what is needed to manage sediment in a reservoir and can it be done on the mekong?
DESCRIPTION
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 engineeringTRANSCRIPT
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Mekong Forum on Water, Food and Energy7-9 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
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Mekong Forum on Water, Food and Energy7-9 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 ReservoirFocus in on MRC Design GuidanceMRC PNPCA Studies for Xayaburi
Can it be done at all?
Do we know enough now?
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Mekong Forum on Water, Food and Energy7-9 Dec 2011, Phnom Penh , Cambodia
Mekong ReservoirsTributary Reservoirs for Irrigation Tributary Reservoirs for HydropowerStorage Reservoirs on mainstreamRun of river above VientianeRun of river below VientianeDiversions at Khone Falls
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Mekong Forum on Water, Food and Energy7-9 Dec 2011, Phnom Penh , Cambodia
Mekong above Vientiane
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Mekong Forum on Water, Food and Energy7-9 Dec 2011, Phnom Penh , Cambodia
Bed Sediments above Vientiane
Xayaburi Spillway Area
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Mekong Forum on Water, Food and Energy7-9 Dec 2011, Phnom Penh , Cambodia
Silt and Clays
2011 In Suspension (Lao) and deposited (Cambodia)
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Mekong Forum on Water, Food and Energy7-9 Dec 2011, Phnom Penh , Cambodia
Managing Sedimentation in ReservoirsEffect of Changes in Water Level and Velocity
Adapted from Palmieri, Shah, Annandale Dinar (2003) Reservoir Conservation
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Mekong Forum on Water, Food and Energy7-9 Dec 2011, Phnom Penh , Cambodia
Sediment TrappingDependence on the Ratio of Inflow to Capacity
Brune Curves (1953)
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Mekong Forum on Water, Food and Energy7-9 Dec 2011, Phnom Penh , Cambodia
Sedimentation in ReservoirsChanges in Water Level and Velocity
Long Section: M2364 - barrage - Stage; 10224.000 h.
Stage; 0 hours: M2364 - barrage - F:\Mekong\xayaburi\isis\sedtests\upzayased\upzayaburiB_sand1.zzlStage; 0 hours: M2364 - barrage - F:\Mekong\xayaburi\isis\sedtests\upzayased\UPZAYABURINB_SAND1.zzlBed Elevation: M2364 - barrage: M2364 - barrage
Node Label
M23
64
M23
56U
M23
44
M23
32
M23
20
M23
08
M22
96U
M22
84
M22
72U
M22
60
M22
48
M22
36
M22
24
M22
12
M22
00
M21
88
M21
76
M21
64
M21
52
M21
40
M21
28
M21
16
M21
04
M20
92
M20
80
M20
68
M20
56
M20
44
M20
32U
M20
20U
M20
08U
M19
96
M19
84
M19
72
M19
60
M19
48
M19
36
M19
24
M19
12
Ele
vatio
n (m
AD
)
360
350
340
330
320
310
300
290
280
270
260
250
240
230
220
210
200
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Mekong Forum on Water, Food and Energy7-9 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)
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Mekong Forum on Water, Food and Energy7-9 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)
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Mekong Forum on Water, Food and Energy7-9 Dec 2011, Phnom Penh , Cambodia
MRC Preliminary Design Guidance Sediment Management Options
Sediment Pass Through/BypassSediment routingSediment flushing’ for sediment Mechanical removal/Sediment Traps Sediment augmentation downstream of dams
Managing sediment in a cascade of dams
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Mekong Forum on Water, Food and Energy7-9 Dec 2011, Phnom Penh , Cambodia
Sediment Pass Through
Aswan Dam 1900s
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Mekong Forum on Water, Food and Energy7-9 Dec 2011, Phnom Penh , Cambodia
Flushing Effect on Velocity
Time Series: M1908 - Velocity: M1908; 8000 - 1.38E005 h.
Time (h)
38,00037,00036,00035,00034,00033,00032,00031,00030,00029,00028,00027,00026,00025,00024,00023,00022,00021,00020,00019,00018,00017,00016,00015,00014,00013,00012,00011,00010,0009,0008,000
Vel
ocity
(m
/s)
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
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
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Mekong Forum on Water, Food and Energy7-9 Dec 2011, Phnom Penh , Cambodia
Isis Sediment ModelSimulated Change in Bed Level with flushing
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Mekong Forum on Water, Food and Energy7-9 Dec 2011, Phnom Penh , Cambodia
Review – RESCON Modelling
Simple spreadsheet model of sedimentBacked up and documented as World Bank
PublicationOne of the Authors employed as consultantUsed for specific study predictions for
Xayaburi on sediment management including flushing
Used for basinwide scenario of total sediment trapping
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Mekong Forum on Water, Food and Energy7-9 Dec 2011, Phnom Penh , Cambodia
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Mekong Forum on Water, Food and Energy7-9 Dec 2011, Phnom Penh , Cambodia
Rescon – flushing calculation
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Mekong Forum on Water, Food and Energy7-9 Dec 2011, Phnom Penh , Cambodia
Basinwide – trapping results assuming no preventative measures
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Mekong Forum on Water, Food and Energy7-9 Dec 2011, Phnom Penh , Cambodia
Conclusions
Significant Deposition of sediments if no preventative measures
Flushing using deep gates can reduce depositionNeed Flexible operating regime to allow pass
through during high flows possibly AugustBut Can be done as MRC Design Guidance
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Mekong Forum on Water, Food and Energy7-9 Dec 2011, Phnom Penh , Cambodia
Conclusions (2)
Needs regulatory regimeSome More studies esp re cascade operationsBut 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