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INTERNATIONAL HYDROLOGICAL PROGRAMME _____________________________________________________________
Water Management in the Mekong Delta:Changes, Conflicts and Opportunities
by
Ian White
Centre for Resource and Environmental StudiesNational Institute for the EnvironmentInstitute of Advance StudiesThe Australian National UniversityCanberra ACT 0200 Australia
_____________________________________________________________IHP-VI Technical Documents in Hydrology No. 61UNESCO, Paris, 2002
The designations employed and the presentation of material throughout the publication do not imply the expression of any
opinion whatsoever on the part of UNESCO concerning the legal status of any country, territory, city or of its authorities, or
concerning the delimitation of its frontiers or boundaries.
SC-2002/WS/47
CONTENTSTerms of Reference...................................................................................................................3Acknowledgments ....................................................................................................................4Summary...................................................................................................................................51. The Mekong..........................................................................................................................8
1.1 River of Change...............................................................................................................81.2 This Study......................................................................................................................11
1.2.1 Purpose....................................................................................................................111.2.2 Study methods.........................................................................................................11
1.3 Geography of the Mekong River Basin .........................................................................121.4 The Lower Basin ...........................................................................................................14
1.4.1 Lower Basin Climate...............................................................................................141.5 Fisheries Resources of the Mekong...............................................................................15
1.5.1 Wild capture fisheries .............................................................................................151.5.2 Future demands and threats to wild capture fisheries .............................................161.5.3 Aquaculture.............................................................................................................161.5.4 Constraints to aquaculture.......................................................................................17
1.6 Social, Cultural and Economic Features of the Basin ...................................................181.7 Institutional Arrangements for Mekong Basin Resource Management.........................20
1.7.1 The Mekong River Commission .............................................................................211.8 Basin Development and Cooperation............................................................................23
2. The Mekong Delta ..............................................................................................................252.1 The Delta at Large .........................................................................................................252.2 Vietnam’s Lower Delta .................................................................................................252.3 Cambodia’s Upper Delta ...............................................................................................282.4 Hydrology and Climate of the Delta..............................................................................30
2.4.1 Floods and seawater intrusion................................................................................312.4.2 Tidal influences.......................................................................................................322.4.3 Seawater intrusion floodgates .................................................................................33
2.5 Surface Water Quality ...................................................................................................352.6 Groundwater in the Delta ..............................................................................................362.7 Soils of the Delta ...........................................................................................................382.8 Acid Sulfate Soils..........................................................................................................39
2.8.1 Oxidation of acid sulfate soils.................................................................................402.8.2 Release of toxic metals ...........................................................................................402.8.3 Discharge of acidity into surface waters .................................................................412.8.4 Impacts of acidity on estuarine ecosystems.............................................................412.8.5 Links between soils, hydrology and atmospheric emissions ..............................42
2.9 Saline Soils ....................................................................................................................432.10 Water and Land Constraints ........................................................................................432.11 Integrated Management and Conflict Resolution........................................................44
2.11.1 The use of multi-agent systems in natural resource management.........................443. Responses to Water and Land Issues of the Delta .............................................................47
3.1 Completed Projects of the Mekong Secretariat .............................................................473.1.1 Salinity intrusion forecasting ..................................................................................473.1.2 Water balance study ................................................................................................483.1.3 Water quality monitoring ........................................................................................493.1.4 Management of acid sulfate soils ............................................................................50
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3.2 Work Plan of the Mekong River Commission Secretariat ............................................513.3 The Mekong Delta Master Plan.....................................................................................533.4 Saline Intrusion Floodgates ...........................................................................................543.5 Sedimentation and Hydrology of the Great Lake ..........................................................563.6 Perspectives for Australian Development Cooperation ................................................563.7 Australian Centre for International Agricultural Research Projects..............................573.8 The Farmers Response ..................................................................................................583.9 Summary........................................................................................................................58
4. Opportunities for Integrated Research ................................................................................604.1 Management and Impacts of Saline Intrusion Floodgates in the lower Mekong Delta.61
4.1.1 Background .............................................................................................................614.1.2 Overall Objectives...................................................................................................624.1.3 Specific Objectives .................................................................................................624.1.4 Expected Outcomes.................................................................................................624.1.5 Beneficiaries............................................................................................................62
4.2 Sedimentation and its Impacts on Cambodia’s Great Lake...........................................624.2.1 Background .............................................................................................................624.2.2 Overall Objectives...................................................................................................634.2.3 Specific Objectives .................................................................................................634.2.4 Expected Outcomes.................................................................................................644.2.5 Beneficiaries............................................................................................................64
4.3 Dry-Season Groundwater Supplies in the Mekong Delta..............................................644.3.1 Background .............................................................................................................644.3.2 Overall Objectives...................................................................................................654.3.3 Specific Objectives .................................................................................................654.3.4 Expected Outcomes.................................................................................................654.3.5 Beneficiaries............................................................................................................65
References...............................................................................................................................66
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Terms of Reference
The terms of reference for this report are to prepare a state-of-the art monograph on theMekong Delta which addresses:
(i) a succinct summary of past and present hydrology and water resource managementactivities, including those under the auspices of the Mekong River Commission and ofother specialised agencies.
(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.
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Acknowledgments
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, Universityof 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 andMr 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.
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Summary
The Mekong River is one of the few great, largely unregulated rivers of the world. Its Deltais 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 focussedon 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
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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 min 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 growthin 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
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the Australian government, Perspectives for Australian Development Cooperation, identifiedkey 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.
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1. The Mekong
1.1 River of ChangeThe Mekong (Thai: Mother of Waters) River has the twenty-first largest drainage basin andis 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 regulatedat 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).
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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).
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Fig. 1.1 The lower Mekong River Basin flowing from China to the South China Sea (MekongRiver Commission, 1999)
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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 tobe considered and the gamut of deleterious impacts that may ensue (White, 1963; Fraser-Darling, 1970; Challinor, 1973; Roberts, 1993b; 1995; Sluiter, 1993; McCully, 1996; Hirschand Cheong, 1996).
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 orderto 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
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Agricultural Research (White et al., 1997b). Because the Delta is an integral part of theMekong 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-meltin the Tanghla Mountains on the Tibetan plateau. It descends through steep, narrow gorgesin 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 240km 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,1996).
Burma Cambodia Lao PDR Thailand Vietnam Yunnan Total
Drainage Area(103 km2)
24 155 202 184 65 165 795
Basin Area(%)
2 20 25 23 8 21 100
Annual Runoff(%)
2 18 35 18 11 16 100
Forest Cover(%)
47(whole
country)
49-62 47 26 27 - -
Rate ofDeforestation
(%)
6(whole
country)
3 2 1.5 3.2(Central
Highlands)
- -
Arable Land(103 km2)
95.7 29.1 8.9 190 56.9 933 -
Irrigated Land(%)
- 15 20 20(northeast)
40-50(Delta)
- -
HydropowerPotential
(MW)
300 2200 13200 1000 2000 13000 31500
HydropowerPotential
(%)
1 7 42 3 6 41 100
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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.
0
100
200
300
400
500
0 200000 400000 600000 800000
Drainage Area (km2)
Mea
n R
unof
f (km
3 /y)
0
50
100
150
200
Sedi
men
t Loa
d (M
t/y)
Chi
eng
Saen
Vien
tiane
Muk
daha
n Paks
e
Krat
iePh
nom
Pen
h
Sout
h C
hina
Sea
Sediment Load
Runoff
Fig 1.2 Variation of mean annual runoff (line) and sediment load (solid square points) withdrainage area for the lower Mekong Basin. The dip between Krate and Phnom Penhillustrates the natural regulation of Cambodia’s Great Lake and the Tonle Sap (fromPantulu, 1986, Mekong Secretariat, 1982).
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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 6to 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/yof 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 cascadesof 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 ClimateThe 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 climateis governed mainly by seasonal monsoon winds. The southwest, wet season monsoon startsin 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
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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. Currently1700 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 propensityof 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 undertakenby 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 fisheriesFish 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
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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 fisheriesIt 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 the
timing of hydrological events,• Pollution from agriculture and urban development.• Construction of dams, weirs or diversions which act as physical barriers to fish
migrations.• Increased sediment load due to deforestation.
1.5.3 AquacultureAquaculture 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 thisis 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).
17
The Mekong Delta has the largest aquaculture area (330,000 ha) and freshwater productionis 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 aquacultureThere 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
18
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 directedat 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,1996)
Burma Cambodia Lao PDR Thailand Vietnam Yunnan
GDP(billion US $)
11 2.03 1.46 140.3 17.4 4.51
GDP per capita(US $)
250 206 335 2377 240 465
GDP AnnualGrowth Rate
(%)
6.4 4.9 8.0 8.5 8.8 11.8
GDP Agriculture(US $)
47.1 44.8 57.4 11.1 32.3 21
19
Burma Cambodia Lao PDR Thailand Vietnam Yunnan
GDP Industry(US $)
14.4 19.6 17.9 42.1 25.3 54
GDP Industry(US $)
38.5 35.6 24.8 46.8 42.4 25
Trade Balance(billion US $)
-0.724 -0.243 -0.205 -9.5 -0.9 -
Current AccountBalance
(billion US $)
-0.294(1994/95)
- -0.104(1992)
-8.4(1994)
-1.1(1994)
-
Foreign Debt(billion US $)
5.5(1993/4)
1.0(1992)
1.92(1992)
27.4(1994)
19.6(1994)
-
Consumer PriceIncrease
(%, 1994)
35 26.1 6.7 5 9.9 21.7
The average level of income between countries in Table 1.2 varies by a factor of 10. This issomewhat misleading in regard to income derived from the Basin. The northeastern region ofThailand is the country’s poorest, while the Delta is Vietnam’s most prosperous region. Inaddition, in the Delta most income comes from local farm or aquatic production whereas asignificant proportion of income in northeastern Thailand comes from off-farm remittances.
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 makesup 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 earnersof 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 biodiversityof 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.
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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 providedby 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 managementin 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 studiesof 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 established1987 Revised Indicative Basin Plan
1992 ADB commences Greater Mekong Subregion Initiative
1994 Hanoi agreement on Cooperation for the Sustainable Development of the MekongRiver Basin
21
Year Institutional Development
1995 “Run-of-River” mainstream hydropower dams proposedMekong 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 CommissionThe 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 Mekongto 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 mannerin the sustainable development, utilization, conservation and management ofthe Mekong River water and related resources for navigational and non-navigational purposes for social and economic development and well-beingof all riparian States, consistent with the need to protect, preserve, enhanceand manage the environmental and aquatic conditions and maintenance ofthe ecological balance exceptional to this river basin.
The Commission’s vision for the Basin is:
22
An economically prosperous, socially just and environmentally soundMekong River Basin.
The mission of the Commission is:To promote and coordinate sustainable management and development ofwater and related resources for the countries’ mutual benefit and thepeople’s well-being by implementing strategic programmes and activitiesand providing scientific information and policy advice (Mekong RiverCommission, 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, PhaseIV and Mekong morphology and sediment transport. The Programme is seeking funds forseveral of these projects.
23
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 RiverCommission, 1999)
1.8 Basin Development and Cooperation
One of the important rôles of the Mekong River Commission is to act as a channel for Basin-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.
The 1990’s saw a marked increase in the number of non-government organisations operatingin 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)
PlanningInformation Analysis/
Environmental monitoring
Implementation
24
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 capacitiesof riparian countries to deal with the issue (Ongley et al., 1997)
25
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 in1975. 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
26
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)
27
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
P or
Ep
(mm
/mon
th)
Rainfall
Penman Evaporation
Mekong Delta
0
5
10
15
20
25
30
35
Jan Feb Mar April May Jun Jul Aug Sep Oct Nov Dec
Q (1
03 m3 /s
)
Phnom Penh
River Flow
Fig 2.2. Mean monthly rainfall and Penman Evaporation for the Mekong Delta andmean monthly river flow for the Mekong at Phnom Penh (from NEDECO, 1993).
28
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 ofup 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
29
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
20
30
40
50
60
70
Feb-62 Apr-62 Jun-62 Jul-62 Sep-62 Oct-62 Dec-62 Feb-63 Mar-63 May-63
Volu
me
(km
3 )
Cambodia's Great Lake
Fig 2.3. The seasonal variation of the volume of Cambodia’s Great Lake, from Carbonneland 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.
30
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 seasonalityof 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 highof 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 isa 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).
31
2.4.1 Floods and seawater intrusionThe 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 inundationin the south (Fig. 2.6, Minh, 1995). A smaller influence from the spatial variation of rainfallis 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 extentof 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 Mekongto 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
32
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 influencesStreams 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 3to 3.5m. The regime has a 15 day cycle average tidal level has a maximum in December anda 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 leadto a dead water zone which can prevent water movement from the Bassac River into the CaMau area (Ghassemi and Brennan, 2000).
33
2.4.3 Seawater intrusion floodgatesStudies of seawater intrusion (Mekong Secretariat, 1992a; 1992b;1993) developed a modelto 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 arerespectively 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.
34
White et al. (1996) used the analogy of the impacts of saline floodgates in eastern Australiato 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 waterin 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 theMekong 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
35
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 theCa Mau Peninsula. The irrigation area protected behind the floodgates is shaded ingrey (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
36
established (Mekong River Commission, 1999). Upstream forest clearing and intensificationof agriculture are key concerns. As mentioned in Section 1.3 above, the Mekong deliversabout 150 M tonnes of sediment to the Delta annually. Sediment loads in the Mekong are ashigh as 0.6 kg/m3 at Tan Chau at the beginning of the flood season. In the middle of the floodseason this drops to around 0.15 kg/m3 and finally to around 0.05 kg/m3 in the dry season.Most of this sediment is fines and clay (Ghassemi and Brennan, 2000).
The water quality monitoring in the Mekong has revealed few chemical contaminants. Theredoes appear to be an increasing trend in nutrients in both the Mekong and Bassac Rivers. Theestimated total annual outputs of nitrogen and phosphorus by these rivers are 0.24 M tonnesand 0.07 M tonnes respectively. There is also an increasing trend in fecal coliforms down therivers due to untreated sewerage. As discussed below acidification of surface waters in theDelta is a major problem.
2.6 Groundwater in the Delta
Groundwater has been extracted in the Mekong Delta for almost 100 years, however itssystematic assessment has only taken place since 1975 (Ghassemi and Brennan, 2000).Because increasing development, the long dry season in the southwest, and pollution ofsurface water from salinity, acidity, domestic wastes and suspended sediment, groundwateruse is growing. The estimated current rate of groundwater extraction is 430,000 m3/day fromwells, many of which have been installed by UNICEF. These serve about 4.5 million peopleout of the Delta’s total population of 14 million (Ghassemi and Brennan, 2000). In additionto fresh groundwater, saline groundwaters are also extracted and used for shrimp and fishaquaculture in Can Tho Province.
Fig 2.10 Groundwater geohydrology transects of the Mekong Delta (Ghassemi andBrennan, 2000)
G
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There are five major aquifers in the Delta ranging in age from Holocene through to UpperMiocene. Geologic transects have been established across the delta together with waterquality monitoring bores (Fig. 2.10). A typical cross section running north west to southeastapproximately along the Bassac River is shown in Fig 2.11 (Ghassemi and Brennan, 2000).The eastern, southern and western boundaries of the aquifers are unknown but oil explorationwells suggest they run hundreds of kilometers off the coastline. This may give rise to thepossibility of substantial submarine groundwater discharges off the coast of the MekongDelta. The importance of such discharges is currently under discussion (Burnett andBokuniewiez, 2002).
The most important freshwater aquifers in the Delta are the confined aquifers. The Upper-Middle Pleistocene, coarse to fine sand aquifer (qp2-3 in Fig. 2.11) has large areas in thenorth and south of the Delta with total dissolved solids less than 1000 mg/L. Below this, theLower Pleistocene, gravel to sand aquifer (qb1 in Fig 2.11) supplies even better quality waterover 60% of the Delta. Extensive extraction of these aquifers occurs in the Ca Mau Peninsulaas shown by the piezometric surface for the Upper-Middle Pleistocene aquifer (qp2-3) in Fig.2.12 (Ghassemi and Brennan, 2000). This shows recharge in the northwest and draw downdue to extraction in the Ca Mau Peninsula. This aquifer outcrops near the Cambodian border.The interaction of the annual surface flooding and recharge to the aquifer has yet to be fullyinvestigated. In addition interaction between acid and saline surface waters and groundwaterremains to be studied.
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Fig 2.11 Geological cross section across section G-H of the Mekong Delta in Fig, 2.10. Theaquifers are in descending order qh-unconfined Holocene, qp2-3-confined UpperPleistocene, qp1-confined Lower Pleistocene, m4-artesian Pliocene, and m3-artesian Upper Miocene (Ghassemi and Brennan, 2000).
Fig. 2.12 Piezometric surface for the Upper-Middle Pleistocene aquifer (qp2-3) in theDelta during the wet season showing recharge in the northwest and draw downdue to extraction in the Ca Mau Peninsula (Ghassemi and Brennan, 2000)
2.7 Soils of the Delta
The soils of the Mekong Delta are an extremely important factor in the production of cropsand fish and in determining water quality in the lower Delta. The soils are all Holocenedeposits, formed in the last 6,000 to 7,000 years, after the last sea level. The seven main soiltypes of the Delta are summarised in Table 2.1.
TABLE 2.1. Main soil types the Mekong Delta and their areas (Ve and Vo-Tong, 1990).
Soil Area(km2)
Area(% total)
Alluvial 10,943 28.9
Acid sulfate 10,543 28.0
Saline 8,903 21.4
Saline acid sulfate 6,214 17.0
Old alluvial 1,090 2.8
Peat 341 0.9
Mountainous 347 1.0
The distribution of soils across the Delta is shown in Fig. 2.13 (Minh, 1995). Depositionalpatterns of the alluvial soils clearly follow the branches of the Mekong and Bassac Rivers.The two soil types which constrain agricultural production (Minh, 1995) are the permanentlysaline soils on the coastal fringes and the acid sulfate soils, most prevalent in the backswampareas and making up a total of 45% of the Delta. It is feared that upstream diversions mayincrease seawater intrusion in the dry season.
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2.8 Acid Sulfate Soils
Acid sulfate soils are soils containing sulfides, mostly the mineral iron pyrite, or its oxidationproducts. They were formed throughout the world in coastal embayments and estuarinefloodplains as a result of the last sea level rise (Pons, 1973). In this marine transgression, sea,or brackish water containing sulfate with concentrations greater than about 10 mg/L,encroached on organic detritus from coastal vegetation, such as mangroves. This, combinedwith iron from the sediments under anaerobic conditions, produces iron sulfides (vanBreemen ,1973; Dent, 1986). Sulfide accumulation in sediments continues to occur inmangrove swamps (Lin and Melville, 1992) salt marshes, coastal lakes and in bottomsediments (Berner, 1984, Howarth, 1979). The Mekong Delta has one of the world’s majoraccumulations of acid sulfate soils. Many of these soils are highly unconsolidated with watercontents as high as 80%. Very large shrinkage s occur when these soils are drained orconsolidated. Drainage can cause the land surface to fall by as much as 1 m (White, 2002).Both the groundwater behaviour and hydraulic properties of these shrinking soils arefundamentally different to those in rigid soil and groundwater systems (White et al., 2001).
Fig 2.13. Distribution of main soil types across the Mekong Delta. Red areas show thelocation of actual acid sulfate soils while brown areas are potential acid sulfatesoils. Dark blue areas are permanently saline soils while yellow shows slightlysaline soils. Alluvial soils are shown in green (Minh, 1995).
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2.8.1 Oxidation of acid sulfate soilsAs long as sulfides deposited in estuarine soils remain in reduced conditions below the watertable or water surface, they pose no problems. It is only when they are exposed to oxygen,such as in periods of prolonged drought, or after draining, dredging or excavation, thatproblems occur through the oxidation of pyrite to sulfuric acid :
FeS (s) +72
0 H 0 Fe 2SO H2 2 22 2
4+ → + + +
− +2 [1]
The ironII, liberated in Eq. [1], is soluble and can be transported by drainage into canals andstreams to considerable distances from the pyrite source, as has been found in the Delta (Tinand Wilander 1995). In streams, further, secondary oxidation of ironII can occur andproduces characteristic red-brown flocs of ferrihydrite, FeOOH and more acid:
+22
+2 2H+FeOOHOH23+O
41+Fe → [2]
These flocs also cause environmental damage in estuaries by smothering benthos (Sammut etal., 1995). This secondary oxidation of ironII also consumes oxygen and can be associatedwith depleted dissolved oxygen in streams.
The overall reaction for the complete oxidation of pyrite in moist soils can be written as(Dent 1986):
FeS 154
O 72
H O Fe(OH) 2SO 4H2 2 2 324
+ + → + + +− [3]
Equation [3] shows that for each mole of pyrite oxidized completely, four moles of hydrogenions are produced. Frequently, partial oxidation products are observed, such as thecharacteristic pale yellow mottles of jarosite, KFe3(SO4)2(OH)6, a mineral which forms at pHbelow 3.7 under strongly oxidizing conditions. Jarosite hydrolyses slowly and represents asubstantial store of acidity in already oxidized profiles. As well as jarosite, large amounts ofacidic products, such as exchangeable aluminium, are stored on the exchange sites onsediment particles. The release of acid from these stores by back hydrolysis reactions or bydilution seems strongly dependent on the prevailing hydrologic conditions, with rising andreceding floods having different water chemistry (Tin and Wilander, 1995). This storedacidity is released and lowers water quality during flood recession (Sammut et al., 1996).
2.8.2 Release of toxic metalsThe acid pore water in oxidized sulfidic sediments reacts with clay minerals in the sediment torelease silica and metal ions, principally aluminium, iron, potassium, sodium and magnesium,as in, for example, the acid hydrolysis of the common estuarine clay mineral illite (Nriagu1978):(K Na Ca )(Al Fe Mg )(Al Si )0 (OH) 7.41H 2.59H O0.5K 0.36Na 0.05Ca 0.3Mg 0.25Fe(OH) 1.95Al 3.46H SiO
0.5 0.36 0.05 1.5 0.253
0.3 0.45 3.46 10 2 22 2
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4 4
+ +
+ + + + +
+ + →
+ + + + + + [4]
Other ions, such as manganese and trace heavy metals can be released as well (van Breemen,1973; Nriagu,1978; Willett et al., 1992). Drainage waters with pH as low as 1.6 and dissolvedmonomeric aluminium concentrations in excess of 100 mg L-1 have been reported. In thesouthern Mekong Delta above My Phûoc sluice gate, we measured soil pH as low as 2.2 infarmers’ fields. Drain pH was higher at around 3.5. These soil and drainage waters can be toxicto plants and marine organisms, not just because of acidity, but also because of the dissolvedmetal iron contents, particularly aluminium and iron (Sammut et al., 1995). In parts of the
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Delta, this acidified water is used for domestic supplies of water. The impact of these waterson human health is unknown. There are unconfirmed reports in eastern Australia abouthealth problems arising from contact with acidic drainage waters.
2.8.3 Discharge of acidity into surface watersAnnual average acid discharges from drained acid sulfate soils in estuarine floodplains inAustralia, have been estimated to be between 100 to 500 kg of pure sulfuric acid/ha/y.Associated are equally large fluxes of toxic dissolved aluminium and iron (Sammut et al.,1996; Wilson, 1996; White et al., 1997b, Wilson et al., 1999). Export rates in the MekongDelta are dependent on cropping system but seem comparable to the above figures (Tuong,1993, Tuong and Minh, 1995; Minh et al., 1997). This export of acidity is intimately linkedto the seasonal water balance and its impact on watertable height and groundwater discharge,and to the crop production system and drainage strategy (White et al., 1993; 1997b; Tuong,1993). In Vietnam, irrigation waters have been used to flush out acidity from the soil. In thePlain of Reeds it has been estimated that there is insufficient freshwater to dilute the acidicdischarge to non harmful levels (Tuong and Minh, 1995; Minh et al., 1997). In our visit tosoutheastern extremity of the Plain of Reeds, near Tan Thanh there were clear indications ofmassive acid outflows. We drove for 45 minutes along the massive main canal where thewater along the entire length had a pH of 3.5. Flooding the soil for rice production lowers theexport of aluminium and acidity.
2.8.4 Impacts of acidity on estuarine ecosystemsDrainage from acid sulfate soils can have major adverse impacts on Stillwater, groundwaterand downstream water quality (Willett et al., 1993; Tuong, 1993; Palko and Yli-Halla, 1993;Tuong and Minh, 1995;Tin and Wilander, 1995; Wilson, 1996; Sammut et al., 1996;Truonget al., 1996; Minh et al., 1997). These impacts include decreases in crop production (Kittricket al., 1982; Dent, 1986; Moore and Patrick, 1993), massive fish kills and outbreaks of fishdiseases (Callinan et al., 1993; Sammut et al., 1995) and accelerated corrosion of concrete,iron, steel and aluminium infrastructures (White et al., 1996). In Australia, it has been shownthat floodgates, similar to the saline intrusion floodgates now completed in the lowerMekong Delta’s Ca Mau peninsula, promote soil and waterway acidification, act as acidreservoirs in dry seasons and are barriers to fish breeding, feeding and migration.
Fig.2.13 shows that most of Vietnam’s acid sulfate soils are concentrated in the Plain ofReeds, the Long Xuyen Quadrangle and the Ca Mau Peninsula.
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Fig 2.14 Extent of surface water acidification (pH<5) in the Mekong Delta in the early wetseason (May to August, Ghassemi and Brennan, 2000).
Most of the substantial research on acid sulfate soils in the Mekong Delta has concentratedon ameliorating the soil-induced toxicity problems in acid sulfate soils for crop production.Farmers in the Delta have led researchers in developing ways of mitigating severe soilacidity. There has been limited work on their wider environmental impacts, the implicationfor fisheries or their interaction with hydrology. The work that has been carried out hasshown massive exports of acid, aluminium and iron (Kham, 1988; Tuong, 1993; Tuong andMinh, 1995; Tin and Wilander, 1995, Truong et al., 1996; Minh et al., 1997). The impact ofthese on fish populations has not been assessed. The extent of acidified surface waters inthe Delta during the start of the wet season is shown in Fig. 2.14 (Ghassemi and Brennan,2000)
2.8.5 Links between soils, hydrology and atmospheric emissionsVan Breemen (1993) found that sulfur budgets could not be closed during the oxidation ofacid sulfate soils. He proposed that up to 30% of the sulfur during oxidation was emitted assulfur dioxide. Recently, Macdonald et al. (2002) have reported the first measurements ofsulfur dioxide from acid sulfate soils. The SO2 appears to evolve during the evaporation ofsoil water containing sulfite, one of the intermediate species in sulfide oxidation. Theirpreliminary field measurements suggested that the flux of SO2 from acid sulfate soils was atleast 4% of the anthropogenic output. It has been reported that the rainfall chemistrymonitoring sites across the Mekong Delta have shown unexpected acidic rainfall. The links
43
between acid sulfate soil hydrology, oxidation and atmospheric emissions need to beexplored.
2.9 Saline Soils
Permanently saline soils are confined to a narrow fringe along the coastal strips along theSouth China sea and Gulf of Thailand (Fig. 2.13). These areas also contain the Deltasdwindling mangrove forests, now reduced to 2,000 km2. Those remaining on the Ca MauPeninsula were devastated by Typhoon Linda in late 1997. These mangrove forests arefundamentally important as fish and shrimp breeding areas and in stabilising the coast fromerosion. In eastern Australia it has been estimated that the value of mangroves to seafoodproduction is around $US5,000/ha/yr.
Dry season saline areas along the south China coast are currently planted to paddy in the wetseason to produce one rice crop. In the dry season farmers have developed a system tomaximise their returns by allowing brackish water into their fields and using them for shrimpproduction (Xuan, 1993; Be, 1994). Shrimp are a much more important source of earningsthan rice. One farmer we visited in the southern Delta above the Hô Phòng floodgates grewtwo crops of prawns to one crop of rice per year (White et al., 1997a). Prawns were his cashincome and the farmer earned 10 times the national average income. He was not worriedabout the impact of the saline intrusion floodgates on saline shrimp production as he hadestimated that by the time the canal salinity had decreased (an estimated three years) hewould have made sufficient to retire. A major concern with dry season shrimp production isthat brackish water aquaculture may lead to the salinization of rice fields.
2.10 Water and Land Constraints
The above demonstrates that the unique combination of hydrology and soils in the Delta poseparticular problems in its sustainable management. These tend to differ between lower andupper regions of the Delta. In Vietnam’s portion of the Delta, the major land and waterresource problems are (NERDECO, 1993; Xuan, 1993; Be, 1994; Minh, 1995; Hirsch, andCheong1996):
• acute flooding in the wet season, with flood depths of more than 4 m in the northernDelta
• acid sulfate soils constraints on crop productivity with association, severedegradation of drainage water quality which threatens aquatic productivity
• seawater intrusion in the dry season in the lower Delta, limiting rice production toone crop per year in seawater affected regions
• impacts of seawater intrusion floodgates on acidification and land and waterproduction
• quality and availability of dry-season domestic water supplies in rural areas• availability and interactions of groundwater and surface waters• loss of coastal mangroves and impacts on coastal protection and fisheries.
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In the upper part of the Delta there are different issues which 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 (H. Milner, SMEC, privatecommunication, November,1997), despite the clear importance to riparian communities.
The principle water and land concerns in the Cambodian section of the Mekong Delta are:
• impacts of upstream flow regulation on the water supply for flooding for riceproduction and fish production in the Great Lake
• impacts of forest clearing on the sedimentation and aquatic production of the GreatLake
• impacts of downstream regulation on flooding and fish and rice production• quality and availability of dry-season domestic water supplies in rural areas.
The major institutional response to these problems has been to plan for and constructinfrastructure such as water diversion canals and saline intrusion floodgates(NEDECO, 1993,Hirsch and Cheong, 1996). Bilateral projects have tended to focus on single issues, such asmitigating the impacts of acid sulfate soils on crop production, ignoring broader scale issuesand interactions. This is in sharp contrast to the farmers’ response. They have had to take anintegrated approach and have adapted remarkably to the changing, very adverse systems byevolving farming systems which maximise returns (Xuan, 1993; Be, 1994).
2.11 Integrated Management and Conflict Resolution
The above demonstrates that the issues concerning land and water resources in the Mekongdelated are inextricably intertwined. Attempts to change the management of one particularlycomponent may have ramifications throughout the whole system. It is clear that a focus onnarrow issues, exemplified by the saline intrusion floodgate installation could haveunforeseen impacts in other parts of the system and can generate considerable conflicts.Because of this a integrated approach to land and water management is required thatencompasses much broader perspectives and includes conflict resolution as an integralstrategy. Such sentiments are often annunciated and tend to become almost ‘motherhood’statements. The complexity of integrating physical, chemical, biological, ecological,geological, social, economic, ethical and cultural issues into a holistic approach are at firstinspection daunting. However their have been some recent approaches that offer promise.One such approach is the development of multi-agent systems, decried briefly below.
2.11.1 The use of multi-agent systems in natural resource managementMulti agent systems, MAS, (Bousquet, 2001) provide powerful tools for studyinginteractions between societies and their environment. They have the potential to greatlyreduce conflict over natural resource management and resource allocation. MAS requireknowledge of the bio-physical processes governing the resource and of the social, culturaland economic rules controlling their use.
MAS are simulation tools that provide a method to reformulate questions in the social andnatural sciences. They have been used for the past decade to study the interactions betweennatural and social systems in ecosystem and renewable resource management and in the use
45
of bottom-up approaches in decision-making (Bousquet et al., 1999). An agent can representany level of organisation from an individual to a village to a herd. MAS rely fundamentallyon field studies to provide information and hypotheses and to test performance (see Fig.2.15). Using that information, MAS challenge understanding of the system and provide newquestions for further field studies (Barreteau and Bousquet, 2001).
Fig. 2.15. Modelling cycle for an MAS system ((Barreteau and Bousquet, 2001).
To take into account links between the natural and the socio-economic systems, a system isconstructed with a set of modules or compartments (the resources) linked by flows (flows ofmaterial, energy or information) and controls (socio-economic rules, legislation). Solutionsemerge from the interaction that become a different portfolio of interventions, includingmediation to resolve conflicts, facilitation of learning, and participatory approaches thatinvolve people in negotiating collective action. Modelling becomes a tool for interactivelearning and conflict resolution (Röling, 1997).
Barreteau and Bousquet (2000, 2001) describe the application of MAS to tackle the viabilityof irrigation in the middle Senegal River Valley. Some parts of this irrigation system havebeen abandoned or redesigned and the system is under used. The MAS assumes that theirrigation system acquires and allocates water and credits. The simulation scheme iscomposed of a pumping station, main canal, water courses and farmers plots. Individualfarmers or groups of farmers are the agents. Each farmer belongs to three groups, one forwater allocation, one for credit issues and one for pumping management. Each agent has aset of rules to describe how it behaves. The MAS system developed, SHADOC, was used tocommunicate the conceptual models of both researchers and farmers and as a negotiationsupport tool to explore scenarios and their long-term outcomes. Even though Senegalesefarmers had never used a computer before, they were very active in selecting scenarios anddiscussing the results.
MAS have been applied to other farming systems involving irrigation in Indonesia andThailand (Becu et al., 2001) and to groundwater in Tunisia and are being developed forgroundwater in the Pacific (White et al., 2002). Current work in the region includes
MAS model
Field study
simulations
assumptionsquestions
Mapping experiments
Assessing assumptionsnew questions
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collaborative work between CIRAD/IRD and other partners in the Red River Catchment(Vietnam), and in the Ping Catchment (Thailand) as well as a training component inBangkok for Training involving Thailand, Vietnam and the Philippines..
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3. Responses to Water and Land Issues of the Delta
Many of the unique water and land issues facing the Delta have long been recognised. TheIndicative Basin Plan of 1970, produced by the Committee for Coordinating Investigations ofthe lower Mekong basin and the revised plan of 1987, identified the need for an overallapproach to the Mekong Delta. Various land and water issues have received attentionthrough the Mekong Secretariat’s work programme, through individual country priorities,and through multi- and bilateral projects. Most of these have been narrowly focussed,concentrating on a single issue or a few related issues, the broader implications andintegration with other fields, such as the linkage between hydrology, water quality, ecologyand fish production, have been largely overlooked. The Master Plan for the Mekong Delta(NEDECO, 1993), attempted a broader approach to the issues in the Delta in Vietnam.
In sharp contrast to the institutional approach, farmers in the Delta have developed ingeniousfarming systems which maximize income from, often, extremely adverse conditions andwhich, of necessity, integrate a wide range of information and conditions. However, becausetheir emphasis is on production, environmental impacts tend to be overlooked if they do notdirectly impact on in-farm production. It is here that research can add value to water and landmanagement. The following examines the key responses to land and water issues in theDelta.
3.1 Completed Projects of the Mekong Secretariat
The Mekong Secretariat has adopted a long-term strategy plan for addressing the problems ofthe Delta as part of the broader management of the Mekong Basin. The Secretariat’s thrusthas been hydrological, with the main effort concentrated on investigations of the impacts ofriver and tributary regulation, irrigation diversions and infrastructure development forhydropower and irrigation. Setting aside river regulation projects, there have several majorcompleted projects with direct relevance to the Delta. These are the Salinity Intrusion Studies(Mekong Secretariat, 1992a; 1992b; 1993), Water Balance Study of the Lower MekongBasin (Institute of Hydrology, 1982; 1984; 1988a; 1988b), the Management of Acid SulfateSoils Project (Ministry of Agriculture and Rural development, 1995) and the water qualitysurvey of the Lower Mekong (Mekong Secretariat, 1982). These studies were narrowlyfocussed.
3.1.1 Salinity intrusion forecastingThe Salinity Intrusion Study had its origin in the 1930’s. During 1935-1942 a dense networkof salinity monitoring sites were established over the main branches of the Mekong and itscanals to establish the extent of dry-season saline intrusion. The goal of the Mekong
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Secretariat’s study was to develop at model of salinity intrusion which could be used topredict the impacts of upstream diversions on intrusion and asses the threats to agriculture inthe Delta. Phase I (Mekong Secretariat, 1992a) modelled the canals and small systems of theDelta, Phase II (Mekong Secretariat, 1992b) studied the main river branches under low flowconditions, Phase III (Mekong Secretariat, 1993), extended the study to the whole Deltaunder all flow conditions. This study developed and tested the MERKSAL model and theVRSAP (Vietnam River System and Plains) and built up local capacity in their use. TheVRSAP model is a one dimensional solution for solute transport for the river/canal networkwith runoff from rice fields.
The Salinity Intrusion Study concentrated on model development. The coupling of thismodel with a marine/freshwater fish population dynamics model may be of considerablebenefit in determining the impact of management strategies on fish populations.
3.1.2 Water balance studyThe Water Balance Study of the Lower Mekong Basin was designed to review the hydrologyof the lower Basin and to determine the impacts of upstream regulation, diversions forirrigation and changes in land use on flow in the Mekong. The objective of the Phase I(Institute of Hydrology, 1982), study was to review available data, carry out a water balancestudy of selected tributary basins and investigate the variability of flows in the Mekongupstream of the Delta (as far as Pakse). A simple water balance model with rainfall,estimates of evapotranspiration, runoff and two part storage was developed.
Phase I identified the absence of long-term hydrometeorological data and the gaps in spatialcoverage as significant limitations. The absence of available solar radiation was a majorlimitation for calculating potential evapotranspiration as was the inadequacies of estimatingareal rainfall. The study demonstrated the difficulty of estimating evapotranspiration for suchareas. The complementary approach was used (Brutsaert and Stricker, 1979; Brutsaert, 1982)together with Penman potential evaporation. The study’s use of Penman rather than thePriestly-Taylor approximation for potential evaporation appears to be an unnecessarycomplication for estimating monthly evaporation since it requires estimates of wind speedand humidity in addition to the principal driver, solar radiation. In work on estimating streamand groundwater flows in tropical northern Australia, Vardavas (1988) was able to predictsuccessfully daily rainfall-runoff relations using equilibrium evaporation and estimated solarradiation. Such an approach would seem particularly appropriate for the Mekong Delta.
It was concluded that mainstream flows did not indicate any significant changes in the low-flow regime of the Mekong River due to upstream developments. Reasonable water balancescould only be achieved by assuming a fixed soil storage at the end of the wet season.Monthly water balances were more reliable than 5-day balances. The study found that theeffects of land-use change on river flow were insignificant and suggested that statisticalmodels were more appropriate than conceptual models.
The following Phase II project (Institute of Hydrology, 1984) had two primary objectives.The first was to develop a network-routing model of the Lower Mekong Basin containingelements that represented storage reservoirs and irrigation schemes, and the second was tostudy problems inherent in estimating areal rainfall from point records. A network-routingmodel was produced which contained reservoir and irrigation submodels and could be usedto investigate different water allocation policies. The analysis of rainfall was restricted to
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monthly data from northwest Thailand were coverage of gauges was adequate in time andspace and data was readily available. Data for the rest of the lower Basin was consideredinadequate. Short period rainfall estimates were inaccurate due to sparse spatial distributionof raingauges. The study showed that the spatial correlation for monthly data dropped offwithin a few tens of kilometres.
The Phase III project (Institute of Hydrology, 1988a; 1988b), was required to determine aframework for the continuous monitoring of the flow regime of the lower Mekong Basin inorder to quantify the effects of existing and ongoing developments, and to review and gatherdata for the effective modelling on planned developments in order to assess the impacts ondownstream flow. This study is particularly relevant since it specifically addressed inflows tothe Delta. Problems of data availability in Cambodia were noted. Simple regression modelsfor wet and dry season flows of the Mekong at Kratie and Tonle Sap were used. It wasconcluded that dry season flows to the Delta had increased however at the expense of floodflows into the Great Lake. The importance of the Lake as a flow regulator for dry seasonflows into the Delta was emphasised. It was predicted that the Great Lake may not be fillingto the same level as previously. Major reservoirs were identified as contributing to thechanged flow regime. There were insufficient time series data to recognise impacts due tochanges in land use or irrigation. The study also recognised the difficulty of estimating riverdischarges in the tidally influenced regions of the Delta.
The terms of reference of the water balance study were quite specific. Because of that thestudies concentrated on surface waters with no reference to the recharge of groundwaters.Since groundwater is an increasingly important component of domestic and urban supplies inthe Delta (NEDECO, 1993). Recent developments in the stochastic analysis of temporal andspatial variations of rainfall which include orographic influences specifically and can be usedto produce areal averages (Hutchinson, 1995a; 1995b) and the application of data-basedmechanistic modelling to rainfall- runoff would seem to be of potential benefit in such waterbalance approaches.
3.1.3 Water quality monitoringEarlier water quality monitoring in the Basin (Mekong Secretariat, 1982) concluded thatthere were insufficient samples taken on a regular basis and that chemical and biologicalmeasurements were inconsistent. These made it impossible to identify past trends in waterquality.
A review of the Basin’s water quality monitoring network (Ongley et al., 1997) identifiedthat there is no clear objective concerning the final use of information and that theprogramme is at risk of being diverted by irrelevant scientific or economic interests. Generalwater quality objectives and criteria were found to be missing for the Mekong. The reviewbelieves that monitoring is a management tool and concludes that it should only be donewhen necessary information is needed by legislation or environmental managers. Thiscurious conclusion seems to stem more from western economic rationalism than rationalriver management. One of the overwhelming conclusions of all Mekong studies is theimportance of long term continuous monitoring data. The review believed that present andpossible future effects of forestry /deforestation and fertilizer use in agriculture were wellcovered. It recommended that salinity and acidity monitoring in the Delta be continued onlyin so far as they contributed to larger issues as fish survival and on loadings of pollutants tothe sea. The key finding of the Review was that the magnitude and complexity of water
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quality concerns is increasing at a rate that exceeds the development capacity of the ripariancountries and the Mekong Secretariat.
One of the surprising aspects of the review is the almost total absence of any suggestedlinkage between water quality monitoring and River hydrology or fish production. Thelinkage of these sectors into a chemical transport and biological production model wouldseem essential. As well, the failure to identify sediment transport as a major nutrient sourceand sink for both agriculture and fish production emphasises the compartmentalisation ofprojects in the Secretariat.
3.1.4 Management of acid sulfate soilsThe overall objective of the Management of Acid Sulfate Soils Programme is to formulateenvironmentally sound reclamation and management strategies for acid sulfate soils. Theproject seeks to anticipate the reactions of acid sulfate soils to various development andmanagement strategies through an understanding of the processes set in motion by thesestrategies (Ministry of Agriculture and Rural development, 1995). In order to achieve theoverall objective two immediate objectives were set: to obtain information on the physical,chemical and biochemical reactions and the basis of soil acidification, such as theirmechanisms, kinetics, interlinkage and dependence on environmental factors; and to developa causal or semi-causal description of these processes, with the ultimate view to construct adynamic mathematical model.
It is by no means clear how these objectives meet the condition in the overall objective forenvironmentally sound development. The claimed project outcomes are upgrading of projectoffices and laboratories; conducting plot-sized field experiments; conducting controlled soilcolumn experiments; evaluating data; the commencement of a model for physical processesin acid sulfate soils; and training staff.
It would seem, with two exceptions, that the scale of this project is not commensurate withthe scale of the problem in the Delta. The exceptions are the work of Tin and Wilander(1995) who studied the rate of transmission of acid drainage in the canal system, Truong etal. (1996) who simulated acid water movement in canals based on the assumption of acidsulfate and aluminium equilibrium with jurbanite (Al(OH)SO4, a mineral postulated butnever observed in acid sulfate soils, and that of Tuong and Minh (1995) and Minh et al.(1997) who studied rates of acid and aluminium production under different crop and soilmanagement regimes. The last study showed that exports from rice crops were less than fromupland and higher value crops which are not under flood irrigation. The outcomes of thisproject may be useful for crop production but they seem to be less useful in examining thebroader scale environmental impacts. The pressing issue of the impact of massive salineintrusion floodgates on acidification of the large areas behind floodgates and dykes in thelower part of the Delta has not been examined nor its impact on fisheries.
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3.2 Work Plan of the Mekong River Commission Secretariat
The Secretariat’s work plan (Mekong River Commission Secretariat, 1996, MRC 2002)details both current and planned priority projects. Those of direct relevance to the Delta arelisted in Table 3.1 . This table provides useful insight into the current priorities of theCommission.
Some of the listed projects are of particular relevance to the land and water needs of theDelta. These include :Improvement of the hydrometeorological network, whose objective isto rehabilitate and construct an adequate number of hydrometeorology stations in Cambodiaand to develop regular measurement and transmission of data; The Groundwaterinvestigation program whose objectives are to: establish a hydrogeological network; to assessthe regional groundwater potential; to predict and monitor changes in groundwater quantityand quality; to provide accurate data for the use of groundwater resources management andprotection. This project is particularly relevant to the domestic water supply needs of ruralcommunities in the Delta in the dry season.
Table 3.1. Mekong Secretariat’s Water and Land Resources Projects of Relevance to theDelta.
Project No. Title Status1.1.20/94 Strategy study on the development of the watershed/management
sector in the Lower Mekong Basin (LMB)Planned
1.1.23/95 Preparation of the Mekong River Commission rules for waterutilization and inter-basin diversion
Existing
2.1.02/86 Groundwater investigation program Existing2.1.09/94 Flood forecasting and damage reduction study in the Mekong
BasinExisting
2..1.10/91 Water balance of the LMB Phase IV Planned2.1.11/90 Mekong morphology and sediment transport Panned2.1.12/91 Salinity forecasting in the Mekong Delta. Stage III (Viet Nam) Completed2.1.13/92 Improvement of the hydrometeorological network Existing2.3.03/89 Mekong geographic information system Existing2..4.11/86 Management of acid sulfate soils (Viet Nam) Completed2.4.12/88 Inventory of wetlands in the LMB Completed2.4.13/92 Inventory and management of the Cambodian wetlands Planned2.4.14/94 Basinwide waterborne diseases management project Planned2.4.15/88 Water quality monitoring network in the LMB, Phase II Completed2.4.20/87 Control of soil erosion, sedimentation and flash flood hazards Completed2.4.23/94 Study on water quality and pollution control Planned3.1.39/93 Development plan for Tonle Sap Existing3.1.47/94 Study on the environmentally sound water management in the
Plain of ReedsPlanned
3.1.51/94 Flood control planning for development of the Mekong Delta Planned3.2.30/94 Irrigation rehabilitation study and capacity building in Cambodia Existing3.2.32/95 Sustainable irrigated agriculture, Phase III Planned
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Project No. Title Status3.2.37/95 Management of salt-affected soils for agricultural development
in the LMBPlanned
3.3.14/94 Feasibility study of the forestry-based coastal protection for theeastern coast of the Mekong-Delta
Planned
3.3.15/94 Melaleuca forest management in the U Minh area (Viet Nam) Planned3.3.16/94 Mangrove forest management in the Ca Mau Peninsula (Viet
Nam)Planned
3.3.48/89 Forestry-based development in the Long Xuyen quadrangle,Mekong Delta
Existing
3.3.49/92 Assessment and monitoring of Mekong Basin forest cover Existing3.3.50/93 Watershed classification in the LMB Existing3.3.51/92 Sustaintainable management of resources in the LMB Existing3.4.14/92 Management of freshwater capture fisheries in Cambodia: Phase
IIExisting
3.4.15/94 Assessment of the impacts of water management on fisheryresources.
Planned
3.4.16/94 Rural extension for aquaculture development in the Mekongdelta: Phase I
Planned
3.4.18/95 Migration and spawning of Mekong fish species Planned3.4.19/95 Strengthening of inland fisheries information systems in the
Mekong
The project as proposed, however, is not focussed on community needs nor is it linked towater balance modelling and the water quality network. Recharge estimation appears not tobe within its objectives nor is the connection between surface water quality, particularly inseawater intrusion areas and regions of acid surface waters. Flood forecasting and damagereduction study in the Mekong Basin and Water balance of the LMB Phase IV expand oncompleted projects. The objective of the Mekong morphology and sediment transport projectis to increase technical capability in the mathematical modelling for river morphologicalstudies in water resources development planning. The possible interaction between rivermorphology and sediment transport and proposed water control structures will be modelled.There is no indication here that the important linkages between land-use, sediment loads,aquatic and terrestrial productivity will be considered.
The objective of the Inventory and management of the Cambodian wetlands project is todesign and implement a Cambodian wetlands conservation programme. This project isrelated to investigations of the social and economic importance of annually inundated areasaround Tonle Sap and the lower Mekong and Bassac areas in the Delta.
The overall aim of the Study on the environmentally sound water management in the Plain ofReeds is to formulate guidelines for water management in Vietnam’s Plain of Reeds. Theimmediate aims are to: assess environmental and social impacts due to water control projectsdeveloped over the past 20 years; propose detailed guidelines for continued development ;and strengthen the capability of national organisations in environmental assessment. There isno suggestion here that a halt to development may be the best option environmentally.
Flood control planning for development of the Mekong Delta seeks to: determine immediateaction plans for flood control; identify long term flood control measures for the development
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of the Delta; and to strengthen capability in flood control planning. This project is aimed atboth the Vietnamese and Cambodian sections of the Delta. This project is a progeny of theMekong Delta Master plan.
3.3 The Mekong Delta Master Plan
The Mekong Delta Master Plan (NEDECO, 1993) was a response to the MekongCommission’s Revised Indicative Plan of 1987. The Delta Master Plan was funded by theUNDP with the World Bank as Executing Agency and the Mekong Secretariat as AssociatedExecuting Agency. The Master Plan focussed on land and water resources in the lower Deltaand was concerned with agriculture, forestry and fisheries. The Vietnam government’s goalof rapid economic growth was a significant driver for the plan. The Master Plan was requiredto:
• produce a master plan• help reinforce the planning capability for the Mekong Delta• undertake five feasibility studies for priority projects.
Development planning had to be environmentally sound and sustainable. Four thematicstudies were undertaken of: the environment of the Delta; its soils; salinity intrusion andwater resources management. The five feasibility studies covered integrated water resourcesdevelopment and agriculture, fisheries and aquaculture, forestry, transportation andnavigation and drinking water supply. The principal thrust of the study was to improveagricultural productivity of the Delta and to raise rice production from 10 million tonnes(1991) to 15 million tonnes by 2015. Since the area of land available for expansion is small,(about 8%), the increase in rice production will have to come from increased productivity inexisting farms and from an expansion of double and triple cropping areas (NEDECO, 1993).Other productivity gains were envisaged to come from a change to higher value crops.
The Master Plan recommended a range of water resources, fisheries, forestry, transportationand water supply projects (NEDECO, 1993). Selection criteria used for water resourcesprojects were: technical feasibility; environmental soundness; high net returns oninvestments; and relation to long-term development perspectives of the whole Delta. Waterresource development adopted a moderate scenario, designed to protect areas of the Deltafrom flooding only during the beginning of the wet season and from saline intrusion onlyduring the beginning of the dry, thus lengthening the growing season. These plans, it wasclaimed, would not cause changes in the upstream flooding regime in Cambodia.
A by-pass for flood flow was envisaged through the Long Xuyen Quadrangle to the Gulf ofThailand. Full flood protection of the Delta in Vietnam was considered not possible ordesirable, as it would unacceptably raise water levels in Cambodia and prevent thedeposition of fertile, nutrient-rich sediments on the floodplains.. In addition, Vietnam’sflooded areas are important fish spawning grounds. Irrigation water supply was planned to beenhanced through opening up of the secondary canal system. Saline intrusion was to behandled through coastal embankments and the closing of canals through sluice gates or salineintrusion floodgates and siphons to bring freshwater from upstream to coastal areas.
Acid sulfate soils were admitted to pose a problem, in terms of the amount of freshwaternecessary to reclaim soils after each dry season, and in terms of their impacts on crop
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production and water quality. Slow reclamation was seen as the only viable method ofreclamation. In the Long Xuyen Quadrangle, the reclamation of acid sulfate soils throughmelaleuca plantations was seen as method of both producing much-needed wood for buildingand fuel and addressing a soil-water problem. Melaleuca’s are adapted to acid soilconditions.
The Plan did not envisage any major increases in the Delta’s freshwater capture fisheries,Increases in this sector were planned to come from increased marine capture and aquaculture.The projected impacts of the proposals in the Master Plan on fisheries production came fromthe decease in flooded area through flood mitigation. No recognition was given to the impactof saline intrusion floodgates on fish production, nor to the possible, wider-scaleacidification of waterways as a result of sluice operations (Sammut et al., 1996).
Possible upstream flow regulation in the lower and upper Mekong was seen to be potentiallybeneficial to the lower Delta, in that they would have no impact on flood volumes but mayincrease dry season low flows decreasing saline intrusion. The Plan claimed a flowregulation structure at Tonle Sap offered the best opportunities for dry season flowregulation.
The Master Plan admitted that the proposed developments may have negative localenvironmental impact (NEDECO. 1993). It also suggested that the proposed developmentsmay limit the flexibility of choice of crops and management systems by farmers. This isparticularly so with the seawater floodgates, where farmers behind barriers may not have thepotential to grow shrimp in dry seasons, thereby foregoing a valuable, high-return crop.
3.4 Saline Intrusion Floodgates
The construction of a series of dykes and massive saline intrusion sluices, from Soc Tranhalong National Route 1, which skirts the southern Delta coast, through Bac Lieu and Gi Raito the Ca Mau Peninsula (see Fig. 2). The project called the Desalination of the Ca MauPeninsula, was an immediate response to the Mekong Delta Master Plan and dry seasonsaline intrusion.. This desalination represents a major re-engineering of the Mekong Delta.
Increasing the production of rice in the Mekong Delta is a national priority of the CentralGovernment of Viet Nam. Saline intrusion, during the dry season, into rivers and canalsaffects about 1,700,000 ha of land in the Ca Mau Peninsula. Salinity is seen as a majorimpediment to rice production since it restricts the area to one wet-season rice crop per year.In order to overcome this impediment the Central Government has decided to re-engineer theLower Mekong Delta by constructing a series of saltwater intrusion sluices, mostly alongNational Route 1. Freshwater will be diverted into the southwest from the Bassac River atthe commencement and end of the wet season to extend the length of the growing season inthe area west of the Bassac. There is insufficient water in the Mekong in the dry season underthe present river regime to continue diversion throughout the dry. Regulation of the Mekongat Tonle Sap, however, may change that. In the Government’s view, sluice gate installationand freshwater diversion will allow the production of two crops of rice per year or otherhigher higher-value irrigated crops, such as fruit trees. The removal of an highly profitableproduction option could lead to possible unrest in the region.
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By installing sluice gates, the government is constraining the options of farmers in this area.Many have developed the semi-intensive, brackish water shrimp-rice rotation system to copewith salinity intrusion and to control acid production from acid sulfate soils. For farmers, thisis an attractive options because the returns on tiger prawns are large compared with rice. Itappears that the Central Government has decided that brackish water shrimp in the MekongDelta will be confined to the area below National Route 1, but behind a strip of mangroves,on the Ca Mau peninsula. This region contains much of the area that is permanently salineand could imply a shift away from rice-shrimp rotation. This move may also signal a shiftfrom semi-intensive to intensive shrimp production and may also place mangroves underconsiderable pressure.
An Environmental Impact Statement and a project description have been prepared on theDesalination of the Ca Mau Peninsula project. Both were unavailable at the time of writing.Installation of sluice gates, an entirely engineering solution to saline intrusion, however,appears to have overlooked several important issues which include:
1. The brackish water canals and streams are highly productive. Local farmers andresidents rely on them for much of their protein requirements (up to 80%). Freshwaterappears less productive. We discovered that there is a dearth of information ondomestic “recreational” fish capture and indeed in wild stocks as well. A usefuldevelopment project would be the quantification of Viet Nam’s wild fish resources.
2. The importance of brackish areas to down stream near-shore fisheries and to upstreamfisheries is unknown. In Eastern Australia, up to 65% f all commercial marine fishspecies spend part of their life cycle in estuaries. By limiting the area of saline waterintrusion, fish feeding and breeding may be reduced.
3. The exchange of brackish water with its higher neutralisation capacity has been usedby farmers to flush out acidity from areas of acid sulfate soils. Freshwater hasapproximately a third of the neutralisation capacity of seawater. (Stumm and Morgan,1996) and more freshwater would be required for flushing. As well, canals will not beas well buffered to acid drainage as they are in the dry season.
4. The freshwater behind the sluices in the dry season will be largely stagnant. This mayallow the build up of acid reservoirs behind closed floodgates (Sammut et al., 1996). Inthe Plain of Reeds the well over 20 km of acidified canal behind sluice gates on the VaiCo River was noted during our visit. Such a pool of acid water would have seriousimpacts on rice and fish production.
5. The diurnal tidal cycle, particularly the once-monthly large tide, is used by farmers todrain, flush and refill rice bays and shrimp ponds. The essentially fixed, canal waterlevel regime means that farmers will have to pump out fields.
6. Changing the salinity regime may have impacts on wetland ecology, biodiversity, in-shore sediment transport as well as coastal mangroves. There appears to be littleinformation on sediment transport in Delta, particularly in the saline intrusion region.Evidence from rice-shrimp farmers, suggest substantial inputs of sediments frombrackish water during the dry-season. The importance of this sediment to aquaticproductivity is unknown.
7. Replacement of the brackish water regime by permanent freshwater bodies which mayincrease mosquito populations and the incidence of malaria as well as other water-borndiseases (Hirsch and Cheong, 1997).
All local groups interviewed had a great deal of concern about the project. This wasparticularly so at the Provincial level, where authorities have had little input to the design or
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installation of floodgates, but will be left to manage them and their impacts. Mostappreciated that the impacts of floodgate may be substantial.
The impacts of already installed sluice gates near Soc Tranh were summed up succinctly byone farmer “floodgates have given us a road (track) and electricity. But no crops and nofish!”
The DFID-CRF project Accelerating poverty elimination through sustainable resourcemanagement in coastal lands protected from salinity intrusion: a case study in Vietnamcurrently underway in the Delta, and being lead by the International Rice Research Instituteseeks to conduct a much broader analysis of the environmental and socio-economic impactsof saline intrusion floodgates. It’s goal is to generate benefits for poor people by applyingnew knowledge about the processes of environmental and socioeconomic change in areasprotected from salinity intrusion in coastal Vietnam. The project has already identifiedpotential areas of conflict and negative impacts as well as benefits for more prosperous ricefarmers on non-acid sulfate soils (Tuong, 2002).
3.5 Sedimentation and Hydrology of the Great Lake
The Muséum d’Histoire Naturelle de Paris, assisted by the French Ministère des AffairesÉtrangères, initiated studies of Cambodia’s freshwater fisheries in the early 1960’s. Thesestudies were to examine the possible impacts of a dam on the Tonle Sap. A key part of thetwo-pronged study was an investigation of the hydrology and sedimentation of Cambodia’sGreat Lake conducted over 1962-63 (Carbonnel and Guiscagfré, 1963). Although thehydrology was conducted over a limited period, the detailed, meticulous study is invaluablesince it provides a benchmark for conditions existing prior to 1963, before much of theupstream development of the catchment took place. The sedimentary record is invaluablesince it provides a rate of sedimentation over the past 5,000 y when Holocene infilling of thelake occurred following the last sealevel rise. This rate, 0.3 mm/y, contrasts sharply withcurrent estimates of large increases in sedimentation.
Information on recent studies on sedimentation in Tonle Sap is sketchy. Two studies,Preliminary study of sedimentation in Lake Tonle Sap Cambodia by S. Tsukawaki, M.Okiwara, K.M. Lao and M. Tada. Tonle Sap Development Strategy Project, No. 103, 1994;and The lower Mekong Basin suspended sediment transport. P.O. Harden and A. Sundborg,Oct 1992, were not available at the time of writing..
3.6 Perspectives for Australian Development Cooperation
The comprehensive report by Hirsch and Cheong (1996) identified key areas for interventionand support by the Australian Government in the Mekong Basin . They recognised two majorchallenges to the delivery of assistance for environmentally sustainable development. Thefirst was the development of programs and projects which assist in environmentalmanagement, rehabilitation, planning and promotion. The second was ensuring fullconsideration of the environmental implications of other projects and programmes andconsultations on them with stakeholders.
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The key areas for intervention and support were the geographical focus, resource tenure,forest and biodiversity protection, rural water supply and human resource development. Interms of geographical focus, the report recommended that the Mekong Delta receive specialattention because it receives less priority development assistance and because of theconcentration of poor there. The areas within the Delta identified for priority focus were: thecoastal zone in Ca Mau and Tra Vinh Provinces; coastal fishing communities andunsustainable, intensive aquaculture in Soc Tranh, Minh Hai and Tra Vinh Provinces; andthe deep flooded upper section of the Delta. 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 important resource inthese areas. Watershed and catchment planning were also identified as opportunities forassistance.
Part of these recommendations have already been acted on with an Australian team currentlyassisting the Mekong River Commission on developing institutional rules on water use andmanagement.
3.7 Australian Centre for International Agricultural Research Projects
The Australian Centre for International Agricultural Research, ACIAR, provides assistanceto developing countries through partnership Agricultural Research directed at significantnational or international problems. Its overall thrust is capacity and agricultural resourcebuilding in developing nations. ACIAR has conducted several projects within or near theMekong Basin which are relevant to the present study.
The first is Integrated Water Resource Assessment and Management Framework: A casestudy of the Upper Chao Phraya headwaters Northern Thailand. This project was initiated in1997 is a collaborative project between the Centre for Resource and Environmental Studieswithin the Australian National University and the Royal Project Foundation of Thailand. Thecentral objective of the study was to develop participatory and analytical approaches to assistthe Thai government and other stakeholders to identify and assess options for highlandresource use, which will provide for the sustainability of the inhabitants’ natural and humanresources. The project aimed to develop a decision support system and a participatorydecision making framework through which it will examine the environmental, economic andsocio-cultural implications of different levels and patterns of cultivation and other water usein two widely representative basins in northern Thailand. The project used an integratedapproach to water resources assessment and management focussing on the 40.000 km2 PingBasin in the northern highlands of Thailand.
The second is An Evaluation of the Sustainability of Farming Systems in the Brackish WaterRegion of the Mekong Delta. This project, also commenced in 1997, and was a collaborativeventure between CSIRO, the University of Sydney, the Centre for Resource andEnvironmental Studies within the Australian National University, Can Tho University, andvarious water and hydrogeological agencies within Vietnam. The overall objective of theproject was to determine appropriate on-farm management strategies and governmentpolicies for farming systems in the brackish water coastal region of the Mekong which are
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aimed at ensuring the economic and environmental sustainability of the farming systems overthe long term. The project involved economic modelling, shrimp nutrient and growth studies,rice production studies and soil and water studies.
3.8 The Farmers Response
The resettlement of the Mekong Delta, which occurred after the end of the Indochina war,placed communities in difficult situations. The increased population pressures and thedemand for increased food production meant that areas unsuitable for intensive productionwere developed. The response of the farmers, who have to cope daily with adverseconditions within the Mekong Delta, is in marked contrast to the institutional response.Farmers’ problems are immediate and require an integrated approach for their solution. Sincethe introduction of the ‘doi moi’ policy in Vietnam, farmers in the lower Delta havedeveloped a range of farming systems which are designed to cope with soil acidity, salineintrusion, floods and dry periods. These solutions maximise returns to farmers. Vietnam’sDelta farmers rely on the availability of freshwater through the labyrinth of existing,government-constructed canals. In Cambodia’s upper Delta, farmers have had to cope withmassive resettlement and the disastrous, dysfunctional ‘Pol Pot’ ‘colmatage’, which are isdesperate need of refurbishment.
Farmers on acid sulfate soils have developed a range of water management regimes, landpreparation and a selection of crops which leach out acidic saline water (Xuan, 1993; Tuong,1993). Crops other than rice tend to yield higher incomes. In severely acidified areas in theLong Xuyen Quadrangle, combinations of timber forestry, eucalypts and melaleuca, orbananas growing in widened bund walls and bees or rice fish, together with fish in irrigationcanals.
In the saline intrusion area, a chance discovery after a farmer broke his leg and could notclose off his rice fields from the encroaching brackish water, led to the highly profitable rice-shrimp rotation system (Be, 1994). All the above systems, however, have externalenvironmental impacts, many of which are beyond the abilities of the farmers to control. It isin this area, sustainable environmental management, that external organisation can be ofmost value.
3.9 Summary
Much of the past and planned future work of the Mekong River Commission Secretariat hasbeen directed at resource assessment for the design infrastructure for hydropower generationand irrigation diversions. Recent advances in spatial-temporal modelling of rainfall and indata based mechanistic modelling could improve resource assessment there. Tributary damshave been built, but, in the lower Basin no run-of-river dams have been constructed.Criticisms of the top-down approach of these costly projects and their impacts on ripariancommunities is increasing. It is felt in many quarters that the issue of resettlement of ripariancommunities alone, without consideration of other environmental impacts, should precludetheir construction.
The key issues of the Delta, wet season floods, dry season saline intrusion, and thedevelopment of growing external earnings capacity and per capita incomes were addressed in
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the Mekong Delta Master Plan. Previous major studies of the Mekong Secretariat ondevelopment of a water balance model, the development of a saline intrusion model and themanagement of acid saline soils were central to the development of the Master Plan. ThePlan relies heavily on engineered solutions to provide the platform for sustained economicgrowth.
One aspect of the Master Plan, the desalination of the Ca Mau peninsula by saline intrusionsluices and dykes has been speedily acted upon. Construction of these has now beencompleted. The project is designed to extend the growing season of rice production in theregion west of the Bassac to permit expansion of the two crop rice growing area. There isinsufficient water in the Mekong under current flows to provide irrigation for the entire dryseason. The implications of this project in terms of capture fisheries and dry seasonwaterway acidification appear not to have been considered.
The above description of responses to the most pressing water and land-related needs of theMekong Delta is by no means exhaustive. There have been a broad range of responses byboth multi- as well as bilateral organisations and non-government organisations. The projectsdiscussed above illustrate the principal thrust of the response of some of the major sponsorsand organisations and their impacts on the Delta. Apart from the study of Hirsch and Cheong(1996) and the farmers’ response, most have been narrowly focussed, concerned with theconstruction of engineering infrastructure. It is easy to be critical of these, yet they addressspecific, national and regional needs.
Unfortunately, some of the solutions appear to conflict with local needs, particularly thesocio-economic and cultural requirements of poorer communities in the Delta. Theconstruction of dykes and saline intrusion floodgates in the lower Delta, a direct outcome ofthe Mekong Secretariat’s saline intrusion studies, is of particular concern because of thepotential impacts of decreasing fish supplies for subsistence farming communities. Inaddition, the impacts of the proposed Tonle Sap barrage has long been of major concern inCambodia’s upper Delta. Securing adequate, good quality domestic water supplies,particularly in rural areas also emerged as a priority issue. These concerns presentopportunities for integrated projects on land and water management.
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4. Opportunities for Integrated Research
Integrated research has became a catch-cry within resource and environmental management.It must be recognised, however, that it is by no means a simple o straightforward task.Integrated environmental research requires the pooling of information from disparatedisciplines whose modus operandi are often, if not incompatible, dissimilar. It requires teamsof people with skills in often narrow fields. To be successful, it demands the mutual respectof participants for their colleagues, good project management and the ability of participantsto devote a substantial fraction of their time to the project. Part of the problem of manypresent, integrated resource projects is that funding requirements dictate that few can focusexclusively on one project, yet this is necessary.
In comprehensive, integrated research projects on environmental management the physical,chemical, biological, economic, social, cultural and political aspects often must be covered.In areas like the Mekong Delta, the jurisdiction of two national governments and manyprovincial and local governments further complicate issues. In outlining research projectsbelow, there has been no attempt to be comprehensive. Rather the notion here has been usedthat integration requires knowledge from more than one discipline.
There are a range of pressing regional, national and local issues in the sustainable water andland resource management of the Mekong Delta which require further research. Many ofthese have long been recognised. It is important that any additional research projects withinthe Delta add value to existing programmes. The Mekong Delta Master Plan (NEDECO,1993) and the Work Plan of the Mekong River Commission Secretariat (1996), discussedabove, summarise perceived regional and national priorities.
In Perspectives for Australian Development Cooperation, Hirsch and Cheong (1996)recommend that attention be focussed on environmentally sustainable development in themost needy communities of the Delta. This recommendation is in keeping with the criticismsby many non-government organisations and individuals of existing programmes initiated bymulti-lateral, international organisations in the Mekong Basin. For needy communities,securing reliable food and water supplies, while not compromising future supplies areessential, as is the ability to generate income. Rice and locally caught fish are the staple foodrequirements of the Delta.
The emphasis of water and land projects within the Delta has been on the production of rice,aquaculture and the prevention of flood and saline water intrusion. Wild capture fisheriessupply a minimum of between 40 to 60% of the protein requirements of ripariancommunities. Yet these have been given less emphasis that the planning and design of
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regulation and diversion structures (Roberts, 1993b; 1995). There is a need for integratedresearch on wild capture fisheries within water and land research projects.
The three projects outlined below build on the last three decades of progress that has beenachieved in the Mekong Delta. They are designed to compliment existing programmeswithin the Mekong Secretariat and to address issues of resource sustainability and use at alocal level. Only project outlines are given. Collaborating organisations are not identifiedhere nor are all the linkages with existing programmes. We have set aside the issue of floodprotection as a research project since its scope is immense. From the Section 3 above, threepressing areas appear in need of research: impacts of saline intrusion floodgates; impacts ofsedimentation in the Great Lake of Cambodia and rural domestic groundwater supplies.
4.1 Management and Impacts of Saline Intrusion Floodgates in the lowerMekong Delta
4.1.1 BackgroundSeawater intrusion and acid production from acid sulfate soils during dry seasons, and theexport of acid through drainage systems during the wet season, are major constraints toagricultural and aquatic production in Vietnam’s lower Mekong Delta. These problems areseen as high priorities by the Vietnamese government and the Mekong River Commission.To limit saltwater intrusion into agricultural areas, saline water intrusion floodgates anddykes have been installed in the Ca Mau Peninsula on the lower Mekong River.
Floodgate design has been based on purely engineering criteria to reduce incursions ofseawater and to extend the length of the rice growing season in the area west of the Bassac.Impacts on soil acidification, the transport and storage of acid, and the impacts of stored acidon agricultural, aquatic productivity and subsistence fishing have been ignored. Up to 5,000km2 may be affected. Work in eastern Australia has shown that floodgates on estuarine, acidsulfate floodplains, promote soil acidification, lower plant production, act as large acidreservoirs, form barriers to fish migration, decrease recruitment and feeding areas, diminishtidally-driven acid neutralisation and release hundreds of tonnes of acidity into estuarinereaches. The impacts on aquatic communities are massive. Research is required to determinefloodplain and floodgate management strategies which optimise agricultural production andminimise upstream and downstream impacts of floodgates, and on ways to reduced conflictsover floodgate operation.
Based on Australian experience, the suggested hypotheses are that firstly, installation offloodgates in Vietnam will results in extremely poor upstream water quality during the dryseason; and secondly, the resulting water quality will cause major decreases in upstream, dry-season, irrigated crop production and fish and aquatic production.
This project will: firstly, quantify the impacts of salinewater intrusion floodgates onhydrology, acid production, storage, neutralisation and export; secondly, determine theinfluence of those impacts on aquatic production; thirdly, to improve floodgate andfloodplain management; fourthly, produce options for floodgate and floodplain managementwhich optimises agricultural production and minimises impacts and which permitssustainable coastal lowland development and production; and fifthly, explore ways for
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integrating biophysical and social-cultural knowledge into systems which assist conflictresolution and avoidance.
4.1.2 Overall ObjectivesThe overall objectives of this project are to determine the impacts of salt water intrusionfloodgates on the hydrology, soil and water quality, atmospheric emissions and agriculturaland fisheries production in the Mekong Delta and to develop strategies and approacheswhich allow the equitable use of resources and reduce conflicts over resource use aandallocation.
4.1.3 Specific ObjectivesThe specific objectives are to:1. quantify the impacts of saline water intrusion floodgates on the hydrology, salt, sediment
and acid transport in acid sulfate soil areas;2. quantify the impacts on SO2 emissions into the atmosphere from acid sulfate soils;3. develop and test a model of the influence of floodgate operation on canal acidification;4. determine the influence of those impacts on harvested fisheries;5. identify options to improve floodgate management so as to maximise benefits and
minimise impacts;6. involve local fishers an farmers in the project7. explore the use of multi-agent systems to reduce conflict in floodgate operation;8. provide training opportunities;9. transfer research findings to fishers, farmers and agricultural, land and water resource
managers and policy makers.
4.1.4 Expected OutcomesThe expected outcomes are an integrated understanding of the impacts and management ofsaline water intrusion sluices, a model to predict the impacts of changes in floodgateoperation; the maintenance of adequate water quality for rice, fish and other crops in thelower Mekong Delta consistent with adequate control of salinity, the maintenance of proteinsupplies for riparian communities and the reduction of potential conflicts. An integralcomponent is to build up of local capacity in land, water and fisheries resources assessmentand management and conflict resolution.
4.1.5 BeneficiariesThe intended beneficiaries of this project are the riparian communities of the lower MekongDelta, farmers in the southwest of the Delta, provincial governments in the lower Delta andthe government of Vietnam.
4.2 Sedimentation and its Impacts on Cambodia’s Great Lake
4.2.1 BackgroundCambodia’s Great Lake is a major freshwater and amazing productive fish resource in theMekong Delta. Its outlet to the Mekong, Tonle Sap, reverses flow in the wet season. Thesystem is a natural floodwater storage reservoir and flow regulator. During the wet season the
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Great Lake fills flooding spawning, feeding and breeding grounds. At the commencement ofthe dry season, the Great Lake starts to discharge into the Mekong and regulates flow into thelower Delta. Plans are being developed to construct a barrage on Tonle Sap to preventflooding of surrounding Cambodian farmlands and to provide downstream irrigationdiversions in the dry season.
The Great Lake’s waters are highly productive providing immense, although declining, fishresources for Cambodia. In the wet season, the massive flooding of the Lake providesnutrient-rich sediments for surrounding forests, farmlands and protected areas for fishspawning and feeding grounds. From benchmark French studies, it is known that thesedimentation rate in the Lake over the 5000 years prior to 1960 was of 0.3 mm/y. Recentfigures suggest that this rate by at least eight-fold. This has been attributed to deforestationboth upcatchment and it areas surrounding the Lake. Declining fish catches in the Lake havebeen blamed on increased sedimentation.
This project will quantify the spatial distribution of recent rates of sedimentation both in theLake and in surrounding regions. Sediment geochemistry, mineralogy and biology will bestudied to provide information on its nutrient status and possible source locations. Theimpact of sedimentation on benthos will be also studied. A model, incorporating appropriaterepresentation of the spatial and temporal distribution of rainfall and landuse, as well aspossible regulation will be developed of upstream water and sediment imports and exportsfrom the Lake. The nutrient imports and their effects on forest growth and crop productionwill be examined. The importance of flooded forests as nutrient supplies for fish will beexamined and a model of the relation between fish production and flooding and sedimentimports will be developed. The impacts of changes in upstream and surrounding landuse andwater management will be predicted and an economic model produced to examine thebenefit/costs of options. Training in the techniques used in this project is an integralcomponent as is communication of the outcomes.
4.2.2 Overall ObjectivesThe overall objectives of this project are to determine the impact of landuse and waterresource changes on the sedimentation and production of Cambodia’s Great Lake, toexamine the benefit/costs of different interventions, provide training and transfer theknowledge gained to resource managers, users and governments in the upper Mekong Delta.
4.2.3 Specific ObjectivesThe specific objectives of this project are to:
1. develop a water and sediment balance for Cambodia’s Great Lake which incorporatesupstream and surrounding landuse and uses recent advances in spatial and temporalmodelling
2. quantify recent rates (post 1960) of sedimentation in the Great Lake3. measure the geochemical, mineralogical and biological characteristics of the Great
Lake and surrounding sediments4. determine impacts of sedimentation on benthic production5. determine the nutrient inputs from Lake and surrounding sediments for fish production6. develop a model of fish production which incorporates impacts of changed sediment
inputs and Lake flooding
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7. examine the cost/benefits of various intervention strategies8. involve local fishers an farmers in the project9. provide training opportunities10. transfer research findings to fishers, farmers and agricultural, land and water resource
managers and policy makers in the region.
4.2.4 Expected OutcomesThe expected outcomes of this project are an integrated understanding of fish production inCambodia’s Great Lake and the impact of changes in upstream and surrounding landuse andwater management; water and sediment balance models of the Great Lake; models of theimpact of sedimentation and water regime on fish production; understanding of theconsequences of landuse and water management changes; estimates of cost/benefits ofvarious intervention strategies and the build up of local capacity in land, water and fisheriesresources assessment, conservation and management.
4.2.5 BeneficiariesThe beneficiaries of this project are the farmers and fishers surrounding Cambodia’s GreatLake, provincial governments, the Cambodian government and the Mekong RiverCommission.
4.3 Dry-Season Groundwater Supplies in the Mekong Delta
4.3.1 BackgroundThe Mekong Delta is a region where annual rainfall exceeds evaporation are there are largeannual outflows of surface waters to the sea. Its monsoonal climate, has marked wet seasonsand dry seasons. During the dry season many of the Delta’s rural communities are forced torely on inferior quality canal water for domestic water supplies, particularly in the southwest.In areas of acid sulfate soils, dry season canal water is acidic and often brackish to salinewith large concentrations of dissolved aluminium. There is no information on the impact ofthis water on human health.
Groundwater in the region is increasingly being used for domestic water supplies. UNICEFhas helped install many groundwater wells of diameter 40 to 400 mm extracting water fromdepths between 100 to 480 m. This extraction is occurring from deeper, confined,Pleistocene aquifers. There are currently few restrictions on extraction rates. As well,groundwater is viewed as a possible source for industrial enterprises and, more importantly,for dry season irrigation. Recharge estimates for the confined groundwater aquifers of theDelta are not available, so estimates of sustainable yields are not possible. In an areasurrounded by the West and East Seas, saline intrusion is a district possibility. In addition,the interactions between lower quality, dry-season surface waters and groundwaters have notbeen measured, so that the linkage between surface water and groundwater quality isunknown. An additional hazard is that in former estuarine sediments that make up theaquifers there is the possibility of acidification of groundwater by pumping-inducedoxidation of sulfidic sediments and the subsequent solution and mobilisation of heavymetals, as has occurred in India and Bangladesh.
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In this project a water balance model of the groundwater resources of the Delta will bedeveloped. Linkages between surface and groundwaters will be examined through thedevelopment of a numerical model and the use of piezometry and groundwater geochemistry.The spatial and temporal distribution of groundwater quality will also be measured.Appropriate options and strategies for extracting groundwater to minimise any sedimentoxidation and saline intrusion will be investigated. The impact of consumption of acidifiedcanal waters in areas of acid sulfate soils on human health will be examined. Options for theequitable allocation, management and wise use of groundwater will be developed inconsultation with communities, and training in the study techniques will be provided.
4.3.2 Overall ObjectivesThe overall objectives of this project is to determine sustainable groundwater extractionstrategies for domestic water supplies and irrigation in the Mekong Delta are to determinethe impacts of acidified domestic water supplies on human health.
4.3.3 Specific ObjectivesThe specific objectives of this project are to:1. develop a model of the water balance of the confined groundwater aquifers of the
Mekong Delta2. develop and test a numerical model of the confined groundwater aquifers in the Delta3. examine the spatial and temporal distribution of groundwater quality and geochemistry in
the Delta4. establish the linkages between surface and groundwater in the Delta5. examine the magnitude of submarine groundwater discharge6. determine the sustainable extraction rates from groundwater in selected areas7. develop appropriate groundwater extraction procedures which minimise sediment
oxidation and salt water intrusion.8. determine the consequences to human health of drinking acidified water in areas of acid
sulfate soils9. determine options for allocating fresh groundwater to other users such as irrigation10. involve local residents and communities in the project11. provide training opportunities12. transfer research findings to communities and water resource managers and policy
makers in the region.
4.3.4 Expected OutcomesThe planned outcomes of this project are an understanding of the groundwater resources andtheir quality and the connection between surface and groundwaters in the Mekong Delta, awater balance model of the groundwater resources, knowledge of sustainable extractionrates and safe extraction procedures in selected areas, understanding of the resourcespotential for irrigation supply, options for the equitable allocation of groundwater,information on the impacts of acidified water supplies on human health and the build up oflocal capacity in groundwater resource assessment, conservation and management.
4.3.5 BeneficiariesThe intended beneficiaries of this project are the rural communities of the southwest MekongDelta, provincial governments in the Delta and the governments of Cambodia and Vietnam.
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