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Greater Mekong Forum on Water, Food and Energy:
Phnom Penh, Cambodia,
21 October 2015
Study of the Impacts of Mainstream Hydropower on the Mekong Delta
Modelling
Study of the Impacts of Mainstream Hydropower on the Mekong River
Outline• Model Configuration
• Modelling of flows
– No operation
– Peak-hour operation
– Dam Break
• Saline Intrusion
• Sediment Transport
– Trapping of silt
– Flood plain sedimentation
• Water Quality
• Coastal sediments
• Summary
Study of the Impacts of Mainstream Hydropower on the Mekong River
Model Configuration
SWAT/MIKE Basin provide inflow of water,
sediment, nutrients to mainstream Mekong
River.
MIKE11 modelling mainstream Mekong River
and Delta flows, water levels, sediment
transport, morphology and salinity intrusion.
MIKE21C modelling reservoirs, operation,
hydraulics, sediment and morphology.
MIKE21 modelling coastal hydraulics.
EcoLab based on MIKE11 modelling nutrient
transport.
Model Configuration
MIKE11
MIKE 21
MIKE11
MIKE21C
SWAT/MIKE
Basin
Study of the Impacts of Mainstream Hydropower on the Mekong River
MIKE11 model setup - Delta
Delta Model setup
� Upstream model: Data for set-up of
MIKE 11 from Chiang Sean to Kratie
provided by MRCS.
� Downstream (delta) model: SIWRP, high
resolution and well proven,
supplemented with new bathymetric
information;
� Cambodia floodplain model: From JICA
WUP study by DHI. Well calibrated and
used extensively to study the flow in
the Mekong River and Tonle Sap Lake.
Detail updates from SIWRP setup.
Study of the Impacts of Mainstream Hydropower on the Mekong River
Storage characteristics of the planned 11 reservoirs
compared with the Mean Annual Flow
Project
Full Supply Level
Lowest Supply Level
Active Volume
Inactive Volume
Mean Annual Flow
Mean Active
Storage Time
Operation
m m Mil. m3 Mil. m3 Mil. m3/y Days
Pakbeng 345.0 340’0 442.4 1.295.0 96,500 1.67 Daily
Luangprabang 310.0 300.0 734.0 1.311.7 100,000 2.63 Daily
Xayabuly 275.0 270.0 738.1 678.3 124,800 2.16 Daily
Paklay 240.0 235.0 383,5 967.8 130,700 1.07 Daily
Sanakham 215.0 210.0 206.1 61.7 133,800 0.56 Daily
Pakchom 192.0 190.0 440.9 656.0 141,600 1.14 Daily
Ban Kum 115.0 110.0 651,5 1.458.5 294,600 0.81 Daily
Latsua 97.5 90.0 550.0 1.000.0 294,600 0.68 Daily
Don Sahong 75.1 71.0 115.0 476.0 325,100 0.13 Daily
Stung Treng 52.0 51.0 150.8 518.0 405,800 0.14 Daily
Sambor 40.0 38.0 1,450.0 4,001.1 432,500 0.98 Daily
Study of the Impacts of Mainstream Hydropower on the Mekong River
Longitudinal water surface profile.
MIKE11 Mainstream – With Reservoirs
Study of the Impacts of Mainstream Hydropower on the Mekong River
Mainstream M11: Discharge Kratie - Without - With
Dams 1985-2008 - Full Supply Level Operation
(Max Power Production over 24 hours)
Study of the Impacts of Mainstream Hydropower on the Mekong River
Dam Operation: Daily operation of power production
for 8 hours during the daytime and 16 hours filling
until next morning
(Max Power Production over 24 hours)
Study of the Impacts of Mainstream Hydropower on the Mekong River
Mainstream M11: Water Level at Kratie - Without
and With Dams operated 24 hours 2007 Baseline
(Max Power Production over 24 hours)
Study of the Impacts of Mainstream Hydropower on the Mekong River
Indicator: Areas of changes in water level
between Baseline and Scenario 1 - 2007
The expected impacts from
the 11 Mainstream Dams on
water levels in the
Vietnamese part of the
Delta are relatively small, on
average less than 2 cm.
Study of the Impacts of Mainstream Hydropower on the Mekong River
Dam Break – Major focus on Sambor.
Reservoir Information
Dam Type Earth Rock Dam
Dam length 18000m
Dam height 56m
Full Supply level 40m
Checked Flood level 40.6m
Dead Level 38m
Crest Level 45m
Design Flood Discharge – PMF (1000 Yrs.) 80400 m3/s
Checked Flood Discharge (10000 Yrs.) 88300 m3/s
Total Storage 5206 mcm
Study of the Impacts of Mainstream Hydropower on the Mekong River
Dam Break – Peak Discharges - Sambor.
Scenario Peak Discharge (m3/s)
Overtoppi
ng - 2000
flood
Overtoppi
ng -
Climate
change
Piping –
2000
flood
Piping –
Climate
change
S1 BFT=1hr,
BW=167m
127107 139788 - -
S2 BFT=10hr,
BW=406m
- - 113569 121240
S3 BFT=13hr,
BW=473m
- - 110058 117813
S4 BFT=13hr,
BW=676m
189879 195798 - -
S5 BFT=18hr,
BW=861m
180616 186927 - -
Highest
calculated
discharge from
Dam Break at
Sambor is
195,798 m3/s
Study of the Impacts of Mainstream Hydropower on the Mekong River
Dam Break – Flooding in Vietnamese Delta.
The Dam Break flood peak at
Sambor is about 8 m. At
Phnom Penh around 0.6 m.
In the Delta below 0.4 m.
Study of the Impacts of Mainstream Hydropower on the Mekong River
Salinity – Baseline CalibrationSalinity baseline model
calibrated against
measurements in the Delta.
y = 0.9636x
R² = 0.9512
0
5
10
15
20
25
30
35
0 10 20 30 40
Simula
ted
Observed
Salinity 2008
Series1
Linear (Series1)
Study of the Impacts of Mainstream Hydropower on the Mekong River
Scenario 1 – Changes in Salinity Intrusion
Changes in salinity
levels (g/l) are
relatively small in
the Delta, around
or below 1 g/l for
2007 with daily
dam operation.
Study of the Impacts of Mainstream Hydropower on the Mekong River
Sediment Transport
• Bed material load 10-20 %
• Wash load 80-90 %
Bed material load is the portion of the
sediment that contains material derived from
the river bed. Bed material load typically
consists of all of the bed load, and the
proportion of the suspended load that is
represented in the bed sediments. The
importance of bed material load is that its
composition is that of the bed, and the
material in transport can therefore be actively
interchanged with the bed. For this reason,
bed material load exerts a control on river
channel morphology.
Wash load (in contrast) is the material that is
not present in the river bed. It is carried in
suspension without interaction with the river
bed and thus has negligible influence on the
river channel morphology.
Study of the Impacts of Mainstream Hydropower on the Mekong River
Sediment Transport – Baseline
Study of the Impacts of Mainstream Hydropower on the Mekong River
Sediment Transport – Baseline
In consistency with the Baseline Mainstream
Hydrological Model covering the period up to
and including 2008, the hydropower
development up to 2008 is included in the
Baseline. A total of 30 hydropower schemes
in tributaries to the Lower Mekong
Mainstream are included in the Baseline
Study of the Impacts of Mainstream Hydropower on the Mekong River
Baseline: Sediment Concentration
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
Se
dim
en
t co
nce
ntr
ati
on
(g
/l)
Simulated
C Rating Curve
Assumptions:• Rating curve based on DSMP data from 2011
• Simulated concetration = Clays + Silt + Fine Sand
Kratie:
Study of the Impacts of Mainstream Hydropower on the Mekong River
Sediment Transport – Scenarios 1
Pak BengLuang Prabang
Xayabuly Paklay
SanaKham
SangThong_Pakchong
Bankum
LatSua StungTrengSambor
0
10
20
30
40
50
60
70
80
,0 200000,0 400000,0 600000,0 800000,0 1000000,0 1200000,0 1400000,0 1600000,0 1800000,0 2000000,0
Mil
l To
ns/
ye
ar
Scenario 1 - Cumulative
Deposition Silt
Scenario 1 - Transport Silt
Baseline Transport Silt
Baseline Transpoirt Clay
Study of the Impacts of Mainstream Hydropower on the Mekong River
Sediment Modelling
Flood Plain Sedimentation (Silt and Clay downstream Kratie):
Study of the Impacts of Mainstream Hydropower on the Mekong River
Model Approach & Parameters
Shields Curve
• Two fractions - silt and clay
• Silt constitutes 60% of TSS at Kratie
and clay 20%
• Silt constitutes 45 % of TSS at Tan
Chau and clay 55%
• Floodplain sedimentation
information and model parameter
from articles: N.V.Manh et.al 2013,
2014, 2015
• Results presented for baseline year
(2007)
Study of the Impacts of Mainstream Hydropower on the Mekong River
Sediment Transport – Sediments measured and
simulated 2009 and 2011 Chau Doc – Tan Chau
cenarios With Dams
With all 11 planned reservoirs in operation (Scenario GA.1) the annual load to the
Delta reduces by approximately 86%. In Scenario GA.3 the reduction is about 15%
Study of the Impacts of Mainstream Hydropower on the Mekong River
Silt Concentration
Scenario Total silt and clay transport (million tons/ per year)
2007 2008
KratieTân Châu + Châu
ĐốcKratie
Tân Châu + Châu
Đốc
Baseline 52.63 32.06 68.81 42.31
Scenario 1 (11
dams)22.41 13.88 24.98 15.30
Study of the Impacts of Mainstream Hydropower on the Mekong River
Tonle Sap - Clay Deposition – Baseline & Scenario 1_2007-08
Baseline
Scenario 1
Study of the Impacts of Mainstream Hydropower on the Mekong River
Nutrients - Baseline
Conceptual
outline of nutrient
model – Example
Phosphorus.
The Nitrogen
model is similar,
however with 2 in-
organic state
variables, nitrogen
and ammonium/
ammonia
Study of the Impacts of Mainstream Hydropower on the Mekong River
Nutrients – Baseline – Model calibration
The phosphorus
and nitrogen
models have been
calibrated against
the sediment and
nutrient survey
obtained for 2014
as part of the
MDS Additional
studies providing
unique insight into
the sediment and
nutrient relations
in the Mekong.
Study of the Impacts of Mainstream Hydropower on the Mekong River
Scenario 1 – Changes in Annual N-deposition
Deposition of
sediments and
their contents of
nutrients.
gN/m2/year
Study of the Impacts of Mainstream Hydropower on the Mekong River
Nutrient Indicator: Transport to the Delta
Annual sediment deposition distribution in the
Vietnamese part of the Mekong Delta. Scenarios
GA.1, GA.3, GA.4 and GA.8.b
GA.3
GA.4 GA.8
Nutrient (Attached to Silt & Clay)
(1000 tons/ per year - 2007)
Kratie Tân Châu + Châu Đốc
Phosphorus (P)
Baseline 19.1 11.6
Scenario 1 (11 dams) 10.1 6.3
Nitrogen (N)
Baseline 48.7 29.6
Scenario 1 (11 dams) 21.2 12.9
Potassium (K)
Baseline 290.0 176.1
Scenario 1 (11 dams) 123.4 75.0
Study of the Impacts of Mainstream Hydropower on the Mekong River
2D/1D Coastal models overview
Study of the Impacts of Mainstream Hydropower on the Mekong River
Sediment plume: Annual average (silt)
Baseline
Scenario 1
Change
Study of the Impacts of Mainstream Hydropower on the Mekong River
Summary• Model Configuration
• Modelling of flows
– No operation
– Peak-hour operation
– Dam Break
• Saline Intrusion
• Sediment Transport
– Trapping of silt
– Flood plain sedimentation
• Water Quality
• Coastal sediments
• Summary
• Flows: Relative modest impact
except immediately d/s dams and in
case of dam break
• Saline intrusion: Some impact
depending on operation
• Sediment Transport: Significant
impact in particular for silt (lower
concentration and reduced flood
plain sedimentation
• Water Quality: Significant reduction
of nutrients
• Coastal sediments: Reduced
sediment concentration mainly in
the vicinity of estuary areas.