mekong delta water resources assessment...
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Vietnam-Netherlands Mekong Delta Masterplan project
MEKONG DELTA WATER RESOURCES ASSESSMENT STUDIES
January 2011
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TABLE OF CONTENTS TABLE OF CONTENTS....................................................................................................... 2
LIST OF FIGURES................................................................................................................4
LIST OF TABLES ................................................................................................................. 5
ABBREVIATIONS AND ACRONYMS................................................................................5
CHAPTER 1. DESCRIPTION OF THE MEKONG DELTA OF VIETNAM..................6
1.1. ADMINISTRATIVE OVERVIEW ................................................................................ 6
1.2. TOPOGRAPHY.............................................................................................................. 6
1.3. RIVER SYSTEM ............................................................................................................ 7
CHAPTER 2. HYDROLOGY AND SURFACE WATER RESOURCES....................... 10
2.1. CLIMATE AND EXPECTED CLIMATE CHANGE ................................................. 10 2.1.1. Air temperature........................................................................................................... 10 2.1.2. Evaporation................................................................................................................. 10 2.1.3. Air humidity ............................................................................................................... 10 2.1.4. Wind........................................................................................................................... 10 2.1.5. Rain ............................................................................................................................ 12 2.1.6. Climate change ........................................................................................................... 13
2.2. HYDROLOGICAL REGIMES .................................................................................... 15
2.3. SURFACE WATER QUANTITY ................................................................................ 16
2.4. FLOODING................................................................................................................... 17
2.5. SALTWATER INTRUSION ........................................................................................ 19
2.6. IMPACTS OF UPSTREAM DEVELOPMENTS ........................................................ 21 2.6.1. Current upstream flow................................................................................................. 21 2.6.2. Further data on the upstream flow of the Mekong river................................................ 23
2.7. POSSIBLE MEASURES TO IMPROVE THE SITUATION ..................................... 24 2.7.1. Integrated water resources planning for MDV and Decision No.84/2006/Q -TTg....... 24 2.7.2. Adaptation measures for climate change and sea level rise........................................... 24
CHAPTER 3. WATER QUALITY ................................................................................... 26
CHAPTER 4. HYDROGEOLOGY AND GROUNDWATER RESOURCES .............. 36
4.1. GEOLOGY.................................................................................................................... 36 4.1.1 Tectonics and faulting ..................................................................................................... 36 4.1.2 Stratigraphy .................................................................................................................... 36
4.2. HYDROGEOLOGY AND GROUNDWATER RESOURCES.................................... 36 4.2.1. The aquifer system in the Mekong Delta ........................................................................ 36 4.2.2. Groundwater quality ...................................................................................................... 39
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4.2.3. Groundwater reserves..................................................................................................... 42 4.2.4. Present Groundwater utilization ..................................................................................... 43
CHAPTER 5. WATER DEMAND AND WATER BALANCE ....................................... 45
5.1. METHODOLOGY........................................................................................................ 45
5.2. RURAL, URBAN AND INDUSTRIAL WATER DEMAND....................................... 45
5.3. WATER FOR NAVIGATION...................................................................................... 48
5.4. PRESENT WATER BALANCE................................................................................... 48
CHAPTER 6. ISSUES TO BE SOLVED .......................................................................... 51
CHAPTER 7. _Toc283708758CONCLUSIVE REMARKS ........................................... 53
References .......................................................................................................................... 55
APPENDIX 1;Water demand assessment source materials............................................. 56 APPENDIX 2; Description of aquifer systems in the Mekong Delta .............................. 59
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LIST OF FIGURES Figure 1: Administrative map of the Mekong Delta of Vietnam...................................6
Figure 2: Topographic map of the Mekong Delta.........................................................7
Figure 3: Map of existing river/canal system of the Mekong Delta in Vietnam ............9
Figure 4: Map of hydro-meteorological stations.........................................................11
Figure 5: Spatial distribution of annual rainfall ..........................................................12
Figure 6: Flooding extent in the Mekong Delta with sea level rise 75cm....................15
Figure 7: Variation of flood levels 2000 at Tân Châu and Châu c..........................17
Figure 8: Spatial distribution of maximum flood flow and total volume of the flood 2000 (using VRSAP model simulation) ...................................................18
Figure 9: Salinity intrusion isolines in some dry years ...............................................20
Figure 10: Water works development plan for Mekong Delta ....................................25
Figure 11: Water quality monitoring network ............................................................27
Figure 12: pH in 2008 at some stations ......................................................................30
Figure 13: pH in different water resources in 2002-2008 ...........................................30
Figure 14: EC in fields and main streams in 2008 ......................................................31
Figure 15: Salinity at M Tho, 2002-2008 ................................................................31
Figure 16: TSS in fields and rivers in 2008 (right) and TSS in rivers in 2002- 2008 (left) ..........................................................................................................32
Figure 17: T-N in river courses and canals in (data for 2008).....................................32
Figure 18: NH4+ and NO2&3
- (data for 2002-2008) ....................................................33
Figure 19: T-N in 2002-2008 & T-P in 2002-2008....................................................33
Figure 20: BOD5 and COD (data for 2008). ..............................................................34
Figure 21: BOD5 in 2002-2008 & COD in 2002-2008 .............................................34
Figure 22. Cross –section III-III . ...............................................................................37
Figure 23: Map of 120 sub-irrigation areas ................................................................47
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LIST OF TABLES Table 1: Rainfall frequency all the Mekong Delta................................................. 13
Table 2. The change of climate and sea level in southern Vietnam up to 2100 by an average emission scenario (B2)............................................................................. 14
Table 3. Level of monthly temperature change (°C) in southern Vietnam up to 2100 by an average emission scenario (B2) ........................................................................ 14
Table 4. Average monthly rainfall change (%) in southern Vietnam up to 2100 by an average emission scenario (B2)............................................................................. 14
Table 5: Total flow volumes in the Mekong Delta at Tan Chau and Chau Doc stations (unit: Million m3). ................................................................................................ 16
Table 6. The Mekong river flow at some locations................................................ 22
Table 7. Comparision of recent flow with previous flow at Pakse (unit: m3/s) ...... 22
Table 8. Comparision of recent flow with previous flow at Kratie (unit: m3/s) ..... 22
Table 9. List of hydropower projects upstream Mekong basin .............................. 23
Table 10: List the standard method of testing water quality .................................. 28
Table 11: Coliform in 2008 (MPN/100 ml)........................................................... 35
Table 14. Results of calculation of static reserves (m3/day)................................... 42
Table 15. Results of calculation of dynamic reserves (m3/day).............................. 42
Table 16: Groundwater utilization in the Mekong Delta........................................ 44
Table 17: Monthly water flow demand ................................................................. 46
Table 18: Monthly water volume demand............................................................. 46
Table 19: Water requirements for navigation/waterway transportation................. 48
Table 20: Present water balance............................................................................ 49
ABBREVIATIONS AND ACRONYMS POR Plain of Reeds LXQ Long Xuyen Quadrant CMP Ca Mau Peninsula MD Mekong Delta of Vietnam TCVN Vietnamese Standard
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CHAPTER 1. DESCRIPTION OF THE MEKONG DELTA OF VIETNAM 1.1 ADMINISTRATIVE OVERVIEW The Mekong Delta of Vietnam (MD) is formed by the lower part of the Mekong river delta, and includes 13 cities and provinces of Long An, Tien Giang, Dong Thap, Vinh Long, Tra Vinh, Can Tho, Hau Giang, Soc Trang, Ben Tre, An Giang, Kien Giang, Bac Lieu and Ca Mau. The total natural area comprises approximately 3.96 million hectares (excluding Duc Hoa District Long An Province and Phu Quoc island province Kien Giang), accounting for 79% of the whole MD and forming 5% of the Mekong River basin. The Mekong Delta of Vietnam is surrounded by: (a) Vietnam-Cambodia border in the North; (b) Pacific ocean / South China Sea to the East (the so-called East sea), (c) Gulf of Thailand in the West (the so-called West sea), and (c) Vam Co Dong River and Ho Chi Minh City in the North-West (Figure 1).
Figure 1: Administrative map of the Mekong Delta of Vietnam 1.2 TOPOGRAPHY The Mekong Delta of Vietnam consists of flat terrain, mostly of average height of 0.7 to 1.2 m, except for some high hills in the northern delta province of An Giang (Map 1/25000, Ministry of Water Resources, 1984 and also in the 2003 Digital Terrain Model of the Mekong delta). Along the Cambodian border, the terrain is highest, from 2.0 to 4.0 m above sea level, then lower to the central plains, from 1.0 to 1.5 m high, and only 0.3 to 0.7 m in the tidal and coastal areas.
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Figure 2: Topographic elevation map of the Mekong Delta 1.3 RIVER SYSTEM The Mekong Delta river system comprises a relatively dense network of river courses and canals, including the natural river systems and canals: - The main natural river branches and canals in the Mekong delta are formed by the two systems of the Tien River and Hau River (respectively the lower branches of the Mekong and Bassac rivers). These rivers flow to the sea in estuaries via nine river mouths as Tieu, Dai, Ba Lai, Ham Luong, Co Chien , Cung Hau, Dinh An, Ba Thac and Tranh De (river mouths in the territory of Ba Thac in Soc Trang province have been covered in the 1970’s) and a short river Vam Nao river linking the Tien and Hau
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main branches. Vam Co River (including the Vam Co Dong-Vam Co Tay) runs parallel to the east of the Tien River, Cai Lon-Cai Be River, My Thanh, Ganh Hao, Ong Doc, Bay Hap rivers flow to the West and East Sea. The Tien and Hau rivers transfer the largest amounts of water with a total annual flow of 325.41 billion m3 observed at station Tan Chau (on the Tien river) and 82.43 billion m3 in station Chau Doc (on the Hau river); the flow rate on the Tien River / Hau River is 80/20. Both the Tien river and Hau river are wide and deep, with the average width of about 1000-1500 m and an average depth of 10-20 m (and locations where the depth is over 40 m). However, near the mouth, the river widens and the riverbed is raised by siltation. Within the two rivers courses many elongate islands have formed. River processes cause shore erosion and sedimentation and complex flow patterns cause instability of river banks. Vam Co River system consists of two branches (Vam Co Dong and Vam Co Tay), that originate in Cambodia, and flow east through the Mekong Delta. - The Cai Lon-Cai Be are tidal rivers, derived from the center of the Ca Mau peninsula and flow to the sea through the Cai Lon river mouth. The estuary is very wide but not deep. - The system of manmade canals in the Mekong delta was constructed primarily during the past century, with the primary purpose to develop agriculture and transportation. Until now, the canal system has developed into a dense network with 3 levels of major, primary and secondary canals. The primary and secondary canal systems have a high density, with some 80-10 m / ha, and a total of 30,000-40,000 km of canals in all the Mekong Delta. Figure 3 below illustrates the density of the irrigation systems.
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Figure 3: Map of existing river/canal system of the Mekong Delta in Vietnam
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CHAPTER 2. HYDROLOGY AND SURFACE WATER RESOURCES 2.1 CLIMATE AND EXPECTED CLIMATE CHANGE The Mekong Delta, being located in a tropical monsoon region, is hot year-round and has a seasonal distribution of dry-wet months depending on the operation of the monsoon. The dry season usually coincides with the period of control of the North-East monsoon that lasts from November to April, and the weather is characterized by dry heat and little rain. The wet season coincides with the period of control of the South-West monsoon that lasts from May to October, and the climate is characterized by hot, humid, and (high) rainfall. Specific features are as follows: 2.1.1 Air temperature The average temperature in January varies from about 27-28oC. May is the month with the lowest temperature (an average of 25.5oC) and the hottest month is IV (28oC). There is a relative equal distribution of temperatures across the delta region. 2.1.2 Evaporation The evaporation regime also changes little over time and space. In terms of time in the year evaporation is highest in the months III, IV and V. The highest amounts for these months vary around 180-220 mm. As soon as the rain starts in months VIII to IX, lower evaporation is reached, from 100-150 mm. 2.1.3 Air humidity Relative humidity reaches high values in May and decreases towards the dry season. Average humidity in months VIII, IX and X ranges from 84-89%, while in months II and III it ranges from 67-81%. 2.1.4 Wind The winds in the north-east of the Mekong delta are prevalent during the dry season, from months XII-IV and in the south-west prevalent during the rainy season, (months V-X). Average wind speeds are about 2.0 m/s. General, closer to the sea, wind speeds often increase in months I, II and III. Wind speeds in low-pressure periods and storms can reach 15-18 m/s (with a storm number of 5 in 1997). Sunshine hours are on average 6 hours per day (approximately 2,000-2,500 hours per year). Months II, III have the highest number of sunshine hours, with 8-9 hours a day, while months VIII, IX have less hours of sunshine, with an average 4.6 to 5.3 hours per day.
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Figure 4: Map of hydro-meteorological stations. Monitoring data are available on monthly temperature T, humidity H, wind speed W, Solar radiation S, water evaporation E. Calculation of potential evaporation (ETo) is on the basis of these meteorological data.
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2.1.5 Rain The Mekong Delta has an average rainfall of approximately 1800 mm, but with an uneven distribution both in space and time. The western region has the most rainfall with annual average from 2000-2400 mm, while the east has from 1600-1800 mm rainfall on average. The central plains stretching from Long Xuyen, Chau Doc-Can Tho to Tra Vinh - Cao Lanh - Go Cong have the lowest rainfall, with averages of 1200-1600 mm. The amount of rain is very unevenly distributed over the year. Approximately 90% of annual rainfall is concentrated in the rainy months. Rainfall in the dry season accounts for only 10%, with months I, II, III having almost no rain (often triggering severe droughts). In the rainy season occasionally, there is continuous rain, which may last for 3-5 days, with a relatively large amount of rain, causing flooding and an increase in water levels.
Figure 5: Spatial distribution of annual rainfall
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Rainfall data: Data on monthly rainfall are available for 23 years in 42 stations distributed evenly throughout the region. Calculated statistical mean ( ) and standard deviation ( ) of monthly rainfall time series are often formulated in a probability distribution Log-normal R = ex, z, where R is the rainfall, x= +z , the z value by -0.8416, or zero or +0.8416 corresponding value R with a frequency of 80% (in low water) or 50% (medium water) or 20% (much water). There are no data gaps in rainfall time series, except for a few month in 2-3 years of U Minh and Ganh Hao stations. By calculating the average arithmetic average of rainfall stations in the whole Mekong Delta region reached approximately 1660 mm, in a wet year the frequency of 20% of annual rainfall reaches 1955 mm (up 17% compared to average), in dry years it only reaches 1410 mm (down 15%). Table 1: Rainfall frequency all the Mekong Delta Unit: mm
Month
Freq. I II III IV V VI VII VIII IX X XI XII
Annual
total
80% 2.5 2.5 3.9 12.5 94.5 140.0 146.1 150.8 171.9 198.0 51.4 8.2 1410.8
50% 7.1 7.9 13.5 36.0 152.4 196.6 220.3 214.4 239.3 278.6 104.4 24.3 1659.3
20% 26.0 29.1 51.6 111.3 251.0 278.1 336.6 306.7 334.9 394.6 222.9 77.2 1955.6
2.1.6 Climate change Climate change is one of the biggest challenges for mankind in the 21st century. Climate change will seriously affect the production, life and the environment throughout the world. Temperature increases, sea level rises causing flooding, salt water intrusion and detrimental effects on agriculture. All this creates a substantial risk for the industrial and socio-economic system in the future. In Vietnam during the last 50 years, average annual temperatures have risen about 0.5 to 0.7°C, sea level rise was about 20 cm. Climate change has caused disasters, particularly typhoons, floods and more intensive droughts. The Ministry of Natural Resources and Environment (MONRE) studied possible climate change and sea level rise scenarios for Vietnam. Under these scenarios, the climate in all regions of Vietnam will undergo changes. In the late 21st century, average temperatures in Vietnam could have increased by about 2.3°C; total annual rainfall and wet season rainfall may have increased while dry season rainfall will have decreased. A sea level rise is anticipated of about 75cm. Scenarios of global greenhouse gas emission levels were selected to calculate the alternative climate change scenarios (A2, B2=average) for Vietnam. The figures represent the calculated changes compared to the figures over the period 1980-1999.
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Table 2. The change of climate and sea level in southern Vietnam up to 2100 by an average emission scenario (B2)
Milestones in the 21st century Parameters
2020 2030 2040 2050 2060 2070 2080 2090 2100
Temperature increase (oC)
0.4 0.6 0.8 1.0 1.3 1.6 1.8 1.9 2.0
Rainfall increase (%) 0.3 0.4 0.6 0.7 0.8 0.9 1.0 1.0 1.0
Sea level rise (cm) 12 17 23 30 37 46 54 64 75
Table 3. Level of monthly temperature change (°C) in southern Vietnam up to 2100 by an average emission scenario (B2)
Milestone in the 21st century Months
2020 2030 2040 2050 2060 2070 2080 2090 2100
XII-II 0.3 0.5 0.6 0.8 1.0 1.3 1.5 1.5 1.7
III-V 0.4 0.6 0.8 0.9 1.2 1.4 1.7 1.8 1.9
VI-VIII 0.5 0.7 0.9 1.2 1.5 1.8 2.0 2.1 2.1
IX-XI 0.5 0.6 0.9 1.2 1.4 1.8 1.9 2.1 2.3
Table 4. Average monthly rainfall change (%) in southern Vietnam up to 2100 by an average emission scenario (B2)
Milestones in the 21st century Months
2020 2030 2040 2050 2060 2070 2080 2090 2100
XII-II -3.0 -4.4 -6.2 -8.1 -8.7 -11.4 -12.8 -14.2 -15.4
III-V -2.8 -4.1 -5.8 -7.5 -9.1 -10.6 -12.0 -13.2 -14.3
VI-VIII 0.3 0.5 0.6 0.9 1.1 1.2 1.4 1.5 1.6
IX-XI 2.6 3.8 5.3 6.8 8.3 9.6 10.9 11.9 13.0
Based on scenarios of sea level rise, inundation maps have been constructed, the first step is for the area of the Mekong delta based on the topographic map scale 1/2000 and 1/5000 and the digital elevation model with a 5x5m resolution for the whole region. Average current sea levels were calculated based on the measured tidal data at Vung Tau (period 1979-2007). An inundation area map of the Mekong delta for 75 cm of sea level rise is shown in the figure below.
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Figure 6: Flooding extent in the Mekong Delta with a sea level rise 75cm 2.2 HYDROLOGICAL REGIMES Hydrological regimes in the Mekong Delta are affected directly by the river flow, the tidal regime of the East Sea (South China Sea) and for some parts of the delta by the tidal regime in the Gulf of Thailand (West Sea). The East Sea has a semi-diurnal and irregular sea-tide regime, while the West Sea is diurnal. Based on the influence of these diverse tidal patterns and cycli, the Mekong Delta can be divided into three different regions hydrologically. These are: (a) the northern plains, including sections of the province of An Giang and Dong Thap, an area about 300,000 ha), where the impact of the river floods is dominant; (b) an area with combined river flood-tidal impacts; this region is bound by the Cai Lon river-Xeo Chit channel Lai Hieu canal - Mang Thit river and Ben Tre-Cho Gao canals with an area of about 1.6 million ha), and (c) the coastal delta regions with direct influence of the primary tides; this includes the entire coastal region of the East Sea, with an area of about 2.0 million ha). Seasonal flooding in the Mekong Delta usually begins in months VI-VII and ends in months XI- XII, with an average peak flow entering the delta of around 28,000-30,000 m3/s. This is followed by a seasonal average dry flow of about 3,000-5,000 m3/s. Both high and low flood regimes prevail for about 6 months.
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Total average annual river flow in the Mekong Delta in the upstream parts of the Tien and Hau rivers is ~408 billion m3 (according to data measured from 2000 to 2008 at Tan Chau and Chau Doc stations). With flooding in the flood season the border region accounts for 14-18% of the total flood into the territory of Vietnam (estimated 57 billion m3) and surface water by rain on the plains accounts for 11% of the whole water volume (estimated 45 billion m3). 2.3 SURFACE WATER QUANTITY Firstly, stations in main tributaries (stations on the river) or primary river/canals (tributary channels) are identified. Statistical analysis can be performed on the monthly flow data of stations to obtain delta-wide hydrological characteristics. In the Mekong Delta there are only five stations along the main river courses i.e. on the Tien river (Tan Chau and My Thuan stations), the Hau river (station Chau Doc and Can Tho) and on the Vam Nao river (Vam Nao station). Vam Nao river is the short connection between the Tien River and Hau River in An Giang province. Data time series for this area are short; stations My Thuan and Can Tho have data continuously from 2003 to 2006, station Tan Chau, Chau Doc and Vam Nao have data continuously from 2000 to 2007. Stations Tan Chau and Chau Doc are most important for measuring the flow of the entire basin, viz. the upstream Mekong River, to the Mekong Delta. Station Vam Nao quantifies flow from the Tien river to the Hau river. Stations My Thuan and Can Tho quantify flow of the two rivers Tien and Hau river after flowing through the Plain of Reeds area (POR) and Long Xiuyen Quadrant (LXQ), and after distribution of water through main irrigation channels in the POR and LXQ regions. Stations My Thuan and Can Tho are also influenced by sea tide. The Mekong Delta has some local hydrological stations that measure the water level in the regular channels and other stations measuring water in coastal estuaries. Estuarine coastal stations and local stations in the coastal provinces measure salinity. However, all the local stations and the estuarine stations do not consistently measure the flow. Therefore, within the delta sub-regions are considered as secondary basins; these are: Plain of Reeds (POR), Long Xuyen Quadrant (LXQ), the Middle Plains, between the courses of the Tien and Hau rivers, and the Ca Mau Peninsula (CMP). Since comprehensive quantification of local flow data for these sub-areas is not possible, a quantitative analysis is performed by means of a river hydraulic model simulation. Table 5: Total flow volumes in the Mekong Delta at Tan Chau and Chau Doc stations (unit: Million m3). Freq. Month Annual
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I II III IV V VI VII VIII IX X XI XII average
P80% (dry) 17329 9577 6918 5989 8056 16257 32953 55687 62951 63397 42290 28527 366162
P50% (AVR) 20536 11844 8390 6924 10328 22699 42177 62745 68040 66297 47917 33353 405207
P20% (Wet) 24338 14648 10174 8006 13243 31693 53984 70697 73540 69331 54293 38996 448415
2.4 FLOODING Every year, the overflowing of the Mekong River floods a large area in the northern part of the Mekong Delta. Floods may reach an area of about 1.2 to 1.4 million ha in a regular flood and even 1.7 to 1, 9 million ha in a major flood, with a depth from 0.5 to 4.0 m and the time from 3-6 months. Flooding in the Mekong Delta can be divided into three periods. Early flood season (months VII-VIII): the main rivers flood quickly and the rivers flowing into canals to fields distribute the floodwaters. During this flood much silt is brought that forms the main source for rice field nutrients in the flood season.
Figure 7: Variation of flood levels 2000 at Tân Châu and Châu c
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Figure 8: Spatial distribution of maximum flood flow and the total volume of the flood in the year 2000 (using VRSAP model simulation).
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A second flooding period is when floodwaters reach high levels (exceeding 4.0 m at Tan Chau, and Chau Doc exceeding 3.8 m). These floodwaters enter the delta from two directions a) perpendicular from the main river courses and b) from the Vietnam-Cambodia border region directly. The border flows spill over after flooding and silt deposition in the most flooded areas of Cambodia, and subsequently overflow into the POR and LXQ The third period is the period when the flood is in recession, usually starting by the end of October when the flow spilling from Cambodia has decreased, down the Mekong delta flood water recedes gradually until December According to the classification of the National Center for Meteo-Hydrological Forecasting, the water levels at Tan Chau for a low flood are: 4.0 m (warning level I), 4.0 to 4.5 m; for an average flood (warning level II) and for a major flood >4.5 m (warning level III), with a corresponding flood frequency of 13.2%, 46.2% and the average large flood 40.6%. Statistics show that in 60 years, on average every 2 years there is a flood alarm for warning level III (at Tan Chau the water level is over 4.5 m). 2.5 SALTWATER INTRUSION Saltwater intrusion in the Mekong Delta is a complex process, depending on the magnitude of the floods, the ability to supply fresh water from upstream during the dry season, summer-autumn paddy production status and timing of the rainy season. In general, with late monsoon rains and with water volumes from upstream to just below 70% of the average, the salt will intrude very far inland, like for example in 1977, 1993, 1998 and 2004-2005. Every year, the highest salinities occur late in the dry season, usually in April, sometimes in early May. With salinity 1g/liter, the length of the salinity intrusion is 40 - 50km upstream, the less likely on the Mekong River branches and higher on the Vam Co River. With the start of the flood season, flood waters from upstream push the salt back to the estuaries. In the mid-flood season (Month IX, X), salt 1g/liter is usually located in the estuaries only. In the Plain of Reeds salt intrusion progresses through the Tien River and Vam Co Tay River. Vam Co Tay has no resources upstream, and salt water may intrude far. Salinity also depends on the Tien River flows from the upstream Mekong River. Years of often large flood flows may push the salt intrusion outwards. In contrast, after a small flood the salt intrusion may reaches far upstream the rivers and canals. In the Ca Mau Peninsula, the salt water intrusion is extremely serious and most complex in the Mekong Delta. The land area is bordered on two side by the East Sea and West Sea respectively. Two different tidal regimes affect the river flow in the canal system and restrict the transfer of fresh water from the Hau river towards the deeper interior fields. The Long Xuyen Quadrant area is directly affected by salt water from the West Sea. The main canals in the Long Xuyen Quadrant from Tri Ton to Cai San take water from the Hau river and drain this out to sea. The West sea tide has only a small amplitude.
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Most of the west coast channels have salinity control gates, but Vam Rang and Ha Giang channels are still open enabling saltwater intrusion.
Figure 9: Salinity intrusion isolines in some dry years
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Utilization of saline water: Salinity in the eastern coastal region is around 30-34 g/l; the salinity in the western coastal region is about 22-28 g/l. This regional pattern is influenced by the country's river systems flowing into the Delta. The salinity gradient in the zone from Soai Rap to the eastern part of Ca Mau Cape shows the largest amplitude. Given the influence of alkalines washed from contaminated soil in the Ca Mau peninsula in the rainy season, the pH in estuarine, coastal areas in the Ca Mau Peninsula changes significantly, from 4.45 to 8.7, However in the dry season there is a stable pH (range 8.1 to 8.7). Like in the Ca Mau peninsula, the west coast territory in Kien Giang province is affected by the flood drainage system to the West sea. During the beginning of the rainy season acid waters with other pollutants are becoming a serious threat to the aquaculture in brackish and salt water in the coastal zone from Hon Dat to Ha Tien. Aquaculture in salt water is a relatively new production method that has brought economic returns, gradually changing the economic structure in the coastal provinces and contributing the food supply, employment, increased income and reduction of poverty. The total area of aquaculture in 2007 reached 660,614 ha (584,065 ha of shrimp, 54,612 ha of fish, and 21,937 ha of farming oysters scallop, buildings, crab). The area of shrimp and fish is found mainly in Ca Mau, Bac Lieu, Tra Vinh, Ben Tre, Tien Giang and Kien Giang. It is already observed that the concentration of ponds and the production systems are contributing to the deterioration of water quality. Salty water for the aquaculture ponds is usually taken directly from the large estuaries of the Mekong; from the Soai, Vam Co River and through canals connecting the East Sea (for parts of Ca Mau, Bac Lieu, Soc Trang, Tra Vinh, Ben Tre, Tien Giang and Long An). At the West sea salt water is directed from the larger rivers such as the Cua Lon, Bay Hap, Ong Doc, Cai Lon and dozens of other canals connecting directly to the West sea. 2.6 IMPACTS OF UPSTREAM DEVELOPMENTS 2.6.1. Current upstream flow Upstream flow at specific locations was computed using hydrological models with the following results: The Great Lake (Ton Le Sap) upstream of the Mekong delta in Cambodia has a full storage volume of 80 billion m3 and regulates upstream flow to store flood waters and release again later to increase dry flow downstream. Impact of upstream developments on the flow pattern of the Mekong Delta Before 1990, there was only 1 hydropower plant in the Mekong River Basin (Nam Ngum, with an active reservoir volume of 4700 million m3). In the period from 1991 to 2003 four additional large hydropower plants (with a total active volume of 1926 million m3) were built. Data analysis for flows at Pakse shows that flows in the dry months have significantly increased in recent years, as compared to before.
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Table 6. The Mekong river flow at some locations
Location Catchment area (km2) Annual volume (billion m3)
nh H ng 74,00
Chiang Sean 189. 000 84,43
Luang Prabang 268.000 121,34
Nong Khai 302.000 140,62
Nakhon Phanom 373.000 249,42
Mukdahan 391.000 269,41
Pakse 545.000 317,09
River mouth 745.000 475,00
Table 7. Comparision of recent flow with previous flow at Pakse (unit: m3/s)
NO Period Jan Feb Mar Apr
Five year average Q(1) 1986 - 1990 2447 2068 1879 1729
Five year average Q(2) 1991 - 1995 2619 2025 1749 1651
Five year average Q(3) 1996 - 2000 2626 2122 1903 1904
Five year average Q(4) 2001 - 2005 2993 2399 2125 2058
Q(4) - Q(1) 546 331 246 329
Q(4) - Q(2) 374 374 376 307
Table 8. Comparision of recent flow with previous flow at Kratie (unit: m3/s)
NO Period Jan Feb Mar Apr
Five year average Q(1) 1986 - 1990 3394 2340 1932 1840
Five year average Q(2) 1991 - 1995 3813 2732 2189 2134
Five year average Q(3) 1996 - 2000 4337 3204 2473 2718
Q(3) – Q(2) 524 472 284 584
The above table 8 also shows monthly flow at Kratie that significantly increased in recent years. These figures indicate the positive impact of upstream reservoirs on the dry season flow.
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Table 9. List of hydropower projects upstream Mekong basin
No Reservoir name River
Active volume (Million m3)
Year of completion Country
1 m Ngum m Ngum 4700 1971 Laos
2 Mam Wan Mêkong 258 1993 China
3 Theun Hiboun Theun Hiboun 694 1998 Lao
4 Yaly Sesan 779 2001 Vietnam
5 Dachao Han Mêkong 240 2003 China
6 Plei Kroong Sesan 948 2008 Vietnam
7 Sesan 4A Sesan 204 2008 Vietnam
8 m Theun 2 Nam Theun 3378 2009 Lao
9 Boun Kuop Serepok 523 2009 Vietnam
10 Nam Ngum 2 Nam ngum 2994 2010 Lao
11 Nâm Lik2 Nam Lik 826 2010
12 Jing Hong Mêkong 230 2010 China
As expected, the upstream reservoirs will increase downstream flow in the dry seasons. However, critical situations will occur in extremely dry years when reservoir water shortages happened with resulting unsuitable operational procedures for reservoir management. Under such conditions, the downstream flow regime is significantly affected. Further data on the upstream flow of the Mekong River: (MRC, 2009)
Six upstream reservoirs in China with a total volume of 21 billion m3 (4,6% of total basin wide water)
Sub-basins of the lower Mekong basin in Laos, Thailand, Cambodia and the Central Highlands of Vietnam:
Existing 40 reservoirs with volume of 22 billion m3 ( 4,7%)
By 2030: 70 reservoirs with additional 20 billion m3 (4,2% )
Main lower stream of Laos, Thailand and Cambodia: The total volume of 11 reservoirs is 2,5 billion m3 (0,5%).
24
Basin total volume of reservoirs is 100 billion m3 and this forms 18 % Mekong annual flow.
Water demand: Water demand in 2030 will increase by 50% compared to demand in 2000. By 2050 it will have increased by about 100%.
Upstream flow at Kratie: changes by 2050:
Annual flow: Increase 870 m3/s, (+6,9 % of average flow in 1985-2000).
Average flood flow: Decrease 1.669 m3/s, (-7,4%)
Average dry flow: Increase 848 m3/s, (+19,7%). In a report of the Asian Development Bank (2009) flow changes in the Mekong basin by 2070-2099 are predicted as follows:
Maximum flow Qmax increase +19% for the Mekong delta.
Minimum flow Qmin decrease -29 % for the Mekong delta.
2.7 POSSIBLE MEASURES TO IMPROVE THE SITUATION 2.7.1 Integrated water resources planning for Mekong Delta and Decision
No.84/2006/Q -TTg In the year 2005 MARD executed a master plan study on integrated water resources planning for the delta, including analysis of local socio-economic developments and particularly looking for more effective crop patterns. Through the study, MARD submitted the water work portfolio for approval by the Prime Minister under the Decision No.84/2006/Q -TTg dated 19/4/2006. The Decision assigned tasks and solutions for the sub-regions POR, LXQ, BTHR and CMP as well as proposed a number of investment projects (water works) for the period 2006-2010 and 2011-2020. The Decision proposed a long/term development plan to adapt and solve critical issues in the dry season caused by upstream developments. The possible measures were identified as suitable changes in cropping patterns, increasing water storage in canals and local storage basins, further studies on development of large sluice gates in main stream mouths. 2.7.2 Adaptation measures for climate change and sea level rise MARD is implementing further water resources planning studies for climate change and sea level rise adaptation. A number of proactive measures and adaptation guidelines for in particular salinity intrusion were recommended as follows: Completion of projects listed in decree 84/2006/QD-TTg and additional works proposed by the provincial authorities
Construction of sea dikes, associated works and coastal roads
Construction of estuary dikes and culverts
25
Construction of water diversion channels/pipes for coastal sub-areas
Construction of flood control systems
Improvement of inland systems for agriculture
Development of urban drainage systems
Building large sluice gates at river mouths: (i) The Cai Lon-Cai Be sluice, (ii) Vam Co sluice, (iii) Ham Luong sluice, (iv) Cung Hau sluice and (v) Co Chien sluice.
The location of important sluices is presented in Figure 10.
Figure 10: Water works development plan for Mekong Delta
Cái L n-Cái Bé sluice
Hàm Luông sluice
Chiên sluice
Cung H u sluice
Vàm C sluice
26
CHAPTER 3. WATER QUALITY Rainwater supply in the Mekong delta is plentiful and of good quality and it can
be used for drinking and as irrigation water for crops. The monitoring and analytical data on the quality of rainwater in the Mekong delta in recent years shows that although there have been some indications for the occurrence of more acid rain, the rainwater in the Mekong Delta in general can be used as a source of water supply. This source is important for people living in areas that still have difficulties with water supply and poor surface water resources and where groundwater is contaminated especially during flood seasons. Rainwater also plays an important role in agricultural production, aquaculture, forest fire prevention in coastal areas due to limited sources of fresh water from rivers.
Water quality in the main river courses varies markedly with the seasons. The content of soluble substances is higher during the dry season and lower in the flood season. Floods are loaded with much silt, especially during the first months of the rainy season. Annually, the Mekong Delta receives about 150 million tons of silt; this process shows an increasing trend in recent years. At Tan Chau, the average concentration of silt in the flood season is about 800 g/m3, with 1000 g/ m3 in August. The variation in water quality of the flooded Mekong Delta region is complicated; it is dominated by several modes of climate, hydrology, soils and human activities. Soluble substances of the Na, K, Ca2+, Mg2+, Fe2+, Al3+, SO4
2-, Cl-, HCO3- content varies with
season, with dry season values usually higher than the those in the flood season, but generally still below critical thresholds. In general, surface water pollution in the Mekong delta is characterized by high concentrations of Coliform, 300.000-1500.000 unit/100ml on average. The main sources are human waste, and waste from livestock and poultry. In the interior fields (“polders”), the water quality situation is usually more serious. According to field research, pesticides pollution is not widespread in the delta, but in some places contamination has certainly affected aquatic ecosystems. Monitoring: To assess pollution levels and to assess water use options, monitoring water quality in the Mekong delta is extremely important. To serve the requirements of sectoral development and water management, since 1999 the Ministry of Agriculture and Rural Development has assigned SIWRP the implementation of surface water quality monitoring in the Mekong delta through a monitoring network in the rivers. From July 2004 to present, this has become a regular monitoring network.
27
Figure 11: Water quality monitoring network
Samples are taken on the 15th of each month from January to December, at two moments of peak and lowest water level of the day.
Monitoring parameters are selected to ensure meeting the goal of monitoring water quality, including silt composition, nutrition components, components indicative of organic pollution, micro pollutants. In 2008, the monitoring indicators include the following groups:
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- The criteria determining physical and chemical characteristics of water: pH, Electrical Conductivity (EC), total dissolved solids (TDS), total suspended solids (TSS). Na, K, Cl, Ca, Mg , SO4, alkalinity / Acidity, Hardness (CaCO3).
- The criteria to determine the nutrients: Total Phosphorus, Total Nitrogen, Ammonia (NH3), nitrate (NO3), Nitrit (NO2), phosphate (PO4).
- The indicators to assess the level of organic pollution, micro-organisms of water: COD, BOD5, DO, Coliform and Ecoli.
- The analysis methods used is the standard method of Vietnam or international standards used around the world.
Table 10: List the standard method of testing water quality
No Parameter Unit standard method 1 pH TCVN 6492 : 1999 2 alkalinity / Acidity mg/l CaCO3 TCVN 6636-1 : 2000 4 Temperature oC SMEWW 2550-B 5 Electric conductivity (EC) mS/cm SMEWW 2510 6 total suspended solids (TSS) mg/l TCTT-TSS 7 Total Hardness mg/l CaCO3 TCVN 2672-78 8 Nat-ri (Na) mg/l TCVN6196-3-2000 9 Kali (K) mg/l TCVN6196-3-2000
10 Can-xi (Ca) mg/l TCVN6198-1996 11 Maggie (Mg) mg/l TCVN6224-1996 12 Clo (Cl) mg/l SMEWW 4500- Cl-C 13 Sulfate (SO4) mg/l SMEWW 4500- SO4
-C 14 Dissolved Oxygen (DO) mg/l TCVN 4599 : 1995. 15 Chemical oxygen demand (COD)Mn mg/l O2 TCVN 4565-88 16 Biological oxygen demand (BOD5) mg/l O2 SMEWW 5210 19 Nitrat (NO3
-) mg/l TCVN 6180-96 20 Nitrit (NO2
-) mg/l TCVN 6178-96 21 Ammoniac (NH4
+) mg/l TCVN 5988-95 22 Total Nitro (N) mg/l TCVN6624-1:2000 23 Total Phospho (P) mg/l TCVN 6202:1996 24 Coliform MPN/100ml SMEWW 9221 25 E.Coli MPN/100ml SMEWW 9221
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In 2007, monitoring water quality in the lower Mekong River Basin was done in 12 stations, including localities on the Tien river, Hau River, and on channels in the Plain of reeds, Long Xuyen Quadrant. Some analytical results are as follows:
- In 2007, the alum water on the channel in Nguyen Tan Thanh at Long Dinh was more acid than in 2006 with the lowest pH value to 4.95 in August. In previous years (2002-2007), the water is less acid, but alum content fluctuates more, the trend line does not change (coefficient = 0 and angular coefficient p = 0.982).
- Saltwater intrusion in 2007was not high; in My Tho the maximum conductivity value is 1680 S/cm in April, with a lower salinity of about 1.3 g / l. In recent years, the saltwater intrusion has minor fluctuations. The year 2004 is the year with the highest saltwater intrusion.
- Silt content on the main streams and the internal canals tends to increase during the period 2002-2007.
- Organic matter, nitrogen and phosphorus content: the data show an increase in periods with heavy rains (July). During the dry season, the nutritional composition of canals is higher than common on the mainstream river courses. In the period 2002-2007, some components tend to show an increase (nitrogen) while others are somewhat lower, such as phosphorus.
- The content of organic matter (BOD5) is quite low, however COD components tend to increase in recent years (the period 2002-2007). Dissolved Oxygen was low in the channels in the dry season.
- Water in the main streams is of good quality (and meets TCVN 5942:1995 standards) based up on most water quality indices observed, except for suspended solids. Water in most smaller canals was polluted. All water bodies have good quality for fresh aquatic life, except for a few months with impact of acid drainage from acid sulphate soils in the Long Dinh area.
- Some local stations were polluted by acid water in May and June by acid soil leakage during the early rainy season.
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Figure 12: pH in 2008 at some stations
Figure 13: pH in different water resources in 2002-2008
For the period 2002-2007, the pH value of water in the main rivers and canals varies not much, only by about 0.5 units (Figure 12.)
Values of SAR (sodium absorption ratio) of the Mekong branches as well as for canals (Cai San, Nguyen Tan Thanh, Tri Ton) is quite low, less than 5 units during the rainy season, during the dry season usually less than 10 (except at My Tho). This means water is suitable as irrigation water for agriculture, according to the Vietnamese Standard TCVN 6673-2000 (with SAR <10).
In 2008, the variability of the mineral chemical composition (through electrical conductivity) of the main river branches (except for My Tho station, since this was affected by saltwater intrusion) and the internal canals did not fluctuate much (about 10 to 20 mS / m (0.06 g / l to 1.3 g / l). Stations Long Dinh, and Kien Binh and Bridge No13 had high conductivities that increased from 40 to 70 mS / m in the last months of the dry season and the start of the rainy season.
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Figure 14: EC in fields and main streams in 2008
Figure 15: Salinity at M Tho, 2002- 2008
In the period 2002-2008 the salinity intrusion in My Tho was weak, while the most strong saltwater intrusion occurred in 2004.
The highest concentration of silt in the major rivers in August is approximately 500 mg/l. Major rivers normally have a higher concentration of silt (TSS) as compared to the smaller canals; this is increasing during the rainy season and low during the dry season. TSS in the channels is higher in the rainy season then in the dry season possibly due to boats movements.
Trends of the TSS on the main river branches in the period 2002-2008 shows that the concentration of TSS is increasing, but this rise is very small.
Suspended solids in the flow, especially in the flood season, are a huge natural resource distributed with the flood waters, leading to annual accretion of the soils in the Mekong Delta region. This is a very positive impact of the floods. But for areas where people have to use surface water (rivers, canals) for domestic water supply (viz. cooking, bathing, etc.), the water quality is not good as the turbidity is too high. (Vietnamese standard: TCVN 5942:1995 requirements: TSS content source A is 20 mg / l, so water in the rainy season almost never meets the requirements for water supply activities). This creates difficulties for people living in the flooded areas.
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Figure 16: TSS in fields and rivers in 2008 (right) and TSS in rivers in 2002- 2008 (left)
In 2008, the concentration of total nitrogen (T-N) with wide range from 0.2 mg / l to 1.7 mg / l.
Figure 17: T-N in river courses and canals in (data for 2008).
Nitrogen composition varies in a range below 1.5 mg NO2
-&NO3- per litre,
which is lower than the limit for good surface water (quality level A of TCVN 5942-1995, the so-called limit A TCVN5942-1995 with NO2
-=10 mg/l). Ammonium concentration is less than 0.05 mg/l, (equivalent to NH3 below 0.01 mg/l, which is smaller than limit A TCVN5942-1995 with NH3= 0.06 mg/l).
33
In the period 2002-2008, these components tend to increase, but their content is low compared with standard.
Figure 18: NH4
+ and NO2&3- (data for 2002-2008)
Figure 19: T-N in 2002-2008 & T-P in 2002-2008
Organic matter in water was determined by using the two indices BOD (biochemical oxygen demand) and COD (chemical oxygen demand). Observed data in 2008 show high BOD with 4 mg/l, above the limit A TCVN5942-1995, at My Thuan on the Tien river and in Can Tho on the Hau river. Other stations have low BOD.
34
Figure 20: BOD5 and COD (data for 2008).
Surface water quality in the Mekong delta, in addition to the impact of wastewater resources from population living in concentrations along rivers and canals, is now also affected by emissions from sources of industrial production. However, the level and scale differs within the area. Every day there is a large amount of wastewater produced that is discharged into the environment. Aquaculture is strongly developed in the Mekong delta, and along with it the problem of wastewater, sludge waste of aquaculture ponds and from seafood processing facilities. Every year the agricultural sector also used to 2 million tons of chemical fertilizers and 500,000 tons of plant protection pesticides. All this waste sources impact the quality of water resources in the Mekong Delta. Also incidental accidents have caused serious environmental and economic damages.
Figure 21: BOD5 in 2002-2008 and COD in 2002-2008
35
In most monitoring locations this year, total coliform and E. Coli is not high. The highest Coli. value was in My Tho on the Tien River (90,000 MPN/100 mL) in October 2008. In the channels, the highest value is at Long Dinh 24,000 MPN/100ml in May. These appear to exceed the threshold value of source A (5000 MPN/100 ml), TCVN 5945:1995 Observed coliform values are low in most monitoring points, while the value of E. Coli is very low, indicating the microbial contamination is not high. The chances for significant microbial contaminations of the larger river branches is very low because the flow volume is large.
Table 11: Coliform in 2008 (MPN/100 ml)
Source Average Minimum Maximum Middle
Canal 2920.036 0 24.000 930
U river 1412.864 23 4.300 700
TI N river 7450.606 90 90.000 900
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CHAPTER 4. HYDROGEOLOGY AND GROUNDWATER RESOURCES 4.1 Geology
4.1.1 Tectonics and Faulting Plate tectonics and related faulting and folding have played an important role in the origin of the Mekong River, the development of its course and the formation of the sedimentary basins now containing the unconsolidated sediments of the delta. The dominant tectonic direction is north-east south-west (NE-SW) causing steps in the bottom of the sedimentary basin which increase towards the coastline. The secondary tectonic directions are north-west south-east and north-south. The NW-SE direction is clearly dominant near the Bassac river, the Mekong river and the Vam Co rivers. The combination of the NE-SW and NW-SE directions caused several basement blocks near the mouth of the Bassac river which subsided to large depths (3,000 m below surface level in the south-east of Tra Vinh province). The N-S direction is only present in the west of the Mekong Delta. Faulting dominated the formation of the Mekong Delta, but is at present not active. The faults have influenced to some extent the thickness and continuity of the clay layers. This has proved to be important in the separation of groundwater from different aquifers.
4.2.2 Stratigraphy The stratigraphy of the Mekong delta is based on the latest results of geological studies done by Division for Geological Mapping for the South of Vietnam (DGMSVN, former Geological Division 6). The most recent study “Research geological structure and classification of N-Q stratigraphy in the Mekong Delta” produced geological maps at scale 1:500,000 based on detailed cross-sections and geological borehole data. Neogene and Quaternary deltaic sediments are grouped into formations having different geological ages. For each formation, sediments are further classified into sub-formations having different types of sedimentary origins
4.2. Hydrogeology and groundwater resources
4.2.1. The aquifer system in Mekong Delta The hydrogeology of the Mekong Delta is complex. The sedimentation regime, the sea level transgressions and regressions and active faulting during deposition of the sediments has caused large variations in aquifer and aquiclude dimensions and water quality. There are eight distinct aquifers in the delta subsurface, namely;
37
the Holocene aquifer (qh);
the Upper Pleistocene aquifer (qp3); the Upper-middle Pleistocene aquifer (qp2-3);
the Lower Pleistocene aquifer (qp1);
the Middle Pliocene aquifer (n22);
the Lower Pliocene aquifer (n21);
the Upper Miocene aquifer (n13) and
the Upper- Middle Miocene aquifer (n12-3).
Figure 22 shows a representative section through the subsurface of the delta, with the eight different aquifer systems. A more detailed description of the various aquifers and their groundwater potential is presented in Appendix 2. The aquifer system in the Mekong Delta MD has an artesian basin structure. The deepest part of the basin bottom is between the two rivers (Tien and Hau rivers) and rises in north-eastern east, northern and north-western directions. Except for the Holocene aquifer, the productivities of all aquifer varies from medium to high (from 1 to greater than 5 l/s). Each aquifer normally consists of two parts, the upper part is composed of silt, clay or silty clay, with no water bearing capacity; the lower part is composed of fine to coarse sand, gravel and pebble, with a medium to high water bearing capacity. In the deep aquifers such as n2
2, n21, n1
3, groundwater is of high temperature (from 32 to 390C). Mineralised water or hot water can be found in some places such as Long Dien, Nhon Trach, Tra Vinh, Vinh Long ... In the eastern part of the delta, groundwater is fresh and recharged by rainfall. In the western part, fresh groundwater exists in limited areas, the recharge mechanism is not well clarified. .
38
Figure 22. Cross – section III-III from the north-east to the southwest, parallel along the coast, approximately 15 km from the delta coastline
39
4.2.2. Ground water Quality
In the Mekong Delta, groundwater quality issues are mainly related to the salinity and only occasionally related to other components, like heavy metals. Chemical components to determine the salinity concentration are the Total Dissolved Solids (TDS) and, in case no TDS data is available, chloride (Cl). These components have been monitored over the whole region for every geological layer for more than 20 years. Additional data is retrieved from Vertical Electrical Sounding (VES) measurements and interpretations, and showing the salt-fresh groundwater interface at depth. This is correlated with borehole logs.
Hydrochemistry of Mekong Delta groundwater
The hydrochemistry of the delta groundwater is very complex due to several sea level transgression and regression periods in the past and human influence more recently. In the western and northern delta groundwater is predominately fresh. In coastal areas groundwater is generally saline. In other areas fresh and saline ground water tend to mix in horizontal as well as vertical directions. Below the characteristic hydro-chemical features for the different stratigraphical layers in 4 regions (see Figure 23) are described.
Figure 23. Hydrogeological - Groundwater zoning in the Mekong Delta
40
Dong Thap Muoi or Plain of Reeds (Between Vam Co Dong and Mekong Rivers): There is a considerable exchange of fresh and salt ground water between layers in this area. Saline water of the type Cl-Na is found in the eastern and western part and increases from the top downwards. An enrichment of Ca in groundwater is encountered resulting from salinization. The fresh groundwater of the type HCO3-Na-Mg is slightly enriched by Na, which is typical for desalinization. In the heart of this area there is a large reserve of fresh groundwater for water supply. However, the groundwater of the deep aquifers (n2
2 and n21) contains considerable arsenic
concentrations, from 24.9 to 35.9 g/l and up to 56.8 g/l, detected in My Tho and Tan An Town; Between Mekong and Bassac River: In the north-western part the whole profile is saline while in the south-eastern part the whole profile is fresh of the type HCO3-Na The fresh groundwater shows enrichment of Na, which is due to desalinization by rainwater. The saline groundwater reveals enrichment of Ca, which is the result of saline water intrusion of seawater. In the north-western part the fresh water is of the type HCO3-Ca-Mg. There is probably a considerable amount of exchange of saline and fresh water between the different layers; Long Xuyen Quadrangle: Brackish groundwater is common and occupies almost the whole profile. The chloride content of the brackish water is lower compared to other regions. There is enrichment of Ca. Fresh water is found only in the north-east where the land surface is relatively high; Ca Mau Peninsula: Fresh water in the Pleistocene and Pliocene aquifers are of the types HCO3-Cl-Na and HCO3-Cl-Na-Mg and show signs of enrichment by Na, which is the result of desalinization by rain water in the past. The TDS of the fresh groundwater is usually higher than that of water in eastern delta. Locally some traces of nitrite are found. Saline water in the Holocene in the north is the result of saline water intrusion in the past. In the area of Ca Mau town the brackish water is fossil, because it shows no enrichment of Ca. In general the groundwater of the Holocene aquifer in the western delta has a relative high SO4 content and low pH value due to the presence of acid-sulphate soils in the area. Furthermore, Pleistocene and Pliocene aquifers often show signs of pollution, which decreases with depth. According to a recent arsenic study, arsenic concentration in groundwater of most aquifers is below the limit of 50 g/l. Some noticeable arsenic concentration were detected locally from the n2
2 and n21 aquifers
at great depth (200-300m). However, this study does not exclude the occurrence of arsenic pollution in the Mekong Delta,as the number of samples for determining arsenic is not considered representative. Further studies are required.
Saline groundwater distribution in the MD
In general, the origin of saline groundwater in all stratigraphical layers in the subsurface of the delta is related to the marine environment during sedimentation and the frequent flooding of the delta by seawater during interglacial (transgression) periods. Flushing of seawater by infiltration of fresh water during glacial periods
41
with lower sea levels was never completely, leaving large areas filled with brackish and saline ground water. Salinization and desalinization processes, responsible for the saline water in the delta subsurface, takes place even today. Combining all the information available on salinity and processes contributing to salinization and desalinization of groundwater, the following conclusions are derived regarding groundwater quality:
Fresh water in all layers is found in mountainous areas where recharge of groundwater is obvious from groundwater level maps;
Brackish water is found in layers near and between the major rivers. During the most recent transgression, the rivers facilitated intrusion of the seawater having free access to the aquifer below the sandy riverbed. So far, the influence of infiltrating river water on the groundwater quality has been limited, due to an actual recharge that is much less than the potential recharge. Increased pumping near and between rivers could cause further salinization or desalinization of the upper layers. This means, salinization by upstream migration of seawater along rivers in the coastal areas and desalinization by fresh river water infiltration upstream;
In areas along the coast where old dune deposits are found at the surface, complicated patterns of fresh and saline ground water are found, like in the Tra Vinh region. Here, infiltration of rainfall takes place in accordance with the higher water potentials in the dune ridges;
In the Plain of Reeds, north of the Mekong River, brackish to saline ground water predominates the Pleistocene layers with low groundwater levels. The deeper Pliocene layers with higher groundwater levels contain fresh water, indicating that there is a hydraulic isolation between the two formations. Studies show that this fresh water originates from a recharge area 170m higher than the Pleistocene one, which should correspond with the north-western extension of the delta and outcrops of the formation in Cambodia. These layers were already desalinized during the early Pleistocene period;
In the Ca Mau Peninsula, south of the Hau River, the deeper Pliocene layers show isolated areas with fresh groundwater in between generally brackish to saline groundwater. Around Ca Mau and Soc Trang this fresh water is exploited for drinking water. More geological and geophysical investigations could reveal more isolated fresh water zones;
The water quality of shallow wells in the southern part of the delta is often fresh, most probably due to surface water infiltration.
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In the west and north-west of the delta; isolated rock outcrops occur (see Chapter 1). Aquifers and aquicludes are thinning out towards the rocky outcrops, which facilitates intrusion of fresh and saltwater from the surface and mixing of water from different aquifers. At micro-scale, around these outcrops, the hydrochemistry is even more complex.
Summarizing, the salt and fresh water in the MD is subject to many natural and artificial processes that alter the salt concentration continuously and consequently the salt and fresh water distribution is complex and heterogeneous.
4.2.3. Groundwater reserves Results of groundwater reserve calculations by the Division for Water Resources Planning and Investigation for the South of Vietnam provide reserves assessments as given in Table 14. Total groundwater reserves in the Mekong Delta are in the order of 26,754,764 m3/day. Of which, 4,045,095 m3/day is dynamic groundwater reserves, and 22,709,669 m3/day is static reserves. Table 12. Results of calculation of static reserves (m3/day)
Aquifer Gravity reserves Elastic reserves Sum (static reserves)
qp3 1,066,570 188,547 1,185,117
qp2-3 5,122,630 401,126 5,523,756
qp1 4,288,296 576,991 4,865,288
n22 3,909,452 81,596 3,991,048
n21 4,651,992 19,015 4,671,007
n13 2,461,638 11,816 2,473,454
Sum 21,500,578 1,209,991 22,709,669
Table 13. Results of calculation of dynamic reserves (m3/day)
Dynamic reserves In aquifers Sum
Inflow from rainfall to aquifers qp3,qp2-3, n22 3,860,850
Natural inflow into aquifers at boundary
qp3,qp2-3,qp1, n22 101,095
Inflow from rivers to aquifers qh, qp3 83,150
Sum 4,045,095
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4.2.4. Present groundwater utilization According to survey data of Hydrogeological Sub-division 806 in 2007, there are an estimated 465,230 groundwater abstraction wells, and abstraction with a total amount of 1,229,031 m3/day (Table 16). This concerns mostly shallow dug wells that exploit only the upper Holocene and Pleistocene aquifers. Water exploitation in the main deeper aquifers is as follows:
In aquifer qp3 and qp2-3: 588 wells, occupied 59,6%. In aquifer qp1 and n2
2: 164 wells, occupied 16,6%. In aquifer n2
1: and 195 wells, occupied 20,0%. In aquifer n1
3: and 38 wells, occupied 3,8%. In general, groundwater in the Mekong Delta is used to serve domestic, industrial purposes and is partly used for aquaculture purposes.
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Table 14: Groundwater utilization in the Mekong Delta
Urban supply Large rural supply Small rural supply
No Province Wells Total
amoun (m3/day) Number
Total amoun
(m3/day)
Aquifer Depth (m) Number
Total amoun
(m3/day)
Aquifer Depth (m) Number
Total amoun
(m3/day)
Aquifer Depth (m)
1 Trà Vinh 88.923 147.301 8 32.210 qp2-3 100-134 102 8.515 - 98-134 88.813 106.576 - 98-134
2 Sóc Tr ng 50.111 100.090 12 31.903 - - 109 8.199 qp2-3 - 49.990 59.988 qp2-3 -
3 c Liêu 88.741 63.681 1 15.165
qp2-3
qp1
n22
106-138 152-168
245 65 8.612
qp2-3
qp1
80-142 146-154 88.675 39.904
-
-
4 Cà Mau 67.185 134.657 13 46.326
qp2-3
qp1
n22
90-111
206-260 132 7.883
qp2-3
qp1
n22
- - -
67.040 80.448
qp2-3
5 n Th 22.643 64.638 - - - - 396 37.942 qp2-3 82-114 22.247 26.696 - -
6 nh Long 6.258 8.705 - - - - 4 1.200 - - 6.254 7.505 -
7 u Giang 29.656 50.045 - - - - 225 14.728 qp2-3 62-118 29.431 35.317 qp2-3 -
8 Ti n Giang 1.029 37.695 8 21.148
n2
1
303-307 78 15.415
n22
n21
n13
253-260 253-347 342-464
943 1.132 -
-
9 ng Tháp 3.213 44.723 8 17.760
- - 165 23.315
qp1
n22
n21
- - -
3.040 3.648 -
-
10 An Giang 4.971 71.917 2 44.930
n22 245-300
6 770 qp2-3
n22
- -
4.963 26.217 qp2-3 22-80
11 B n Tre 2.063 6.683 17 3.342 - - 20 910 - - 2.026 2.431 - -
12 Kiên Giang 96.950 328.970 1 6.240 - - 49 19.464 - - 96.900 303.266 - -
13 Long An 3.487 169.956 27 35.953 - - 1.079 78.147 - - 2.381 55.856 - -
Total amount 465.230 1.229.061 97 254.977 2.430 225.100 465.703 748.984
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CHAPTER 5. WATER DEMAND AND WATER BALANCE
5.1 METHODOLOGY Water in the Mekong Delta is used for a wide variety of purposes: irrigation
for agricultural crops, fresh water for fresh water aquaculture, animal husbandry, poultry, supply of domestic use and industry. Total water demand also includes surface water evaporation and bare land evapotranspiration.
Water demand for crop is calculated on the basis of area and growing season for the crops. Water needs of other sectors such as fisheries, livestock, poultry, cattle and people's livelihood and industry will define the total water demand in the Mekong delta region. The calculated water needs were made for the 120 irrigation subdivisions. The results have been calculated using documentation on land use in 2005, the progress of sowing and harvesting crops and the Mekong Delta provinces, also salt water and fresh water supply figures in 2005 and on the basis of earlier water balance calculations done by SIWRP in 2004.
The water demand was calculated for categories: Paddy, crops, forestry, freshwater fisheries, domestic use, loss due to evaporation on the canal and bare land. Where:
- The demand for water for rice, annual crops, perennial crops is calculated using CROPWAT-FAO model.
- The demand for water for livestock by three categories: cattle: 20 liters / head /day; pig: 40 liters / head /day; chickens, ducks: 2 liters / head /day
- The demand for water for forest: 0.15 l/s/ha - Water loss on bare land: 0,05 l/s/ha - Water for freshwater fisheries: surface water evaporation estimated 5
mm/day. - Water for population: urban 65 l/person/day; rural 45 l/person/day
(according to Vietnamese standard TCXDVN33:2006). - Water for industry: 45 m3/ha/day (TCXDVN33:2006). - Time step for calculations: assuming 10 days.
5.2 RURAL, URBAN AND INDUSTRIAL WATER DEMAND
Water demand is calculated for all regions including areas with fresh water and salt-affected areas. This is performed for the 120 sub-irrigation areas presented in Figure below. Table 23 and table 24 summarize the total water demand flow and volume of each month the whole Mekong Delta. The calculated data show the water demand for agriculture is the largest, accounting for 68% of the total water demand. The months of January and February require the largest amounts of water use due to the lack of rain.
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Table 15: Monthly water flow demand
Monthly water demand (m3/s) Month Rice Crops Poultry Fishery Forestry Population
& Industry Total
I 764.56 129.71 2.51 31.90 52.95 18.93 1000.56 II 834.95 161.06 2.51 31.90 35.62 18.93 1084.97 III 522.17 174.77 2.51 31.90 19.53 18.93 769.80 IV 450.29 162.39 2.51 31.90 19.46 18.93 685.48 V 440.44 63.76 2.51 21.27 26.32 18.93 573.23 VI 396.33 24.71 2.51 - 72.01 18.93 514.49 VII 225.11 31.08 2.51 - 86.17 18.93 363.79 VIII 86.21 20.24 2.51 - 82.16 18.93 210.05 IX 33.83 4.32 2.51 - 53.04 18.93 112.63 X 16.04 13.66 2.51 - 63.62 18.93 114.75 XI 110.27 56.11 2.51 10.20 63.46 18.93 261.49 XII 372.64 108.74 2.51 27.05 56.86 18.93 586.73 Average 354.40 79.21 2.51 15.51 52.60 18.93 523.16
Table 16: Monthly water volume demand
Monthly water demand (million m3) Month Rice Crops Poultry Fishery Forestry Population
& Industry Total
I 2,048 347 7 85 142 51 2,680 II 2,020 390 6 77 86 46 2,625 III 1,399 468 7 85 52 51 2,062 IV 1,167 421 7 83 50 49 1,777 V 1,180 171 7 57 70 51 1,535 VI 1,027 64 7 - 187 49 1,334 VII 603 83 7 - 231 51 974 VIII 231 54 7 - 220 51 563 IX 88 11 7 - 137 49 292 X 43 37 7 - 170 51 307 XI 286 145 7 26 164 49 678 XII 998 291 7 72 152 51 1.572
Average 11,089 2,483 79 487 1,663 597 16,398 Ratio 68% 15% 0% 3% 10% 4% 100%
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Figure 24: Map of 120 sub-irrigation areas.
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5.3 WATER FOR NAVIGATION The minimum depth of water that is required for navigation in the dry season (LAD, m) is used as an indicator for the planning needs of the waterways. For the main channels to ensure access for ships from 200-300 DWT, requires a LAD from 2.5 to 3.0 m. For the main rivers to ensure access for ships from 1000-5000 DWT, requires a LAD from 4.0 to 7.0 m. Table 17: Water requirements for navigation/waterway transportation
Project Route Distance (km)
Ship size
(DWT)
LAD (m)
TP.HCM-Kiên L ng Te canal – Dem market -Vam Co Dong... Rach Gia – Ha Tien canal
297,8 300 3,0
TP.HCM-Kien Luong-Ba Hon
Ong Lon- Cay Kho canal - S i canal - Rach Gia – Ha Tien canal - Ba Hon canal
320,8 300 3,0
TP.HCM-Ca Mau-Nam Can
Te canal –Ong Lon canal - Can Giuoc river - Ganh Hao river –Bay Hap canal- Tac Nam Can canal
393,3 300 3,0
Moc Hoa – Ha Tien Upward Vam Co river - Cai Bat canal- Hong Ngu canal... Ha Tien
183,5 200 2,5
Tan Chau-Hong Ngu-Cua Tieu
VN-CPC boundary-Tan Chau-Dong Thap-Vinh Long-Ben Tre-Cua Tieu
260,4 3.000 6,0
Rach Gia-Ca Mau- Ong Doc river
TX. Rach Gia-Ca Mau- Ong Doc river 182,6 1.000 4,0
Tien river From VN-CPC boundary to the sea 260,4 5.000 7,0 Hau river From VN-CPC boundary to the sea 228,0 5.000 7,0 Ham Luong river Tien river -Ham Luong river 86,0 1.000 4,0 Quan Lo - Phung Hiep Phung Hiep-Hau Giang-Quan Lo - Phung
Hiep canal- Ca Mau 104,5 300 3,0
Go Dau-Vam Co Dong river - Xoai Rap river
Ben Soi -Vam Co Dong river-Go Dau-Duc Hue - Ben Luc-Xoai Rap
189,0 3.000 6,0
Moc Hoa-Xoai Rap river Moc Hoa-Vam Co Tay river-Tân An-Xoai Rap river
163,5 1.000 4,0
5.4 PRESENT WATER BALANCE
Based on the amount of surface water available and water demand for the various user functions as calculated above, a preliminary balance for the entire Mekong Delta region is based on the principle of: total water supply volume, with subtracted the amount of water that is used each month. Surface water supply equals the total water volume of the two stations Tan Chau and Chau Doc with the frequency of 80%, 50% and 20%. For water consumption the situation in 2005 is used.
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Table 18: Present water balance
Month Sub-basin Level of Frequency Unit
1 2 3 4 5 6 7 8 9 10 11 12 Annual
Supply – 80% Mil.m3 17329 9577 6918 5989 8056 16257 32953 55687 62951 63397 42290 28527 366162
Supply – 50% Mil.m3 20536 11844 8390 6924 10328 22699 42177 62745 68040 66297 47917 33353 405207
Supply – 20% Mil.m3 24338 14648 10174 8006 13243 31693 53984 70697 73540 69331 54293 38996 448415
Demand 2005 Mil.m3 2680 2625 2062 1777 1535 1334 974 563 292 307 678 1572 16398
Balance – 80% Mil.m3 14649 6952 4856 4212 6521 14923 31979 55124 62659 63090 41612 26955 349764
Balance – 50% Mil.m3 17856 9219 6328 5147 8793 21365 41203 62182 67748 65990 47239 31781 388809
Mekong Delta
Balance – 20% Mil.m3 21658 12023 8112 6229 11708 30359 53010 70134 73248 69024 53615 37424 432017
Source Balance = (Supply-Demand). Supply calculated in section 3.3.2. Demand = Calculated in section 3.4.1
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According to figures calculated in the above table, the volume of water resources for the whole of the Mekong Delta water is sufficient, so there is excess water in each month. In the dry months from January to May the water demand forms 20-30% of the total flow from upstream, while in the rainy months the total water demand accounts for only 0-6% of the total water volume. In an average year water demand accounts for about 5% of the total. It can be concluded that on the basis of these figures, most water still flows out to the sea. Actually, water shortages do occur for sub-regions due to lack of water storage facilities and salinity control structures. In addition water for environmental purposes – ecosystems, and water for controlling salinity intrusions should be considered as well.
Comparison of water volumes through Tan Chau (Tien river) and Chau Doc (Hau river) with the total of the two stations at My Thuan and Can Tho in the dry season shows that the Plain of Reeds region and the use of freshwater in the Long Xuyen Quandrant covers about 20-25 % of the total freshwater volume of Mekong Delta region. Approximately 75-80% of the freshwater flows through the Mekong Delta, to Can Tho and My Thuan, and a large amount of this flows to the sea. The Ca Mau Peninsula and the coastal zone of the Plain of Reeds and South Muang Thit can use less fresh water due to saltwater intrusion in the estuaries.
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CHAPTER 6. ISSUES TO BE SOLVED In the field of groundwater, many subjects are worthwhile to be studied further. In brief, these subjects are discussed below:
Mobilisation of arsenic from sediments in the Mekong Delta. From the literature study of arsenic in the Mekong Delta sediments, it becomes clear that the delta has a high potential for the development of arsenic. A study to this extent should focus on the presence of arsenic in several soils, the simulation of different environments at small scale level in a laboratory to study the mobilisation of arsenic from sediments and following this perhaps a full scale experiment in the field.
Isotope analysis (C-14 dating) so far has mainly concentrated on the absolute age of groundwater in the top aquifers of the Mekong Delta and with this its general flow patterns. More isotopes can be tested providing more specific information about recharge from rainwater, river water, etc. A project could be set up to determine the origin of water in selected areas.
Groundwater chemistry. This subject has not been studied in detail. Subjects to be studied in this context are the cation exchange capacities of the clays, the ion balances in the clays and the relation with the results of the isotope analysis.
Groundwater reserve assessments. Present procedures for assessment of groundwater reserves in Vietnam are not acceptable in terms of sustainability. They are not considered feasible and realistic. Modern literature is now available on groundwater reserve calculations. This literature can be studied by a panel of specialists and new guidelines for reserve calculations can be formulated.
In certain areas the groundwater levels are dropping. A study on the application of suitable artificial recharge methods could be useful for sustainable groundwater development in the delta.
Groundwater demand studies. Based on the population per province, growth rates, present number of wells and availability of other water resources, an estimate of the future water demand from groundwater is necessary. Based on the location of the inhabitants, wells were planned and designed in outline and the total number of required wells may be determined. Based on these
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prognoses, potential locations of wells and well fields should be investigated by modeling. The result could form the basis for the water supply master planning for the entire Mekong Delta.
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CHAPTER 7. CONCLUSIVE REMARKS The Mekong Delta has abundant water resources, but these are mainly concentrated in the six-month rainy season. The amount of water resources in the Mekong Delta is affected by the upstream flow to the Delta, rainfall, regulation of Great Lake (Ton Le Sap), tidal regimes, wind and sea level rise. These factors must be considered in assessing water resources in the Mekong Delta. The quality of the water resources in the delta is affected by floods, salinity intrusions, acid drainage water, alkaline soils, agro-chemicals, industrialization waste discharges, and ships navigation. There is flooding over an area of about 1.4-1.9 million ha in the upper area of the delta. Salinity intrusion occurs over an area of about 1.2-1.6 million ha in the coastal areas with saline density of over 4g/l. There are widespread acid-sulfate soils and the spread of acid soil drainage water occurs over an area of about 1.0 million ha in the lower delta plains. These processes may create, locally a shortage of fresh water for production and domestic uses over an area of about 2.1 million ha in areas far from rivers, and close to the coast. The situation will become more critical as a consequence of climate change and its impact on the upstream flow regimes, different rainfall and weather patterns in the Mekong Delta itself and threats from sea level rise. Water shortages occur annually in Ca Mau Peninsula due to lack of diversion canals and water control structures. The present alternation of paddy fields and shrimp ponds constitute a difficult to regulate water works system. The Plain of Reeds is the most critical area for flood control due to large overland flood flow. The flood control plan has to deal with trans-boundary issues. Future agricultural and other economic sectoral development plans for the Mekong delta should be formulated with the additional objective to save water. Because climate change effects, sea level rise, upstream agricultural development, upstream water diversions and unfavourable upstream reservoir operation will cause more acute water shortages and more salinity intrusion for the Mekong delta. A quantitative water resources assessment is feasible on the basis of currently available data, viz.:
Long-term meteo-hydrological data and rainfall data are available from the Southern Meteo-hydrological Station.
Salinity intrusion data are observed at coastal stations.
Ten year water quality data are available at SIWRP.
Upstream meteo-hydrological data are available in the database of the Mekong River Commission (also available at SIWRP).
Meteo-hydrological stations are distributed throughout the Mekong delta. Time series data are long and good quality.
There are few flow monitoring stations (only 5 stations on the main Mekong courses at Tan Chau, Chau Doc, Vam Nao, My Thuan and Can Tho). For about 20
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years time series data are available. In addition, SIWRP have carried out 2-week flow monitoring at all Mekong river mouths to assess dry flow distribution in main streams.
Overland flood flow in the upper parts of the Plain of Reeds and the Long Xuyen Quadrant is observed in recent years.
Flood and dry flow in canals can be simulated using existing calibrated hydraulic model VRSAP by SIWRP.
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REFERENCES
[1] MRCs-DSF (2004), WUP-A Decision support framework Version 1.0.0;
Modeler’s grant access for Dang Thanh Lam of SIWRP. [2] SIWRP (2002), Study on water balance for MD for sustainable development
strategy of the Mekong water resource, Main report. [3] SIWRP (2005), Integrated water resources planning for MD. [4] SIWRP (2008), Annual report on water quality monitoring for the lower
Mekong basin. [5] To Van Truong (2005), Research study on Flood analysis, flood forecasting and
flood control for ‘living with flood’ on demand in the MD. [6] www.mcdvietnam.org (2010), ‘Climate change and sea level rise scenarios for
Vietnam’ issued in 2009 by MONRE in PDF format. [7] State government (2006), Decision No.84/2006/Q -TTG. [8] GROUND WATER STUDY MEKONG DELTA, FINAL REPORT 2001.
[9] NGUYÊN HUY DUNG, Research geological structure and classification of N-Q stratigraphy in MD, 2004.
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APPENDIX 1: Water demand assessment source materials
Document/ Database/ Model/ Material
Author/ Owner/ User
Contents/ Descriptions
MRC-DSF Owner: MRC and Three line agencies VNMC, SIWRP, IMHR
The MRC Decision Support Framework, or DSF, is a tool for managing and sharing observed and modelled datasets for the Mekong river basin. These data can be time series, spatial or other miscellaneous data. The datasets are contained with the DSF Knowledge Base database, which is packaged with the DSF software. All of these data can then be utilised to investigate the behaviour of the river basin and, thus, facilitate the decision-making process over how to react to future impacts on and changes to the basin. The Decision Support Framework contains a Main Interface and a series of associated tools. These applications are as follows: Main DSF Interface Impact Analysis Tools Time-Series Plotting Tool Probability Exceedence Tool Event Analysis Tool Low Flow Analysis Tool MQUAD DSF Model Interfaces DSF SWAT Interface DSF IQQM Interface DSF ISIS Interface
Study on water balance for MD for sustainable development strategy of the Mekong water resource
Owner: MARD Author: SIWRP
The main report contains information as follows
- Assessment of existing water utilization in the MD.
- Computing water demand by 2010. - Computing upstream impacts on
monthly flow with development of hydropower and irrigation.
- Computing existing and future water balance.
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Integrated water resources planning for MD
Owner: MARD Author: SIWRP
The content of main report consists of:
- Analysis of characteristics of MKD meteorology, hydrogeology and water resources .
- Assessment of welfare of the people, social and economical situation of the Mekong Delta to 2004.
- Assessment the opportunities and demand for development of MKD, consisting of development orientation of agriculture, forestry, aquaculture, transportation, and construction.
- Calculation of water demand for agriculture, aquaculture, transportation and domestic water supply at present 2005 and to 2010.
- Formulation of water resources development projects.
- Analysis of hydrology, hydraulic, cost estimation of construction of water resources works according to the planned development projects.
- Choice of the list of water resources works for investment for the periods of 2006-2010 and 2011-2020.
Research study on Flood analysis, flood forecasting and flood control for ‘living with flood’ on demand in the MD.
Owner: MOST Author: Dr. To Van Truong, SIWRP
The content of main report consists of:
- Investigation of control flood and living with flood models; of production model in flood areas; Assessment of impacts of infrastructure development to the flow of MKD.
- Analysis of basic data on topography, meteo-hydrology of MKD;
- Building the methodology on recognition of flood in MKD and the methodology to control, manage and live with floods in MKD;
- Calculation of parameters to recognise river floods; building the technology to recognise river floods in MKD and
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application of the technology to recognise the level of flood peak in 2003-2004;
- Upgrading the data on topography, boundary conditions and building a hydraulic model to simulate the floods in 2000, 2001 in MKD;
- Building the technology to recognise floods in MKD and its application to forecast;
- Building the series of maps of floods in MKD according to frequencies using GIS technology;
- Researching of measures to control floods, to construct infrastructure, to develop economy, to protect environment, and to control floods for living with flood in MKD;
Climate change and sea level rise scenarios for Vietnam
Owner & Author: MONRE
Report of MONRE on Climate change and sea level rise scenarios for Vietnam
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Appendix 2: Description of Aquifer systems in the Mekong Delta
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Holocene aquifer (qh)
The Holocene aquifer occurs at the surface of almost the whole delta with an area of 40,000km2 (see Figure 33), and consists of the following sediments: - Lower – middle Holocene sediments (qh1-2), consisting of clayed silt, fine sand
and organic matters. - Alluvial and coastal sediments (qh2-3), consisting of silt, clay, fine to medium
sand to form sandy dunes ( indicative of ancient sea shores). - Sediments (qh3), consisting of clayed silt and fine sand, accumulated in river
valley.
Figure 25. Hydrogeological map of the Holocene aquifer.
Sediments formulated in the period of sea regression (qh2-3) are characterized by sand dunes bearing fresh groundwater. These sand dunes are located in Mo Cay, Ba Tri, Tra Cu, Long Toan districts of Tra Vinh province. Its lithology consists of fine to medium sand, having a thickness of 5 to 10m.
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The boreholes placed in this aquifer are mainly shallow boreholes, with depths from several meters to 30 m, having yields from 0.1 to 2.0 l/s and groundwater levels from 0.5 to 3.0m. Fresh groundwater (TDS<1 g/l) is distributed in an area of 5,816 km2, between the Tien and Hau rivers and in Tra Vinh, Tien Giang provinces (see Figure 33).
Upper Pleistocene aquifer (qp3)
The Upper Pleistocene aquifer is distributed widely throughout the whole Mekong Delta, and is mainly overlain by the Holocene aquifer. It only surfaces in the northeastern part of the delta, and consists of the formations Cu Chi and Moc Hoa, having alluvial and marine-alluvial origins. This is a weakly confined aquifer. The aquifer can be divided into two parts. The top part is an aquitard layer, consisting of silt, clay or silty clay, having a depth to the top of 10.1 to 37.3m and a thickness from 12.1 to 20.6m. The lower part is an aquifer, consisting of fine to coarse sand, having a depth to the top from 22.2 to 57.8m and a thickness from 9.4 to 22.4m. Fresh groundwater is distributed in an area of 8,541 km2, located in Vinh Hung (Long An province); My Tho (Tien Giang province); Tieu Can, Cau Ngang (Tra Vinh province) (see Figure 26). In summary, the upper Pleistocene aquifer qp3 is found in wide areas, but it has complicated hydrogeological conditions. Groundwater is fresh in some areas. It is suitable to abstract water for domestic use.
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Figure 26. Hydrogeological map of Upper Pleistocene aquifer
Upper-middle Pleistocene aquifer (qp2-3)
Upper middle aquifer (qp2-3) distributes widely in the whole MD, is mainly overlain by upper Peistocene aquifer, just outcrops in some place such as An Giang province. Its lithology is composed of sediments of alluvial, marine alluvial and marinal origines, consisting of pebble, gravel, sand, silt, clayey silt and clay. The depth to the top and the thickness of the aquifer varies in space and on cross-sections. It is weakly confined aquifer. The aquifer can be divided into two parts. The top part is an aquitard layer, consisting of silt, clay or silty clay, having the depth to the top of 31.6 to 81.7m and the thickness from 3.6 to 13.5m. The lower part is an aquifer, consisting of fine to coarse sand, having the depth to the top from 44.2 to 85.5m and the thickness from 17.3 to 56.2m.
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Figure 27. Hydrogeological map of upper- middle Pleistocene aquifer
There are several hydraulic windows where groundwater in this aquifer has direct hydraulic relationship with groundwater in qp3 aquifer overlain. Fresh groundwater distributes on the areas of 21,798 km2, located in Tra Vinh, Bac Lieu and Ca Mau provinces (see figure 27). Fresh groundwater is of good quality and large amount.
Lower Pleistocene aquifer (qp1)
Aquifer qp1 distributes on the whole MD. It is a confined aquifer. Sediments in the lower Pleistocene aquifer have mainly alluvial origin, although that in Ca Mau province has marine origin. The aquifer is a confined aquifer and can be divided into two parts. The top part is an aquitard layer, consisting of clayey silt, clay or silty clay, having the average depth to the top from 65.8 to 141.6 m and the average thickness from 7.9 to 15.9m. The lower part is an aquifer, consisting of fine to coarse sand, having the average
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depth to the top from 73.7 to 157.6 m and the average thickness from 14.2 to 43.9m. The depth to the top of the aquifer inclines in direction from north and west to the southern east.
Figure 28. Hydrogeological map of lower Pleistocene aquifer
There are several hydraulic windows where the groundwater in this aquifer has direct hydraulic relationship with groundwater in qp2-3 aquifer . Fresh groundwater distributes on the areas of 17,918 km2, located in Hochiminh city and Can Tho, Kien Giang, Bac Lieu, Ca Mau provinces (see Figure 28). This groundwater is now being abstracted for water supply in such city and province.
Middle Pliocene aquifer (n22)
Aquifer n22 distributes widely on the whole MD, it is composed of sediments having
alluvial, marine-alluvial and marine origins.
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The aquifer is a confined aquifer and can be divided into two parts. The top part is an aquitard layer, consisting of clayey silt, silty clay, having the average depth to the top from 79.7 to 202.7 m and the average thickness from 4.6 to 20.6m. The lower part is an aquifer, consisting of fine to coarse sand, having the average depth to the top from 84.3 to 223.1 m and the average thickness from 29.9 to 57.1m.
Figure 29. Hydrogeological map of middle Pliocene aquifer
Fresh groundwater distributes in two big areas with a total of 19,000 km2, one is located in the northern part of Tien river, and the other is located in Can Tho, Bac Lieu and Ca Mau provinces (see figure 29).
Lower Pliocene (n21)
Aquifer n21 is not outcropped on the surface, and is composed of sediments of
alluvial, marine-alluvial origins. It is highly-confined aquifer and can be divided into two part. The top part is an aquitard layer, consisting of clayey silt, silty clay, having the average depth to the
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top from 196.5 to 279.2 m and the average thickness from 11.8 to 20.5 m. The lower part is an aquifer, consisting of fine to coarse sand, having the average depth to the top from 209.4 to 296.5 m and the average thickness from 40.9 to 45.5m
Figure 30. Hydrogeological map of lower Pliocene aquifer
Fresh groundwater distributes in areas of 16,198 km2, located in Dong Thap, Long An, Hochiminh, Can Tho, Bac Lieu and Ca Mau (see figure 30).
Upper Miocene aquifer (n13)
Aquifer n13 has not yet been studied in detail. There are very few boreholes drilled
through this aquifer. It is very highly-confined aquifer, not outcropped on the surface. The upper part consists of silt, weathered silty clay, is at a depth from 257.9 to 364.1m, and a thickness varying from 11.7 ÷ 24.1m; The lower part consists of compacted fine to coarse sand, is at 260.6 to 377.9m, having a thickness from 40.1 to 71.5m.
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Figure 31. Hydrogeological map of upper Miocene aquifer
Fresh groundwater distribute on areas of 7,612km2, located in Hochiminh, Dong Thap provinces (see Figure 31).
Upper- middle Miocene aquifer (n12-3)
Aquifer n12-3 is deepest confined aquifer in MD, overlain on the bed-rocks. There
are not many boreholes drilled through this aquifer (see figure 32). At the two boreholes HG1 and CL1, the depth to the top and bottom of the aquifer and the lithological components are as following: At boreholes HG1: From 508 to 602m, is an aquitard layer, consisting of clay and sandy silt. From 602 to 798m is an aquifer layer, consisting of compacted fine to medium sand At boreholes CL1: From 724,6 to 914m, is an aquitard layer, consisting of clay and silty clay. From 914 to 1000m, an aquifer layer, consisting of pebble and gravel.
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Figure 32. Hydrogeological map of upper – middle Miocene aquifer