IMPACT OF UPSTREAM DEVELOPMENT SCENARIOS ON FLOW REGIMES, ENVIRONMENTAL QUALITY, AND SOCIO-ECONOMIC DEVELOPMENT IN THE MEKONG DELTA OF VIETNAM

IMPACT OF UPSTREAM DEVELOPMENT SCENARIOS ON FLOW REGIMES, ENVIRONMENTAL QUALITY, AND SOCIO-ECONOMIC DEVELOPMENT IN THE MEKONG DELTA OF VIETNAM To Quang Toan 1, Tang Duc Thang 2,Le Manh Hung 3, and Oliver Saavedra 4 1 Southern Institute of Water Resources Research, Toan_SIWRR@yahoo.com 2 Vietnam Academy for Water Resources, tdthang.siwrr@gmail.com 3 Southern Institute of Water Resources Research, manhhungvawr@gmail.com 4 Tokyo institute of Technology, osaave@yahoo.com ABSTRACT The Mekong River ranks 12 th among the world s longest rivers. It has high amounts of biological diversity and productivity, and the annual fish output from the riveris the highest of all major rivers on Earth. The Mekong River is an important food supply source for approximately 300 million people. The river supports the generation of about 53,000 MW of hydropower,and of this total, 23,000 MW are realizedin the upper Mekong River in China, 13,000 MW are in the lower Mekong River mainstream, and more than 17,000 MW are in tributaries to the lower Mekong RiverBasin. This paper investigates the potential future impactsfrom upstream development scenarios. Specifically, changes in flow regimes, environment quality, and socio-economic development in the Mekong Delta were evaluated to identify the advantages as well as disadvantages of future development patterns. Keywords: Mekong Delta; Mekong River; upstream development; impact of hydropower; flooding; salinity intrusion Received 28 January 2016.Accepted 4, May 2016 1 INTRODUCTION The Mekong River flows through the territories of six countries including China, Myanmar, Laos, Thailand, Cambodia, and Vietnam (Figure 1). It has a length of about 4,800 km, a basin area of 795,000 km 2, and an annual discharge rate of 15,000 m 3 /s (MRC, 2003a), (MRC, 2010a). The upper Mekong Basin (UMB) extends upstream of Chiang Saen and has a basin area of 188,460 km 2. The lower Mekong Basin (LMB) has a total area of 606,540 km 2 ; 33.3% of this area is in Laos, 25.6% is in Cambodia, 30.4% in Thailand, and 10.7% of this area is in Vietnam (this area includes the Central Highlands and the Mekong Delta). The Mekong River Basin (MRB) has a large potential development as it was considered as abundant water resources, hydropower potential, and fisheries products. This is only possible due to the heavy rainfall during the rainy season. The MRB have been classified as a highly biodiverse area in comparison with many other areas around the world, and it is one of the top areas for freshwater fish yields. More than 1,200 species have been reported in the MRB, and 781 fish species have been officially recognized (MRC, 2004), (Baran E., 2010). The present development condition for agriculture and hydropower at the upstream has already caused a lot of negative impact for drought and salinity intrusion in the Mekong Delta of Vietnam. The development plan of hydropower dams in Mekong tributary could cause more negative impact to the Mekong delta of Vietnam (Nguyen Quang Kim at al, 2010), (To Quang Toan, 2015). In addition the plans for 11 hydropower dams development in the lower Mekong mainstream (LMM) region pose potential risks to environmental quality and biodiversity, and these impacts could affect the livelihoods of millions people in the downstream area. However, Lao s Government has announced to build the Xayabury dam on November 2012 and the Don Sahong Dam in early 2015. While Vietnamese Government would like to postpone the construction of any dam about 10 years for further in deep study about the negative impacts of these dams (ICEM, 2010). A number of national and international organizations have been concerned about the negative impacts of these dams and expressed their 119

International Water Technology Journal, IWTJ Vol. 6 No.2, June 2016 concern on the websites: vrn.org.vn; Savethemekong.org; Internationalrivers.org; n-h-i.org; Stimson.org THE MEKONG RIVER BASIN Characteristics N W E Basin area: 795.000 km2(ranked 21st) Lenth of mainstream: 4.800 km (ranked 12th) Annual discharge 15.000 m3/s S LEGENDS Up p Mekong mainstream river Country boundary â City, capital ع Mekong mainstream hydrological stations Main tributaries Mekong delta Upper Mekong basin (China and Myanma) Lower Mekong river basin From Chiang Saen to Kratie From Kratie to boder of VN-Cam Mekong delta of Vietnam Tonle Sap lake er M ek on sin g ba China Myanma Jinghong 16% Viet Nam â 2% Ha Noi Chiang Saen ع Luang Prabang Lao PDR 35% Vientiane â in Bas area m fro Hoµng Sa paracels an C hi gs ra to K aen Thailand 18% tie ع Pakse Bangkok â EAST SEA Basin area from Kratie to border of Vie tnam -Ca mbod ia n B i س Cambodia h ه n To le 18% Sa p Phnom Penh Kratie 11% Me â ko T n Ch u d riv er ng Ch u èc عع elta WEST SEA Mek ong De lta Viet Nam 70 0 70 140 210 280 350 Kil om eter s Tr êng Sa Paracels Figure 1. Map of the Mekong River Basin The Mekong River is very important to the Mekong Delta of Vietnam (MDV), which is an area known as the granary of Vietnam. The total output of food from this region increased from 6.3 million tons in 1985 to 23.4 million tons in 2012 (CSO, 2014), and this region contributes to more than 50% of the food and 90% of the rice exports from Vietnam. Upstream development may have an undesirable impact on sustainable development in the Mekong Delta in general and on national food security in particular. This research aims to evaluate the impacts of different upstream development scenarios on the flow and environmental conditions in the Mekong River; possible impacts on socio-economic development in the Mekong Delta of Vietnam are also discussed. 2 2.1 DATABASE AND MODELLING TOOLS Database Data were gathered from the Mekong River Commission (MRC) (MRC, 2003b), (MRC, 2010b); these data includedhydrometeorology data from 1985 to 2008 and development plans for hydropower and agricultural infrastructure in upstream countries. The cross-section data of Mekong River and the Modelling tools of the MRC were also employed in our analyses. On the basis of the analytic synthesis 120

Knowledge base 500 0 500 Kilome ter s International Water Technology Journal, IWTJ Vol. 6 No.2, June 2016 of data collected on present conditions and future plans for hydropower and agricultural developments, several analysis scenarios were devised. These scenarios and their development characteristics are presented in Table 1. Table 1. Development contexts in the upstream Mekong River Basin No. Context Symbol Irrigation area (1000 ha) Active volume of reservoirs (10 6 m 3 ) Lower China basin 1 Baseline 2000 development condition BL00 3.400 13.680-2 Chinese hydropower dams CND 22.700 3 Near futurehydropower dams (dams on tributaries and China) NFD 26.230 22.700 4 Mainstream Mekong hydropower dams in downstream side MMD 2.633 5 Low agricultural development (LAD) LAD 4.200 6 High agricultural development (HAD) HAD 6.620 2.2 Application of modelling tools and establishment of analytic scenarios The modelling tools used inthis research were extended fromthe Decision Support Framework (DSF) of the MRC. The modelling tools are capable of updating changes in the region based on meteorological and hydrological data.the modelling tools (Figure 2)consisted of (i) theknowledge base, (ii) simulation models (SWAT, IQQM, and MIKE 11), and (iii) analysis systems (including times series and geographic information system tools). The SWAT model was used to simulate the flow from rainfall.the IQQM model was used to simulate the basin water balance resulting from reservoir operations, agricultural cultivations, and household and industrial intakes; the IQQM model for the upstream Kratie region wasnamed the IQQM-T and the IQQM model for the region in Cambodia wasnamed the IQQM-C. The MIKE 11 model was applied to the mainstream area of the upstream Mekong River (named as MIKE11-DC) and the Mekong Delta area (named as MIKE11-DB) to simulate the hydraulic conditions and salinity intrusion conditions. N RESEARCH MODELLING TOOLS W S E SWAT Model China Zoning model s appl icat ion MIKE11-DC MIKE11- B SWAT & IQQM-T SWAT & IQQM-C IQQM-DB IQQM Model Myanmar Vietnam â Hµ Néi MIKE11 Model Lao PDR Vientiane MIKE11-DC â Tools for analysis Times series MikeToGIS Spatial data SWAT & IQQM-T Thailands Bangkok â SWAT&IQQM-C Cambodia Phnom Penh â West sea IQQM- B MIKE11- B Parac el Islands اQu n o Hoµng Sa East sea Parac el islands اQu n o Tr êng Sa Figure 2. Modelling tools for related research on water resources and the environment 121

The models were calibrated and validated to ensurethe reliability of the results.with the SWAT and IQQM models, the correlation coefficients (R 2 ) between actual measurement data and simulated data were as high as 0.92 0.99, the Nash Sutcliffe coefficients weregreater than 0.7, and the volume ratiosreached 97 101%. The MIKE11-DC and MIKE11-DB models both produce reliable values and shapes for floods and salinity intrusion (Nguyen Quang Kim et al,2010), (Nguyen Sinh Huy et al, 2010), (To Quang Toan, 2014),(To Quang Toan, 2015), (To Quang Toan et al, 2015). Modelling tools were also used to simulate upstream development scenarios as shown in Table 2.Scenario groups were based on agricultural and hydropower development contexts as mentioned in Table 1, and the agricultural and hydropower development contexts were taken as the main factor and combined with other development contexts to create an upstream development scenario. In addition, examinations were conducted for further agricultural development in the whole basin or only in Thailand and Laos (upstream Kratie). Hydropower scenarios considered the following possible operation modes: (i) normal operations, (ii) peak coverage operations meeting the demand for high power loads, (iii) day and night peak coverage operations, (iv) early water retention operations, (v) late water retention operations, and (vi) abnormal water retention. Table 2. Synthesis of the simulated upstream development scenario groups combination of scenarios Agricultural development context Hydropower development context Distribution Operation BL00 LAD HAD by space BL00 NFD CND MMD (OPE) BL00 X X CND* X X X X X X X NFD* X X X X X X X X HAD* X X X X X X X MMD* X X X X X X X In which: * means combination scenarios. The CND* scenarios consist of the following scenarios described below. Similarly, other scenario combinations NFD*, HAD* and MMD* have relevant scenarios. - CND+LAD: Chinese hydropower combines with low agricultural development in the basin; - CND+LAD-UK: Chinese hydropower combines with LAD in the upstream of Kratie; - CND+LAD+OPE: Chinese hydropower + LAD and hydropower operation scenarios; - CND+HAD: Chinese hydropower combines with HAD in the basin. - BL00: a baseline scenario with development condition in year 2000. 2.3 Simulation and indicators for analysis and evaluation The SWAT and IQQM modelsimulations were used to evaluate the changes in the flow corresponding to development scenarios and climate conditions (wet, average, and dry years). MIKE11-DCand MIKE11-DB were used in simulations of ahigh water year (2000), an average water year (1999), and a drought year (1998). The MIKE11-DB results were combined with unfavorable tide conditions in the most recent years, the year 2011 for floods, and the year 2005 for salinity intrusion. Based on the developed scenarios, this research analyzed the following indicators: Changes in the discharge into the plain during the dry season and flood season according to different scenarios; Changes in the spatial distribution and area of salinity intrusion. Given the analytic results for differences in the discharge at the Kratie station, this research proposed evaluation criteria for the impacts of the scenarios based on the extent that the scenarios changed the flow on the downstream side. Three impact rates are advanced in Table 3. 122

Table 3. Evaluation and analysis indicators for rate changes in the discharge into the Mekong Delta according to upstream development scenarios No. Month Positive influence: increasing discharge > changing discharge rates (m 3 /s) Very good (GGG) Good (GG) Positive (G) Negative influence: absolute decreasing discharge changing discharge rates (m 3 /s) Very bad (BBB) Bad (BB) Negative (B) 1 January 489 337 0 489 337 0 2 February 320 221 0 320 221 0 3 March 278 191 0 278 191 0 4 April 349 240 0 349 240 0 In which: - Very good or (/) very bad makes the discharge increase/decrease more than the difference in the discharge between probability of P 50% and P 85% in corresponding months.; - Good or bad makes the discharge increase/decrease more than the difference in the discharge between P 50% and P 75% ; - Positive or negative : increases or decreases as compared with a baseline scenario. 3 RESULTS 3.1 Changes in the flow into the Mekong Delta 3.1.1 Changes in discharge and water levels in the Mekong Delta The results (Table 4) show that during normal operation conditions for hydropower reservoirs in the NFD scenario, the discharge during the dry season into the Mekong Delta increases from 600 m 3 /s to 1000 m 3 /s compared with the baseline condition. With some agricultural development scenarios (CND+LAD or NFD+HAD), the increase in flow still achieves 300 m 3 /s to 800 m 3 /s on average. In HAD, if there is a lack of regulation of water, the lowest flow into the plain could go down to 1,300 m 3 /s, which would be very unfavorable for agricultural production in the plain region. Table 4. The minimum monthly average discharge into Kratie according to different upstream scenarios involving normal operations to produce hydropower Unit: m 3 /s Month BL00 CND NFD CND+LAD NFD+HAD HAD January 2,935 3,477 4,006 3,323 3,582 2,347 February 1,969 2,696 3,164 2,553 2,774 1,597 March 1,543 2,351 2,664 2,273 2,402 1,298 April 1,568 2,302 2,549 2,275 2,375 1,317 May 2,135 2,567 2,817 2,541 2,725 1,787 June 5,520 5,720 5,860 5,659 5,685 3,762 With abnormal operations duringthe CND scenario, the capture of water by reservoirs during distinct periods could cause dramatic changes in the flow into the Mekong Delta; such effects could alter high flow condition as of wet year into low flow condition as of drought year in a certain periods and alter flow in opposite way for both wet and drought years. The flow into the plain will decrease at the beginning of the dry season because the reservoirs retain water later than usual (at the end of the flood season). In addition, there is reduced flow at the beginning of the rainy season because reservoirs retain water earlier than usual. In such cases, salinity may appear earlier or disappear later than is typical for these months. 123

Water level (m) Water level (m) International Water Technology Journal, IWTJ Vol. 6 No.2, June 2016 The results demonstrate that if the plant units in the CND are only operated at a 60% capacity continually, the reservoirs will go down to a dead storage water level and there will be many months out of regulatory compliance for 30 40% of the number of years studied; this trend may explain the abnormal and sudden decrease of flow into Kratie in recent years (2010 2013). In the case of day and night peak coverage operation with the MMD,this scenario may lead to disadvantagesfor downstream dams at distancesof 300 to 700 km (Figure 3a). For MMD* scenarios, in general, it seems that there will be small changes in the downstream flow. The results of simulations and analyses in the cases where the capacity for hydropower generation is increased by the use of active volumes of these reservoirs show that the ability to use active volumes to increase generation is small because reservoirs on the MMR have the form of long channels, and thus, the water column decreases rapidly when an increase in the discharge exceeds the ability of the inflowing water source. In the case of day and night peak coverage operation in the MMD, it was found that the last hydropower cascade (e.g. Sambor Dam) will have a direct impact on the Mekong Delta. This type of operation at Sambor Dam can make the downstream water level fluctuate by 1 2 m (Figure 3b) and the downstream discharge at night can drop below 1,000 m 3 /s, which would be very harmful because it would allow for salinity intrusion into the Mekong Delta. 275.0 7.5 274.8 274.6 274.4 274.2 274.0 273.8 2/15 2/20 2/25 3/2 3/7 3/12 3/17 a) Water level at Luang Prabang due to peak coverage operation of 1 2 plant units for CND b) Water level at Kratie due to peak coverage operation at Sambor for 3 plant units Figure 3. Fluctuations in water levels at some selected places due to day and night peak coverage operation during the MMD scenario. 3.1.2 Evaluation of the impacts from changing flows into the Mekong Delta An impact analysis of changes in the discharge into the Mekong Delta according to simulated scenarios aas compared with BL00 was conducted with the indicators proposed in Table 3; the results are shown in Table 5. The results in Table 5 can be summarized as follows: Normal operation Peaking 1 turbine Peaking 2 turbines Time (hourly) Water level at Kratie 5.0 2/20 2/25 3/2 3/7 3/12 3/17 3/22 The scenarios depict hydropower and agricultural development at different development levels, and with normal operation of hydropower, nearly all increase in the flow into the Mekong Delta was at the very good rate; the small monthly increase was also positive. Abnormal water retention can weaken positive impacts. HAD scenarios for hydropower like conditions in the NFD were associated with positive impacts that were good and very good in March and April, but the impacts in January and February were still negative. HAD scenarios upstream of Kratie showed impacts on the Mekong Delta that were bad and at a negative rate. HAD scenarios upstream of the MDV showed impacts on the Mekong Delta that were at a very bad rate. 7.0 6.5 6.0 5.5 Time (hourly) 124

Table 5. Positive/negative impacts of upstream development scenarios on changes in the flow into the Mekong Delta through Tan Chau and Chau Doc No. Upstream scenarios Impact by the month January February March April 1 BL00 - - - - 2 CND GGG GGG GGG GGG 3 CND+LAD-UK* G GGG GGG GGG 4 CND+LAD G GGG GGG GGG 5 NFD GGG GGG GGG GGG 6 NFD+HAD-UK GG GGG GGG GGG 7 NFD+HAD B B GG GGG 8 HAD-UK BB BB B BB 9 HAD BBB BBB BBB BBB 10 CND+LAD-UK+OPE** G GG GGG GG Note: UK*: the scenario examines agricultural development in Upstream Kratie instead of the whole basin in related scenarios. OPE**: Abnormal water retention operation. 3.2 Changes in salinity intrusion in the Mekong Delta The results of salinity intrusion in some upstream development scenarios are illustrated in Figures4 and 5. Fig.4a: CND+LAD, salinity concentration 125 Fig.4b: HAD, salinity concentration Figure 4. Changes in salinity intrusion into the Mekong Delta during different scenarios The HAD scenario showed salinity intrusions penetrating deeper into the Mekong mainstream and interior fields from river mouths, e.g. intrusions deeper in the Mekong River of 5.4 km and 6.2 km in the Bassac River. The area affected by salinities of more than 4 g/l increased to more than 19,000 hectares as compared with the baseline scenario. These areas are also subjected to early appearances of high salinity. The research showed that water intakes for agricultural development in Cambodia can cause an unfavorable impact on the plain to a greater extent than development in the area of Thailand. Research into various upstream development scenarios (for hydropower and agriculture) during normal operation conditions showed that it might still be possible to increase the flow and reduce salinity intrusion in the plain by pushing salinity towards river mouths. For example, in the CND+LAD scenario, the salinity intrusion receded by 4.5 km in the Mekong River and by 6.3 km in

Area (1000ha) Area (1000ha) International Water Technology Journal, IWTJ Vol. 6 No.2, June 2016 the Bassac River; the total area affected by salinity of more than 4 g/l decreased to more than 57,000 hectares as compared with the baseline scenario. Salinity intrusion area by concentration in some simulated scenarios Salinity intrusion area by duration of salinity concentration > 4g/l in some simulated scenario 1600 1400 1200 1000 800 600 400 200 0 BL00 CND+LADNFD+HAD 0.2-2g/l HAD CND+LAD_UK+OPE (a) > 4g/l 2-4g/l BL00 CND+LAD NFD+HAD HAD CND+LAD_U K+OPE 0.2-2g/l 475.2 437.3 430.9 471.8 447.2 2-4g/l 704.2 619.4 607.7 714.0 640.4 > 4g/l 1587.9 1530.6 1515.1 1607.3 1556.0 >3 months <3 months <1 month BL00 CND+LADNFD+HAD <1 week HAD CND+LAD_UK+OPE Figure 5. The area of salinity intrusion during different scenarios as categorized by the (a) salinity concentration and (b) duration The research into the cases of reservoir operation as well as interventions in Tonle Sap showed that there may be unfathomable impacts that will cause disadvantagesin the MDV due to changes in the flow and salinity intrusion. For example, (i) early water retention in reservoirs could cause long-term salinity events that last 1 month and affect the summer autumn rice crop; (ii) late water retention in reservoirs could cause the salinity to appear early (by 1 to 2 months), which would affect the winter spring rice crop; and (iii)abnormal water retention in reservoirs or operations to meet power demand loads (capacity increases) could cause the salinity to change suddenly, which would be very unfavorable for agricultural production in the plain. The results suggest that sudden changescould occur for 30 40% of the number of years analyzed or even permanently every year, which would lead to negative impacts during certain periods of time. During such times,the salinity intrusion is predicted to be even larger than the cases that happen currentlyand the salinity could appear sooner or end later as compared with natural conditions. 3.3 Impacts of the change on the aquatic environment: sediment and aquatic life The analytic results for upstream water use rates andwater discharges into the plain according to the simulated scenarios (Table 6) show that the upstream water use rate is very small in BL00. With the highest rate given in the HAD scenarios, demand for water exceeds 40% of the water potential in February. Water use in excess of 30% of the water potential without reasonable protection measures and waste discharge source control would very likely affect the water quality and ecological environment; therefore, risks from water pollution during the dry season in the future are possible as a result of an increase in the upstream water use, even with regulations forhydropower. Table 6. Rate percentages between upstream water demand as compared with the possibility for water discharge into Kratie Month Rate of Water demand in upstream Kratie compared with discharge at Kratie (%) BL00 CND+LAD NFD+HAD HAD January 15.81 21.52 30.90 35.24 February 18.83 23.27 33.53 40.76 March 18,80 17,45 26,68 34,49 April 11.00 13.14 19.10 24.45 May 7.21 9.63 11.48 12.77 June 4.30 4.97 6.35 6.25 In the MMD* scenarios, most sediment will deposit in reservoirs and sediment inputs into the plain will be reduced; the sediment is forecasted to decrease by 50% (ICEM, 2010) as compared with the 1500 1000 500 0 BL00 CND+LAD NFD+HAD HAD CND+LAD_U K+OPE <1 week 41.6 32.2 30.9 44.2 36.1 <1 month 141.2 121.6 117.2 145.1 127.5 <3 months 528.9 480.4 468.9 539.0 499.2 >3 months 1011.1 1007.7 1006.5 1016.0 1009.6 (b) 126

status quo.as a consequence of declining sedimentinputs, erosion of riversides and coastal zonescan occur, and this would affect agricultural production in the Mekong Delta. The heights of mainstream Mekong dams vary from 10m to 76m, and these dams would be a great impediment to the migration of aquatic species, which could impair reproduction even when artificial migration paths for fish are designed. Moreover, the high water level of reservoirs can cause reductions in the dissolved oxygen and temperature at depth, which can affect biological productivity and the output of fisheries products.this would affect the ecological balance and biological diversity of the basin, which would in turn affect the livelihoods of people who depend seasonally on aquatic species for food and income. 3.4 Impacts of the change on the social economy This research showed that with good operations of hydropower dams, the impacts could be beneficial, i.e. discharge during the dry season is predicted to increase considerably, the water intake ability would be more favorable, the area of salinity intrusion would decrease from 10,000 to 57,000 hectares, and productivity and food output of thewinter spring and summer autumn crops would increase from 0.1 to 0.57 million tons, which would help to stabilize the lives of 60,000 300,000 people, or approximately 0.4 2.4% of the rural population in the Mekong Delta. However, the generation of hydropoweris always associated with unfathomable risks, which could affect sustainable development in the plain. In particular, abnormal operationscould cause the downstream flow to change, which could lead to regulation violations and make it difficult for people to the determine the appropriate times to plant crops. If reservoirs were to retain water early, salinity intrusions could appear sooner, which would affect thewinter spring rice crop; if reservoirs were to retain water late, this could prolong salinity events and affect the area available and cultivating timesfor summer autumn rice in coastal provinces. The area affected by salinity intrusion could increase by up to tens of thousands of hectares, and therefore, changes could directly affect the lives of hundreds of thousands of residential households that depend on agricultural outputs in coastal areas. According to the observed flow in recently periods, it can be concluded that these types of operations have already happened in the basin. The impact of the MMD scenario is still hard to fathom because it involves declines in sediment, an increase in erosion, and a decrease in incomes fromfisheries products, and these changes are complex and may be associated with cumulative and long-term impacts. Furthermore, erosion and high landslide risks along the banks of the river and coastal areas could cause valuable land and residential infrastructure to be lost. At present, annual expenses for anti-landslide measures in the Mekong Delta have amounted to hundreds of billions ofvietnamese dong, while demand for such services is still much higher. The output of aquatic products during the flood season in the Mekong Delta amounts to hundreds of thousands of tons, and the loss of this income source would affect people s lives drastically. The loss of aggraded sediment not only poses a nutritional problem for crop plants;it will also affect natural aggradation and increase agricultural production costs in the plain. 4 CONCLUSIONS AND RECOMMENDATIONS The research investigated both the positive and negative impacts of future hydropower and agricultural development in the Mekong River Basin. Findings showed that the operation of hydropower dams may have unfathomable risks, and abnormal operation conditions could lead to changes in hydrological regimes, sediment deposition alternations, worsening salinity intrusion events, and degradations in fisheries and cropland productivity.the positive impacts may happen only in reasonable operation of dams to increase the flow into the downstream side, thus helping to minimize salinity intrusions considerably. International co-operation in the basin will be necessary to ensure the appropriate operation of reservoirs in a manner that will minimize harm to downstream communities. Recommended measures that could help to ensure sustainable water resources in the Mekong River Basin include the installation of modernized irrigational systems, active control of sluice gates,and implementation of supplemental pump houses. Furthermore, grouping small irrigation projects into 127

larger systems (e.g. Go Cong+Bao Dinh, Ba Lai+Southern Ben Tre, Tiep Nhat+Quan Lo Phung Hiep) could help to alleviate management costs. Governments should also try to establish better forecast and warning systems for water resources and salinity intrusionevents. These systems should be implemented by water management boards that oversee large areas not limited by provincial boundaries (institutions, laws). Lastly, it is necessary to conduct more research, surveys, and evaluations of possible impacts prior to the construction of any mainstream Mekong dams in the LMB. ACKNOWLEDGEMENTS This work was partially supported by the Japan Society for the Promotion of Science (JSPS) Coreto-Core Program B, Asia-Africa Science Platforms. Wewishto thankdr.oliver Saavedra attokyo institute of Technologyfor coordinating the scientific effort for the Megadelta project, and wealsothanktheanonymous reviewersforprovidingvaluableandusefulcomments. ABBREVIATIONS CND China dams HAD High agriculture development LAD Low agriculture development LMB Lower Mekong Basin MD Mekong Delta MDV Mekong Delta of Vietnam MMD Mainstream Mekong River s dams MMR Mainstream Mekong River MRB Mekong River Basin MRC Mekong river commission NFD Near future dams UMB Upper Mekong Basin REFERENCES Baran E. (2010) Mekong fisheries and mainstream dams. Fisheries sections in: ICEM 2010. Mekong River Commission Strategic Environmental Assessment of hydropower on the Mekong mainstream, International Centre for Environmental Management, Hanoi, Viet Nam; 145. CSO (Central Statistical Office of Vietnam) (2014) Area and food output are distributed by provinces, https://www.gso.gov.vn/default.aspx?tabid=717. Last access August 10 th, 2015. ICEM (2010) MRC Strategic Environmental Assessment (SEA) of hydropower on the Mekongmainstr eam, International Centre for Environmental Management,Hanoi, Viet Nam; 198. MRC. (2003a) State of the Basin Report. Phnom Penh, Cambodia. ISSN: 1728:3248; 316. MRC. (2003b) Decision Support Framework (DSF). Vientian, Lao PDR. MRC. (2004) Distribution and Ecology of Some Importance Riverine Fish Species of the Mekong River Basin. Phnom Penh, Cambodia; 116. MRC. (2010a) State of the Basin Report. Vientiane, Lao PDR. ISBN: 979-993-2080-57-1; 232. 128

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