Water Management in the Mekong Delta- Changes, Conflicts and Opportunities pps

This work was sponsored by the United Nations Scientific and Cultural Organization,UNESCO, and supported by the Australian Centre for International Agricultural Research,ACIAR and Centre

Water Management in the Mekong Delta: Changes, Conflicts and Opportunities

by

Ian White

Centre for Resource and Environmental Studies

National Institute for the Environment

Institute of Advance Studies

The Australian National University

Canberra ACT 0200 Australia

_

IHP-VI  Technical Documents in Hydrology  No 61

UNESCO, Paris, 2002

legal status of any country, territory, city or of its authorities, or concerning the delimitation of its frontiers or boundaries

SC-2002/WS/47

Acknowledgments 4

Summary 5

1 The Mekong 8

1.1 River of Change 8

1.2 This Study 11

1.2.1 Purpose 11

1.2.2 Study methods 11

1.3 Geography of the Mekong River Basin 12

1.4 The Lower Basin 14

1.4.1 Lower Basin Climate 14

1.5 Fisheries Resources of the Mekong 15

1.5.1 Wild capture fisheries 15

1.5.2 Future demands and threats to wild capture fisheries 16

1.5.3 Aquaculture 16

1.5.4 Constraints to aquaculture 17

1.6 Social, Cultural and Economic Features of the Basin 18

1.7 Institutional Arrangements for Mekong Basin Resource Management 20

1.7.1 The Mekong River Commission 21

1.8 Basin Development and Cooperation 23

2 The Mekong Delta 25

2.1 The Delta at Large 25

2.2 Vietnam’s Lower Delta 25

2.3 Cambodia’s Upper Delta 28

2.4 Hydrology and Climate of the Delta 30

2.4.1 Floods and seawater intrusion 31

2.4.2 Tidal influences 32

2.4.3 Seawater intrusion floodgates 33

2.5 Surface Water Quality 35

2.6 Groundwater in the Delta 36

2.7 Soils of the Delta 38

2.8 Acid Sulfate Soils 39

2.8.1 Oxidation of acid sulfate soils 40

2.8.2 Release of toxic metals 40

2.8.3 Discharge of acidity into surface waters 41

2.8.4 Impacts of acidity on estuarine ecosystems 41

2.8.5 Links between soils, hydrology and atmospheric emissions 42

2.9 Saline Soils 43

2.10 Water and Land Constraints 43

2.11 Integrated Management and Conflict Resolution 44

2.11.1 The use of multi-agent systems in natural resource management 44

3 Responses to Water and Land Issues of the Delta 47

3.1 Completed Projects of the Mekong Secretariat 47

3.1.1 Salinity intrusion forecasting 47

3.1.2 Water balance study 48

3.1.3 Water quality monitoring 49

3.1.4 Management of acid sulfate soils 50

3.2 Work Plan of the Mekong River Commission Secretariat 51

3.3 The Mekong Delta Master Plan 53

3.4 Saline Intrusion Floodgates 54

3.5 Sedimentation and Hydrology of the Great Lake 56

3.6 Perspectives for Australian Development Cooperation 56

3.7 Australian Centre for International Agricultural Research Projects 57

3.8 The Farmers Response 58

3.9 Summary 58

4 Opportunities for Integrated Research 60

4.1 Management and Impacts of Saline Intrusion Floodgates in the lower Mekong Delta.61 4.1.1 Background 61

4.1.2 Overall Objectives 62

4.1.3 Specific Objectives 62

4.1.4 Expected Outcomes 62

4.1.5 Beneficiaries 62

4.2 Sedimentation and its Impacts on Cambodia’s Great Lake 62

4.2.1 Background 62

4.2.2 Overall Objectives 63

4.2.3 Specific Objectives 63

4.2.4 Expected Outcomes 64

4.2.5 Beneficiaries 64

4.3 Dry-Season Groundwater Supplies in the Mekong Delta 64

4.3.1 Background 64

4.3.2 Overall Objectives 65

4.3.3 Specific Objectives 65

4.3.4 Expected Outcomes 65

4.3.5 Beneficiaries 65

References 66

(ii) a critique of existing and past projects in terms of their success rate of implementation;(iii) recommendations for future inter-disciplinary and inter-agency projects in the broadfield of land-use (water management) which require an integrated approach at thesubregional level on water management issues The recommended programme should beable to attain achievable results within 3 years, take into account any limitations on-siteinfrastructure and incorporate the socio-cultural aspects of water management (i.e.community water management) in the proposal.

(iv) to submit one copy of the manuscript as well as a typewritten mission report toUNESCO

This work was sponsored by the United Nations Scientific and Cultural Organization,UNESCO, and supported by the Australian Centre for International Agricultural Research,ACIAR and Centre for Resource and Environmental Studies Australian National University.The author wishes to thank Dr Mike Bonell, UNESCO-IHP, Dr Fereidoun Ghassemi, CRES,ANU, Hugh Milner and Andy Marr, SMEC, Brian Cummins, Cummins and Associates, DrPhilip Ford, CSIRO Land and Water, Dr Ian Willett, ACIAR, Associate Professor MikeMelville, University of NSW, Dr Phillip Gibbs, NSW Fisheries, Dr Philip Hirsch, University

of Sydney, Professor Vo-Tong Xuan¸ Dr Le Quang Minh, Professor Vo Quang Minh,Nguyen Anh Tuan, Dr Troung thi Nga and Dr Nguyen Huu Chiem , Cân Tho University,Vietnam, Dr Pascal Perrez, CIRAD, France, Ms Erica Donner, CRES ANU, Dr Truong and

Mr Nguyen Than Tin Sub, Institute Water Planning, Vietnam, Professor Nguyen An Nienand Professor Dong, Southern Institute of Water Resources Research, Vietnam, Dr To PhucTuong, IRRI, the Philippines, and Dr Sok, Hydrology, Mekong River Commission forassistance and many helpful discussions Mr Vincent Leogardo, UNESCO IHP, is thankedfor his generous help in preparing this report

The Mekong River is one of the few great, largely unregulated rivers of the world Its Delta

is both agriculturally and aquatically highly productive and a major contributor to theregion’s food production and export earnings Water and land issues of the Delta must beconsidered as integral with those of the Mekong Basin as a whole A majority of the MekongBasin’s 60 million, ethnically diverse peoples rely on the River’s aquatic resources and riceproduction for their subsistence For many, 40 to 60% of their protein intake is from fishfrom the Mekong The prodigious fish resources rely on the annual fllooding of the Mekong.The marked seasonal ebbs and flows of the River also impose severe constraints on itsriparian communities, with vast wet season floods and dry season water shortages that allowseawater intrusions into the Delta

These annual hardships are superimposed on nearly 60 years of devastating external andinternal conflicts in the region The six riparian countries making up the Basin have generallylow external and per capita earnings Harnessing the Mekong for hydropower generation andirrigation supplies, through cascades of main-stream and tributary dams, coupled withharvesting the Basin’s forests are ways of stimulating growth, increasing per capita incomeand regulating seasonal flows These developments, however, are potentially in conflict withthe subsistence needs and the livelihood security of the region’s poorest people Riverregulation and diversions pose dilemmas, since they may decrease substantially theMekong’s prodigious aquatic productivity Up-catchment forestry also threatens waterquality, productivity and dam capacity through potential increased sediment loads

The Mekong River Commission’s task is to plan the sustainable development, use,conservation and management of the River’s water and related resources in mutuallybeneficial manner and to channel resources into its work program Understanding thehydrology of the Basin and impacts of its regulation are central themes in its work plan,financed mainly by international multilateral or bilateral organisations Major financingorganisations have been criticised by non-government organisations as too narrowly focussed

on infrastructure development and reliant on top-down approaches which ignore the needs ofpeople A key issue, identified by both proponents and critics of regulation structures is thepaucity of reliable data on climate, hydrology, sediment yields, capture fisheries, social,economic and cultural aspects upon which to base sound decisions In some important areas,such as water quality monitoring, the magnitude and complexity of water quality concernsare increasing at a rate that exceeds the capacities of riparian countries

The low-lying Mekong Delta faces unique water land issues because of its sedimentarycomposition and geomorphology The issues of Vietnam’s lower Delta differ from those ofCambodia’s upper Delta, which is dominated by the Delta’s natural flow regulator, Tonle

Sap and Cambodia’s Great Lake In Vietnam’s lower Delta, the major land and waterresource problems are: acute flooding in the wet season, with flood depths of more than 4 m

in the northern Delta; acid sulfate soils constraints on crop productivity in over 40% of thelower Delta and associated, severe, acidic drainage waters with major implications foraquatic productivity; seawater intrusion in the dry season in the lower Delta, limiting riceproduction to one crop per year in saline intrusion areas; impacts of seawater intrusionfloodgates on acidification; loss of coastal mangroves and impacts on coastal protection andfisheries

In the Cambodia’s upper part of the Delta different issues need to be addressed There is asurprising dearth of information on sediment fluxes and on the quantitative relation betweenflooding and the breeding/ feeding/ life cycle of fish despite their importance to ripariancommunities The principle water and land concerns in the Cambodian section of theMekong Delta are: impacts of upstream flow regulation on the water supply for flooding forrice production and fish production in the Great Lake; impacts of forest clearing onsedimentation and aquatic production in the Great Lake; impacts of downstream riverregulation on flooding, rice and fish production Recent estimates of sedimentation rates inthe Great Lake are at least 8 times higher than those of the past 5,000 y In both the upperand lower Delta, the availability and quality of domestic water supplies is a major issue Thecontrol of downstream flooding and of saline intrusion in the lower Delta could bepotentially in conflict with the need to reduce flooding in the upper Delta

In the past, projects relevant to the specific needs of the Delta have tended to be narrowlyfocussed The highest priority has gone to planning and design for hydropower and irrigationdiversion Main projects completed by the Mekong River Commission Secretariat with directrelevance to the Delta are: the Saline Intrusion Studies; the Water Balance Studies; theManagement of Acid Sulfate Soils Project; and the Water Quality Monitoring Programme.Even in these, the central thrust has been the impacts of upstream regulation, diversions toincrease crop production and changes in landuse on the quantity of water in the Delta.Broader issues such as the influence of saline intrusion on fish production and theimportance of recent sedimentation to aquatic and terrestrial productivity have not beenexamined The Secretariat’s present Work Plan still has a concentration of effort oninfrastructure development but there are broader-based projects planned and underway.The Secretariat’s water balance, salinity intrusion and acid sulfate soil management projectsformed the basis of the Mekong Delta Master Plan, intended to underpin sustainable growth

in the lower Delta A central thrust of this plan is increased rice and aquaculture production

A key outcome of this plan was a proposal to increase rice production in the region west ofthe Bassac by supplying a longer irrigation season and lowering or preventing salt-waterintrusion into the region This proposal, the Desalination of the Ca Mau Peninsula, hasrecently been completed It is suggested, by analogy with the Australian situation that theimpacts of this project on local fish production and waterway acidification may be severewith significant consequences for local communities The impacts of already installed sluicegates near Soc Tranh were summed up succinctly by one farmer “floodgates have given us aroad (track) and electricity But no crops and no fish!”

A seminal, French benchmark study of sedimentation in Cambodia’s Great Lake provides anopportunity of assessing the impacts of changes in upcatchment and surrounding landuse onsediment and nutrient dynamics and fish production in the Lake A comprehensive report to

the Australian government, Perspectives for Australian Development Cooperation, identified

key areas for assistance in the Delta because it receives less priority development assistanceand because of the concentration of poor there Salinity and acid sulfate soils requiredassistance It recommended an integrated approach to acid sulfate soils because they involvedcross-sectoral land and water issues and one which was both precautionary and curative Thereport also pointed out the uncertainty of dry season domestic water supplies in the Delta andthe problems with acidity and salinity Groundwater was seen as an increasingly importantresource in these areas Watershed and catchment planning were also identified asopportunities for assistance The farmer’s response to the adverse conditions they face dailyhas been innovative and courageous

Three proposed integrated projects for the Mekong Delta were developed out of the aboveanalysis: Management and Impacts of Saline Intrusion Floodgates in the lower MekongDelta; Recent Sedimentation and its Impacts on Cambodia’s Great Lake; and Dry-SeasonGroundwater Supplies in the Mekong Delta Brief backgrounds, overall objectives, specificobjectives, expected outcomes and beneficiaries are given for these projects

1 The Mekong

1.1 River of Change

The Mekong (Thai: Mother of Waters) River has the twenty-first largest drainage basin and

is the twelfth longest river with the eight largest annual discharge and second most diverseriverine fishery in the world It is one of the world’s great, largely unregulated rivers Thewater, land and biological resources of the Mekong Basin sustain an ethnically diverse andgrowing population in six countries; China, Burma, Lao PDR, Thailand, Cambodia andVietnam (Fig 1.1) The Mekong Basin’s resources provide both great benefits and hardshipsfor its peoples The river is biologically highly productive and is a major source of protein.Its wet season floods nurture vast rice crops However, wet season flooding is severe withover 50% of the Mekong Delta (1.9 Mha) annual inundated The floods of 1961, 1978,

1991, 1996 and 2000 caused major devastation and all except the 1996 flood had returnintervals of greater than 1 in 50 years Paradoxically, water shortages arise in the dry season,particularly in southwestern region of the Mekong Delta These water shortages lead toseawater intrusion in streams in the lower Delta Seawater intrusion, severe acid sulfate andsaline soils and upstream deforestation impose social and economic constraints anduncertainties and limit agricultural production of staples such as rice and fish (Be, 1994;Minh, 1995) The seasonal extremes, however, are necessary to sustain the Basin’sexceptional aquatic productivity (Roberts, 1993a) on which its riparian communities dependfor most of their protein

Since the 1930’s the Basin has been ravaged by wars of liberation and inter and intra countryconflicts These have had massive, long-term social, economic and cultural impacts on thepeoples of the lower Basin and depleted populations, resources and institutional capacity,especially in resource management International organisations are seeking to assist theregion’s peoples by promoting development and growth in the Basin, mostly through largeinfrastructure construction projects, principally hydropower, flood mitigation and irrigationsupply dams The Mekong is seen by many as one of the great “undeveloped resources” ofSoutheast Asia Less than 5% of both the Basin’s annual flow and its catchment are regulated

at present There are plans for a cascade of up to 9 mainstream “run-of-river” hydropowerschemes in the Mekong together with as many as 50 tributary dams (Rothert, 1995) Theseplans have been criticised as fundamentally flawed (White, 1997) because of the dearth ofinformation on climate, hydrology, ( Institute of Hydrology, 1982; 1984; 1988a, 1988b) andecology, as well as a paucity of social, economic and cultural data and knowledge of theaspirations of riparian communities likely to be affected by river regulation (Greater MekongTask Force, 1996)

The Basin is undergoing accelerating, political, cultural, economic, and water and land usechanges These changes have the potential to both benefit individual countries and todisadvantage their downstream or upstream neighbours as well as their own ripariancommunities River regulation and changed landuse have major implications for thesustainability of many rural communities along the River (Derasary, 1996).

Fig 1.1 The lower Mekong River Basin flowing from China to the South China Sea (Mekong

River Commission, 1999)

Clearing of upstream forests has reportedly changed rainfall-runoff relations, resulting inlarger, more frequent floods (Hirsch and Cheong, 1996) and an increase in dry season flows,primarily as a result of reservoir construction on tributaries (Institute of Hydrology, 1988a).The frequency of major 1 in 50 year floods over the past 40 years is a of major concern,especially in the Delta These factors, coupled with the putative impacts of global climatechange, which suggest an increase in frequency of extreme events but with overall lowermean river flows for the Mekong (Lettenmaier, 2000) have led to increasing calls forregulation of Mekong flows.

Most major projects in the Basin or proposed projects have been criticised as narrowlyfocussed, involving a single or a small number of infrastructure-dependent outcomes (White,1997) This is particular so in developments for flood mitigation, irrigation supply,hydropower generation or seawater intrusion mitigation Such schemes have been faulted fortheir perceived lack of appreciation of the broad range and complexity of issues that need to

be considered and the gamut of deleterious impacts that may ensue (White, 1963; Darling, 1970; Challinor, 1973; Roberts, 1993b; 1995; Sluiter, 1993; McCully, 1996; Hirschand Cheong, 1996)

Fraser-1.2 This Study

The issues involved in the equitable management and sharing of the whole Basin’s resourceswhile retaining local sovereignty and protecting local interests are complex It is clear thatthe availability and sharing of knowledge on the prevailing hydrology, climate, ecology,economics, sociology and cultures and listening to and addressing the aspirations of itspeoples are fundamental to the development, use and management of this vitally importantBasin The issues in the Mekong Delta mirror those of the Basin as a whole but also presentsome unique problems because of the Delta’s geomorphology

1.2.1 Purpose

The purpose of this study is to overview broad issues in the Mekong Delta, to examine thesuccess and failures of hydrologic developments in the Delta and to identify gaps in currenthydrologic knowledge which require a broader, integrated approach to their solution in order

to use and manage water and land resources of the Delta sustainably and equitably It isundertaken at a time when major infrastructure developments are under way, and whenimportant studies are being carried out such as the review of water quality monitoring(Ongley et al., 1997) and the Mekong River Commission-Murray-Darling BasinCommission/SMEC Mekong River Utilisation Program (H Milner, private communication,Nov 1997) to develop Basin-wide water use and management rules Like the River itself, thesituation is fluid and constantly changing

1.2.2 Study methods

In this study, relevant, accessible publications and documents were reviewed, discussionswere conducted, particularly with current study teams, and a field trip to the lower Delta wascarried out in May 1997 with the assistance of the Australian Centre for International

Agricultural Research (White et al., 1997b) Because the Delta is an integral part of the

Mekong and will bare the brunt of any large-scale changes in upstream hydrology, it isnecessary to first consider background and status of the Mekong Basin as a whole beforefocussing on the Delta

1.3 Geography of the Mekong River Basin

The Mekong River rises 5,000 m above sea level, where it is fed primarily from snow-melt

in the Tanghla Mountains on the Tibetan plateau It descends through steep, narrow gorges

in south-western China, where it is called the Lancang (Turbulent) River, passes through the

‘Golden Triangle’ junction of Burma, Laos and Thailand, at an elevation of about 500m,crosses the highlands of Laos It then forms a 900 km boundary between North-East Thailandand Laos, before descending the Khone Falls in southern Laos and 120 km of rapids innorthern Cambodia (see Fig 1.1) After its confluence with the Tonle Sap River at PhnomPenh at the ‘Quatre Bras’, the Mekong splits into the 220 km long Bassac River and the 240

km Mekong, which runs almost parallel to the Bassac These flow into the Mekong Deltathrough the 9 tributaries of the Cuu Long, the “nine dragons”, and out into the South ChinaSea at the end of its 4,200 km long journey (Pantulu, 1986; Sluiter, 1993; MekongSecretariat, 1994; Hisrch and Cheong, 1996) The maximum width of the Mekong in theDelta during non flood periods is close to 1.2 km at Vam Nao A summary of biophysicaland landuse data of the Basin is given in Table 1.1

TABLE 1.1 Biophysical and landuse data for the Mekong River Basin (Hirsch and Cheong,

(CentralHighlands)

The 795,000 km2 Mekong Basin covers a wide range of bioclimatic zones Annual Riverfrom the discharge from the Basin is 475 km3, or a remarkable 600 mm on a whole basinareal average The variation of annual runoff with drainage area down the Basin is shown inFig 1.2 (Pantulu, 1986) The changes in runoff down the basin reflect the impact oftributaries and the orographically-driven rainfall variation The minimum between Kratie andPhnom Penh represents natural regulation by Cambodia’s Great Lake fed and dischargedthrough Tonle Sap Mean runoffs are misleading since the monsoonal climate results in an,

on average, 15-fold variation between low (April or May) and high (September or October)flow This flow variation imposes the combined annual hardships of wet seasons floods, andwater shortages and saline intrusion in the dry season on populations in the Mekong Deltaand leads to an inherent resource uncertainty in agricultural production, particularly in staplessuch as rice, and water-supply related health problems

Fig 1.2 Variation of mean annual runoff (line) and sediment load (solid square points) with

drainage area for the lower Mekong Basin The dip between Krate and Phnom Penh illustrates the natural regulation of Cambodia’s Great Lake and the Tonle Sap (from Pantulu, 1986, Mekong Secretariat, 1982).

The sediment loads are relatively low (concentrations between about 0.2 to 0.8 kg/m3)compared to other major Asian Rivers The organic content of the sediments is high, about 6

to 8% of total suspended solids (Mekong Secretariat, 1982) Annual sediment loads down theBasin are also plotted in Fig 1.1 It can be seen that there is a mean net deposition of 35 Mt/y

of sediment at Phnom Penh, presumably during the flooding of the Great Lake

Table 1.1 also lists the enormous potential for generating electricity from the fall of theMekong and its tributaries, particularly in Laos and Yunnan Province, China Currently, theonly mainstream run-of-river dam on the Mekong is the Manwan hydropower Dam inYunnan Province (Kunming Hydroelectric Investigation, Design and Research Institute,1993) This hydropower potential has attracted strong interest because of its ability toprovide power for industrialisation and much needed external earnings for the ripariancountries of the Basin In addition, hydropower dams can be used to provide irrigation water,safe, reliable domestic supplies and to promote interbasin transfers Major plans for cascades

of dams along the Mekong and its tributaries, however, have attracted mounting andconcerted opposition, particularly from community-based, non-government organisations.These organisations argue that the full environmental, ecological, economic, social andcultural costs of the hydropower cascades could exceed their benefits For decades, riverregulation has been the central, contentious issue in the management and use of the MekongRiver Basin

1.4 The Lower Basin

The lower Mekong Basin, downstream from China and the Burma-Laos -Thailandintersection, covers parts of Lao PDR, northeast Thailand, 86% of Cambodia and 20% 0fVietnam The lower Basin represents 77% of the total Basin area and more than 80% of theannual flow Much of the available data relates to the lower Basin because of thecomposition of the previous Mekong Committee (the river’s former main institutionalmanagement and development authority), as well as those of the subsequent Interim MekongCommittee and now the Mekong River Commission (Lao PDR, Thailand, Cambodia andVietnam) The lower Basin’s resources are of particular interest to the member nations

1.4.1 Lower Basin Climate

The lower Basin is in the centre of the Asian tropical monsoon region with a summer-winterwind reversal due to differential heating of the extensive land and water masses Its climate

is governed mainly by seasonal monsoon winds The southwest, wet season monsoon starts

in mid March to mid-May and ends around mid-September to mid-October The northwestdry season monsoon runs from mid-October to March Rainfall in the wet season is typicallyafternoon or early evening, convective falls In higher regions, rainfall is topographicallydriven A short 7-14 day dry period frequently occurs in June or July due to high anticyclonecirculation There are occasional tropical storms with large rainfalls in August and September(Pantulu, 1986; Mekong Secretariat, 1968; 1975) Mean annual rainfall of the lower Basinranges from approximately 1,000 mm in northeast Thailand to more than 3,500 mm in themountainous fringe of northeast Laos, where there is no clearly defined dry season.Elsewhere in the lower Basin, little rain falls during the dry season Relative humiditiesrange from 50 to 98% and mean solar radiation is estimated to be 1.12 MJ/m2/d Estimatedannual potential evaporation ranges from 1500 to 1800 mm The seasonality of rainfall

excess and its consequent impact on river and tributary flow, largely govern the water, landand biological resources of the lower Basin., As it flows from the upper Basin to the lowerBasin, at Chiang Soen, the Mekong has a less pronounced seasonality in flow because of theinfluence of upstream snowmelt.

1.5 Fisheries Resources of the Mekong

The Mekong is one of the most biologically diverse river systems in the world Currently

1700 fish species have been recognised, although the list is by no means complete (Bao, etal., 2001; MRC, 2002a) There is also a corresponding diversity amongst other aquaticanimals and insects The annual flooding of the vast floodplains of the Mekong fuels thisdiversity, by when fish take advantage of the vast expanse of rich feeding grounds and theopportunities to breed, spawn and raise young In the dry season, fish retreat to river channelsand to permanent lakes and deep pools in the river This annual flooding means that fishmigration is the norm (Bao et al., 2001)

The Lower Mekong Basin has three major interconnected migration systems The lowersystem lies downstream from the Khone Falls, and includes the Tonle Sap River and GreatLake system in Cambodia and the Mekong Delta The middle system extends from aboveKhone Falls to the Loei River In this system, floodplain habitats are connected with thelarge tributaries of the Mekong The upper system runs upstream from the Loei River (MRC,2002a) The complexity and interconnectedness of the migratory systems and thefundamental importance of the annual flooding are some of the main reasons behind growingopposition to regulating the main flows in the Mekong and to concerns over sediment loadsfrom cleared areas The fundamental importance of the Tonle Sap River and Great Lakesystem cannot be overstated

Bao et al (2001) highlighted the critical nature of habitat and flood patterns to the propensity

of fish species to migrate, spawn and find dry-season refuges Changes in flood patterns orwater quality, blockage of important migration channels and destruction of dry seasonrefuges could all adversely affect fish stocks that are crucial to the health, nutrition andlivelihoods of some of the poorest people in the Lower Basin countries Fish migrationstherefore have many implications for regional development, planning and management Theyrecognised important fish stocks are shared between countries and concluded that jointmanagement strategies are needed to ensure appropriate development

Many fish species migrate trans-boundary during their life cycle Several migratory stocksare shared, including the endangered Giant fish species There are, however, no institutionalarrangements at the regional level for joint management of trans-boundary fish resources Atthe local level, there are long standing traditions of fisheries management being undertaken

by communities in the Lower Mekong Basin Local rules on fishing are often connected withspiritual beliefs These help sustain local resource levels and to ensure equitable distribution(MRC, 2002a)

1.5.1 Wild capture fisheries

Fish is the major source of protein for people in the lower Mekong Basin It is estimated thatwild capture fisheries produce annually over 1.6 million tonnes (Bao et al., 2001; MRC,2002a) The total value of the catches is about $US1.4B.The size of inland fisheries, however

has been grossly under-reported because of the subsistence nature of the sector (MekongRiver Commission, 1999) During a field trip to the lower Delta, fisheries experts had ampledata on aquaculture production but had no information and little curiosity about wild capturefisheries In boat trips along the canals it was evident that wild capture fisheries effort wasenormous with major netting structures at least every 50m.

Average fish consumption ranges from about 30 kg per capita in mountainous areas, to 70 kgaround the Great Lake Tonle Sap area in Cambodia During the dry lean seasons, fermentedand dried fish are used in place of fresh fish and most households use fish sauce all yearround Most fish are consumed locally or traded fresh at village, district and provincialmarkets There is also trade in fish within the Mekong Basin and its neighbouringcatchments Exports are limited, but increasing (MRC, 2002a)

1.5.2 Future demands and threats to wild capture fisheries

It has been predicted that there will be a 20 percent increase in fish demand in the LowerMekong Basin over the next 10 years Increased fishing may increase in overall catches inthe short term This however will be accompanied by a continued decrease in the larger slow-growing migratory species in the catches To mitigate the decline in biodiversity will requirecoordination and integration of management interventions at all levels Current analysessuggest there is no indication that future increases in fishing effort will lead to decreasedcatches or reduced diversity for the non-migratory fish species(MEC, 2002) However, thispredicated on the major assumption that the integrity and spatial extent of the floodplainsremain intact

The major threats to sustaining capture fisheries include (MRC, 2002a):

• Destruction of spawning grounds or dry season refuges by habitat alterations

• Local changes in the quantity and quality of water available for sensitive habitats and thetiming of hydrological events,

• Pollution from agriculture and urban development

• Construction of dams, weirs or diversions which act as physical barriers to fishmigrations

• Increased sediment load due to deforestation

1.5.3 Aquaculture

Aquaculture in the Lower Mekong Basin is diverse and includes the production and sale offry and fingerlings and raising wild or artificially produced fingerlings in enclosed or semi-enclosed water bodies Total production Basin is estimated to be 260,000 tonnes per yearwith a farm gate value of about US$ 270,000M million There are relatively few large-scalecommercial farms in the Lower Mekong, although there are large catfish farms in the BassacRiver and large integrated fish farms near towns and cities in Northeast Thailand Mostaquaculture production comes from small-scale operations run by rural households and this

is becoming increasingly important throughout much of the Basin Small-scale aquaculturecontributes to food supply in areas where wild fish are deficient It also providesopportunities for supplementary income and diversity Except in Cambodia, fish ponds andrice fields are the most common means of producing fish throughout the Basin (MRC,2002a)

The Mekong Delta has the largest aquaculture area (330,000 ha) and freshwater production

is above 170,000 tonnes An estimated 80,000 ha are presently under rice-fish culture, with amean annual production of 370 kg/ha There are more than 100 hatcheries in the area and themost commonly farmed species are catfish, barbs, carps, tilapia, gouramis and sand goby.There are about 5,000 fish cages in the Delta that are mostly stocked with fry and juvenilesfrom the wild

In Cambodia, most of the aquaculture production comes from cages and pens River catfishand snakeheads are the dominant species Northeast Thailand is the second largest area in theLower Mekong Basin for aquaculture production There production has expandedsignificantly over the last decade and annual output is in the range of 65,000 tonnes Cageculture of tilapia has recently expanded in reservoirs and in the Mekong River

Governments see aquaculture as a high priority They support investments in aquaculture andfund research, infrastructure, education and extension As with many governmententhusiasms, effort is focussed on narrow outcomes without consideration of broader andinterconnected issues There is no separate legislation on aquaculture in any MRC-membercountry However it is under review in all

Trans-boundary issues such as genetic quality of broodstock have yet to be addressed Thereare major environmental concerns about the more intensive forms of aquaculture Thereinclude :

• the balance between exotic and indigenous species,

• culture of predator species,

• collection of juveniles form the wild,

• water pollution and

• the spread of fish disease (MRC, 2002a):

The past 10 years has seen five-fold increase in aquaculture production Continued expansioncould contribute to meeting some of the needs for fish products in the Lower Mekong.However, aquaculture sales are strongly influenced by market demand, particularly in thelocal market The demand will depend on the number of consumers who can pay the price,often US$ 1.00 or more per kg

Aquaculture growth in the lower Mekong needs an expansion in hatcheries and nursingcapacity Centralised large government hatcheries have not been successful Development oflocal, small-scale hatcheries, trading networks, and on-farm breeding appear to offer morepromise in supporting rural, small-scale aquaculture (MRC, 2002a)

1.5.4 Constraints to aquaculture

There are several constraints to the development of aquaculture Many of these areinstitutional rather than technical The capacity and resources of government institutions forparticipatory extension and research is limited Capacity building is required to supportdevelopment The development of aquaculture to date has been a narrow sectoral approach

It is now acknowledged that the promotion of aquaculture in the Mekong Basin should takefood security and poverty alleviation as a starting point for interventions and there needs to

be an emphasis on building capacity in local institutions Aquaculture needs to be integratedinto fisheries projects and wider rural development strategies Aquaculture, capture fisheriesand reservoir management are parts of a holistic system The past focus on policy anddevelopment efforts for aquaculture alone, while ignoring wild fisheries, could result in adramatic loss of fundamentally important wild fisheries resources This could severely affectfood security for the entire Lower Mekong Basin, particularly for poor people (MRC, 2002a).

A recent analysis of finances and risks of selected aquaculture activities in the Basinconcludes that pond and cage aquaculture has high potential in Lao PDR, Cambodia and VietNam, in terms of both commercial development and small-scale family enterprises directed

at poverty alleviation (MRC, 2002b) It found from a financial perspective, aquaculturecompares well with alternative traditional enterprises such as rice and fishing, and other newenterprises such as fruit and coffee production While risk levels were necessarily somewhathigher than traditional activities, they were generally similar to, or lower, than other newenterprise types

The Mekong River Commission has espoused an individual catchment approach to resourcemanagement in the Basin This is designed to be a bottom-up planning and data gatheringprocess, with assistance from people whose livelihoods depend on the resources of thecatchments It is modelled on catchment management throughout Australia’s Murray-DarlingBasin and elsewhere There, it is probably too early to determine whether the voices of thosewho depend on the catchment for their livelihood is truly heard

1.6 Social, Cultural and Economic Features of the Basin

The lower Mekong Basin has an estimated population of 60 million About 45-50 million ofthese inhabitants are farmers and fishers relying directly on the Mekong River and itsassociated land resource (Mekong River Commission, 1999) This population is ethnicallyvery diverse Only in Cambodia does one ethnic group, the Khmer, dominate the country’sbasin area In China, minorities exceed the Han Chinese Lao PDR has 68 ethnic groups.Vietnam’s Delta population is mainly Kinh but concentrations of Khmer, Chams and ethnicChinese exist there Economic indicators for the Mekong’s riparian countries are listed inTable 1.2

TABLE 1.2 Economic indicators of Mekong River riparian countries (Kirsch and Cheong,

Burma Cambodia Lao PDR Thailand Vietnam Yunnan

(1992)

-8.4(1994)

-1.1(1994)

1.92(1992)

27.4(1994)

19.6(1994)

The figures in Table 1.2 take no account of the late 1997 financial crises in Asia and areindicative only of relative wealth of countries within the Basin Financial crises have majorimplications for the development and management of the Basin It is quite clear from Table1.2 that most of the Basin’s inhabitants are subsistence farmers and fishers In the lowerMekong Basin, fish is as important to riparian communities as rice (Sluiter, 1993) and makes

up 40-60% of protein intake (Pantulu, 1986) The limited and dated information on fishconsumption shows that the average annual per capita fish consumption in Cambodia was25.4 kg which exceeds others in the lower Basin, with Vietnam 20.8 kg, northeast Thailand,11.5 kg and Laos, 10.2 kg (University of Michigan, 1976) These figures, however, must beconsidered approximate

In subsistence economies, there are clearly extremely limited internal resources to undertakethe necessary planing, monitoring, implementation and management of Basin-wide projects.There are two main external, loans-funded resource developments proposed for the Basin,hydropower and forestry These are seen as important sources of national income and earners

of foreign exchange, however both activities are potentially at odds with the subsistenceneeds and livelihood security interests of the region’s poorest people (Hirsch and Cheong,1996), a issue emphasised by many non-government agencies working within the region Theimpacts of both hydropower and forestry developments on the productivity and biodiversity

of Mekong fisheries is a major concern (Roberts 1993b; 1995) Internal development projectsalso have not been problem free The thrust for increased rice production from the MekongDelta has seen farmers move into areas badly affected by salinity and acidity and hasgenerated the need for salinity intrusion protection

1.7 Institutional Arrangements for Mekong Basin Resource Management

Table 1.3 (modified from Hirsch and Cheong, 1996) provides a summary of regional,institutional evolution in the management of the Mekong Basin as an entity

The Committee for Coordination of the Comprehensive Development of the Lower MekongBasin, or Mekong Committee as it became known, was established through funding provided

by the United Nation’s Economic Commission for Asia and the Far East, ECAFE, in order tocatalyse development of the Basin and to increase per capita income of the riparian countries(ECAFE, 1957) The United Nations Development Programme, UNDP, has been a majorand consistent supporter of the Committee since its inception Some have considered theCommittee as a type of Marshall Plan for mainland Southeast Asia (Jacobs, 1995) As aconsequence, the Committee and its successors have both coordinated resource management

in the Basin and channelled development assistance to approved projects This dual role hasbeen seen by some as a potential conflict of interest

The US Army Corps of Engineers and the US Bureau of Reclamation have long beeninterested in large scale engineering works on the Mekong and its tributaries They saw theannual flooding of millions of hectares of Mekong lowlands as the major impediment tomodernizing the region’s agriculture (Gráiner Ryder in Sluiter, 1993) Their solution was topropose impoundment of water in large storage dams, from which controlled releases wouldfeed all-year-round, export-crop production and would generate income-earning hydropower.The Corps report (United Nations, 1958), together with the Basin Indicative Plan (MekongSecretariat, 1970), which was a synthesis of earlier projects, formed the basis for plannedBasin development The Mekong Committee and its successors have been seen by somecritics as being progeny of the Corps of Engineers, having a “one dimensional”preoccupation with infrastructure construction, despite the existence of contemporary studies

of the non-engineering aspects of Basin development (White, 1963)

TABLE 1.3 Evolution of institutional arrangements for the management of the Mekong Basin

Year Institutional Development

1957 Formation of Mekong Committee

1970 Indicative Basin Plan

1971 Nam Ngum Dam Completed

1975 Cambodia withdraws from Mekong Commission

1978 Interim Mekong Committee established

1987 Revised Indicative Basin Plan

1992 ADB commences Greater Mekong Subregion Initiative

1994 Hanoi agreement on Cooperation for the Sustainable Development of the Mekong

River Basin

Year Institutional Development

1995 “Run-of-River” mainstream hydropower dams proposed

Mekong River Commission established

1999 Restructuring of the Secretariat to achieve its goals

The withdrawal of Cambodia under Pol Pot regime forced the Mekong Committee intoabeyance in 1975 In order to fill the vacancy, Vietnam, Thailand and Laos formed theInterim Mekong Committee in 1978 This remained almost dormant until the mid 1980’swhen a Revised Indicative Plan was developed and released (Interim Mekong Committee,1988) Disagreements arose in the early 1990’s on the procedures under which one membercountry could veto plans of another and also on the conditions for the re-entry of Cambodia

1.7.1 The Mekong River Commission

The Mekong River Commission came into being in 1995 after UNDP-sponsored meetingsculminated in the signing of the draft of the Agreement on the Cooperation for theSustainable Development of the Mekong River Basin, on 28 November 1994 The four lowerMekong riparian countries endorsed this draft Hanoi agreement It was based on theprinciples of sovereign equality, territorial integrity and environmental protection to enablethe four signatory countries to use the resources of the Mekong in a reasonable and equitablemanner The Agreement provided freedom of navigation throughout the mainstream Mekong

to promote regional cooperation and development Importantly, it allowed for adding newmembers to the Commission, but removed the right of individual country veto

The four countries also adopted the concept of a Basin Development Plan to identify andprioritize joint and basin-wide projects for action Geography, hydrology, environment,climate and the rights and interest of all riparian countries were to be accommodated in thePlan It has been seen by some as significant that the UNDP press release on the Agreementfailed to mention the rights and interests of riparian citizens of the Basin when it recognisedthe need to harness the “destructive power of the River during peak wet seasons.”

The mandate of the Mekong River Commission is:

To cooperate and promote in a constructive and mutually beneficial manner

in the sustainable development, utilization, conservation and management of

the Mekong River water and related resources for navigational and

non-navigational purposes for social and economic development and well-being

of all riparian States, consistent with the need to protect, preserve, enhance

and manage the environmental and aquatic conditions and maintenance of

the ecological balance exceptional to this river basin

The Commission’s vision for the Basin is:

An economically prosperous, socially just and environmentally sound

Mekong River Basin

The mission of the Commission is:

To promote and coordinate sustainable management and development of

water and related resources for the countries’ mutual benefit and the

people’s well-being by implementing strategic programmes and activities

and providing scientific information and policy advice (Mekong River

Commission, 1999)

The Mekong River Commission consists of three permanent bodies There are: the Council,

at Ministerial and Cabinet level which makes policies, decisions, and resolves differences;the Joint Committee at permanent secretary level to carry out policies; and the Secretariat,responsible for technical and administrative support for the Council and the day-to-dayoperations of the Commission The priorities of the Council can be judged from the workprogramme of the Secretariat which concentrates on four major areas of work: policy andplanning; environment and monitoring; resources development and management; andprogramme support (Mekong River Commission Secretariat,1995, Mekong RiverCommission, 1999) More recently the Commission has reorganised its work into threeprogrammes (Mekong River Commission, http://www.mrcmekong.org/programme; 2002):

• The Core Programmes consisting of :

− the Basin Development Plan

− the Water Utilisation Programme

− the Environment Programme

• Support Programmes which sustain the implementation of other MRC programmesthrough a Capacity Building Programme

• The Sector Programmes focus on specific sectors and address regional issues that aresignificant to the management of the entire Mekong River Basin There are 5 SectorProgrammes:

− the Fisheries Programme

− the Agriculture, Irrigation and Forestry Programme

− the Water Resources and Hydrology Programme

− the Navigation Programme

− the Tourism Programme

The Secretariat’s Water Resources and Hydrology Programme, a key programme in theoverall planning and management of the Basin, has four main components: monitoring; real-time forecasting; planning and design; and applications Present and planned projects of theprogramme include improvement of the Basin-wide hydrometeorological network,groundwater investigations, flood forecasting and damage reduction, upgrading of salinityintrusion forecasting in the Mekong Delta, water balance of the lower Mekong Basin, Phase

IV and Mekong morphology and sediment transport The Programme is seeking funds forseveral of these projects

The early 1990’s also saw sweeping changes in natural resource management within membercountries The most significant of these was the creation of ministries specifically concernedwith the environment in each of the member countries In order to meet these changingcircumstances the Secretariat was restructured in 1999 Its operational structure is shown inFig 1.3 (Mekong River Commission, 1999).

Fig 1.3 Operational structure of the Mekong River Commission Secretariat (Mekong River

Commission, 1999)

1.8 Basin Development and Cooperation

One of the important rôles of the Mekong River Commission is to act as a channel for wide development assistance The three most important multilateral or international agenciesinvolved in large scale Mekong project financing and administration are the AsianDevelopment Bank, the World Bank and the UNDP Other UN agencies, such as UNESCO,UNEP and ESCAP also play important rôles in heritage listing, and providing training forresource assessment and management A variety of bilateral agencies, from Australia,Canada, Denmark, the European Union, Germany, Japan, Sweden, the UK and the US, alsoprovide important assistance

Basin-The 1990’s saw a marked increase in the number of non-government organisations operating

in the Mekong Delta Their main rôles in natural resource management has been at thecommunity level, in advocacy for community rights and environmental values and incommunity capacity building Many of these organisations have been strident in theircriticisms of projects planned or undertaken by the Asian Development Bank (Uramoto etal., 1997; Imhof; 1997a), the World Bank (Imhof, 1997b) the UNDP (Probe Alert, 1995) andJapan (Lammers, 1997) whom they accuse of “ignoring people and embracing top-down

Policy Decisions (CEO)

Planning Environmental monitoring Information Analysis/

Implementation

development” In relation to this, major donor countries to the Commission’s work,Denmark, Sweden and Australia, have also urged the Commission to address publicparticipation and consultation in its projects.

It is clear from the above that the Mekong is undergoing rapid and far-reaching changes Ofthe many pressing issues in this evolving area, a key issue, identified by both proponents andcritics of structures to regulate flow on the Mekong is the paucity of reliable data on climate,hydrology, sediment yields, capture fisheries, social and cultural aspects upon which to basesound decisions In some important areas, such as water quality monitoring, the magnitudeand complexity of water quality concerns are increasing at a rate that exceeds the capacities

of riparian countries to deal with the issue (Ongley et al., 1997)

2 The Mekong Delta

2.1 The Delta at Large

The Mekong Delta is a 49,520 km2 triangle of recent (<10,000 y BP), generally fertile,alluvial and marine deposits extending from Kratie in southeastern Cambodia throughPhnom Penh and southern Vietnam to the south China Sea (see Fig 2.1) The Delta is flatand low-lying with elevations between 0.5 and 3m above mean sealevel apart from a smallarea in the northwest with elevations over 100m Vietnam’s portion covers 74% of theDelta, while Cambodia occupies the rest Deltaic sediments vary in depth from over 500 m atthe mouth of the Delta to 30 m at Kratie Deposition in the Delta expands the coast of the CaMau Peninsula at a rate of up to 150 m/y, while coastal erosion occurs along the South Chinacoast ( Pantulu, 1986) The Delta’s population of 16 million people make it the most denselypopulated part of the Basin Nearly 85% of the population are rural

Drainage and canal construction in the upper Delta for agriculture and transport wascommenced during the Angkor empire, over a 1000 y ago (Van Zuylen, 1991) Major canalconstruction over much of the Delta, particularly for transport, commenced in earnest withthe French colonisation of Indochina 120 years ago (Sluiter, 1993) Canal construction forirrigation and drainage has accelerated in 1910-30 and since the end of the Indochina War in

1975 The Delta has now over 10,000 km of major canals that have profoundly altered theBasin’s hydrology

The Delta suffered severe damage during the Indochina War Defoliants, bombing, landclearing and drainage destroyed wetlands and forests About 1,300 km2 of melaleuca and1,200 km2 of mangrove forests were lost At the end of the war in 1975, considerableresettlement occurred throughout the Vietnamese portion of the Delta as the governmentsought to feed its people (Sluiter, 1993) About 8,000 km2 of marsh lands in the Plain ofReeds, in the Delta’s northeast were rendered unfit for fish and agricultural productionthrough drainage of estuarine acid sulfate soils

2.2 Vietnam’s Lower Delta

The Vietnamese portion of the Delta occupies 39,000 km2, of which 24,000 km2 are nowused for agriculture and aquaculture and 4,000 km3 for forestry Cultivation in the Delta is arelatively recent practice with floating rices being used prior to paddy rice during wet seasonflooding (Brocheux, 1995) Primary products from the Delta contribute over 30% to theGross Domestic Product and the Delta is Vietnam’s rice bowl, producing 50% of the nation’s

rice (NEDECO, 1993) and contributing to Vietnam’s place as the second largest riceexporter in the world This increase has been largely the result of the 1986 Congress of theCommunist Party’s ‘doi moi’ (renovation) policy, allowing private enterprise in agriculture,trade and industry This enabled farmers to lease land for up to 50 years.

Fig 2.1 The Mekong Delta (NEDECO, 1993)

This liberalization of agriculture has seen a shift to higher yielding “green-revolution” ricesand cultivation, which has been accompanied by a steep increase in the use of artificialfertilizers, herbicides and pesticides with subsequent impacts on water quality and concernswith effects on fish and shrimp (Be, 1994) Fish and shrimp aquaculture production are alsoimportant contributors to the Vietnamese economy and export earnings, particularly inbrackish areas (NEDECO, 1993) Major concerns in this sector are the impacts ofagricultural chemicals on the quality of shrimp and the transmission of diseases in drainagewaters (Be, 1994) The 1 in 100 year late 1997 typhoon Linda destroyed most of the semi-intensive aquaculture ponds and remaining mangroves on the Delta’s Ca Mau Peninsula (seeFig 2.1) It demonstrated the lower Delta’s extreme vulnerability to storm surge.

0 50 100 150 200 250 300

Jan Feb Mar April May Jun Jul Aug Sep Oct Nov Dec

0 5 10 15 20 25 30 35

Jan Feb Mar April May Jun Jul Aug Sep Oct Nov Dec

Fig 2.2 Mean monthly rainfall and Penman Evaporation for the Mekong Delta and

mean monthly river flow for the Mekong at Phnom Penh (from NEDECO, 1993).

The Vietnamese government has earmarked the Delta as a prime area for expanding theproduction of food, export commodities and consumer goods (Sluiter, 1993) and is planningfor a 6.5% to 8% per annum growth in the region The potential for expansion of agriculturalland is only a further 2,000 km2 (NEDECO, 1993) It follows that the expected increases of

up to 50% in rice production to 16 million tonnes by 2015 will have to come from improvedvarieties, increased chemical inputs and increased double and triple cropping Double andtriple cropping is limited mainly by the availability of fresh water from the Mekong in thedry season and flooding in the wet season (Minh, 1995) There are approximately 1,000 km2

of triple rice cropping, 10,000 km2 of double cropping and 1,300 km3 of single cropping peryear The demand for increased production has direct implications for freshwater availabilityand perhaps also for water quality and fisheries production Currently about 80% of surfacewater abstracted is used for agriculture while only 5% is domestic consumption Expandingdemands for water have increased the use of groundwater, particularly for domestic supplies(Hirsch and Cheong, 1996, Ghassemi and Brennan, 2000)

2.3 Cambodia’s Upper Delta

Cambodia’s upper part of the Delta has about 2,000 km2 of irrigation At least 30,000 km2 isflooded during the wet season or covered by permanent wetlands Farmers here have activelyencouraged flooding for over 100 years by digging ‘colmatage’ or irrigation canals throughriver levees In addition to supplying irrigation water, canals also supply nutrient-richsediment to fields Extensive, and in human terms, devastating ‘Pol Pot’ irrigation canalsconstructed in Cambodia in 1975-1979 were failures due to poor hydraulic design and are indesperate need of refurbishment

The hydrology of the upper Delta (Figs 2.2 and 2.3) is dominated by the Tonle Sap andCambodia’s Great Lake (Figs 1.2 and 2.1) Flow in the low relief Tonle Sac reversesdirection from filling the Great Lake during the peak of wet season to draining it during thedry season, making it a natural regulator of flows into the lower Delta During the fillingprocess the Great Lake quadruples in area to over 15,000 km2 and increases in depth in someplaces from 1 to 9 m with a maximum volume of 60 km3 (Fig 2.4, Carbonnel andGuiscafre, 1963) Flooding of surrounding forests and fields exposes increased, rich soil-and forest-sources of nutrients to fish and provides protected spawning areas (Dennis, 1986)The Great Lake is an immense resource to Cambodia and is the heart of its agriculturalproduction Its fisheries are of major importance, but catches have declined over the past 50years from of order 100,000 tonnes in the 1940’s to of order 30,000 tonnes to-day Inaddition to its importance to Cambodia, Tonle Sap provides fish that migrate as far asYunnan (Hirsch and Cheong, 1996)

Clearing of forests around the Great Lakes and the Quatre Bras started early this century andhas accelerated In the late 1960s there were an estimated 8,000 km2 of surrounding forestswhich had dwindled to 3,000 km2 in 1992 (Dennis and Woodsworth, 1992) Cutting offlooded forests around the Great Lake has been banned since 1987, however, the pressuresfor development of this fertile area for agriculture have not abated There are varyingestimates of the total amount of Cambodian forests remaining, from 30 to 60% In 1992,Cambodia’s logging was more than 1.5 million m3 This is estimated to be about 7 times thesustainable yield (Economist Intelligence Unit, 1993) Deforestation is blamed for thedecreasing fish catches It has also been claimed to be responsible for increased

sedimentation in the Lake It has been estimated that sedimentation has increased from 20mm/y, in the 1960’s, to 40 mm/y, in 1990, (Sluiter, 1993) Invaluable, comprehensive benchmark studies of the Lake’s hydrology and sedimentation in the early 1960’s (Carbonnel andGuiscafre, 1963) gave a mean sedimentation rate of 0.3 mm/y over the past 5,000 y Thedeposition of 35 Mt/y of sediment, evident in Fig 2 at Phnom Penh (Mekong Secretariat,1992), can also be used to estimate a mean sedimentation rate If we assume that this isdeposited annually over the 15,000 km2 of the flooded Great lake, and that the meansediment density is 1 t/m3, then the deposition rate is a more creditable 2.3 mm/y, or an 8-fold increase over the previous 5,000 y average of Carbonnel and Guiscafre (1963).Increased sedimentation is a major issue as it gradually reduces the capacity of the GreatLake to regulate dry season flows in the Delta.

0 10

Cambodia's Great Lake

Fig 2.3 The seasonal variation of the volume of Cambodia’s Great Lake, from Carbonnel

and Guiscafre (1963).

The Mekong Secretariat has proposed a dam on the Tonle Sap, at the entrance to the GreatLake, as a strategy to reduce flooding around the Lake in the wet season It would alsoprovide downstream irrigation in the dry, boosting agricultural production, particularly inVietnam Cambodia has strongly opposed and continues to oppose this dam (Sluiter, 1993).Its impact on fisheries production and on the subsistence farmers and fishers around the Lakecould be enormous and may prevent the current fish migration up the Mekong, from the sea

In addition, if the proposed dam prevents flooding around the Lake in the wet season, it maytherefore increase downstream flows, exacerbating flooding in Vietnam’s potion of theDelta

2.4 Hydrology and Climate of the Delta

The climate in the Delta is tropical monsoon and is influenced by both the southwest andnortheast monsoons In general the dry season runs from December to April while the wetseason spans May to November Fig 2.2 (redrawn from NEDECO, 1993) summarises themean monthly rainfall and Penman evaporation of Vietnam’s lower Delta Also shown is andthe mean monthly stream flow for the Mekong at Phnom Penh The pronounced seasonality

of the rainfall and stream flow is obvious in Fig 2.2 Average annual temperature in theDelta is close to 28°C Mean monthly temperatures run from 25°C in January through to high

of around 28.9°C in April The mean monthly relative humidity varies from a low of around74% in the dry to 83% in the wet season The marked seasonality is also reflected in thevolume of Cambodia’s Great Lake in the upper Delta Fig 2.3, using the invaluable data of(Carbonnel and Guiscafre, 1963) shows the variation in the volume of the Lake The Lake is

a natural flow regulator for the lower Mekong acting as a flood storage in the wet seasonuntil early October and a supply reservoir in the dry as the Lake drains from October on Themagnitude of its importance as a flow regulator for the Delta can be judged from Figs 2.3 and1.2

There is also a marked spatial variation in annual rainfall across the Delta which depends onthe direction of the monsoon in the southwest and an orographic influence in the north (Fig2.4, Minh 1995) The length of the rainfall season is also spatially dependent (Fig 2.5, Minh,1995) It varies from 4 months in the north, to 7 months in the southwest and also reflectsthe direction of the monsoon

Fig 2.4 Distribution of annual rainfall across the Mekong Delta (Minh, 1995).

2.4.1 Floods and seawater intrusion

The marked seasonality in rainfall leads to both annual floods and water shortages in theBasin In the wet season almost 50% of the Delta is flooded (1,900 km2) The maximumdepth of inundation in the wet season is principally governed by the topography of the basin,the influence of the upstream flow from the Mekong and Bassac Rivers and tidal inundation

in the south (Fig 2.6, Minh, 1995) A smaller influence from the spatial variation of rainfall

is also evident in Fig 2.6 In the northern part of the Delta, in the Plain of Reeds, inundationdepths can exceed 4 m The original rice production systems in the Delta took advantage ofwet season flooding by using floating rice crops

Fig 2.5 Distribution of length of rainfall season over the Mekong Delta (Minh, 1995).

In the dry season, flow in the Mekong is insufficient to prevent saline intrusion and extensivesalinization of waterways occurs in the lower Delta Fig 2.7 (Minh, 1995) shows the extent

of salinity intrusion at the beginning of the saline intrusion (BSI) and the end of the salineintrusion (ESI) The whole of the Ca Mau Peninsula in the Delta’s southwest, in Fig 2.7, issalinized for 6 months during the dry as there is insufficient freshwater flow in the Mekong

to displace saline intrusion from the southwestern sector of the Delta Figures 2.6 and 2.7exemplify two of the main hydrologic problems of the Delta, wet season floods and dryseason saline intrusion

The length of the wet season is an important factor in rice production, particularly for doubleand triple cropping The frequency of occurrence of early season and mid season drought is

also critical The delay of the onset of the wet season (early season drought), and theoccurrence of mid season drought are key determinants of rice production These droughtsare also spatially distributed across the basin (Fig 2.8, Minh 1995) Proposed dams on upperMekong, especially at the Tonle Sap, are designed to address this problem and provide waterresource security during dry seasons and droughts.

Fig 2.6 Mean annual depths of wet-season flooding across the Mekong Delta (Minh, 1995).

2.4.2 Tidal influences

Streams and canals in the Mekong Delta are influence by the tides of both the East and WestSeas In the East Sea the tide is semidiurnal but irregular and has a large tidal amplitude of 3

to 3.5m The regime has a 15 day cycle average tidal level has a maximum in December and

a minium in July The tidal effects from the East Sea propagate over much of the Deltathrough the main and farm canal systems Farmers use these tidal fluctuations to drain andflood their lands Drainage of floodwaters can be impeded if wet season floods coincide withthe spring tide

Tides in the West sea are diurnal with a tidal range of about 0.8 to 1.2m Canals in the CaMau Peninsula are influenced by both East and West Sea tides simultaneously This can lead

to a dead water zone which can prevent water movement from the Bassac River into the CaMau area (Ghassemi and Brennan, 2000)

2.4.3 Seawater intrusion floodgates

Studies of seawater intrusion (Mekong Secretariat, 1992a; 1992b;1993) developed a model

to predict seawater intrusion into the lower Delta Following these major studies, a proposalwas developed to install saline intrusion floodgates on main canals along the Ca MauPeninsula and South China Coast (NEDECO, 1993) The idea behind this scheme is tolengthen the growing season for rice from one to two crops in the saline intrusion affectedareas The discharges of the Mekong River are considered adequate to meet irrigationdemand in the protected areas during the early periods of the dry and wet season, thuslengthening the growing season In the dry season, Mekong flows are insufficient forirrigation in the protected areas (NEDECO 1993)

Fig 2.7 Seawater intrusion into the Mekong Delta during the dry season BSI and ESI are

respectively the beginning and end of the seawater intrusion (Minh, 1995).

A series of 12 massive sluices or tidal floodgates have been installed on the major rivers andcanals connected to the East and West Seas (Fig 2.9) in an effort to prevent seawaterintrusion into the Ca Mau Peninsula The project, called the Quan Lo Phung Hiep Projectcost over $US 12B and included the dredging of over 250 km of secondary canals Theproject commenced in 1992 and was completed in 2001 The sluice gates are between 5 and25m wide They open automatically on the ebb and close on the spring tide The objective ofthe project was to permit two rice crops per year to be grown in the irrigation area behind thesluices (Fig 2.9) by decreasing the salinity ingress into the area behind the floodgates andincreasing the flow of freshwater from the Bassac River during the dry season

White et al (1996) used the analogy of the impacts of saline floodgates in eastern Australia

to point out the possible severe consequences that could arise in areas with acid sulfate soils.This included the prevention of fish passage, the acidification of waterways behindfloodgates and the loss of seawater species behind the floodgates Since the brackish watercanals are more productive that freshwater canals, this may have considerable consequencesfor subsistence farmers in the region, given the importance of fish as a protein source in theregion Our field trip to the area appeared to confirm these predictions The impacts ofalready installed sluice gates near Soc Tranh were summed up succinctly by one farmer

“floodgates have given us a road (track) and electricity But no crops and no fish!” The water

in his field drains had a pH 3.5 and there was little tidal fluctuation to permit him to irrigateand drain his field

A project is underway to examine the impacts of the saline intrusion floodgates (Tuong,2002) It has found thus far that farmers on non-acid sulphate soils in the eastern partbenefited from the salinity protection schemes, which allowed them to increase riceintensification Farmers on acid sulphate soils in the western part had to abandon shrimpfarming, which meant sharp decline in household incomes Rice farmers in the eastern partdesired to retain the salinity protection scheme while those in the western part preferred todispose of the scheme such that brackish water could re-enter the area

Fig 2.8 Spatial distribution of early season (ESD) and mid season drought (MSD) in the

Mekong Delta (Minh, 1995).

Farmers perceived that the salinity prevention measures caused a decline in abundance ofnatural fishery products in rivers and canals Trawling was carried out as part of the study in

six villages at the beginning of the rainy season (May and June) 2002 It found fish biomassdeclined sharply in area with pH < 6 This resulted in the decline in income earnings fromcapture fisheries, which was not only an important income source for the poor householdsbut also an important protein source for them Although the income decline from catchingfish among the poor has been compensated for to some extent by other income-generatingopportunities in several hamlets surveyed, this nevertheless reveals an important ecologicalconsequence of preventing tidal ingress into the study area As more sluices went intooperation year by year, the rapid change in hydrological conditions had profound economicand social impacts on farmer’s livelihood (Tuong, 2002) As a result, conflicts over theoperations of sluices have arisen.

Fig 2.9 Location of the 12 saline intrusion sluices in the Quan Lo Phung Hiep Project in the

Ca Mau Peninsula The irrigation area protected behind the floodgates is shaded in grey (Ghassemi and Brennan, 2000).

2.5 Surface Water Quality

Water quality is of fundamental importance in the Mekong Delta, now just because of humanconsumption but also because of its significance in wild capture and aquaculture fishproduction in the Mekong Delta Because of this an extensive water quality network has been