea.

SubdivisionofTramChimNationalParkinmanagementunits BirdLifeInternationalrankedTramChimNationalParkasoneofthemostimportantsitesfor conservation in the Mekong Delta. The park receives international recognition as seasonal habitatforthegloballyendangeredeasternraceoftheSarusCrane(Grusantigone).Thesiteis an important feeding area along the migratory route of the Eastern Sarus Crane in the dry season,supportingasmuchas60%ofthetotalpopulationintheLowerMekongBasinduring thelastdecade.ThetubersofEleocharisspp.grassesfoundintheparkaretheprimaryfoodof thecrane.Itisalsoanimportantbreedingsiteforwaterbirdsandotherwildlifesuchasthe Bengal Floricans (Eupodotis bengalensis), another globally endangered species. Tram Chim is alsooneofthefewplacesintheMekongDeltawherewildricevarietiesstillgrow.Atlandscape level,TramChimNationalParkcurrentlyisalittlespotofnaturalwetlandareasurroundedbya largeareaofagriculturallandsandhumansettlements. ThemanagementgoalsinzonesA1andA2aretorestorethenativevegetationofthePlainof Reeds including the maintenance of seasonal feeding grounds for the Eastern Sarus Cranes. ManagementgoalsofzonesA4andA5aretoprovidehabitatforcranesaswellasotherbird speciesdependentonvegetationassociatedwithearlierpatternsofseasonalwaterdrawͲdown, forexample,Bengalfloricans,OrientalpraticolesandgreenbeeͲeaters. ThefirstInvestmentPlanofTramChimNatureReserve(1994)proposedabufferzoneforTram Chim National Park covering an area of 20,500 ha. However, the extent, boundaries and purposeofthebufferzonehavenotbeendefinedinpracticeorintheInvestmentPlan.Thereis a proposal to expand the buffer zone incorporating land from the following communes: Phu Tho,PhuDuc,PhuHiep,TanCongSinhandPhuThanhthoughthisisthoughtnottoberealistic bythepresentparkmanagementpartlybecauseofcompensationissues. Thereareapproximately32,000peoplelivinginthecommunesadjacenttotheboundaryofthe park,themajorityofwhicharericefarmers,fishers,oragriculturallaborers.Atpresentthepark suffersfromconstantandsignificantpoachingandimpactfromthesurroundingcommunities. LangSenWetlandReserve LangSenisanotherremnantoftheoriginalwetlandlandscapeofthePlainofReeds,locatedin Vinh Loi commune, Tan Hung District, Long An province, approximately 23 km northeast of TramChimNationalPark.UnlikeTramChim,LangSenisnotconnectedtoordrainedbythe MekongRiver,butbythewesternbranchoftheVamCoRiver.Inseverefloodyears(suchas 1996and2000),LangSenisfloodedunder2.5to3.0mofwaterforadurationofthreetofour

StrategicDirectionsFloodRiskManagementͲ133Ͳ December2009 MRCFloodManagementandMitigationProgrammeComponent2:StrucuralMeasuresandFloodProofing months.However,withdevelopmentandenlargementofthecanalnetwork,thefloodperiod hasshortenedbyaboutonemonthcomparedtopreviousperiods. LangSenisnotincludedinanygovernmentdecisionorofficialsetofproposalsregardingthe nationalspecialͲuseforestssystem,asisTramChim.However,theestablishmentofanature reserveatLangSenwasproposedbytheLongAnProvincialPeople'sCommitteein1994,at which time an investment plan was prepared. This investment plan proposed establishing a 1,124hanaturereserve,withthenameDongThapMuoi.Thisproposaltoestablishanature reserve at Lang Sen is apparently still under consideration. However, in 2004, Lang Sen was officiallyestablishedasaProvincialWetlandReservebyLongAnProvincePeoplesCommittee. The Lang Sen Wetland Reserve covers an area of some 5,030 ha, among which 1,500 ha is swamplandprovidinghabitatsforavarietyofwetlandfaunaandfish. IntheVietnameselanguage,LangSenmeansLotusswamp.Substantialareasofnaturallotus swamparepreservedatLangSen.ThisvegetationtypeischaracteristicofthePlainofReedsbut is now seldom found anywhere to any great extent. The survey of key wetland sites in the MekongDeltabyBirdLifeInternationalin1999reportedthatLangSenwastheonlysitevisited wheresemiͲnaturalMelaleucaforestoccursalonga naturalriverchannel,and,assuch,is of notablebiodiversityvalue.ThesiteislistedasanImportantBirdArea(IBA)becauseasignificant numberoflargewaterbirds,includingtheEasternSarusCrane(Grusantigone)andtheglobally nearͲthreatenedPaintedStork(Mycterialeucocephala),enͲroutebetweentheirbreedingareas inCambodiaandtheirnonͲbreedingareasintheMekongDeltaofVietNam,useLangSenasa stopͲoverarea. Arecentbiodiversitysurveyrecorded156plantspecies,149vertebratespecies(amongwhich 13speciesarelistedintheVietNamRedBookforendangeredspecies)and11benthicanimal species.TypicalhabitatsfoundinLangSenWetlandReserveare: - naturalstreamsandrivers; - riparianforests(average10Ͳ15mwidebandofmultiͲspecieswoodytrees)alongrivers andcanals; - seasonallyfloodedgrasslands,floodedforfivetosixmonthsperyearandsusceptibleto fireinthedryseason; - swamp with water almost year round, providing good refuge for wildlife like snakes, turtles,tortoisesandvariousfishspecies; - Melaleucaforests; - ricefields;and - canals. AmajorchallengeatLangSenWetlandReserveisthatmuchofthereserveandsurrounding areaisinhabitedbylocalcommunities,predominantlyalongthenetworkofcanalsthatcrissͲ crossthepark.ThisisdifferentfromthesituationintheTramChimNatureParkwherethereare nocommunitieslivingwithintheparkboundary. 6 Fisheries 6 Fishprovide40Ͳ60%oftheproteininthedietofpeoplelivingintheMekongDelta.Fishingis carriedoutalmosteverywhere,fromthesmallestcanalstothelargestriverchannels.Inmany ofthemajorrivers,netsareplacedacrosshalfthechannelormore.Bothfreshandsaltwater speciesarefishedforandawiderangeoffishingmethodsused.Fishtrapsarewidespread,the useofgillͲnetsisfrequentandmoredestructivemethods,suchaselectroͲfishing,arecommon. Ofthe260speciesoffishknownfromthedelta,200contributetothecommercialfishery(Le DienDuc,1989).Inaddition,shellfish,mainlyMolluscaandCrustacea,constituteanimportant

StrategicDirectionsFloodRiskManagementͲ134Ͳ December2009 MRCFloodManagementandMitigationProgrammeComponent2:StrucuralMeasuresandFloodProofing element of the fishery. A study by Sjorslev (2001) in the An Giang Province (Long Xuyen Quadrangle)indicatedthatfor40%ofthehouseholdsfisheries(andcollectingaquaticanimals) is a major part of food collection for family consumption, while for 23% of the households, fishing provides supplemental income. Seven % of the households have fishing as a major sourceofincome. Intermsofhabitatsused,floodedirrigatedricelandsorriverinefloodplainisusedforfishingby 67%ofthehouseholds,followedbyperennialrivers(28%),perennialcanals(25%),andrainfed rice paddies (8%). All habitats are used for fishing throughout the year. The fishery is very diverseandatotalof76speciesgroupswerereportedtobecaught.Onespeciescontributes most to the total catch in terms of kg, namely Cirrhinus jullieni. Apart from fish, freshwater musselsandprawnsarealsoveryimportantincatches.For1999,theofficialtotalcatchfigure forAnGiangprovincewas64,000tons. MaincharacteristicsofthefisheriesintheDongThapProvinceoftheprojectareaareillustrated by the results of a household survey carried out in 2004 (Nguyen Van Trong and Pham Mai Phuong: Preliminary results of socioͲeconomic survey on fisheries in the flooded area in the Mekong Delta, Binh Thanh and an Binh A villages, Hong Ngu district in Dong Thap Province, ResearchInstituteforAquacultureNo.2,2005). NguyenVanTrongandPhamMaiPhuong(2005)reportedonthefisheriesintheDongThap province(PlainofReeds).Duringthefloodseason,fromAugusttoDecember,allpaddyfields areinundatedbyafloodwiththewaterdepthof1.5Ͳ3m.InordertoprotecttheSummerͲ Autumnricecropfromtheearlyflood,lowͲdikeandsluicesystemshavebeenbuiltaroundmost ofthepaddyfields.InAugust,afterthericeharvest,thefloodwillbeallowedintothericefields throughopensluicegatesorrunningoverdikesatthefloodpeak.Bythismeasure,negative impactsonfisheriesresourcesfromthefloodcontrolsystems(obstructionoffishmigrationand diminishingoffeedingandspawninggrounds)isprevented. About65%ofthehouseholdsinthesurveyedareaareinvolvedinfisheries,butonlysome9% fullͲ time (or professional). Rivers and irrigation canals are main fishing grounds for local fishermanduringthedryseason.Floodedricefieldsarethemajorfishinggroundsduringthe floodseason. There were about 40 species of 12 families commonly identified in the fish catch. Besides Henicorhynchussiamensisthatwerecapturedinalargequantity,bringinginhighincome,most oftheotherfishspecieswereharvestedatsmallsize,lessthan10cminlength,givinglowvalue ofproduction. ThemostabundantfamilywasCyprinidaewith19species,including(i)asmallsizefishgroup withalowproduction:Paralaubucaspp.,Rasboraspp.,Systomusaurotaeniatus,(ii)asmallsize fishgroupbutwithalargeproduction:Henicorhynchossiamensis,Dangillaspp.,.and(iii)bigfish with low production: Puntioplites spp., Cirrhinus microlepis, Barbodes goinionotus, Cyclocheilichthysrepasson,Labeochrysophekadion.FivespeciesofSiluridaewereidentifiedin thefishcatchwhereasotherfamiliesonlyconsistedof1Ͳ3speciesrecorded. ThefamilyCyprinidaewasrecordednotonlytobemostabundantinspeciescompositionbutalso intotalyield.TheproductionoffishspeciesbelongingtoCyprinidaeaccountedfor59%ofthe total production, in which, Henicorhynchus siamensis and Dangila spp. account for 37% . The bagriidswerethesecondgroupintermofquantitywithaproductionof3.6tons(19%),including MystusgulioandMystusnemurus. Someprawnspecieswererecordedaswell.

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Allfishinghouseholdsusedpartofthefishcatchforconsumption.Mostfamiliessoldpartofthe catchtoincreasefamilyincome(93%).Itwasfoundthat50%ofcapturefishproductionwas soldtomarkets. 7 Forestry Melaleucaandmangroveforestsprovideanumberofbenefitstolocalpeople.Thetimberis valuedforconstructionofhousing,andisalsousedasafuelwood.Theproductionofhoneyis practicedinMelaleucaforest,andhoneyharvestedfromwildbeesisparticularlyhighlyvalued. MelaleucaisalsonowwidelyrecognizedasbeingsuitableforplantingonacidͲsulphatesoils,as its cultivation does not involve the creation of raised beds. Melaleuca cropping cycles often involveafirstcropofpolestakenafter8Ͳ10yearsgrowth,afterwhichstumpsareleftinthe ground to regenerate. When fully reͲgrown, the forest crop is clearͲfelled and new saplings planted.Duringtheinitialeightyears,otherforestproductsaretakentoprovideasourceof income. These include aquatic fauna for food, Melaleuca oil (a valuable medicine), chaoi Stenochlaenapalustris(aplantusedformakingropeandfishnets),mopAlstoniaspathulata(a woodyplantusedformakingfishingfloats)andMelaleucabark(usedforthermalinsulation). ForestsareanimportanteconomicresourceintheMekongDelta.Previously,largeareaswere covered in Melaleuca and mangrove forests, but wartime conflict devastated much of this, particularlyduetothesprayingofdefoliants.Morerecently,thebenefitsofMelaleucaplanting have been widely recognized, and the area of this forest type has increased in recent years. Mangrovehasalsobeenwidelyreplanted,mainlyinanefforttocounteractshorelineerosion. References BirdLifeInternational,1999,TheconservationofkeywetlandsitesintheMekongDelta, ConservationReportNumber12. Douven,W,2008,RoadsandFloods,recommendationsforthePlanningandDesignof EconomicallySoundandEnvironmentallyFriendlyRoadsintheMekongFloodplainsof CambodiaandVietnam,SynthesisReport. Le Dien Duc, 1989, Socialist Republic of Vietnam. pp. 749Ͳ793, in D. A. Scott, ed. A directoryofAsianwetlands.Gland,Switzerland:IUCN. MRC,2006,BasinDevelopmentPlanSubArea10ͲV. Nguyen,V.X.andA.Wyatt,2006,Situationanalysis:PlainofReeds,VietNam.Mekong Wetlands Biodiversity Conservation and Sustainable Use Programme, Vientiane, Lao PDR. NguyenVanTrongandPhamMaiPhuong,2005,PreliminaryresultsofsocioͲeconomic surveyonfisheriesinthefloodedareaintheMekongDelta,BinhThanhandanBinhA villages,HongNgudistrictinDongThapProvince,ResearchInstituteforAquaculture No.2. Sjorslev,J.G.(Ed.),2001,AnGiangFisheriesSurvey,AMFC/MRCandRIA2;Vientiane.

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11.7 TheTonleSapGreatLakeecosystemanditsimportanceforecologyandLowerMekong fisheries

1 Introduction ThischapteraimstoexplaintheuniqueroleoftheTonleSapGreatLakeasafishfactoryfor theLowerMekongfisheries.Emphasisisonmigratoryfishspeciesandthekeyfeaturesofthe Mekong River hydrological system and flood characteristics that are important for the maintenanceofthesesspeciesandtheirHabitats. The information presented in this paper has been taken directly from a number of key publicationsontheTonleSapecosystem,fishmigrationandspawningpatternsandinlandfish production.ThemostimportantpublicationsusedarelistedintheReferencelistattheendof thischapter. TheTonleSapGreatLakeisoneofthelargestfreshwaterlakesinSoutheastAsia.Itappearsthat thelakeoriginatedabout5,000yearsago.TheuniquehydrologicalregimeofTonleSapLakeis characterizedbyanannualinflowofMekongwatersintothelakebasinduringthewetseason, whenthewaterlevelsintheMekongfall.Attheendofthewetseason,theflowreversesandthe lake empties again. This hydrological cycle supports and maintains high biodiversity and productivity,particularlyfish,plantcommunities,andwildlife,whicharetheresourcebaseforthe nationaleconomyofCambodia.NearlyhalfoftheCambodianpopulationdependsontheLakes resources,aboutonemillionofwhichisfishdependentcommunity.TonleSapLakefurthermore playsavitalroleinKhmerculturalidentity,whichisreflectedinthetraditions,livelihood,festivals, andtaste.ItisbelievedthattheKhmerAngkorcivilizationandmanytemplescouldnotprosper withouttherichnaturalresourcesofTonleSapLakeassourcesofwealth.Evidenceofcultural influenceofTonleSapLakecanbe foundinthebasͲreliefs oftheBayontemple. Figurebelow showsthegenerallayͲoutofthearea(AfterADB,2005). Recognizing the ecological, economical, and socioͲcultural value of the Lake, the Royal GovernmentofCambodiadecidedtodesignatethewholeTonleSapLakeasBiosphereReserve under the Man and Biosphere Program of UNESCO in October 1997. Parts of its wetlands are includedinthelistofRamsarsites(RamsarConventiononWetlands,1971).

GenerallayoutoftheTonleSapGreatLake(AfterADB,2005)

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2 Physicalresources 2.1 Climate Cambodia's climate is dominated by the tropical wet and dry monsoons. The southwest monsoonbringstherainyseasonfrommidͲMaytomidͲSeptemberorearlyOctober,whilethe northeast monsoons flow of drier and cooler air lasts from early November to March. Temperaturesarefairlyuniformataround25°CthroughouttheTonleSapBasinarea.Average annual rainfall is between 1,300 and 1,900 millimeters, with the largest amounts in the southeast. 2.2 Topographyandsoil TheTonleSapLakeissurroundedbyaratherflatfloodplain.Thesoilsaremainlydevelopedin unconsolidatedalluvialdeposits,comprisingclay,silt,sand,andgravel. 2.3 Groundwater Groundwater depth in the area varies considerably. The water table changes with rainfall, specificlocalgeomorphologicconditions,andthedistancetothepermanentwateroftheTonle SapLake.Manganeseisreportedtobefoundinthegroundwaterinconcentrationsthatmight causesomeconsumerinconvenience(e.g.,stainingoflaundryandsanitaryware,taste),though itisnotbelievedtohaveanynegativehealtheffects.Althougharsenicconcentrationsarefound inthegroundwaterthroughoutCambodia,theycommonlydonotposeaproblem. 2.4Surfacewater TheTonleSapLakeisconnectedtotheMekongRiverthroughthe100kmlongTonleSapRiver. FiftysevenpercentofthewaterintheTonleSapLakecomesfromtheMekongRiver.Duringan average wet season, about 52 percent comes in directly through the Tonle Sap River, and 5 percent flows overland through the floodplain from the Mekong. Another 30 percent comes fromriversthatflowdirectlyintothelakeandabout13percentcomesfromrainfalloverthe lakeitself. The annual flood pulse, the cyclical changes between high and low water levels, is crucial in maintaining this highly productive system that has adapted to the exceptionally high natural variabilityofthelakelevel.Betweenthedryandthewetseasonthevolumeofthelakeranges fromabout1.3km3upto75km3,itssurfaceareavariesfrom2,500km2uptoabout15,000km2, anditswaterlevelincreasesfrom1.4mto10.3mabovesealevel. Thequalityofsurfacewatershowsextremevariations.Inthedryseason,pollutionbyhuman andhouseholdwastecanbehighneardenselypopulatedareas. 3 Ecologicalresources 3.1 Fisheriesandaquaticbiology Thefloodingoftheextensiveplaincoveredwithforestandothertypesofvegetationenables thetransferofterrestrialprimaryproductsintotheaquaticphaseandentryintolakeͲwidefood webs.Sedimentationoccursalmostexclusivelyinthefloodplain.Thefloodplainvegetationplays a crucial role in ecosystem productivity by providing habitats, substrate area, and food for aquaticorganisms.Manyvarietiesoffishhavecommercialvalue,andmorethan100speciesare caughtregularly.However,aboutadozenmakeupthebulkofthecatches,byweightandvalue. A wide variety of active (seining, lifting, casting) and passive (traps, hooks and line, gillnets)

StrategicDirectionsFloodRiskManagementͲ138Ͳ December2009 MRCFloodManagementandMitigationProgrammeComponent2:StrucuralMeasuresandFloodProofing fishing gear and methods are used. Fish behavior (migration, habitat preference, reaction to waterqualitychanges,feedingstrategies)isexploitedinthefishery.Theuseofdestructivegear andpractices(poisoning,electrocution,brushparks,damming,andpumpingofchannels)are widespread. The importance of the area for fisheries in the entire Lower Mekong Basin is discussedinmoredetailinSection6. Other aquatic animals with direct livelihood significance include water snakes, mollusks, and invertebrates suchas shrimp.Water snakesare commonintheTonle Sap ecosystem,and five species commonly are caught and traded. Around the lake, commercial rearing of captive crocodilesispracticed.IndicatorssuggestthatthecurrentuseoftheTonleSapsnaturalresources hasexceededoptimumecosystemproductivity. 3.2 TimberandnonͲtimberforestproducts ThenaturalfloodplainvegetationisusedforthecollectionofavarietyofwoodandnonͲwood forestproducts.Woodiscollectedfordomesticuse,includingfor(i)fuelwoodorcharcoal,(ii) constructionmaterial,(iii)useinbrickkilns,(iv)fishprocessing(smokinganddrying),and(v)the constructionoffishinggear.ThedominantspeciesincludeBarringtoniaacutangula,Diospyros cambodiana, Terminalia cambodiana, Gmelina asiatica, Ficus heterophylla, and Vitex holoadenon. NonͲwood forest products include a wide range of plants used as food, and for medicinal purposes for humans and animals. Lianas (in particular Combretum trifoliatum, Breyniarhamnoides,Tetracerasarmentosa,andAcaciathailandica)arecollectedforfurniture andfishinggearproduction.Otherplantproductsincludefruits,seeds,resins,tubers,bark,and mushrooms. Some forest animals and their products are collected, including bee wax and honey.Somelargeranimalsareusedaspets(macaques,iguanas,birds),traded,orconsumedas food.Birdsarehuntedforfood,pets,andtrade.Eggsarecollectedforconsumption.Aquatic plantsarecollectedforhumanconsumption,asfeedforfarmanimals,orforfurthercultivation (e.g.,lotus). 3.3 Biodiversity Withthegloballossofwetlands,theTonleSapLakeanditsrelativelyintactecosystemprocesses are exceptionally important for global biodiversity. The species richness of the Tonle Sap ecosystemisonlypartlyknown.Inarecentinventory,885speciesoffloodplainplantsandanimals were found in the Tonle Sap. However, this does not include, for instance, the 197 species of phytoplankton that have been identified separately. The 2004 International Union for ConservationofNatureandNaturalResources(IUCN)RedListofThreatenedSpeciesmentions 197speciesinCambodiaconsideredatriskofextinction,endangered,criticallyendangered,or vulnerable.ManyofthesearefoundintheTonleSapecosystem.Ofthe197speciesmentionedby IUCN,24arecriticallyendangered,39areendangered,and53arevulnerable.IntheTonleSap ecosystem, 5 critically endangered species (2 fish species, 2 bird species, and the Siamese crocodile)arepotentiallystillpresent.However,noneofthesespeciesisendemictoTonleSap.As aconsequenceof3decadesofunrest,accesstotheprojectareahasbeenattimesdifficult,anda biodiversityinventoryoftheTonleSapecosystemisfarfromcomplete. In Cambodia,22 species are classified as data deficient. This could mean that some of these speciesarethreatened,thoughdataareinsufficienttoassesstheirconditioninfull.Severalfish species,particularlyamongthosethatgrowlarge,areendangered.Inits2004RedList,IUCN classifiedthegiantMekongcatfish(Pangasianodongigas)ascriticallyendangered.Theheavy exploitationofcrocodileandtheendemicTonleSapwatersnake(Enhydrislongicauda)alsoisof particular conservation concern. The Siamese crocodile (Crocodylus siamensis) is critically endangeredinthewild,thoughitiswidelybredandkeptincaptivity.Orcaellabrevirostris,the freshwaterIrriwaddydolphinthatisfoundintheMekong,isoccasionallyalsoseenintheTonle SapLake.ThebiodiversityintheTonleSapisbestknownforbirds.Ofthe104waterbirdspecies

StrategicDirectionsFloodRiskManagementͲ139Ͳ December2009 MRCFloodManagementandMitigationProgrammeComponent2:StrucuralMeasuresandFloodProofing that have been recorded in the Tonle Sap, 89 are abundant, while 14 are considered internationallysignificant.ThetwocoreareasoftheTonleSapBirdReserve,PrekToalandLake Chhmar,havethemostendangeredspecies.PrekToalisthemostimportantbreedingarea. 3.4 LandandCrops The continuous expansion of agricultural land into the floodplain to address the rising populationandlowproductivityofpaddyfieldshascomeattheexpenseofthenaturalflooded forestvegetation.Thecompetitionbetweenthenaturalassetsoffloodedforestandriceand otheragriculturecropsisincreasinglyunderminingtheproductivityoftheTonleSapecosystem. TheforeshoreoftheTonleSap'spermanentlakeandtheriverbanksprovideland,evenonly seasonally,tothelandlesspoor,whoalsobenefitfrombeinginthevicinityofwaterfortheir crops. 3.5 Livestock Livestockisimportantforthelivelihoodofmanypeople.Pigsareheldwidelyinfloatingvillages and throughout the floodplain. Cattle provide traction for rice farmers, and flooded forest is burnedinplacestopromotethegrowthofgrassforcattlegrazing.Eventhepoorerhouseholds canaffordducksandchicken.Ducksalsogenerateincomethroughtheiruseinpestcontrolin ricefields. 4Economicdevelopment Mostoftheactivitiesintheprojectareaarebasedonfisheriesoragriculture.Fishprocessingis widespread,whileagriculturefocusesonriceproductioninmostplaces.Infrastructurefacilities arelargelyabsent,particularlyinthefloatingorstiltedvillages.Thefewaccessroadsaremostly in poor condition. Although ports and landing sites lack basic infrastructure, they contribute effectively to livelihood generation. The lake is used for transportation of people and goods, includingpetroleumproductsandfish.Mostofthepeopletransportedareforeigntourists.Low waterlevelsinthedryseasonlimitthesizeandtrafficofboats. 5Socialandculturalresources More than 1.2 million people in the Tonle Sap area depend on fishing for their livelihood. People typically live in villages, grouped in communes. Many fisher folk are highly mobile, migratingwithinthefloodplainandlaketofindfishingopportunities.TheTonleSapfishand floodplainresourcesarealsopartofthelivelihoodstrategiesformanypeoplelivingoutsidethe projectarea.Thedistributionandqualityofhealthandeducationfacilitiesvary.Botharelacking inlakeͲbasedcommunities.ThehistorictemplecomplexofAngkorWat,locatedinthearea,is an important tourist attraction. Buildings and features of archaeological and historical significance(e.g.,KhmerEmpireeratemplesandshellmounds)arescatteredthroughoutthe projectarea. 6 ImportanceoftheTonleSapwetlandsystemforfisheries Cambodia has the world's most productive inland fishery. A single hectare of floodplain can produceupto230kilogramsoffishayear.Intermsofvalue,theoverallfishingsectoraccounts for10to12percentofgrossdomesticproduct(GDP)andcontributesmoretoincome,jobsand foodsecuritythaninanyothercountry.Theinlandfisherieshasanannualcatchconservatively estimatedatabout400,000tons.TonleSapfisheriesaccountforalmosttwoͲthirdsofthetotal catch in Cambodia. In 2006, the Inland Fisheries Research and Development Institute of the Fisheries Administration estimated the value of fisheries and other aquatic resources of the TonleSapLakeconservativelyat$233millionayear(Baranetal.,2007).

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6.1 Relationshipbetweenfishproduction/catchesandfloodcharacteristics BasedonliteratureonotherlargeriversystemselsewhereintheworldBaranetal.(E.Baran,N. van Zalinge, Ngor Peng Sun, Floods, floodplains and fish production in the Mekong Basin: present and past trends, MRC miscellaneous publications, not dated) identified a number of factorsthatdeterminefishproductionintheMekongBasin.Theyarediscussedbelow: 6.1.1 Waterlevel The correlation between the total catch and the river discharge in the same year has been extensivelydocumentedforlargeriversystemsaroundtheworld.Ithasalsobeenshownmore specifically that catches could be strongly related to the highͲwater flood regime at the beginningofeachseason,andthatfishgrowmorequicklywhenfloodlevelsarehigher. AlsofortheLowerMekongithasbeenshownthathigherfloodsdirectlyresultinhigherfish production.Althoughmanyfactorsareinvolved,higherfloodsproducelargeramountof fish andkeepanumberofimportanthabitatsviable.ObservationsonthebagͲnet(Dai)fisheryfor migratingfishintheTonleSapRiverduring19952002indicatethatyearͲtoͲyearvariationsin maximumMekongRiverfloodlevelsandrelatedTonleSapfloodplaininundationstronglyaffect thefishyield,seefigurebelow.

RelationshipbetweenthemaximumfloodleveloftheseasonandthefishcatchoftheDaior BagnetfisheryintheTonleSapRiver. Highfishyieldsinyearswithhighfloodsisexplainedbyanumberoffactors.Firstlyspawning success of fishes is related to available spawning grounds: higher floods inundate larger floodplain areas, so creating larger spawning areas. Secondly, a high flood also means that fishingactivitiesaredispersedmoreevenlyoverlargerareasgivingbetterpossibilitiesforyoung fishes to survive. The above stated is not valid for all fish species: the fishing lot catch of snakehead (Channa micropeltes) was highest one year after a high flood (Van Zalinge et al. 2003). Other factors of importance are the sediment concentrations of the floodwater and the dissolvedoxygenconditions.Sediments carriedbytheMekongwaterstotheTonleSapLake bringintheessentialnutrientsthatenterintothelakesfoodwebs.Thehigherthefloodthe moresedimentisbroughtin.Thisleadstoimprovedsurvivalandgrowthoffishandhenceto higherfisheryyields(seealsoSection6.1.6).

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6.1.2 Durationoftheflood Alongerperiodoffloodprovidesalongergrowthperiodforfishes,andthereforeahigheryield. Thisstrongcorrelationbetweentheannualfishproductionandthedurationofthefloodhas beenclearlydemonstratedformanyriversystems.However,astheprocessislinkedtoorganic matter decay and nutrient release, the relationship seems to be asymptotic, a plateau being reachedafteracertainduration. 6.2.3 Timingoftheflood Most tropical fish species release eggs just before or during the flood, which results in their spreading into floodplains. In the Mekong River, rising waters trigger spawning in adults of manyspeciessuchasPangasiidsandjuvenilesdrifttowardstheTonleSapsystemwherethey grow.Timingofthefloodanddurationofthefloodseasonduringwhichthejuvenilescangrow arethereforetwoparametersthatwillinfluencethetotalproduction(seealsoSection7). Delays in the onset of the flood will result in delays in the arrival of oxygenͲrich waters. DissolvedoxygenlevelsinTonleSapwatergenerallydeclineduringdryseason,untiltheinflow ofoxygenͲrichwateratthebeginningoffloodseason.Whilefishmayswimtomoreoxygenated waters,eggsandlarvaeareunabletomoveandmaybeadverselyaffectedifthearrivalofthe floodisdelayed.Flowchangesalsohaveanimpactonthedriftoffishlarvaeandjuveniles. 6.1.4 Regularityofflooding Afterearlyrainfallsandriverlevelrisehavepromptedmigrationandspawning,smalldrought periodscancausemassivemortalityofeggs,fishlarvaeandfryaswellasamphibians.Stickyfish eggscanbecomesuddenlyexposedonvegetation,whilelarvaeandjuvenilescangetkilledas the water recedes and small ponds dry up. This factor has scarcely been mentioned in the literature, but sometimes happens in the Tonle Sap region where it can result in massive mortality. 6.1.5 Characteristicsofthefloodedzone Forfishes,floodplainsarefavorableasafeedingzone(releaseofnutrients,primaryproduction anddetritusͲbasedfoodchain),andbecausetheyprovidesheltertojuvenilesagainstpredation (shallow water, flooded vegetation). The importance of different flood plain habitats for the ecosystems functioning is partly unknown, but the diversity of food resources and habitats allows multiple strategies, species, sizes, stages and life cycle strategies. Flooded forests are essentialinprovidingshelterandlivinghabitatsforlargevarietyofbiota,butontheotherhand shrubandgrasslandprovidesoftenthelargestvarietyofbiodiversity.Grasslandisobviously playingamajorroleinnutrientcyclingandsupportsahighfishproduction. 6.1.6 Physical/chemicalconditions The quality of flood waters has an impact on the flood plain ecosystem e.g. by bringing sediments and nutrients to the system. Nutrient bearing sediment is important for primary productiondrivingthefishgrowth.Changesinthesedimentloadcancausemajorchangesin thefishproduction. IntheTonleSaparea,sedimentsarelargelybeingtrappedattheinterfacebetweentheoxygenͲ richwatersofthelakeandriversandtheoxygenͲpoorwatersofthefloodplain,givingrisetoa richriparianvegetationoftalltrees.Thewatersabovethefloodplainaremuchclearerthanthe lakewaters,asnearlyallsedimentshavebeenfilteredout. AccordingtoVanZalinge(2003)thisexplainswhythecatchperhectareappearstobestableno matterwhethernaturalhabitatsoragriculturallandsareflooded.Thebiologicalproductivityis derivedfromthesedimentsinthewatersofthelake,riversandespeciallytheirborderareas andnotfromtheextensivefloodplainsthemselves.Thesedimentscontainthenutrientsneeded by the phytoplankton. Phytoplankton blooms do not occur in the lake, because of intensive grazingbyzooplanktonandfish.

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Oxygenconditionsobviouslyaffectwherefishcanliveandreproduceandhowdifferentspecies have developed strategies for avoiding unfavorable conditions. Floodplains are by and large oxygenpoorenvironments.Becauseofoxygentransportanddispersion,borderareasbetween thewelloxygenatedlakeproperandtributariesandfloodplainshavemorefavorableoxygen conditionsthanareasdeeperinthefloodplains.Openareasinsidethefloodplainssuchaslakes andfieldsofferbetteroxygenenvironmentsandsafetyzonesforfish.Flowcantransportlarge massesofanoxicwaterbothinthehorizontalandverticaldirectionandtraporkillfishinthese limitedareas.Oneexplanationfortheobservedfishdeathsmaybetheanoxicwaterinflow. 7 Fishmigration 7.1 Introduction TheimportanceofmigratorybehavioramongMekongRiver fishes hasbeenacknowledgedfor long,manyeconomicallyimportantfishspeciesareknowntobehighlymigratory.Somespecies undertake longitudinal migrations, while others make only localized and lateral migrations. LongitudinalmigratoryfishspeciesbegintospawnintheMekongRiveratthebeginningofthe rainy season (MayͲAugust). Fish eggs and fry are carried by the current and swept into the floodplainareasaroundtheTonleSapGreatLakeandtheareassouthofPhnomPenh.Whenthe flood recedes, most of fish species migrate to deeper waters in the lakes, rivers or tributaries (lateralmigration),butmanyspecieswillundertakelongermigrations(longitudinalmigrations)to theMekongRiver Basedontheirmigrationbehaviortwogroupsoffisharedistinguished:whitefishandblackfish. When floodplains drain at the end of the wet season, water remains in lakes and scattered depressions, which continue to shrink in size and number during the dry season. Floodplain waterbodiesbecomehot,oxygenisdepletedandfoodandshelterdiminish,withmanyponds dryingͲoutcompletely.Sothefish,whichfeedandgrowonfloodedareasmusteitherreturnto theriverasthewatersrecede,orremainandendurethepoorconditionsonthefloodplain. Specieswhichleavefloodedareasandreturntoriversarereferredtoaslongitudinalmigrants orwhitefishes,astheyspendmostoftheirlivesinturbid(white)riverwater.MostwhiteͲfish speciesmigrateintofloodedareasduringthemonsoonseasonandmigrateoverlongdistances todryͲseasonrefugesattheendofthefloodseason.Representativesofthisgrouparesomeof the cyprinids, such as Cyclocheilichthys enoplos (Soldier river barb or Chhkok) and Cirrhinus microlepis (Small mud carp or Prul/Kralang), as well as the river catfishes of the family Pangasiidae. Thespeciesoffishwhichremaininlakesandswampsonthefloodplainareknownaslateral migrantsorblackfishes,astheyspendtheirlivesinrelativelyclearwaterthatisteaͲcoloredby chemicalsdissolvedfromfloodplainvegetation.Decompositionofvegetationcausesfloodplain watertobeacidicanddepletedinoxygen,stresseswhichblackfishescantolerate.Mostblack fishescanbreatheair,whilemanyspeciescansurviveoutofthewaterforlongperiods,and most can move overland in search of new water bodies. A few species can bury themselves deepinthemudandwaituntilthenextflood.Manyblackfishesareusedinaquacultureand aretransportedalivetomarkets.TheyarenormallyreferredtoasnonͲmigratory,althoughthey performshortseasonalmovementsbetweenpermanentandseasonalwaterbodies.Examples of blackͲfish species in the Mekong are the climbing perch (Anabas testudineus), the clarias catfishes(e.g.Clariasbatrachus)andthestripedsnakehead(Channastriata). Anadditionalgroup,intermediatebetweenblackͲfishesandwhiteͲfishesisformedbythesoͲ calledgreyfish.Speciesofthisgroupundertakeonlyshortmigrationsbetweenfloodplainsand adjacentriversand/orbetweenpermanentandseasonalwaterbodieswithinthefloodplain.

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7.2 Spawninghabitats Spawninghabitatsaregenerallybelievedtobeassociatedwitheitherrapidsanddeeppoolsof the Mekong mainstream and tributaries or with floodplains (e.g. among certain types of vegetation,dependingonspecies).Riverchannelhabitatsare,forexample,usedasspawning habitatsbymostofthelargespeciesofpangasiidcatfishesandsomelargecyprinidssuchas Cyclocheilichthys enoplos, Cirrhinus microlepis, and Catlocarpio siamensis. Floodplain habitats areusedasspawninghabitatsmainlybyblackͲfishspecies. Many species that spawn in river channels in the openͲwater column rely on particular hydrologicalconditionstodistributetheoffspring(eggsand/orlarvae)todownstreamrearing habitats.Informationonspawninghabitatsformigratoryspeciesintheriverchannelsofthe MekongBasinisscarce.Onlyforveryfewspecies,spawninghabitsarewelldescribed.Formany species, in particular for deepͲwater mainstream spawners such as the river catfish species, spawning is virtually impossible to observe directly. Information about spawning has been obtainedindirectlyfromobservationsofripeeggsinfishes Forfishesthatspawninmainriverchannels,spawningisbelievedtooccurinstretcheswhere therearemanyrapidsanddeeppools,e.g.(1)theKratieͲKhoneFallsstretch;(2)theKhone Falls to Khammouan/Nakhon Phanom stretch; and (3) from the mouth of the Loei River to Bokeo/Chiang Khong. The KratieͲKhone Falls stretch and the stretch from the Loei River to LuangPrabangareparticularlyimportantforspawning. 7.3 Fishmigrationandhydrology There is a clear relationship between fish life cycles, fish habitats, and hydrology. Migrating fishesrespondtohydrologicalchangesandusehydrologicaleventsastriggersforthetimingof their migrations. This is illustrated in the figure below, where peak migration periods are correlatedwiththeannualhydrologicalcycle.Mostspeciesmigrateatthestartoftheannual floodandreturnattheendoftheflood,producingthetwopeaksshowninthefigurebelow.

Relationship between migratory activity levels and water discharge in the Lower Mekong Basin.BlueLine:averagemonthlydischarge(m3/sec)oftheMekongRiveratPakse,RedLine: number of migrations reported (based on 50 species from 51 sites along the Mekong mainstream).(AfterPoulsenetal,2002) Also,thespawningseasonistunedaccordingtoriverhydrology,andalmostallspeciesspawnat theonsetofthemonsoonseason.Onlyafewspecies,spawnduringthedryseason.

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7.4 MajormigrationsystemsintheMekong Different species have developed different life strategies to cope with the environmental circumstances,however,generalizationscanbemade,e.g.onmigratorypatterns.Threemain migrationsystemsassociatedwiththelowerMekongRivermainstreamhavebeenidentified. These three systems are called the Lower Mekong Migration System, the Middle Mekong MigrationSystem,andtheUpperMekongMigrationSystem.Althoughthesedifferentsystems areinterͲconnectedand,formanyspecies,overlapping,theLowerMekongMigrationSystemis themostimportantsystemfortheTonleSapfisheries. TheLowerMekongMigrationSystemcoversthestretchfromtheKhoneFallsdownstreamto southernCambodia,includingtheTonleSapsystem,andtheMekongDeltainVietNam.The migrationisdrivenbythespatialandtemporalseparationoffloodͲseasonfeedingandrearing habitatsinthesouthwithdryͲseasonrefugehabitatsinthenorth.Theriseinwaterlevelsatthe beginning of the flood season triggers many migrating fishes to move from the dry season habitatsjustbelowtheKhoneFalls,e.g.indeeppoolsalongtheKratieͲStungTrengstretch, towardsthefloodplainhabitatsinsouthernCambodiaandtheMekongDeltainVietNam.Here theyspendthefloodseasonfeedinginthefertilefloodplainhabitats.Somespeciesspawnon, ornearthefloodplain,whereasothersspawnfarupstream,i.e.aboveKratie,andrelyonthe water current to bring offspring to the floodplain rearing areas. The Tonle Sap Great Lake systemisoneofthekeyfactorsfortheintegrityofthissystem. As a result of increasing water discharge from the Mekong River at the onset of the flood season,thewatercurrentoftheTonleSapRiverchangesitsdirection,flowingfromtheMekong intotheTonleSapRiverandtowardstheGreatLake.Thisenablesfishlarvaeandjuvenilesto entertheTonleSapfromtheMekongbydriftingwiththeflow.Togetherwiththefloodplainsof the Mekong Delta in south Cambodia and Viet Nam, these floodplains are the main fish factoriesofthelowerbasin. Animportantgroupofspecies,whichundertakesthistypeofmigration,belongstothegenus Henicorhynchus.Intermsoffisheriesoutput,thesefishesareamongthemostimportantofthe Lower Mekong. For example, in the Tonle Sap River Dai fishery, species of the genus Henicorhynchus account for 40 percent of the total annual catch. Larger species, such as Catlocarpiosiamensis,Cirrhinusmicrolepis,Cyclocheilichthysenoplos,andProbarbusjullieni,as wellasseveralmembersofthefamilyPangasiidae,alsoparticipateinthismigrationsystem. TheSesantributarysystem(includingtheSekongandSrepokRivers)deservesspecialattention here. This important tributary system is intimately linked with the Lower Mekong Migration System, as evidenced by many species such as Henicorhynchus sp. and Probarbus jullieni extending their migration routes from the Mekong River mainstream into the Sesan tributary system.Inaddition,theSesantributarysystemalsoappearstocontainitsownmigrationsystem. Many of the species (e.g. all the species mentioned above) are believed to spawn within the Mekongmainstreamintheupperstretchesofthesystem(fromKratietotheKhoneFalls,and beyond) at the beginning of the flood season in MayͲJune. Eggs and larvae subsequently drift downstreamwiththecurrenttoreachthefloodplainfeedinghabitatsinsouthernCambodiaand VietNam.ThemaincharacteristicsoftheLowerMekongMigrationSystemareshowninFigure below.

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TheLowerMekongMigrationSystem.Blackarrowsindicatemigrationsatthebeginningof thedryseason,greyarrowsindicatemigrationatthebeginningofthefloodseason The importance of drifting larvae and juveniles has been documented through intensive samplingoflarvaefisheriesintheMekongDeltainVietNam.Duringasamplingperiodofonly 45daysinJuneͲJuly1999127specieswereidentifiedfromthelarvaeandjuveniledrift. Ageneralmigrationcalendar,asitisvalidforanaverageyearandtheaverageMekongfish speciesisgiveninError!Referencesourcenotfound.afterPoulsenetal(2004).Triggersfor initiationofmigrationsarenotwellunderstood,althoughitisgenerallyassumedthatincreased discharge in itself is a main trigger for migrations: fish typically start to migrate upstream to spawninggroundswhenthewaterlevelstartstoincrease,spawningwhilethewaterlevelisstill increasingtoensurethatthecurrentbringseggsandlarvaeintonurseryareasonthefloodplain furtherdownstream. Afterspawning,theadultfishalsomoveintothefloodedareas.Duringthefloodseasonthefish feed intensively in the flood zone, growing and building up fat layers for the following dry season,whenfoodisscarce. Asthewaterlevelstartstodropandthefloodplaindries,mostfishseekrefugeinpermanent waterbodies,mainlyindeeperpartsofthemainriverchannel.Fishfollowingthispatternthus utilizethreedistincthabitats(spawninggrounds,feedinghabitatsanddryseasonrefuges).

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GeneralmigrationcalendarforMekongfishspecies 7.5 KeyissuesforthemaintenanceoftheTonleSap/LowerMekongfisheries Althoughemphasisisonissuesrelatedtomigratoryfishes,theissuesareequallyrelevantforall fish species and indeed for the ecosystem as a whole. Basically, the most important issue in relationtotheecologicalfunctioningoftheMekongRiverfromthepointofviewofmigratory fishesisthatcriticalhabitatsaremaintainedintimeandspace.Thisincludesthemaintenance of connectivity between them, i.e. through migration corridors. The annual hydrological pattern,includingitsroleinthecreationofseasonalfloodplainhabitats,aswellasitsroleasa distributoroffishlarvaeandjuvenilesthroughpassivedrift,isofahighimportance. Thefollowingkeyecologicalattributesformigratoryspeciesareidentified:

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Dry season refuge Deep pools in the KratieͲStung Treng stretch of the Mekong habitats mainstream. These habitats are extremely important for recruitment for the entire lower Mekong Basin, including floodplainsinsouthernCambodia(includingtheTonleSapGreat LakeSystem)andtheMekongDeltainVietNam. Floodseasonfeedingand Floodplains in the Mekong Delta in Viet Nam, in southern rearinghabitats Cambodia,andintheTonleSapsystem.Thesehabitatssupport themajorpartofMekongfisheries. Spawninghabitats RapidsanddeeppoolsystemsintheKratieͲKhoneFalls,andin the Sesan catchment. Floodplain habitats in the south (e.g. floodedforestsassociatedwiththeGreatLake). Migrationroutes The Mekong River from KratieͲStung Treng to southern CambodiaandtheMekongDeltainVietNam. BetweentheMekongRiverandtheTonleSapRiver(longitudinal connectivity). Between floodplain habitats and river channels (lateral connectivity). Between the Mekong mainstream and the Sesan subͲcatchment(includingSekongandSrepokRivers). Hydrology Theannualfloodpatternresponsiblefortheinundationoflarge areasofsouthernCambodia(includingtheTonleSapsystem)and the Mekong Delta is essential for fisheries productivity of the system. TheannualreversaloftheflowintheTonleSapRiverisessential for ecosystem functioning. If the flow is not reversed (or if reversalisdelayed),fishlarvaedriftingfromupstreamspawning sitesintheMekongRivercannotaccesstheimportantfloodplain habitatsoftheTonleSapSystem.Adelayedflowreversalwould alsoleadtoareducedfloodplainareaadjacenttotheriverand lake,andthus,reducedfishproduction. Changed hydrological parameters e.g. as a result of water managementschemes,resultinchangedflowpatterns,whichin turn may change sedimentation patterns along the river. Examples of this already exist in some tributaries where hydropower dams have been constructed, resulting in sedimentation,andthusindisappearanceofdeeppoolhabitats. Theimportanceof(longitudinal)migratoryfishthatrelystronglyontheecologicalconnectivity betweenfloodplainsandriverchannels,inthetotalfishcatchisconsiderably.VanZalingeetal. (2000)estimatethatlongitudinalmigrantscontribute63%tothecatchofthemajorTonleSap fisheries.Poulsenetal.(2002)estimatethecontributiontobe48%. The remaining proportion of the floodplain yield originates from the blackͲfish species, i.e. speciesthatspendtheirentirelifeonthefloodplain.However,manyblackͲfishesarepredators, includingtheabundantChanna(snakeheads),anditmaybeassumedthattheyfeedheavilyon whitefisheswhichhavemovedintotheirfloodplainhabitat.

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8. ImplicationsfortheproposedMekongͲTonleSapdiversion Basedonabovereviewoftheliteratureanumberofconclusionscanbedrawnthatmayhave implicationsfortheproposeddiversionofpartoftheMekongfloodflowtotheTonleSapGreat LakeviaadiversionchannelconnectingtheMekongmainstreamnearRokaKongwiththeTonle SapnearPrekChic: - TonleSapGreatLakehasahighanduniqueecologicalvalue,harboringalargenumber ofrareandendangeredfloraandfaunaspecies; - the socioͲeconomic value of the Tonle Sap fisheries is extremely high. Longitudinal migrating(betweenTonleSapandthemainriver)fishmakeupforprobablymorethan 50%oftheyield; - to maintain ecosystem integrity and ecosystem production, the system should be operatedwithgreatcaretakingintoaccountthat: x fishmigrationshouldnotbehindered.Itisextremelyimportantthatfreefloating eggsandlarvaeshouldbeallowedtodriftintoheTonleSapareaintheperiod MaytillmidͲJuly; x earlyfloodingoftheareaisalsoimportantbecauseattheendofthedryseason thewaterqualityintheremainingrefugesmaybecomeverypoor(anoxic).Inflow of oxygenͲrich floodwater has to improve this situation, if not the lateral migratingspecies(blackfish)maynotsurvive; x the deeper the flood and the larger the flooded area, the higher the fish productionwillbe; x inflow of fine sediments is of crucial importance for the maintenance of the productivityofthesystem; x a variety of floodplain habitats is important for the functioning of the system. Althoughshrubandgrasslandsareprobablymoreimportantthanfloodedforests, the latter habitat is of crucial importance as well. The impacts of deeper and longer flooding on the flooded forests is not well known at the moment and requiresfurtherinvestigation;and x atthestartofthedryseason(February)longitudinalmigrationtothedryseason refugesshouldbepossible. References AsianDevelopmentBank,2005,Summaryinitialenvironmentalexaminationreportfor TonleSapsustainablelivelihoodsprojectinCambodia. Baran, E., N. van Zalinge, Ngor Peng Sun, Not dated, Floods, floodplains and fish production in the Mekong Basin: present and past trends. MRC miscellaneous publications. Baran,E.,P.StarrandY.Kura,2007,InfluenceofbuiltstructuresonTonleSapfisheries, synthesisreport.CambodiaNationalMekongCommitteeandWorldFishCenter.2004 IUCN,2004,RedListofThreatenedSpecies:AGlobalSpeciesAssessment.Editedby JonathanEMBaillieetal. Poulsen A.F., Ouch Poeu, Sintavong Viravong, Ubolratana Suntornratanaand Nguyen ThanhTung.2002,FishmigrationsoftheLowerMekongRiverBasin:implicationsfor development,planningandenvironmentalmanagement.MRCTechnicalPaperNo.8, MekongRiverCommission,PhnomPenh. Poulsen, A.F., K.G. Hortle, J. ValboͲJorgensen, S. Chan, C.K. Chhuon, S. Viravong, K. Bouakhamvongsa, U. Suntornratana, N. Yoorong, T.T. Nguyen, and B.Q. Tran, 2004, DistributionandEcologyofSomeImportantRiverineFishSpeciesoftheMekongRiver Basin,MRCTechnicalPaperNo10. Ramsar Secretariat/Wetlands International, 2007, Ramsar list of wetlands of internationalimportance.

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Srun Phallavan and Ngor Peng Bun, 2000, The dry season migration pattern of five Mekong fish species: Riel (Henicorhynchus spp.), Chhkok (Cyclocheilichthys enoplos), Pruol (Cirrhinus microlepis), Pra (Pangasianodon hypophthalmus) and Trasork (Probarbus jullieni). Paper presented at the annual meeting of the Department of Fisheries.MinistryofAgriculture,ForestryandFisheries,PhnomPenh,January2000. Van Zalinge, N., Deap Loeung, Ngor Pengbun, J. Sarkkula and J. Koponen, 2003, MekongfloodlevelsandTonleSapfishcatches.SecondInternationalSymposiumon theManagementofLargeRiversforFisheries,PhnomPenh,11Ͳ14February2003.

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