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

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?

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

Mekong Forum on Water, Food and Energy7-9 Dec 2011, Phnom Penh , Cambodia

Mekong above Vientiane

Mekong Forum on Water, Food and Energy7-9 Dec 2011, Phnom Penh , Cambodia

Bed Sediments above Vientiane

Xayaburi Spillway Area

Mekong Forum on Water, Food and Energy7-9 Dec 2011, Phnom Penh , Cambodia

Silt and Clays

2011 In Suspension (Lao) and deposited (Cambodia)

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

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)

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

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)

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)

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

Mekong Forum on Water, Food and Energy7-9 Dec 2011, Phnom Penh , Cambodia

Sediment Pass Through

Aswan Dam 1900s

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

Mekong Forum on Water, Food and Energy7-9 Dec 2011, Phnom Penh , Cambodia

Isis Sediment ModelSimulated Change in Bed Level with flushing

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

Mekong Forum on Water, Food and Energy7-9 Dec 2011, Phnom Penh , Cambodia

Mekong Forum on Water, Food and Energy7-9 Dec 2011, Phnom Penh , Cambodia

Rescon – flushing calculation

Mekong Forum on Water, Food and Energy7-9 Dec 2011, Phnom Penh , Cambodia

Basinwide – trapping results assuming no preventative measures

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

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