What is needed to manage sediment in a reservoir and can it be done on the Mekong?

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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

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What is needed to manage sediment in a reservoir and can it be done on the Mekong?

  1. 1. 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
  2. 2. 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 Reservoir  Focus in on MRC Design Guidance  MRC PNPCA Studies for Xayaburi Can it be done at all? Do we know enough now?
  3. 3. Mekong Forum on Water, Food and Energy7-9 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. 4. Mekong Forum on Water, Food and Energy7-9 Dec 2011, Phnom Penh , Cambodia Mekong above Vientiane
  5. 5. Mekong Forum on Water, Food and Energy7-9 Dec 2011, Phnom Penh , Cambodia Bed Sediments above Vientiane Xayaburi Spillway Area
  6. 6. Mekong Forum on Water, Food and Energy7-9 Dec 2011, Phnom Penh , Cambodia Silt and Clays 2011 In Suspension (Lao) and deposited (Cambodia)
  7. 7. Mekong Forum on Water, Food and Energy7-9 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. 8. Mekong Forum on Water, Food and Energy7-9 Dec 2011, Phnom Penh , Cambodia Sediment Trapping Dependence on the Ratio of Inflow to Capacity Brune Curves (1953)
  9. 9. Mekong Forum on Water, Food and Energy7-9 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. 10. 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)
  11. 11. 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)
  12. 12. Mekong Forum on Water, Food and Energy7-9 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. 13. Mekong Forum on Water, Food and Energy7-9 Dec 2011, Phnom Penh , Cambodia Sediment Pass Through Aswan Dam 1900s
  14. 14. 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. 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. 15. Mekong Forum on Water, Food and Energy7-9 Dec 2011, Phnom Penh , Cambodia Isis Sediment Model Simulated Change in Bed Level with flushing
  16. 16. Mekong Forum on Water, Food and Energy7-9 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. 17. Mekong Forum on Water, Food and Energy7-9 Dec 2011, Phnom Penh , Cambodia
  18. 18. Mekong Forum on Water, Food and Energy7-9 Dec 2011, Phnom Penh , Cambodia Rescon – flushing calculation
  19. 19. Mekong Forum on Water, Food and Energy7-9 Dec 2011, Phnom Penh , Cambodia Basinwide – trapping results assuming no preventative measures
  20. 20. 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 deposition  Need Flexible operating regime to allow pass through during high flows possibly August  But Can be done as MRC Design Guidance
  21. 21. Mekong Forum on Water, Food and Energy7-9 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

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