UNESCO-JASTIP Joint Symposium on Intra-Regional Water Security and Disaster Management

EVALUATION ON THE IMPACTS OF UPSTREAM DAM
DEVELOPMENT ON SALINITY INTRUSION INTO
VIETNAMESE MEKONG DELTA
TRUNG LA1, MAI NGUYEN2, SAMEH KANTOUSH3, TETSUYA SUMI3, BINH DOAN3

1Research Management Department, Vietnamese-German University
2Faculty of Civil Engineering, Thuyloi University, Southern Campus
3Water Resources Research Center, Disaster Prevention Research Institute, Kyoto University

Manila, 15 – 16 November, 20171UNESCO-JASTIP Joint Symposium on Intra-Regional Water Security and Disaster ManagementCONTENT1.
2.
3.
4.

• Background of the project• Objectives of the study• Results and discussion• Conclusions and recommendation2

1. Background of the project
MEKONG RIVER BASIN
Upper Mekong• 24% of total area

Length: 4,880 km
Annual suspended sediment: 160
Mt/yearLower Mekong• 76% of total area

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MAINSTREAM AND TRIBUTARY DAMS

Upper Mekong: 21 dams

There are many plans for dam
construction along Mekong River andits tributaries

Lower Mekong: 136 dams

+ 31: under construction+ 82: completed within 20 years+ 136: completed within 40 years

Keskinen et al., 20124

THE OVERALL OBJECTIVES OF THE PROJECT
Evaluate the impacts of upstream dams on sediment flux
along main rivers in Vietnamese Mekong Delta

Sediment
reduction

Correlate the erosion rate of Mekong and Bassac riverbankswith the development of upstream dams
Evaluate the combined influence of upstream dams and dyke
system on lateral flow and sediment interchange between
rivers and floodplains
Evaluate the impacts of upstream dams on salinity intrusion
into Vietnamese Mekong Delta

Salinity Intrusion

Evaluate the effectiveness of the operation of existing
irrigation system in preventing salinity intrusion
Propose the appropriate change of agricultural, aqua-cultural
structure for the whole VMD for adaptation
5Turbidity meter
Salinity meter

Map of the installed equipment
Tan Chau

Vam Nao

Thot Not

An Lac Tay
Bac Trang

Dinh An6

2. Specific objectives of the study

1. To assess the current status of thedrought and salinity intrusion in2016
2. To determine the correlation
between the discharge to thedelta and salinity concentration atsome monitoring stations
3. To elucidate the impact of damoperation
onsalinity
concentrationandintrusion
length by numerical simulations
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3. Results and discussions
3.1. The extreme salinity condition in 2016

• The salinity in 2016 is extremely high.
• The maximum salinity concentration (Smax) in Jan
almost equals to the peaks of other years• The peak in 2016 shifts from Mar or Apr to Feb

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3.2. Change of flow and salinity concentration in the post-cascade dam period• The flood flow recorded at Kratie station decreases significantly in the period
2009-2011 and 2012-2016. It is due to the appearance of the 2 large reservoirs,Xiaowan (2010 – 14.56x109m3) and Nuozhadu (2014 – 23.7x109m3)• The active volume of the 2 reservoirs accounts for 12.2% of annual meandischarge in many years, from 1990 to 2009.

93.2. Change of flow and salinity concentration in the post-cascade dam period• In the dry season, the total active storage capacity of two Xiaowan andNuozhadu dams accounts for 22.2x109m3, about 25% of the average total dryflow (Nov - May) at Kratie station.

• The dam operation strongly affects on water releasing downstream and so assalinity intrusion in Vietnamese Mekong Delta• The dry flow increases slightly in the middle of dry season10

3.2. Change of flow and salinity concentration in the post-cascade dam period

Correlation between discharge to the VMD and max salinity concentration in Jan and Feb, 201611

3.3. Numerical simulation

Comparison of observed and simulated discharge at
Chau Doc station

Comparison of observed and simulated salinity
concentration at Dai Ngai station
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No.

Scenario

Smax in DaiNgai (g/l)

1Baseline (Sc0)13.82Sc1

7.4

Smax in Tra
Vinh (g/l)

Salinity intrusion length
From Tran
De estuary(km)From Co
Chienestuary (km)

12.7

57

54

8.3

4147

No.

Scenario

Baseline(Sc0)

Real condition ofdry season in 2016

Sc1

Dam operation 1
month earlier

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4. Conclusions and recommendation• The flood flow gets decreasing gradually but becomes considerable in the periodof 2009-2011 and 2012-2015 due to the 2 largest dams completion and water
storing process.
• The dry flow increases slightly in the mid-dry season. It should be due the dam
operation for electric generation.
• The dam operation strongly affects on water releasing downstream and so as
salinity intrusion in Vietnamese Mekong Delta• The salinity intrusion tends to start and reach the peak sooner than previous years• Information about dam operation and hydrological/meteorological data upstream
should be transparent sharing for preparedness downstream, especially in thecontext of climate change and sea level rise.

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