By Anthony Green, Modelling Advisor IKMP MRCS Presented at the Mekong Forum on Water and Food Phnom Penh, Cambodia December 7-9, 2011 Session 2a: Water engineering

1. Mekong Forum on Water, Food and Energy
7-9 Dec 2011, Phnom Penh , Cambodia
What is needed to Manage Sediment
in a Reservoir and can it be done on
the Mekong?
Anthony Green
Modelling Advisor
IKMP MRCS

2. Mekong Forum on Water, Food and Energy
7-9 Dec 2011, Phnom Penh , Cambodia
Question to be debated:
What technologies (designs, turbines and other
equipment) can reduce some of the
negative, long-term costs of water infrastructure
 Sediment Movement in a Reservoir
 Focus in on MRC Design Guidance
 MRC PNPCA Studies for Xayaburi
Can it be done at all?
Do we know enough now?

3. Mekong Forum on Water, Food and Energy
7-9 Dec 2011, Phnom Penh , Cambodia
Mekong Reservoirs
 Tributary Reservoirs for Irrigation
 Tributary Reservoirs for Hydropower
 Storage Reservoirs on mainstream
 Run of river above Vientiane
 Run of river below Vientiane
 Diversions at Khone Falls

4. Mekong Forum on Water, Food and Energy
7-9 Dec 2011, Phnom Penh , Cambodia
Mekong above Vientiane

5. Mekong Forum on Water, Food and Energy
7-9 Dec 2011, Phnom Penh , Cambodia
Bed Sediments above Vientiane
Xayaburi Spillway Area

6. Mekong Forum on Water, Food and Energy
7-9 Dec 2011, Phnom Penh , Cambodia
Silt and Clays
2011 In Suspension (Lao) and deposited (Cambodia)

7. Mekong Forum on Water, Food and Energy
7-9 Dec 2011, Phnom Penh , Cambodia
Managing Sedimentation in Reservoirs
Effect of Changes in Water Level and Velocity
Adapted from Palmieri, Shah, Annandale Dinar (2003) Reservoir Conservation

8. Mekong Forum on Water, Food and Energy
7-9 Dec 2011, Phnom Penh , Cambodia
Sediment Trapping
Dependence on the Ratio of Inflow to Capacity
Brune Curves
(1953)

9. Mekong Forum on Water, Food and Energy
7-9 Dec 2011, Phnom Penh , Cambodia
Sedimentation in Reservoirs
Changes in Water Level and Velocity
Long Section: M2364 - barrage - Stage; 10224.000 h.
360
350
340
330
320
310
300
Elevation (m AD)
290
280
270
260
250
240
230
220
210
200
M2364
M2344
M2332
M2320
M2308
M2284
M2260
M2248
M2236
M2224
M2212
M2200
M2188
M2176
M2164
M2152
M2140
M2128
M2116
M2104
M2092
M2080
M2068
M2056
M2044
M1996
M1984
M1972
M1960
M1948
M1936
M1924
M1912
M2356U
M2296U
M2272U
M2032U
M2020U
M2008U
Node Label
Stage; 0 hours: M2364 - barrage - F:MekongxayaburiisissedtestsupzayasedupzayaburiB_sand1.zzl
Stage; 0 hours: M2364 - barrage - F:MekongxayaburiisissedtestsupzayasedUPZAYABURINB_SAND1.zzl
Bed Elevation: M2364 - barrage: M2364 - barrage

10. Mekong Forum on Water, Food and Energy
7-9 Dec 2011, Phnom Penh , Cambodia
Changes in Water Velocity/Speed
Pre- impoundment – velocity 1-2m/s
With Reservoir – velocity much reduced (0.05-1.0m/s)

11. Mekong Forum on Water, Food and Energy
7-9 Dec 2011, Phnom Penh , Cambodia
PNPCA Review –Findings
 Backwater can extend 100km -200km
upstream
 Large Differences between current fast
velocity throughout the year and expected slow
movement in reservoir (5% near dam)

12. Mekong Forum on Water, Food and Energy
7-9 Dec 2011, Phnom Penh , Cambodia
MRC Preliminary Design Guidance
Sediment Management Options
 Sediment Pass Through/Bypass
 Sediment routing
 Sediment flushing’ for sediment
 Mechanical removal/Sediment Traps
 Sediment augmentation downstream of dams
 Managing sediment in a cascade of dams

13. Mekong Forum on Water, Food and Energy
7-9 Dec 2011, Phnom Penh , Cambodia
Sediment Pass Through
Aswan Dam 1900s

14. Mekong Forum on Water, Food and Energy
7-9 Dec 2011, Phnom Penh , Cambodia
Flushing Effect on Velocity
Time Series: M1908 - Velocity: M1908; 8000 - 1.38E005 h.
2
1.95
1.9
1.85
1.8
1.75
1.7
1.65
1.6
1.55
1.5
1.45
1.4
1.35
1.3
1.25
1.2
1.15
1.1
Velocity (m/s)
1.05
1
0.95
0.9
0.85
0.8
0.75
0.7
0.65
0.6
0.55
0.5
0.45
0.4
0.35
0.3
0.25
0.2
0.15
0.1
0.05
0
8,000 9,000 10,000 11,000 12,000 13,000 14,000 15,000 16,000 17,000 18,000 19,000 20,000 21,000 22,000 23,000 24,000 25,000 26,000 27,000 28,000 29,000 30,000 31,000 32,000 33,000 34,000 35,000 36,000 37,000 38,000
Time (h)

15. Mekong Forum on Water, Food and Energy
7-9 Dec 2011, Phnom Penh , Cambodia
Isis Sediment Model
Simulated Change in Bed Level with flushing

16. Mekong Forum on Water, Food and Energy
7-9 Dec 2011, Phnom Penh , Cambodia
Review – RESCON Modelling
 Simple spreadsheet model of sediment
 Backed up and documented as World Bank
Publication
 One of the Authors employed as consultant
 Used for specific study predictions for
Xayaburi on sediment management including
flushing
 Used for basinwide scenario of total
sediment trapping

17. Mekong Forum on Water, Food and Energy
7-9 Dec 2011, Phnom Penh , Cambodia

18. Mekong Forum on Water, Food and Energy
7-9 Dec 2011, Phnom Penh , Cambodia
Rescon – flushing calculation

19. Mekong Forum on Water, Food and Energy
7-9 Dec 2011, Phnom Penh , Cambodia
Basinwide – trapping results assuming
no preventative measures

20. Mekong Forum on Water, Food and Energy
7-9 Dec 2011, Phnom Penh , Cambodia
Conclusions
 Significant Deposition of sediments if no
preventative measures
 Flushing using deep gates can reduce deposition
 Need Flexible operating regime to allow pass
through during high flows possibly August
 But Can be done as MRC Design Guidance

21. Mekong Forum on Water, Food and Energy
7-9 Dec 2011, Phnom Penh , Cambodia
Conclusions (2)
 Needs regulatory regime
 Some More studies esp re cascade operations
 But design can be adaptive to take of varying
sediment regime – data coming in already from
MRC Sediment project can reduce uncertainty
 Conditions below Vientiane Differ – cannot assume
same