Appendix A-5
DSF Demonstration Scenario No.5:
China Dams
Mekong River Commission - Water Utilisation Project Component A:
Development of Basin Modelling Package and Knowledge Base (WUP-A)
Technical Reference Report:: DSF 650 DSF Testing and Evaluation
Contents
5
Demonstration Scenario 5: Impact of Proposed China Dams
5.1 Scenario Objective
5.2 Specification of Scenarios in the DSF
5.2.1 Climate Component
5.2.2 System Demand Component
5.2.3 Assumed Interventions Component
5.3 Model Setup
5.3.1 SWAT Models
5.3.2 IQQM Model
5.3.3 iSIS Model
5.4 Demonstration Scenario 3: Impact of China Dams – Test Results: Primary Level
5.5 Scenario 5: China Dams – Test Results: Secondary Level
5.5.1 Test 1: Acceptable Minimum Monthly Dry Season Flow
5.5.2 Test 2: Acceptable Reverse flow of Tonle Sap in Wet Season
5.5.3 Test 3: Average Daily Peak Main Stream Flow in the Flood Season
5.5.4 Test 4: Extent and Duration of Flooding
5.5.5 Test 5: Extent and Duration of Saline Intrusion
5.5.6 Test 6: Irrigated agriculture performance
5.5.7 Test 7: Degree of Connection for Fisheries Purposes
5.5.8 Impacts on flows in the tidal areas
5.6 Conclusions and Recommendations
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A.5-ii
5
5
5
5
5
6
6
6
6
8
9
11
11
19
21
23
26
27
27
27
30
Mekong River Commission - Water Utilisation Project Component A:
Development of Basin Modelling Package and Knowledge Base (WUP-A)
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Figures
Figure A 5-1:
China Dams verses Baseline Scenario flows at Vientiane (1997 – 2000)
11
Figure A 5-2:
China Dams verses Baseline Scenario flows at Kratie (1997 – 2000)
12
Figure A 5-3:
Dry season flow duration curves for Vientiane and Kratie (dry season; 1 Dec –
31 May data period; 1 Dec 1985 – 31 Dec 2000)
16
Figure A 5-4:
Percentile flow distribution of 90 %, 50% and 10% at Vientiane with
comparisons to Baseline conditions for 50% and 10% (dotted lines) – truncated
vertical axis
16
Figure A 5-5:
Percentile flow distribution of 90 %, 50% and 10% at Kratie with comparisons
to Baseline conditions (dotted lines)
17
Figure A 5-6:
Percentile flow distribution of 90 %, 50% and 10% at Kratie with comparisons
to Baseline conditions (dotted lines) – truncated vertical axis
17
Figure A 5-7:
Annual flood frequency at Kratie
Figure A 5-8:
Daily flows showing high flows for Vientiane and Kratie (Feb 1985 – Dec 2000)
21
Figure A 5-9
Map showing the difference in inundated area downstream Kratie for peak flood
conditions in year 2000 (Baseline Conditions verses China Dams)
24
Figure A 5-10
Map showing the difference in the depth-duration >0.5 m for year 2000
(Baseline Conditions verses China Dams)
20
25
Figure A 5-11: Map of maximum inundated area in the year 2000 for the China Dams Scenario
26
Figure A 3-11
Comparison of flows at Chau Doc for year 2000 (Baseline Conditions versus
China dams scenario)
27
Figure A 3-12
Comparison of flows at Tan Chau for year 2000 (Baseline Conditions versus
China dams scenario)
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A.5-iii
27
Mekong River Commission - Water Utilisation Project Component A:
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Technical Reference Report:: DSF 650 DSF Testing and Evaluation
Figure A 3-13
Comparison of flows at Phnom Penh (Mekong) for year 2000 (Baseline
Conditions versus China dams scenario)
28
Tables
Table A 5-1:
Between scenario comparison of annual minimum daily flows (cumec) over 15
years (1986 – 2000) .........................................................................................................13
Table A 5-2:
Mean daily dry season flow for each month of the dry season ...............................14
Table A 5-3:
Mean start and end of the dry season based on the Baseline Scenario’s median
annual flow (Oct 1985 – Dec 2000) .............................................................................17
Table A 5-4:
Duration of Stable Flow Conditions relative to the Baseline Scenario (days) (Oct
1985 – Dec 2000) ............................................................................................................19
Table A 5-5:
Mean annual peak daily flow at Kratie.........................................................................20
Table A 5-6:
Comparison of Highest and Average Annual Peak Daily Flows ............................22
Table A 5-7:
Comparison of flood return periods for mainstream monitoring sites ..................23
Table A 5-8:
Maximum inundation areas by depth class in the year 2000 ....................................25
Table A 5-9:
Maximum dry-season salinity intrusion areas .............................................................26
Table A 3-12:
Impacts of China dams scenario on flows and water levels at Chau Doc, Tan
Chau and Phnom Penh (Mekong) for year 2000 .......................................................29
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A.5-iv
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5
Mekong River Commission - Water Utilisation Project Component A:
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Technical Reference Report:: DSF 650 DSF Testing and Evaluation
Demonstration Scenario 5: Impact of Proposed
China Dams
5.1
Scenario Objective
This demonstration scenario represents the impact of an additional large dam in
the Yunnan Province of the People’s Republic of China; based on the bigger of
those proposed or under construction, i.e. Nuozhadu. The purpose of both these
dams is hydro-power generation. It is believed that at least one dam is currently
under construction.
The impact of these dams will be additional to the two existing dams on the mainstem of the Mekong River in Yunnan. Of concern is the potential increase in dry
season flows, decrease in peak wet season flows and a delay in the on-set of the
wet season. The scale these impacts will be a function of the dams’ active storage
capacity relative to the annual flow.
5.2
Specification of Scenarios in the DSF
5.2.1
Climate Component
Climate conditions prevailing for the Demonstration Scenario 1: Baseline
Conditions were utilised also for this demonstration scenario. Consequently, no
changes were required to the evapo-transpiration, precipitation or temperature
parameters or model configuration.
5.2.2
System Demand Component
The new Chinese hydro-power dams effectively introduced an instream demand,
simulated through the operational release rules for those dams. These release rules
are included in the new dam nodes in the extended IQQM model. Apart from
location, the only known parameter of the proposed dams was their proposed
maximum storage volumes. Hence all other parameters were simplified
assumptions, including the release rates for power production and during times of
spillway flow.
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Consumptive water demands within the LMB were not altered from Baseline
Conditions for any water use sector, i.e. irrigation, urban or industrial. This allows
the potential positive and negative impacts of the new Chinese dams to be
quantified at all reporting sites without complication by various changes in use due
to altered water availability.
5.2.3
Assumed Interventions Component
Little is known of the structural and operational parameters of the eight proposed
dams in Yunnan Province PDR of China. Two of these dams are either under
construction, or are imminent. Apart from their approximate total capacity and
approximate location, no other information was known, hence a number of
assumptions were made with respect to turbine and spillway release rates, active
storage, etc.
Consequently, only one dam was introduced to represent these two possible dams.
It is based on the bigger of the two, i.e. Nuozhadu Dam.
5.3
Model Setup
5.3.1
SWAT Models
Model Configuration
No changes were required to the configuration of SWAT models
Model Input Variables
No changes were required to the variables used in the Baseline Conditions.
5.3.2
IQQM Model
Model Configuration
The Baseline scenario IQQM model did not include representation of the existing
dams in China due to lack of data on those dams. Given the minimal available
data on the storage or operational parameters, of both the existing dams and
proposed dams (modelled as one), some major simplifications were made in
simulating the two new dams.
106727594
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First it was noted that the two new dams are both upstream of the existing dams.
Therefore to properly simulate the new dams, the existing dams should also be
modelled. However, with the limited data and time, it was decided that this type of
scenario could be adequately demonstrated by assuming that both new dams were
downstream of the existing dams. This allowed the existing China inflow data at
the upper end of the LMB to be used as inputs to the new dams.
The existing upstream Kratie IQQM model was extended upstream by the
addition of new river nodes and a new dam node to represent the new dam. The
flows routed by these nodes then formed the input to the previous upstream limit
of the model.
Model Input Variables
Apart from the introduction of the new river and dam nodes, no changes were
required to the input variables. The following parameters were assumed for the
new dam:

Assumed total storage 24.7 x 103 MCM

Assumed dead storage 12.7 x 103 MCM
These figures are close to figures quoted in Plinston and Daming. In addition:

Storage curve, valve release curves, and spillway characteristics were
based on the volume of a prism formula (based on an Excel spreadsheet,
"Dam Calcsheet.xls" used for Nam Ngum dam in Laos PDR)

Hydropower release rate was assumed to be 1200 m3/s, which is
approximately equal to the median daily flow at the Chinese Border

Evaporation and precipitation on the storage was assumed to be zero
A key simplification in introducing the new dam, was that it was placed at the Laos
border. This was because the current demonstration Baseline Scenario does not
model flows in China. Therefore, as noted above, if the new dam had been placed
in the true geographic position, it would have been upstream of existing dams and
would have commanded only a fraction of the catchment upstream of the Laos
border. There is no information on which to base the portion of flows that would
be captured by the dam at that location, nor the release rules and other structural
parameters of the existing dams. In effect, it would have required not just the
106727594
A.5- 7
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introduction of the new dam, but the existing ones as well. This was beyond the
intent of the demonstration scenario and well beyond any reasonable assumptions
that could be made with the information at hand. The decision was made to
introduce the simple dam outlined above, such that the general nature of the
impacts could be demonstrated.
5.3.3
iSIS Model
Model Configuration
No changes were required.
Model Input Variables
No changes were required.
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A.5- 8
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5.4
Demonstration Scenario 3: Impact of China Dams – Test Results: Primary
Level
Tests 1 to 3 : MRC Agreement, Article 6 requirements
Tests against Article 6
Scenario
conforms?
Most Critical
Location?
By how much?
Test 1:
Acceptable Minimum Monthly Dry
Season Flow
No
Kratie
Flows decrease by up to 6% in January
Test 2:
Acceptable Reverse flow of Tonle
Sap in Wet Season
Yes
Kratie*
Mean annual peak flows not changed
Test 3:
Average Daily Peak Main Stream
Flow in the Flood Season
Yes
N/A
Mean annual peak flows not changed by
more than 1% at any site
* As defined in the 1995 Mekong Agreement
Test 4: Extent and Duration of Flooding (km2) – downstream of Kratie
Flooded Area >0.5 m by Duration (km2)
Year 2000 (Wet Year)
Scenario
> 1 day
> 1 mth
> 2 mths
> 4 mths
> 6 mths
Baseline Conditions
59,300
55,444
51,687
43,679
29,650
Scenario 5: China Dams
59,233
55,402
51,630
43,570
29,617
Difference
Area (km2)
-67
-42
-57
-109
-33
Difference
Percent (%)
-0.1
-0.1
-0.1
-0.2
-0.1
Test 5: Extent of Saline Intrusion (km2) – in the delta.
Potential Saline Areas by Salinity Class (km2)
Jan 2000 – June 2000
Scenario
Baseline Conditions
> 1 g/l
China Dams Scenario
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Difference
Area (km2)
Difference
Percent (%)
> 4 g/l
> 8 g/l
> 15 g/l
19,153
17,593
16,786
15,253
19,153
0
17,593
0
16,786
0
15,253
0
0.0
0.0
0.0
0.0
A.5- 9
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Test 6: Irrigated agriculture performance
Total Deficit Upstream of Kratie
(million hectare days)
Baseline Conditions
42.77
Scenario
Illustrations of approach in Scenarios (1) – (3)
Difference (million hectare days)
-
Difference (%)
-
Test 7: Degree of Connection for Fisheries Purposes
Maximum Connected River Length
(km)
Maximum Flooded Area (>0 m)
(downstream Kratie)
(km2)
Baseline Conditions
45,571
26,918
Scenario 5: China Dams
45,571
26,973
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Difference (hectare days)
0
54.9
Difference (%)
0
0.2
A.5- 10
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5.5
Scenario 5: China Dams – Test Results: Secondary Level
5.5.1
Test 1: Acceptable Minimum Monthly Dry Season Flow
Figure A 5-1 and Figure A 5-2 display daily flows for the last three years for
Vientiane and Kratie. The difference between them is shown by the residual series
(lowest black line). The negative values of the residual line indicate that the impact
of the new China Dams is to substantially lower the early wet season flows,
sometimes by over 4,000 cumec. This volume is redistributed to the dry season, as
evidenced by the higher dry season flows.
Time Series Analysis Tool
17,000
16,000
15,000
14,000
13,000
12,000
11,000
Flow(cumecs)
10,000
9,000
8,000
7,000
6,000
5,000
4,000
3,000
2,000
1,000
0
-1,000
-2,000
-3,000
-4,000
26/03/1998
24/07/1998
21/11/1998
21/03/1999
19/07/1999
16/11/1999
15/03/2000
13/07/2000
10/11/2000
01/Feb/1985 - 31/Dec/2000
Figure A 5-1:
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China Dams verses Baseline Scenario flows at Vientiane (1997 – 2000)
A.5- 11
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Time Series Analysis Tool
50,000
45,000
40,000
Flow(cumecs)
35,000
30,000
25,000
20,000
15,000
10,000
5,000
0
26/11/1997 26/03/1998 24/07/1998 21/11/1998 21/03/1999 19/07/1999 16/11/1999 15/03/2000 13/07/2000 10/11/2000
01/Feb/1985 - 31/Dec/2000
Figure A 5-2: China Dams verses Baseline Scenario flows at Kratie (1997 – 2000)
Differences between the Baseline and China Dams Scenarios’ lowest minimum
flows, on an annual basis, are presented in Table A 5-1. The table compares both
the extreme lowest daily flow over the entire 16 years, as well as the mean annual
lowest flow.
The new China Dams cause a dramatic increase in lowest and mean minimum
annual dry season flows at all but Kratie where the increase is just 2% and 4%
respectively. At all other sites, the increase is well over 10%, becoming 250% and
68% respectively at Chiang Saen. This is due to the steady release of water from
the dams for hydropower generation during the dry season that was stored from
the previous wet season.
106727594
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Table A 5-1:
Between scenario comparison of annual minimum daily flows
(cumec) over 15 years (1986 – 2000)
Chiang
Saen
Lowest Annual Minimum
Baseline
Flow
China Dams Lowest Annual Min. Flow
Difference in lowest (cumec)
Difference in lowest (%)
Baseline
Mean Annual Minimum Flow
China Dams Mean Annual Min. Flow
Difference in mean (cumec)
Difference in mean (%)
Luang
Prabang
Vientiane
Nakhom
Phanom
Mukdahan
Pakse
Stung
Treng
338
582
680
909
975
1,014
1,328
1,324
1,182
844
250
713
1,198
486
68
1,156
574
99
803
1,245
442
55
1,085
404
59
844
1,158
314
37
1,187
278
31
1,220
1,489
269
22
1,191
217
22
1,235
1,499
265
21
1,232
218
22
1,298
1,551
253
19
1,556
227
17
1,814
2,061
248
14
1,353
28
2
1,819
1,896
77
4
Using Test 1.1, the mean daily dry season flows for each month of the dry season
are tabulated below in Table A 5-2. Whilst the differences do not exceed one
standard deviation, there are some percentage increases in excess of 10% between
the Baseline and China Dams scenarios at all sites for two or more months of the
dry season.
All sites except Kratie show a greater than one standard deviation increase in mean
monthly flows for at least the three months February to April, with the March
increase of 39% at Chiang Saen being the maximum change. The maximum
increase at other sites is also felt in March, except for Mukdahan where the April
increase is marginally higher and at Kratie, where its 11% increase is also in April.
It is this lag in flows down the river due to travel time that results in the maximum
effect of the dams being felt at Kratie one month after the Baseline’ minimum
annual flow, thereby explaining why the increases in the Kratie’s annual minimum
flows (Table A 5-1 above) is so small relative to the other sites, particularly Stung
Treng not far upstream.
Opposing these increases are smaller decreases earlier in the dry season, not
exceeding 6%. From Nakhon Phnom downstream flows decrease slightly in
January. For Kratie they decrease in January and March, remaining unchanged in
February.
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A.5- 13
Kratie
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Table A 5-2:
Mean daily dry season flow for each month of the dry season
Station Name
Scenario
Chiang Saen
Base Line mean
B-L Std Dev
China Dams
Dec
Difference (cumec)
Luang
Prabang
Difference (cumec)
Difference (%)
Base Line mean
B-L Std Dev
China Dams
Difference (cumec)
Nakhon
Phanom
Difference (cumec)
Mukdahan
Difference (cumec)
Pakse
-
Difference (%)
Base Line mean
B-L Std Dev
China Dams
Difference (cumec)
Difference (%)
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-
Difference (%)
Base Line mean
B-L Std Dev
China Dams
Difference (cumec)
Kratie
-
Difference (%)
Base Line mean
B-L Std Dev
China Dams
Difference (cumec)
Stung Treng
-
Difference (%)
Base Line mean
B-L Std Dev
China Dams
-
Mar
1150
149
1,294
944
137
1,216
66
144
272
April
May
876
137
1,215
939
169
1,234
339
295
1421
302
1,433
12
4
12
29
39
31
1
2182
344
2,229
1436
239
1,600
1105
174
1,279
980
169
1,246
1126
197
1,394
1778
416
1,953
47
164
174
266
268
175
2
11
16
27
24
10
2170
351
2,183
1383
241
1,529
1065
132
1,279
975
158
1,246
1145
165
1,394
1897
467
1,953
13
146
214
271
249
Difference (%)
Base Line mean
Standard Deviation
China Dams
Feb
1580
224
1,646
Difference (%)
Base Line mean
B-L Std Dev
China Dams
Vientiane
Jan
56
1
11
20
28
22
3
3053
464
2,985
1888
400
2,038
1462
189
1,665
1362
228
1,630
1614
243
1,879
2908
772
3,031
68
150
203
268
265
123
-2
8
14
20
16
4
3111
474
3,025
1907
413
2,056
1473
192
1,675
1389
232
1,658
1676
256
1,946
3063
785
3,196
86
149
202
269
270
133
-3
8
14
19
16
4
3600
530
3,442
2046
471
2,197
1537
212
1,741
1474
264
1,745
1969
367
2,240
3795
1233
3,937
151
204
271
271
142
158
-4
7
13
18
14
4
5482
688
5,277
3077
753
3,281
2259
384
2,498
2025
359
2,322
2512
501
2,810
4724
1747
4,917
204
239
297
298
193
205
-4
7
11
15
12
4
5618
760
5,289
3130
794
3,119
2283
406
2,240
2044
370
2,153
2552
532
2,839
4851
1830
5,049
109
287
198
329
-6
11
0
43
-2
5
11
A.5- 14
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Test 1.2 compares the dry season flow duration curves (daily flows between 1 Dec
and 31 May) for two representative mainstream primary reporting stations,
Vientiane and Kratie (Figure A 5-3). The curves present the cumulative duration
(frequency) of flows equal to or greater than each flow level. It can be seen that
whilst there are differences in flows between the two scenarios at both sites, they
are most noticeable at Vientiane where they can be seen best in the truncated
annual distribution plot (Figure A 5-4).
Figure A 5-4 to Figure A 5-6 provide a between scenario comparison for the 90, 50
and 10 percentile flow volumes by month (in million cubic metres, MCM) over the
whole year for Vientiane and Kratie respectively. Whilst these curves are
generated directly in the DSF, the data they draw on is effectively obtained by
‘reading off’ values from the types of flow duration curves shown in Figure A 5-3,
but calculated for each month not the entire dry season. The vertical axis in Figure
A 5-4 and Figure A 5-6 are truncated to highlight the differences in dry season
flows. These curves confirm that the greatest dry season differences in the
between the Baseline and China Dams Scenarios are at Vientiane. They also show
that the changes at Vientiane are of the same scale for both the 50th and 90th
percentile flows and somewhat less for the 10th percentile flows.
cumecs
Flow: Exceedence-Probability
10,000
9,500
9,000
8,500
8,000
7,500
7,000
6,500
6,000
5,500
5,000
4,500
4,000
3,500
3,000
2,500
2,000
1,500
1,000
500
0
5
10
15
20
25
g
b
c
d
e
f
b
c
d
e
f
g
b
c
d
e
f
g
b
c
d
e
f
g
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30
35
40
45
50
55
60
65
Cumulative Exceedence Probability %
70
75
80
85
90
95
100
[S12] Vientiane ([01/Dec-31/May], 85-00)
[S12] Kratie ([01/Dec-31/May], 85-00)
[S7] Kratie ([01/Dec-31/May], 85-00)
[S7] Vientiane ([01/Dec-31/May], 85-00)
A.5- 15
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Figure A 5-3:
Dry season flow duration curves for Vientiane and Kratie (dry season; 1 Dec – 31
May data period; 1 Dec 1985 – 31 Dec 2000)
Flow: Percentile Distribution
10,000
9,500
9,000
8,500
8,000
Monthly Total [MCM]
7,500
7,000
6,500
6,000
5,500
5,000
4,500
4,000
3,500
3,000
2,500
2,000
1,500
Jan
Feb
g
b
c
d
e
f
b
c
d
e
f
g
b
c
d
e
f
g
Figure A 5-4:
Mar
Apr
May
Jun
Jul
b
c
d
e
f
[S12] Vientiane 50%ile (85-00) g
b
c
d
e
f
[S12] Vientiane 90%ile (85-00) g
b
c
d
e
f
[S12] Vientiane 10%ile (85-00) g
Aug
Sep
Oct
Nov
Dec
[S7] Vientiane 50%ile (85-00)
[S7] Vientiane 90%ile (85-00)
[S7] Vientiane 10%ile (85-00)
Percentile flow distribution of 90 %, 50% and 10% at Vientiane with comparisons
to Baseline conditions for 50% and 10% (dotted lines) – truncated vertical axis
Flow: Percentile Distribution
120,000
110,000
100,000
Monthly Total [MCM]
90,000
80,000
70,000
60,000
50,000
40,000
30,000
20,000
10,000
Jan
Feb
g
b
c
d
e
f
b
c
d
e
f
g
b
c
d
e
f
g
106727594
Mar
Apr
May
Jun
b
c
d
e
f
[S12] Kratie 10%ile (85-00) g
b
c
d
e
f
[S12] Kratie 50%ile (85-00) g
b
c
d
e
f
[S12] Kratie 90%ile (85-00) g
Jul
Aug
Sep
Oct
Nov
Dec
[S7] Kratie 10%ile (85-00)
[S7] Kratie 50%ile (85-00)
[S7] Kratie 90%ile (85-00)
A.5- 16
Mekong River Commission - Water Utilisation Project Component A:
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Technical Reference Report:: DSF 650 DSF Testing and Evaluation
All assessments are made for
DEMONSTRATION purposes only
Figure A 5-5:
Percentile flow distribution of 90 %, 50% and 10% at Kratie with comparisons to
Baseline conditions (dotted lines)
Flow: Percentile Distribution
19,000
18,000
17,000
16,000
15,000
Monthly Total [MCM]
14,000
13,000
12,000
11,000
10,000
9,000
8,000
7,000
6,000
5,000
4,000
3,000
Jan
Feb
g
b
c
d
e
f
b
c
d
e
f
g
b
c
d
e
f
g
Figure A 5-6:
Mar
Apr
May
Jun
b
c
d
e
f
[S12] Kratie 10%ile (85-00) g
b
c
d
e
f
[S12] Kratie 50%ile (85-00) g
b
c
d
e
f
[S12] Kratie 90%ile (85-00) g
Jul
Aug
Sep
Oct
Nov
Dec
[S7] Kratie 10%ile (85-00)
[S7] Kratie 50%ile (85-00)
[S7] Kratie 90%ile (85-00)
Percentile flow distribution of 90 %, 50% and 10% at Kratie with comparisons to
Baseline conditions (dotted lines) – truncated vertical axis
Low flow variability is quantified by Test 1.3. One part of this test is provided by
Table A 5-3 which tabulates the start, end and duration of the dry season (where
the definition of the dry season is based on the flows below the median flow under
Baseline Conditions). Only at Chiang Saen is there an increase greater than 10% in
the duration of the dry season, although there are also minimal increases at Luang
Prabang, Vientiane and Kratie. The other sites display either no change or a slight
reduction in durations.
Table A 5-3:
Mean start and end of the dry season based on the Baseline Scenario’s median annual
flow (Oct 1985 – Dec 2000)
Reporting Site
Chiang Saen
(Sc1 median = 1,768)
Luang Prabang
(Sc1 median = 2,355)
106727594
Baseline
Start Date
End Date
Duration (days)
Start Date
End Date
9-Dec
27-May
168
8-Dec
4-Jun
China Dams
6-Dec
4-Jun
179
6-Dec
8-Jun
Difference (days)
-3
8
11
-2
4
A.5- 17
All assessments are made for
DEMONSTRATION purposes only
Reporting Site
Vientiane
(Sc1 median = 2,416)
Nakhon Phanom
(Sc1 median = 3,869)
Mukdahan
(Sc1 median = 4,028)
Pakse
(Sc1 median = 4,972)
Stung Treng
(Sc1 median =7, 189)
Kratie
(Sc1 median = 7,369)
Mekong River Commission - Water Utilisation Project Component A:
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Baseline
Duration (days)
Start Date
End Date
Duration (days)
Start Date
End Date
Duration (days)
Start Date
End Date
Duration (days)
Start Date
End Date
Duration (days)
Start Date
End Date
Duration (days)
Start Date
End Date
Duration (days)
178
5-Dec
3-Jun
180
30-Nov
1-Jun
183
29-Nov
31-May
184
28-Nov
29-May
182
4-Dec
1-Jun
179
4-Dec
1-Jun
180
China Dams
184
5-Dec
4-Jun
181
29-Nov
29-May
181
28-Nov
29-May
182
26-Nov
27-May
182
2-Dec
1-Jun
181
30-Nov
1-Jun
184
Difference (days)
6
0
1
1
-1
-3
-2
-1
-2
-2
-2
-2
0
-2
0
2
-4
0
4
Relative flow height changes are analysed by the low flow variability tool. Table A
5-4 shows the median duration of events where the flow does not change by more
than 10% of the median annual flow for at least 30 days. Chiang Saen, Luang
Prabang, Pakse and Stung Treng all exhibit substantially longer mean durations of
stable events, with smaller increases at other sits, except Mukdahan which displays
a decrease of eight days. The increases at Luang Prabang and particularly Chiang
Saen at double the Baseline’s mean duration, are dramatic. They are evidence of
the stable flow conditions imposed by artificially high dry season flows created by
the hydro-power releases from the new China dams.
The peak in higher durations at Pakse and Stung Treng can not easily be explained,
but are probably due to the lag in flows down the system that cause the new
mainstream flows to be more, or less coincident with tributary inflows, thereby
evening out the mainstream flow at these locations.
106727594
A.5- 18
All assessments are made for
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Table A 5-4:
Mekong River Commission - Water Utilisation Project Component A:
Development of Basin Modelling Package and Knowledge Base (WUP-A)
Technical Reference Report:: DSF 650 DSF Testing and Evaluation
Duration of Stable Flow Conditions relative to the Baseline Scenario (days) (Oct
1985 – Dec 2000)
(Where flows change by < 10% of the Baseline Condition’s mean annual flow for events of at least 30 days duration)
Reporting Site
Baseline Annual
Median Flow (cumec)
Mean Number of Days of Stable Flow per event
Baseline Conditions
China Dams
Difference
Difference
(days)
(%)
Chiang Saen
1,768
50
151
101
203
Luang Prabang
2,355
44
53
9
21
Vientiane
2,416
56
61
5
9
Nakhom Phanom
3,869
57
59
2
3
Mukdahan
4,028
62
57
-5
-8
Pakse
4,972
62
69
7
11
Stung Treng
7,189
57
65
9
15
Kratie
7,369
56
58
2
4
5.5.2
Test 2: Acceptable Reverse flow of Tonle Sap in Wet Season
Test 2.1 compares the mean peak annual wet season (daily) flows and standard
deviation for Baseline Conditions with the development scenario at Kratie. The
1995 Mekong Agreement defines wet season flows at Kratie as the basis for
determining if acceptable inundation level in Tonle Sap lake is achieved.
Consequently, the difference between mean peak annual wet season flows at Kratie
are compared for Baseline and China dam conditions in Table A 5-5. Surprisingly,
there is only a 0.2% decrease in mean annual flow, whereas a larger decrease might
have been expected. Obviously, the impact of the dams filling at the
commencement of the wet season each year does not impact on the peak flows on
average.
Figure A 5-7 displays the relationship of peak annual discharge with the average
annual return period. Tabular values are presented in Table A 5-7.
106727594
A.5- 19
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Table A 5-5:
Mean annual peak daily flow at Kratie
Reporting Site
Baseline Conditions
Mean Annual Peak
Flow (cumec)
44,651
Kratie
China Dams
Standard Deviation
(cumec)
9,785
Difference
Mean Annual Peak
Flow (cumec)
44,748
cumec
97
Annual Flood Frequency Analysis
Kratie K = 0.152:
Flow (Simulated flow) (cumecs)
105,000
100,000
95,000
90,000
85,000
80,000
75,000
70,000
65,000
60,000
55,000
50,000
45,000
40,000
35,000
30,000
25,000
20,000
15,000
10,000
5,000
0
1
2
g
b
c
d
e
f
b
c
d
e
f
g
4
5
10
20 25
Return Period (years)
[S12] Kratie - Gringorten (1985-2000)
c
d
e
f
g
50
100
200
500
[S12] EV1 Kratie - Gringorten (1985-2000)
[S12] GEV Kratie - Gringorten (1985-2000)
Figure A 5-7: Annual flood frequency at Kratie
The peak water levels and Tonle Sap inundated area is shown in Error! Reference
source not found. for the wet season of the year 2000 (an above average wet
season flood of about 1 in 15 years return period under Baseline Conditions).
106727594
A.5- 20
%
-0.2
All assessments are made for
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5.5.3
Mekong River Commission - Water Utilisation Project Component A:
Development of Basin Modelling Package and Knowledge Base (WUP-A)
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Test 3: Average Daily Peak Main Stream Flow in the Flood Season
A portion of the daily flow time-series data are plotted in Figure A 5-8 to provide
a visual reference as the scale of changes between the Baseline and China dam
Scenarios. Only two stations have been plotted to retain clarity.
Time Series Analysis Tool
55,000
50,000
45,000
Flow(cumecs)
40,000
35,000
30,000
25,000
20,000
15,000
10,000
5,000
0
26/11/1997 26/03/1998 24/07/1998 21/11/1998 21/03/1999 19/07/1999 16/11/1999 15/03/2000 13/07/2000 10/11/2000
g
b
c
d
e
f
b
c
d
e
f
g
b
c
d
e
f
g
b
c
d
e
f
g
Vientiane: Flow (Simulated flow) [WUPA Scenario 5 - China Dams]
Kratie: Flow (Simulated flow) [WUPA Scenario 5 - China Dams]
Vientiane: Flow (Simulated flow) [WUPA Scenario 1 - Baseline]
Kratie: Flow (Simulated flow) [WUPA Scenario 1 - Baseline]
01/Feb/1985 - 31/Dec/2000
Figure A 5-8: Daily flows showing high flows for Vientiane and Kratie (Feb 1985 – Dec 2000)
As can be seen from Table A 5-6 the highest annual flood over the 16 year period
decreased by no more than 3% under the China Dams scenario and then only at
the two most upstream sites. The highest peak flow increased by 3% and 2% at
Luang Prabang and Vientiane, whilst slight decreases or no change were felt and
the other sites.
Mean annual flood peaks display effectively no change, the greatest difference
being 1% or less. The impact of the China Dams is therefore confined to the early
part of the wet season, with no discernable impact on peak flows.
106727594
A.5- 21
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Table A 5-6:
Baseline
China Dams
Comparison of Highest and Average Annual Peak Daily Flows
Highest Annual
Peak Flow
Highest Annual
Peak Flow
Difference - highest
(cumec)
Difference - highest
(%)
Baseline Mean Annual Peak
Flow
China Dams
Mean Annual
Peak Flow
Difference in
means (cumec)
Difference - means
(%)
Chiang
Saen
Luang
Prabang
Vientiane
Nakhom
Phanom
Mukdahan
Pakse
Stung
Treng
Kratie
13,300
17,997
17,830
31,654
35,195
47,212
66,067
67,268
12,889
18,599
18,139
31,496
35,000
47,030
65,917
67,122
-411
603
309
-158
-195
-183
-151
-145
-3
3
2
-1
-1
-0.4
-0.2
-0.2
9,754
14,058
14,733
23,828
25,827
34,035
43,502
44,651
9,775
14,158
14,925
23,837
25,847
34,001
43,556
44,748
21
100
192
9
20
-34
54
97
0.2
1
1
0.0
0
-0.1
0.1
0.2
In addition to the comparison of average annual flood peaks, Table A 5-7 shows
the changes in peak flows for different return periods for each mainstream
monitoring site. As would be expected, the changes in peak flows (cumec) for
each return period are zero or nearly zero for most sites. They largely mirror the
changes in mean and extreme peak values shown above in Table A 5-6. The
exception is Chiang Saen, which shows an increasing reduction in peak annual
flows at less frequent return periods, cumulating in a 6% reduction for the 100 year
event.
Figure A 5-7 above provides a graphical representation of the Annual Flood
Frequency Curve at Kratie, this being a critical location for determining changes in
flooding in both the Tonle Sap Lake and the Cambodian and Vietnamese
floodplain areas.
106727594
A.5- 22
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Technical Reference Report:: DSF 650 DSF Testing and Evaluation
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Table A 5-7:
Comparison of flood return periods for mainstream monitoring sites
(Changes >10% highlighted in bold)
Main Stations
Scenarios
Return Periods (years)
2
Chiang Saen
Luang Prabang
Vientiane
Nakhon Phanom
Mukdahan
Pakse
Stung Treng
Kratie
5.5.4
Baseline
China Dams
% change
Baseline
China Dams
% change
Baseline
China Dams
% change
Baseline
China Dams
% change
Baseline
China Dams
% change
Baseline
China Dams
% change
Baseline
China Dams
% change
Baseline
China Dams
% change
10,126
10,161
0.3
15,112
15,011
-1
15,914
15,927
0.1
24,500
24,439
-0.3
26,092
26,084
-0.0
33,803
33,682
-0.4
42,795
42,750
-0.1
43,989
43,983
-0.0
5
11,815
11,553
-2
16,922
16,746
-1
17,265
17,361
1
27,817
27,902
0.3
30,321
30,439
0.4
40,261
40,180
-0.2
51,347
51,210
-0.3
52,622
52,514
-0.2
10
20
50
100
12,449
12,030
-3
17,402
17,241
-1
17,556
17,709
1
29,091
29,280
1
32,265
32,464
1
43,678
43,686
0.0
56,199
56,101
-0.2
57,476
57,405
-0.1
12,844
12,318
-4
17,631
17,492
-1
17,676
17,865
1
29,896
30,173
1
33,672
33,943
1
46,435
46,555
0.3
60,327
60,323
-0.0
61,578
61,600
0.0
13,159
12,553
-5
17,769
17,652
-1
17,737
17,952
1
30,551
30,922
1
35,003
35,355
1
49,373
49,666
1
64,998
65,180
0.3
66,184
66,391
0.3
13,305
12,553
-6
17,816
17,711
-1
17,754
17,979
1
30,858
31,284
1
35,731
36,136
1
51,189
51,620
1
68,062
68,417
1
69,182
69,561
1
Test 4: Extent and Duration of Flooding
Figure A 5-9 shows the difference in inundated area for peak flood conditions in
the year 2000. As would be expected from the above time-series analysis results,
there is little difference between the two scenarios, with the differences in depth
being not more than a 0.1 m reduction in peak flood levels throughout the area
downstream of Kratie.
106727594
A.5- 23
All assessments are made for
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Figure A 5-9
Mekong River Commission - Water Utilisation Project Component A:
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Technical Reference Report:: DSF 650 DSF Testing and Evaluation
Map showing the difference in inundated area downstream Kratie for peak flood
conditions in year 2000 (Baseline Conditions verses China Dams)
Figure A 5-10 shows the difference in the duration of inundation of depth greater
than 0.5 m for the wet season of the year 2000. Half a metre was chosen for the
analysis, as at this depth water begins to be a substantial influence on agriculture
and transport.
Again, as would be expected from the above time-series analysis results, there is
little difference between the two scenarios. The differences are not more than 7
days more or less than the Baseline in either direction.
106727594
A.5- 24
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Figure A 5-10 Map showing the difference in the depth-duration >0.5 m for year 2000 (Baseline
Conditions verses China Dams)
The actual area of each depth class and the differences to the Baseline Conditions
are tabulated in Table A 5-8. There is less than a 2% change in the area of any
depth class.
Table A 5-8:
Maximum inundation areas by depth class in the year 2000
Flooded Area by depth class (km 2)
Year 2000 (Wet Year)
Scenario
>0m
Baseline Conditions
China Dams Scenario
106727594
(km2)
Difference
Area
Difference
Percent (%)
>0.5 m
> 1.0 m
> 2.0 m
26,918
25,594
22,203
13,255
26,973
54.9
25,625
30.8
22,220
17.1
13,232
-22.3
0.2
0.1
0.1
-0.2
A.5- 25
Mekong River Commission - Water Utilisation Project Component A:
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All assessments are made for
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5.5.5
Test 5: Extent and Duration of Saline Intrusion
Figure A 5-11 below shows the maximum saline intrusion area in the year 2000.
The lack of any differences between the two scenarios is clear from Table A 5-9
which tabulates the area of each salinity exceedance class and the differences with
the Baseline Scenario.
Figure A 5-11: Map of maximum inundated area in the year 2000 for the China Dams Scenario
Table A 5-9:
Maximum dry-season salinity intrusion areas
Maximum Saline Inundation by Salinity Class (km 2)
Jan 2000 – June 2000
Scenario
Baseline Conditions
> 1 g/l
China Dams Scenario
106727594
Difference
Area (km2)
Difference
Percent (%)
> 4 g/l
> 8 g/l
> 15 g/l
19,153
17,593
16,786
15,253
19,153
0
17,593
0
16,786
0
15,253
0
0.0
0.0
0.0
0.0
A.5- 26
Mekong River Commission - Water Utilisation Project Component A:
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5.5.6
Test 6: Irrigated agriculture performance
See Scenarios (1) – (3) for demonstration of this test.
5.5.7
Test 7: Degree of Connection for Fisheries Purposes
There is no change in the maximum longitudinal fish migration network extent
within the LMB, as the China dams are located upstream of it.
5.5.8
Impacts on flows in the tidal areas
Impacts of China dams scenario on flows below Kratie are illustrated by reference
to representative flows in the year 2000 at Chau Doc, Tan Chau and Phnom Penh
(Mekong) in the figures and table below.
Figure A 5-12 Comparison of flows at Chau Doc for year 2000 (Baseline Conditions versus China
dams scenario)
Time Series Analysis Tool
9,000
8,000
Flow(cumecs)
7,000
6,000
5,000
4,000
3,000
2,000
1,000
15/01/2000
15/03/2000
14/05/2000
13/07/2000
[S1] Chau Doc: Flow
11/09/2000
10/11/2000
[S5] Chau Doc: Flow
01/Jan/2000 - 30/De c/2000
Figure A 5-13 Comparison of flows at Tan Chau for year 2000 (Baseline Conditions versus China
dams scenario)
106727594
A.5- 27
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Time Series Analysis Tool
28,000
26,000
24,000
22,000
Flow(cumecs)
20,000
18,000
16,000
14,000
12,000
10,000
8,000
6,000
4,000
2,000
15/01/2000
15/03/2000
14/05/2000

13/07/2000
[S1] Tan Chau: Flow 
11/09/2000
10/11/2000
[S5] Tan Chau: Flow
01/Jan/2000 - 30/De c/2000
Figure A 5-14 Comparison of flows at Phnom Penh (Mekong) for year 2000 (Baseline
Conditions versus China dams scenario)
106727594
A.5- 28
Mekong River Commission - Water Utilisation Project Component A:
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Time Series Analysis Tool
40,000
38,000
36,000
34,000
32,000
30,000
Flow(cumecs)
28,000
26,000
24,000
22,000
20,000
18,000
16,000
14,000
12,000
10,000
8,000
6,000
4,000
2,000
15/01/2000
15/03/2000
14/05/2000
13/07/2000
[S1] Phnom Penh (Mekong): Flow
11/09/2000
10/11/2000
[S5] Phnom Penh (Mekong): Flow
01/Jan/2000 - 30/De c/2000
Table A 5-10: Impacts of China dams scenario on flows and water levels at Chau Doc, Tan
Chau and Phnom Penh (Mekong) for year 2000
Flow (m3/s)
106727594
Stage (mAD)
Max
Value
Max
Date
Min
Value
Min
Max
Value
Max
Date
Min
Value
Min
Date
Phnom Penh Mekong
upstream – China Dams
40,799
18/07
1,888
03/04
9.96
16/09
0.86
02/04
Phnom Penh Mekong
upstream - Baseline
40,815
18/07
1,632
03/04
9.98
16/09
0.79
02/04
Phnom Penh Mekong
upstream - Difference
-16
0 days
256
0 days
-0.02
0 days
0.07
0 days
Tan Chau – China Dams
27, 991
20/9
2,050
07/04
5.60
19/09
0.40
01/04
Tan Chau - Baseline
28,063
20/9
1,826
03/04
5.61
19/09
0.37
01/04
Tan Chau - Difference
-72
0 days
224
4 days
-0.01
0 days
0.03
0 days
Chau Doc - China Dams
9,782
23/09
100
06/04
4.90
22/09
0.19
29/04
Chau Doc - Baseline
9,813
23/09
73
06/04
4.92
22/09
0.18
29/04
Chau Doc - Difference
-31
0 days
27
0 days
-0.02
0 days
0.01
0 days
Date
A.5- 29
All assessments are made for
DEMONSTRATION purposes only
5.6
Mekong River Commission - Water Utilisation Project Component A:
Development of Basin Modelling Package and Knowledge Base (WUP-A)
Technical Reference Report:: DSF 650 DSF Testing and Evaluation
Conclusions and Recommendations
The introduction of two new large hydro-power dams in China’s Yunnan
province, having a combined storage area of 27.3 million cubic meters in storage
volume, has noticeable effects on the hydrology of the mainstream.
Technically, the scenario marginally fails the ‘acceptable low flows in the dry
season’ test, as mean daily flows decrease by up to 6% in January at Kratie.
However, at Kratie and more substantially at upstream sites, monthly mean flows
increase, with the highest increases of 39% being observed at Chiang Saen in
March. In fact, for the months of February, March and April, flows increase by
more than one standard deviation from the Baseline’s mean monthly flows for all
sites but Kratie.
These monthly change are mirrored on an annual basis, except that there are no
decreases in either the mean minimum, or lowest minimum, annual flow. With the
exception of Kratie, increases in the lowest minimum annual flow range from
250% at Chiang Saen to 17% at Stung Treng. The corresponding mean annual
minimum flow increases are 68% and 14% respectively.
Peak annual daily flows are essentially unchanged by the new China Dams, the
impact being limited to the rising limb of the flood. Neither the highest annual
peak flow over the 16 years of the simulation, nor the mean annual peak flow,
show more than a 3% and 1% change respectively at any site. The flood frequency
analysis does show a slightly larger change at Chiang Saen for floods of infrequent
occurrence. Peak flows are reduced by up to 6% for a 1 in 100 year event at
Kratie, but only by 3% for a 10 year event.
Because peak wet season flows are not substantially changed at Kratie, the scenario
passes the test for ‘acceptable Tonle Sap flow reversal’.
The new China dams do not reduce the LMB’s maximum longitudinal fish
migration network, as they are located upstream of the area defined as the LMB.
Of course, fish do not recognise international borders and any analysis of dams in
China should include the effects on fish migration networks in this area to be
complete.
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All assessments are made for
DEMONSTRATION purposes only
Mekong River Commission - Water Utilisation Project Component A:
Development of Basin Modelling Package and Knowledge Base (WUP-A)
Technical Reference Report:: DSF 650 DSF Testing and Evaluation
The spatial analyses clearly show the lack of any significant changes in flooding or
dry-season salinity intrusion in the area downstream of Kratie. The effect of dams
in China progressively lessens in the downstream direction, being unobservable for
changes in salinity in the delta for the maximum penetration conditions.
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