Journal of Japan Society of Civil Engineers, Ser.
B1 (Hydraulic Engineering), Vol. 73, No. 4, I_109-I_114, 2017.

IMPACT OF UPSTREAM HYDROPOWER DAMS AND
CLIMATE CHANGE ON HYDRODYNAMICS OF
VIETNAMESE MEKONG DELTA
Sameh KANTOUSH1, Doan Van BINH2, Tetsuya SUMI3 and La Vinh TRUNG4
1 Member of JSCE, Dr. of Eng., Associate Professor, Water Resources Research Center, Disaster Prevention ResearchInstitute, Kyoto University (Goka-sho, Uji-shi, 611-0011, Japan)
E-mail:kantoush.samehahmed.2n@kyoto-u.ac.jp
2 Member of JSCE, Doctoral Student, Water Resources Research Center, Disaster Prevention Research Institute, Kyoto
University (Goka-sho, Uji-shi, 611-0011, Japan)
E-mail:binhdv@tlu.edu.vn
3 Member of JSCE, Dr. of Eng., Professor, Water Resources Research Center, Disaster Prevention Research Institute,
Kyoto University (Goka-sho, Uji-shi, 611-0011, Japan)
E-mail:sumi.tetsuya.2s@kyoto-u.ac.jp
4 Ph.D., Faculty of Civil Engineering, Thuyloi University-Second Base
(No.2, Truong Sa Street, Ward 17, Binh Thanh District, Ho Chi Minh City, Vietnam)
E-mail:trunglv@tlu.edu.vn

Between 2015 and 2016, Vietnamese Mekong Delta (VMD) has undergone the most severe drought
event over the last 90 years, causing damages to agriculture, aquaculture, and fresh water suply.
Moreover, upstream Mekong River development by constructing hydropower dams will magnify theseverity to the region. This research therefore aims at summarizing some damaged information causedby drought event 2015-2016 and analyzing the impacts of eleven proposed mainstream dams in
Thailand, Lao PDR, and Cambodia on hydrology of Vietnamese Mekong Delta under the effect of sea
level rise. Results show that the flow discharge is reduced by maximum 14.9% whereas the maximum
increase in water level exceeds 220%. This leads to more intrusion of saltwater into the delta andreduction of fine sediment and natural nutrients settling in floodplains.
Key Words : drought, sea level rise, saltwater intrusion, mainstream dams

1. INTRODUCTION
The Mekong River (MR), 4,880km long, ranks as
the 12th longest river worldwide 1). The Vietnamese
Mekong Delta (VMD) is located at the lowermostof MR and considered as the rice bowl of Vietnamese people2),3). The total area of VMD is 39,000
km2, stretching from Vietnam-Cambodia border,
several kilometers upstream of Tan Chau and Chau
Doc gauging stations, to the East Sea (Fig. 1). Tien
and Hau Rivers (names of Mekong and Bassac
Rivers in Vietnamese territory) are the two main
waterways in VMD, of 250 and 220km long respectively. The VMD has a highly complex channel
network with a total length of around 87,500km.
Annually, the Upper Mekong (UM) provides an

Fig. 1 Study area – Vietnamese Mekong Delta.
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350

5

300

3m

4

SSC (mg/l)

Water level (m)

6

3

2
1
0

-1
25-May

250 mg/l

200
150
100
50

04-Jul13-Aug22-Sep020-May01-Nov

Date
1998

250

2000

2011

2014

9-Jun

29-Jun19-Jul

Date

2015

2008

2011

2014

2015

2016

Fig. 3 Suspended sediment concentration at Vam Nao station.

Fig. 2 Measured water level during flood season at Tan Chau station.

8

abundant amount of fine sediment that settles
throughout the VMD through a dense network of
distributaries. The VMD is therefore one of the mostproductive agro-aquaculture and fisheries worlwilde3).
However, these plentiful resources are under threat
due to dam construction projects in the upper part of
the MR. Such impacts were reported by DHI and
HDR4) that reduction in discharges at Tan Chau andChau Doc are 1.9% and 2.5% respectively in between
January to May and 0.5% in June. At the basin scale,one hundred and thirty-three (133) hydropower dams
have been built or planned5), with six dams operating
already in China and eleven mainstream dams being
planned in Thailand, Lao PDR, and Cambodia4). Hydropower dams reduce the variability of water flow
and sediment budget in VMD because a proportion offlow and sediment is stored inside of reservoirs.
Moreover, fluctuation of water level is reduced because of the increasing dry season flow and decreasing
wet season flow. This induces detrimental impacts on
geomorphology features, nutrients, ecosystem, fishpassage and river connectivity in VMD6).

4 g/l

Salinity (g/l)

6

6 g/l

4
2
0
31-Jan11-Mar20-Apr30-May

Date

2005
2007
2014
2015
2016
Fig. 4 Salinity concentration at An Lac Tay station.

Under this project, suspended sediment and salinity
concentrations are continuously measured at several
locations in Tien and Hau Rivers since February
2016 (Fig. 1).
The drought event in 2015-2016 was accompanied
by saltwater intrusion in the VMD. Saltwater has
intruded 45-65km in Tien River and 55-60km in Hau
River, which is 20-25km further than seasonal average values. Salinity concentrations at An Lac Tay(located 50km from the East Sea – Fig. 1) in 2015
and 2016 are much higher than recorded values inprevious years (Fig. 4). The figure shows that salinity
concentration of 2016 is 6 g/l higher than that of2005 and 2007. Also, salinity intrusion began approximately two months earlier than average thatcauses serious damages to agriculture and livelihoods of people in the Delta. By the end of 2015,
about 159,000 hectare (ha) paddy fields were damaged; around 195,217 households with approximately 976,000 people lacked fresh water for daily
consumption.
It is obvious that drought will become extremely
serious in case more dams are built in the UM. Several questions arise therefore:(1) What would be the impacts of upstream development activities on flow and sediment budget in
the VMD?
(2) What would be the impacts of river dammingon the downstream ecosystem and agro-aquaculture
production during drought periods?

2. RECENT DROUGHT EVENT (2015-2016)
River-damming along with the effect of El Nino,
have induced the most severe drought over 90 years
in 2015-2016. All provinces in VMD have been
impacted by this drought event. The measured waterlevels were at their lowest values since 1926, evenmuch lower than those measured in the drought yearof 1998 (Fig. 2). The figure shows a reduction of 3m
by comparing water level on 22 of September 2000
and 2015. Correspondingly, sediment concentrationsin 2015 were lower compared to precedent years(one fourth of 2011) (Fig. 3). For these considerations, in the framework of JASTIP project7) (Japan-ASEAN Science, Technology and Innovation
Platform) we established a project to study the
impact of hydropower development in the UM onhydrology, sediment, and salinity changes in theLower Mekong (LM) with special focus on VMD.
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Table 1 Simulation scenarios.

Scenarios

Description of boundary condition

Baseline-Upstream: discharge hydrograph of 2015
- Downstream: water level stage of 2015

(Sc0)

RemarkWithout dam and without sea level rise

With dam and without sea level rise
Scenario 1 -Upstream: discharge hydrograph of 2015, - Jan. – May : -1.9% at TanChau and -2.5% at ChauDoc4)
considering 11 proposed dams
- Jun.
: -0.5% at both TanChau and ChauDoc4)(Sc1)-Downstream: water level stage of 2015
With dam and with sea level rise
-Upstream: discharge hydrograph of 2015, -Jan. – May : -1.9% at TanChau and -2.5% at ChauDoc4)Scenario 2
considering 11 proposed dams
- Jun.
: -0.5% at both TanChau and ChauDoc4)(Sc2)-Downstream: water level stage of 2015, -Water level of 2015 + 47cm (high emission scenario considering sea level rise 47 cm
A1FI – increasing 5.5mm/year8))(3) What happens if such impacts take place under
sea level rise induced by global climate warming?
To date, there have been a few studies evaluating
the impacts of hydropower dams and sea level rise on
sediment dynamics3), hydrological change4) andflooding9) and even less studies pay attention on
drought in VMD. Therefore, the present work addresses the expected effects of eleven planned upstream dams on the hydrology of VMD under theeffect of sea level rise. To do this, a one-dimensional
numerical model is used. The dry season of 2015
(from January to June) is considered as the reference
event.

year 2015. Scenario 1 (Sc1) considers the impact of 11
dams. In scenario 1, discharges at Tan Chau and Chau
Doc are reduced by 1.9% and 2.5%4), respectively, inbetween January and May and by 0.5% in June4)compared to the baseline (Table 1), but water levels
remain unchanged. Scenario 2 (Sc2) is similar to Sc1
but sea level rise is considered at the downstream ends.
Untitled
Tien River
1200000
Hau River
1150000

1100000

3. MODEL SETUP AND SCENARIOSThe prediction of hydrology changes in the VMD
under the development of 11 dams along with sea
level rise is performed using Mike 11 hydrodynamic
model developed by DHI10). The model solves the
1-D Saint Venant equations using an implicit finite
difference scheme. The model was set up for thewhole VMD, including 2,551 branches with 13,429
points as in Fig. 5. In the model, hourly discharges at
Tan Chau and Chau Doc stations are used as upstream boundaries whereas hourly water levels atseven stations along the coast, including My Thanh,
Ben Trai, Vam Kenh, Ganh Hao, Song Doc, Binh
Dai, and Rach Gia are prescribed as downstream
boundary conditions. One hundred and fourty-five(145) cross sections describing the geometry of Tien
River from Tan Chau to My Thuan (see Fig. 1) are
updated to 2014 whereas cross sections measured in2010 are applied elswhere.
Three scenarios are used to simulate changes ofhydrology in VMD (Table 1). The baseline (Sc0)refers to discharges and water levels of the drought

West Sea
East Sea

1050000

Modeled channel network

1000000

Upstream boundary stations
Downstream boundary stations
Stations for model validation

950000500000600000700000Fig. 5 1-D hydrodynamic model setup.
Table 2 Values of two performance indicators at three stations.

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Station

VamNaoMyThuan

CanThoCalibration (2015)
R2

0.913

0.936

0.978

Ef

0.807

0.862

0.913

Validation (1998)
2

R

0.877

0.97

0.95

Ef

0.727

0.912

0.890

Table 3 Average discharge reduction and water level increase within the simulated period (Jan. – Jun.) in VMD under different
simulation scenarios at eight measurement stations.

Station

TanChau VamNao MyThuan MyTho ChauDoc LongXuyen CanTho DaiNgai
Discharge reduction (m3/s)
-63.8
-31.6
-27.0
-9.6
-13.8
-50.6
-50.0
-17.1
(Sc1-Sc0)
-1.7
-2.2
-1.2
-0.5
-2.1
-2.8
-2.9
-3.6
P (%)
-63.8
-24.1
-34.8
-16.3
-13.8
-213.8-260.2-22.2(Sc2-Sc0)
-1.7
-1.0
-2.8
-2.7
-2.1
-11.6
-14.9
-4.6
P (%)
Water level increase (cm)
0.423
0.436
0.456
0.467
0.436
0.452
0.458
0.467
(Sc2-Sc0)
94.6
127.1
75.5
221.2
139.2
172.6
162
25.7
P (%)

According to Doyle et al. (2010) 8), sea level increases by 5.5 mm/year under high emission scenario.Therefore, water levels of scenario 2 are thoseof 2015 increased by 47 cm as the total increase inwater level up to the year 2100.

baseline (Sc0); AScx_i, ASc0_i: discharge or water levelof scenario x and the baseline, respectively, at day ith;
P(%): the difference of discharge or water level
between scenarios and the baseline in percentage; N:
number of days within Jan. – Jun. If (Scx-Sc0) (or
P(%)) is possitive, discharge or water level will
increase, vice versa they will decrease.
Under the reduction of discharges at Tan Chau andChau Doc (Sc1), flow discharges at stations VamNao, My Thuan and My Tho in Tien River and at
Long Xuyen, Can Tho, and Dai Ngai in Hau Riverare reduced by 0.5 to 3.6% in average (Table 3). In
Tien River, the maximum reduction of discharge is
obtained at Tan Chau station with a mean value of
63.8 m3/s, while in Hau River it is Long Xuyen stationthat experiences the maximum reduction (50.6 m3/s).
More seriously, discharges in VMD are even more
reduced in Sc2 which further considers the influenceof sea level rise. For example, mean discharge at Can
Tho station drops by 260 m3/s, corresponding to
14.9% - the maximum reduction among stations (Table 3). In contrast, water levels at all stations in VMD
are increased, a clear example from My Tho station isshown in Fig. 8. Water levels in stations near the sea
increase faster than those in upstream sections (Table
3). Among these, water levels at My Tho station
increase the most with over 220% (Fig. 8).

4. MODEL VALIDATION AND RESULTS
Water levels at Vam Nao and My Thuan stations inTien River and Can Tho station in Hau River (see Fig.
1) of the year 2015 are used to calibrate the model.
The model is validated using water levels measured at
the same stations during the drought year 1998.
Computed versus measured water levels at Can Tho
station are plotted in Fig. 6. The accuracy of the numerical results is evaluated using correlation coefficient (R2) and Nash-sutcliffe coefficient (Ef) (Table 2).
Based on these performance indicators, one can seethat a satisfactory model-data agreement is obtained.
Hydrological parameters of VMD are directly
affected by changes in the upstream discharges at
Tan Chau and Chau Doc and downstream waterlevels along the coast. Table 3 shows the reduction in
average simulated discharges and the increase inaverage simulated water levels within the studied
period (Jan. – Jun.) under different scenarios.
Moreover, Fig. 7 shows a comparison between the
difference in Sc1 and Sc2. The difference between
scenarios is calculated as follow in equations 1 and 2:

( A( Scx  Sc0)  i 1NP(%) [( AScx _ iScx _ i

 ASc0 _ i )NWater level (m)

N

1

(1)

 ASc0 _ i ) / ASc0 _ i .100]( 2)
N
where: (Scx-Sc0): the difference of discharges orwater levels in absolute values between scenario x(x=1: scenario 1 and x=2: scenario 2) and the
i 1

0.5

0
-0.5

-1
-1.5

13/4/1998

17/4/1998

21/4/1998

Time
Simulated

MeasuredFig. 6 Predicted and measured water levels at Can Tho station.
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15-02-15

06-04-15

26-05-15

Mean annual discharge (m3/s)

Daily discharge (m 3/s)

400
200
0
-200
-400
-600
-800
-1000
27-12-14

15-07-15

Time
Sc1-Sc0

14000
12000

10000
8000
6000
4000
2000

Sc2-Sc0

Water level (m)1995 1997 1999 2001 2003 2005 2007 2009 2011 2013 2015

Year

Fig. 9 Mean discharge at Tan Chau station.

Fig. 7 Discharge reduction of scenario 1 and 2 compared to thebaseline in solid and dash lines at Long Xuyen station.
1.2
1
0.8
0.6
0.4
0.2
0
-0.2
-0.4
27-12-14

0

Ditch

Mangros
25-02-15

26-04-15

25-06-15

Weeds

Time

Scenario 0
Scenario 2
Fig. 8 Increase in water level of scenario 2 compared to thebaseline at My Tho station.

Fig. 10 Damaged fruit-garden in Ke Sach district – Soc Trangprovince. Died mangosteen was replaced by new mango.

Low discharge observed at the upper of VMD
during the drought event of 2015-2016 caused
saltwater intruding deeply into lands, thereby resulting in detrimental impacts on agriculture andaquaculture. The drought of 2015-2016 has led tototal damages of 31,198.94 ha (approximately 2.2
million US dollars) in only Soc Trang province.
Many regions, where paddy fields with 27,004.16
ha were affected, have reduced their agricultural
productivity (Fig. 10).
As predicted by scenario 2, flow discharges aremuch reduced and water levels are increased in
VMD (Table 3). Discharges at Can Tho station decrease the most with 14.9% while My Tho station
faces an increase of more than 220% in water level.
This causes saltwater significantly to intrude into theupper parts. It means that more areas, including regions having not been affected before, will be covered by saline water with higher concentration.
Sea level rise may also increase flooding incoastal regions of VMD9). Furthermore, because of
decreasing discharges and increasing water levels,
flow velocity will be reduced in the channels. Nutrient-rich sediment will deposit preferentially inrivers instead of conveying into floodplains that
may lead to a reduction of agricultural productivity
in a near future.

5. DISCUSSIONS
Because of the geographical location, hydrology
of VMD is strongly dependent on activities of upstream countries such as dam construction and irrigation development. To date, China has completed
six dams of the Lancang cascade in the Upper Mekong Basin (UMB), in which Manwan was fully
operated in 1996 and Nuozhadu in 201211). Consequently, VMD has undergone a decreased trend inflow discharge (Fig. 9). Obviously, Chinese dams
must be the cause of water decrease in VMD. Moreseriously, two drought events happened just after the
first and the last dams, in 1998 and 2015.
Recently, there are other eleven dams proposedby Thailand, Lao PDR, and Cambodia in themainstream of MR. Results from scenario 1 showthat these eleven dams will cause flow discharge
declining in VMD from 0.5 to 3.6%. The Hau River
experiences higher reduction than Tien River.
Moreover, the further the areas from Vietnam-Cambodia border is, the more the reductionin flow discharges will be. Importantly, these proposed dams together with existed ones in China
may lead to the disappearance of floods in the upperparts VMD, which is extremely crucial to livelihoods of millions of people there.
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The impacts of upstream hydropower dams andclimate change on hydrology of VMD figured out inthis paper is the first-hand results based on 1-D
simulation analysis. Two dimensional numericalsimulations will be implemented to evaluate theimpacts of these drivers on both flow regime andsediment dynamics of VMD.

6. CONCLUSIONS AND RECOMMENDATIONS
Many areas in VMD have been impacted by drought
event in 2015-2016. Low discharge entering from the
upstream end resulted in the shortage of fresh watersupply for irrigation. Saltwater has intruded up to 65km
and 60km in Tien and Hau Rivers, respectively, which
is about 20-25km deeper in land than average. These
have caused damages to thousands of hectares of agriculture and aquaculture, corresponding to dozens of
millions of US dollars. Also, livelihoods of thousandsof people were endangered by lacking of fresh water fordaily consumption.
The situation of drought will become more serious
if eleven proposed mainstream dams in Thailand,
Lao PDR, and Cambodia are constructed. This paper
shows that VMD will experience a maximum reduction of flow discharge of 3.6%. More dangerously, discharge will be reduced up to a maximum
value of 14.9% while maximum water level increase
will be more than 220% under the combined effect of
47cm sea level rise and 11 mainstream dams. These
allows saltwater significantly intruding into the upper parts of the Delta, even in areas having not been
affected before, with higher salinity concentration.
The research also predicts that flooding in coastal
regions will frequently occur if sea level continues
rising. In addition, rice crops are foreseen to lack finesediment carrying abundant natural nutrients becauseof reduced exchange between rivers and floodplains.
In general, increase of salinity intrusion andcoastal flooding, disappearance of flooding in upper
VMD, and lacking of fine sediment and natural nutrients to floodplains as a result of upstream dam
development and sea level rise will have tremendously negative effects on agriculture, aquaculture,irrigation and fishery. Finally, livelihoods of millions
of people in VMD will be severely affected.
The authors recommend alternative design types toinvestors of these eleven proposed mainstream damsin Thailand, Lao PDR, and Cambodia to modify themas run-of-the-river hydropower plants. For new proposed dams in the mainstream as well as in the tributaries, the design should take into account their negative impacts on the downstream countries in order tohave an integrated utilization of limited fresh water intransboundary Mekong River. Furthermore, local
governments in the impacted areas by salinity intrusion should temporarily change the purpose of land
use from freshwater agriculture to saltwater aquaculture if it can improve livelihoods of local people. Finally, it is necessary to urgently develop an early
warning system of drought and salinity intrusion to
help people actively deal with such hazards.

ACKNOWLEDGEMENT: This research is fundedby JASTIP. The authors thank Mr. Vinh (Department ofAgriculture and Rural Development of Soc Trang province) for his kindly help in site visits and data sharing. We
also acknowledge Dr. Kamal El Kadi of EDF for his
reading and discussions about numerical simulations.

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(Received September 30, 2016)6I_114