INTERNATIONAL HYDROLOGICAL PROGRAMME _____________________________________________________________ Water Management in the Mekong Delta: Changes, Conflicts and Opportunities by Ian White Centre for Resource and Environmental Studies National Institute for the Environment Institute of Advance Studies The Australian National University Canberra ACT 0200 Australia _____________________________________________________________ IHP-VI    Technical Documents in Hydrology    No. 61 UNESCO, Paris, 2002 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 CONTENTS Terms of Reference 3 Acknowledgments 4 Summary 5 1. The Mekong 8 1.1 River of Change 8 1.2 This Study 11 1.2.1 Purpose 11 1.2.2 Study methods 11 1.3 Geography of the Mekong River Basin 12 1.4 The Lower Basin 14 1.4.1 Lower Basin Climate 14 1.5 Fisheries Resources of the Mekong 15 1.5.1 Wild capture fisheries 15 1.5.2 Future demands and threats to wild capture fisheries 16 1.5.3 Aquaculture 16 1.5.4 Constraints to aquaculture 17 1.6 Social, Cultural and Economic Features of the Basin 18 1.7 Institutional Arrangements for Mekong Basin Resource Management 20 1.7.1 The Mekong River Commission 21 1.8 Basin Development and Cooperation 23 2. The Mekong Delta 25 2.1 The Delta at Large 25 2.2 Vietnam’s Lower Delta 25 2.3 Cambodia’s Upper Delta 28 2.4 Hydrology and Climate of the Delta 30 2.4.1 Floods and seawater intrusion 31 2.4.2 Tidal influences 32 2.4.3 Seawater intrusion floodgates 33 2.5 Surface Water Quality 35 2.6 Groundwater in the Delta 36 2.7 Soils of the Delta 38 2.8 Acid Sulfate Soils 39 2.8.1 Oxidation of acid sulfate soils 40 2.8.2 Release of toxic metals 40 2.8.3 Discharge of acidity into surface waters 41 2.8.4 Impacts of acidity on estuarine ecosystems 41 2.8.5 Links between soils, hydrology and atmospheric emissions 42 2.9 Saline Soils 43 2.10 Water and Land Constraints 43 2.11 Integrated Management and Conflict Resolution 44 2.11.1 The use of multi-agent systems in natural resource management 44 3. Responses to Water and Land Issues of the Delta 47 3.1 Completed Projects of the Mekong Secretariat 47 3.1.1 Salinity intrusion forecasting 47 3.1.2 Water balance study 48 3.1.3 Water quality monitoring 49 3.1.4 Management of acid sulfate soils 50 2 3.2 Work Plan of the Mekong River Commission Secretariat 51 3.3 The Mekong Delta Master Plan 53 3.4 Saline Intrusion Floodgates 54 3.5 Sedimentation and Hydrology of the Great Lake 56 3.6 Perspectives for Australian Development Cooperation 56 3.7 Australian Centre for International Agricultural Research Projects 57 3.8 The Farmers Response 58 3.9 Summary 58 4. Opportunities for Integrated Research 60 4.1 Management and Impacts of Saline Intrusion Floodgates in the lower Mekong Delta.61 4.1.1 Background 61 4.1.2 Overall Objectives 62 4.1.3 Specific Objectives 62 4.1.4 Expected Outcomes 62 4.1.5 Beneficiaries 62 4.2 Sedimentation and its Impacts on Cambodia’s Great Lake 62 4.2.1 Background 62 4.2.2 Overall Objectives 63 4.2.3 Specific Objectives 63 4.2.4 Expected Outcomes 64 4.2.5 Beneficiaries 64 4.3 Dry-Season Groundwater Supplies in the Mekong Delta 64 4.3.1 Background 64 4.3.2 Overall Objectives 65 4.3.3 Specific Objectives 65 4.3.4 Expected Outcomes 65 4.3.5 Beneficiaries 65 References 66 3 Terms of Reference The terms of reference for this report are to prepare a state-of-the art monograph on the Mekong Delta which addresses: (i) a succinct summary of past and present hydrology and water resource management activities, including those under the auspices of the Mekong River Commission and of other 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 broad field of land-use (water management) which require an integrated approach at the subregional level on water management issues. The recommended programme should be able to attain achievable results within 3 years, take into account any limitations on-site infrastructure 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 to UNESCO. 4 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, Dr Philip Ford, CSIRO Land and Water, Dr Ian Willett, ACIAR, Associate Professor Mike Melville, University of NSW, Dr Phillip Gibbs, NSW Fisheries, Dr Philip Hirsch, University of Sydney, Professor Vo-Tong Xuan¸ Dr Le Quang Minh, Professor Vo Quang Minh, Nguyen Anh Tuan, Dr Troung thi Nga and Dr Nguyen Huu Chiem , Cân Tho University, Vietnam, Dr Pascal Perrez, CIRAD, France, Ms Erica Donner, CRES ANU, Dr Truong and Mr Nguyen Than Tin Sub, Institute Water Planning, Vietnam, Professor Nguyen An Nien and Professor Dong, Southern Institute of Water Resources Research, Vietnam, Dr To Phuc Tuong, IRRI, the Philippines, and Dr Sok, Hydrology, Mekong River Commission for assistance and many helpful discussions. Mr Vincent Leogardo, UNESCO IHP, is thanked for his generous help in preparing this report. 5 Summary The Mekong River is one of the few great, largely unregulated rivers of the world. Its Delta is both agriculturally and aquatically highly productive and a major contributor to the region’s food production and export earnings. Water and land issues of the Delta must be considered as integral with those of the Mekong Basin as a whole. A majority of the Mekong Basin’s 60 million, ethnically diverse peoples rely on the River’s aquatic resources and rice production for their subsistence. For many, 40 to 60% of their protein intake is from fish from 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 its riparian communities, with vast wet season floods and dry season water shortages that allow seawater intrusions into the Delta. These annual hardships are superimposed on nearly 60 years of devastating external and internal conflicts in the region. The six riparian countries making up the Basin have generally low external and per capita earnings. Harnessing the Mekong for hydropower generation and irrigation supplies, through cascades of main-stream and tributary dams, coupled with harvesting the Basin’s forests are ways of stimulating growth, increasing per capita income and regulating seasonal flows. These developments, however, are potentially in conflict with the subsistence needs and the livelihood security of the region’s poorest people. River regulation and diversions pose dilemmas, since they may decrease substantially the Mekong’s prodigious aquatic productivity. Up-catchment forestry also threatens water quality, 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 mutually beneficial manner and to channel resources into its work program. Understanding the hydrology of the Basin and impacts of its regulation are central themes in its work plan, financed mainly by international multilateral or bilateral organisations. Major financing organisations have been criticised by non-government organisations as too narrowly focussed on infrastructure development and reliant on top-down approaches which ignore the needs of people. A key issue, identified by both proponents and critics of regulation structures is the paucity 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 concerns are increasing at a rate that exceeds the capacities of riparian countries. The low-lying Mekong Delta faces unique water land issues because of its sedimentary composition and geomorphology. The issues of Vietnam’s lower Delta differ from those of Cambodia’s upper Delta, which is dominated by the Delta’s natural flow regulator, Tonle 6 Sap and Cambodia’s Great Lake. In Vietnam’s lower Delta, the major land and water resource problems are: acute flooding in the wet season, with flood depths of more than 4 m in the northern Delta; acid sulfate soils constraints on crop productivity in over 40% of the lower Delta and associated, severe, acidic drainage waters with major implications for aquatic productivity; seawater intrusion in the dry season in the lower Delta, limiting rice production to one crop per year in saline intrusion areas; impacts of seawater intrusion floodgates on acidification; loss of coastal mangroves and impacts on coastal protection and fisheries. In the Cambodia’s upper part of the Delta different issues need to be addressed. There is a surprising dearth of information on sediment fluxes and on the quantitative relation between flooding and the breeding/ feeding/ life cycle of fish despite their 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 rice production and fish production in the Great Lake; impacts of forest clearing on sedimentation and aquatic production in the Great Lake; impacts of downstream river regulation on flooding, rice and fish production. Recent estimates of sedimentation rates in the Great Lake are at least 8 times higher than those of the past 5,000 y. In both the upper and lower Delta, the availability and quality of domestic water supplies is a major issue. The control of downstream flooding and of saline intrusion in the lower Delta could be potentially 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 narrowly focussed. The highest priority has gone to planning and design for hydropower and irrigation diversion. Main projects completed by the Mekong River Commission Secretariat with direct relevance to the Delta are: the Saline Intrusion Studies; the Water Balance Studies; the Management 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 to increase 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 the importance of recent sedimentation to aquatic and terrestrial productivity have not been examined. The Secretariat’s present Work Plan still has a concentration of effort on infrastructure development but there are broader-based projects planned and underway. The Secretariat’s water balance, salinity intrusion and acid sulfate soil management projects formed the basis of the Mekong Delta Master Plan, intended to underpin sustainable growth in the lower Delta. A central thrust of this plan is increased rice and aquaculture production. A key outcome of this plan was a proposal to increase rice production in the region west of the Bassac by supplying a longer irrigation season and lowering or preventing salt-water intrusion into the region. This proposal, the Desalination of the Ca Mau Peninsula, has recently been completed. It is suggested, by analogy with the Australian situation that the impacts of this project on local fish production and waterway acidification may be severe with significant consequences for local communities. The impacts of already 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!” A seminal, French benchmark study of sedimentation in Cambodia’s Great Lake provides an opportunity of assessing the impacts of changes in upcatchment and surrounding landuse on sediment and nutrient dynamics and fish production in the Lake. A comprehensive report to 7 the Australian government, Perspectives for Australian Development Cooperation, identified key areas for assistance in the Delta because it receives less priority development assistance and because of the concentration of poor there. Salinity and acid sulfate soils required assistance. It recommended an integrated approach to acid sulfate soils because they involved cross-sectoral land and water issues and one which was both precautionary and curative. The report also pointed out the uncertainty of dry season domestic water supplies in the Delta and the problems with acidity and salinity. Groundwater was seen as an increasingly important resource in these areas. Watershed and catchment planning were also identified as opportunities for assistance. The farmer’s response to the adverse conditions they face daily has been innovative and courageous. Three proposed integrated projects for the Mekong Delta were developed out of the above analysis: Management and Impacts of Saline Intrusion Floodgates in the lower Mekong Delta; Recent Sedimentation and its Impacts on Cambodia’s Great Lake; and Dry-Season Groundwater Supplies in the Mekong Delta. Brief backgrounds, overall objectives, specific objectives, expected outcomes and beneficiaries are given for these projects. 8 1. The Mekong 1.1 River of Change The Mekong (Thai: Mother of Waters) River has the twenty-first largest drainage basin and is the twelfth longest river with the eight largest annual discharge and second most diverse riverine fishery in the world. It is one of the world’s great, largely unregulated rivers. The water, land and biological resources of the Mekong Basin sustain an ethnically diverse and growing population in six countries; China, Burma, Lao PDR, Thailand, Cambodia and Vietnam (Fig 1.1). The Mekong Basin’s resources provide both great benefits and hardships for 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 with over 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 return intervals 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 to seawater intrusion in streams in the lower Delta. Seawater intrusion, severe acid sulfate and saline soils and upstream deforestation impose social and economic constraints and uncertainties 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’s exceptional aquatic productivity (Roberts, 1993a) on which its riparian communities depend for most of their protein. Since the 1930’s the Basin has been ravaged by wars of liberation and inter and intra country conflicts. These have had massive, long-term social, economic and cultural impacts on the peoples of the lower Basin and depleted populations, resources and institutional capacity, especially in resource management. International organisations are seeking to assist the region’s peoples by promoting development and growth in the Basin, mostly through large infrastructure construction projects, principally hydropower, flood mitigation and irrigation supply dams. The Mekong is seen by many as one of the great “undeveloped resources” of Southeast Asia. Less than 5% of both the Basin’s annual flow and its catchment are regulated at present. There are plans for a cascade of up to 9 mainstream “run-of-river” hydropower schemes in the Mekong together with as many as 50 tributary dams (Rothert, 1995). These plans have been criticised as fundamentally flawed (White, 1997) because of the dearth of information on climate, hydrology, ( Institute of Hydrology, 1982; 1984; 1988a, 1988b) and ecology, as well as a paucity of social, economic and cultural data and knowledge of the aspirations of riparian communities likely to be affected by river regulation (Greater Mekong Task Force, 1996). [...]... 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 extensive salinization of waterways occurs in the lower Delta Fig 2.7 (Minh, 1995) shows the extent of salinity intrusion at the beginning of the saline intrusion (BSI) and the end of the saline intrusion... meet irrigation demand in the protected areas during the early periods of the dry and wet season, thus lengthening the growing season In the dry season, Mekong flows are insufficient for irrigation in the protected areas (NEDECO 1993) Fig 2.7 Seawater intrusion into the Mekong Delta during the dry season BSI and ESI are respectively the beginning and end of the seawater intrusion (Minh, 1995) A series... of the basin, the influence of the upstream flow from the Mekong and Bassac Rivers and tidal inundation in the south (Fig 2.6, Minh, 1995) A smaller influence from the spatial variation of rainfall is also evident in Fig 2.6 In the northern part of the Delta, in the Plain of Reeds, inundation depths can exceed 4 m The original rice production systems in the Delta took advantage of wet season flooding... on the ebb and close on the spring tide The objective of the project was to permit two rice crops per year to be grown in the irrigation area behind the sluices (Fig 2.9) by decreasing the salinity ingress into the area behind the floodgates and increasing 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. .. intrusion (ESI) The whole of the Ca Mau Peninsula in the Delta’s southwest, in Fig 2.7, is salinized for 6 months during the dry as there is insufficient freshwater flow in the Mekong to displace saline intrusion from the southwestern sector of the Delta Figures 2.6 and 2.7 exemplify two of the main hydrologic problems of the Delta, wet season floods and dry season saline intrusion The length of the wet season... forecasting and damage reduction, upgrading of salinity intrusion forecasting in the Mekong Delta, water balance of the lower Mekong Basin, Phase IV and Mekong morphology and sediment transport The Programme is seeking funds for several of these projects 23 The early 1990’s also saw sweeping changes in natural resource management within member countries The most significant of these was the creation of ministries... varieties, increased chemical inputs and increased double and triple cropping Double and triple cropping is limited mainly by the availability of fresh water from the Mekong in the dry 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 per year The demand for increased production has... and drainage has accelerated in 1910-30 and since the end of the Indochina War in 1975 The Delta has now over 10,000 km of major canals that have profoundly altered the Basin’s hydrology The Delta suffered severe damage during the Indochina War Defoliants, bombing, land clearing and drainage destroyed wetlands and forests About 1,300 km2 of melaleuca and 1,200 km2 of mangrove forests were lost At the. .. reflects the direction of the monsoon Fig 2.4 Distribution of annual rainfall across the Mekong Delta (Minh, 1995) 31 2.4.1 Floods and seawater intrusion The marked seasonality in rainfall leads to both annual floods and water shortages in the Basin In the wet season almost 50% of the Delta is flooded (1,900 km2) The maximum depth of inundation in the wet season is principally governed by the topography... model to predict seawater intrusion into the lower Delta Following these major studies, a proposal was developed to install saline intrusion floodgates on main canals along the Ca Mau Peninsula and South China Coast (NEDECO, 1993) The idea behind this scheme is to lengthen the growing season for rice from one to two crops in the saline intrusion affected areas The discharges of the Mekong River are considered . has been the central, contentious issue in the management and use of the Mekong River Basin. 1.4 The Lower Basin The lower Mekong Basin, downstream from China and the Burma-Laos -Thailand intersection,. in northeast Thailand to more than 3,500 mm in the mountainous fringe of northeast Laos, where there is no clearly defined dry season. Elsewhere in the lower Basin, little rain falls during the. and interconnectedness of the migratory systems and the fundamental importance of the annual flooding are some of the main reasons behind growing opposition to regulating the main flows in the Mekong