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Exploring environmental flow regimes in the lower sesan in cambodia

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3rd Mekong Forum on Water, Food & Energy 2013. Presentation from Session 9: Managing the impacts of dams across cascades.

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Exploring environmental flow regimes in the lower sesan in cambodia

  1. 1. Exploring environmental flow regimes in the Lower Sesan in Cambodia MK3: Optimizing cascades or systems of reservoirs in small catchments Jeremy Carew-Reid, Tarek Ketelsen, Peter-John Meynell, Timo A. Räsänen and Simon Tilleard
  2. 2. ENVIRONMENTAL FLOWS
  3. 3. Environmental flows Environmental flows: the provision of water for freshwater dependent ecosystems to maintain their integrity, productivity, services and benefits Broad consultation and negotiation Multidisciplinary technical studies to define environmental water demands Non-environmental sector water demands
  4. 4. Environmental flows in the Mekong
  5. 5. Exploring environmental flow regimes in the Lower Sesan in Cambodia • We examined impacts of managing different flow regimes from a cascade of dams in the Upper Sesan upon the existing ecology and ecosystem services of the Lower Sesan • Explored the use of Flow Health software as a tool to link hydrological and ecological impacts • Explored the use of dynamic programming tool CSUDP to assess hydropower generation impacts
  6. 6. Flow Health software • Breaks down the complex and variable flow regime into 9 indicators of flow health that have been shown to be related to geomorphology and ecological health • Indicators are general and direct links between the hydrological indicators and ecological impacts are not defined within the program • Monthly flows do not show daily impacts from peaking
  7. 7. Dynamic programming tool CSUDP • CSUDP allows user specified definition of system state equations and objective functions, and includes efficient solution procedures for a variety of problem types • Used to quantify reduction in hydropower generation
  8. 8. THE SESAN RIVER
  9. 9. Geomorphological character of the Sesan River • Eight distinct geomorphological zones Zone 4 Zone 5 Planned Sesan 1 • Zone 4: sand banks and islands. 250-350m wide. Few minor rapids in upstream section • Zone 5: No longer in natural state. Flow retention by the dams result in a shallow river characterized by a succession of wetlands and rapids, with some rocky channels
  10. 10. Hydropower development on the Sesan River Planned Sesan 1
  11. 11. Sub-indicator scor 0.8 Flow Health analysis - Modification of flow regime by existing dams 0.6 0.4 0.2 0 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 Year Construction Yali Falls dam Yali Falls dam fully operational Sub-indicator scores Seasonality flow shift (SFS) 1 0.8 0.6 0.4 0.2 0 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 Year •Lowest flow is shifting back from April to March •Highest flow occuring earlier, shifting from September to August •Disrupting the behavior of aquatic organisms whose life cycle has adapted to a particular seasonal flow pattern
  12. 12. Flow Health analysis - Modification of flow regime by existing dams Sealing of Yali Falls dam Yali Falls dam fully operational Sub-indicator scores Persistently higher (PH) 1 0.8 0.6 0.4 0.2 0 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 Sub-indicator scores Year •Decrease inSeasonality flow shift (SFS) period of time when flow is notably higher than expected in the low flow period •Smoothing out of the low flows by the removal of natural high flow pulses because of regulation by the dams Year •Change in channel morphology 1 0.8 0.6 0.4 0.2 0 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004
  13. 13. FLOW SCENARIO IMPACT ASSESSMENT
  14. 14. Scenarios • Hydrological and energy modelling to assess impacts from 11 dam cascade for two scenarios – Full regulation - In the ‘A. Full regulation’ scenario the simulation allowed each project to use freely the full storage capacity of reservoirs in order to maximize energy production – No regulation – In the ‘B. No regulation’ scenario the reservoir levels of all projects were kept constant at full supply level so that the natural flow regime was passed through the dam unaltered. In scenario B. simulations, each hydropower project was allowed to use only 3 Mm3 of reservoir storage to improve the stability of the simulation/optimization process.
  15. 15. Impacts on energy production Full No regulation[GWh] regulation[GWh] Upper Kontum Plei Krong Yali Sesan 3 Sesan 3A Sesan 4 Sesan 1 VIETNAM TOTAL Prek Liang 2 Prek Liang 1 Lower Sesan 3 Lower Sesan 2 CAMBODIA TOTAL TOTAL OF 11 Reduction[%] 998 470 3,721 1,184 439 1,425 638 8,875 238 313 1,626 2,196 4,373 820 473 3,202 1,011 374 1,304 512 7,695 166 211 1,323 2,086 3,786 17.9 -0.6 14.0 14.7 14.6 8.5 19.8 13.3 30.2 32.6 18.6 5.0 13.4 13,248 11,481 13.3
  16. 16. Hydrological impacts below the planned Sesan 1
  17. 17. Flow Health analysis– Fully regulated Reference period Test period Sub-indicator scores 6 5 Flood flow interval (FFI) 4 Seasonality flow shift (SFS) 3 Persistently very low (PVL) 2 Persistently higher (PH) Low flow (LF) 1 High flow (HF) 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
  18. 18. Flow Health analysis– Fully regulated geomorphic implications Sub-indicator scores Flood flow interval (FFI) 1 0.8 0.6 0.4 0.2 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 Decreasing occurrence of 23 yr ARI flood • 2yr ARI flood characterizes geomorphology of the river where not rock confined • Contraction of the river channel • Increased sedimentation • Sediment aggradation reducing overall capacity of the river
  19. 19. Flow Health analysis– Fully regulated ecological implications Sub-indicator scores Persistently higher (PH) 1 0.8 0.6 0.4 0.2 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 Post-dams Pre-dams Increasing period when flow is higher than normal for more than two months in the low flow period •Change of regime for inchannel wetlands used to dry/wet variation • Wetland plants dependent on exposure of roots during dry season will be less productive and some may die out
  20. 20. Flow Health analysis– No regulation • Minor difference between the no-regulation and natural scenarios because the noregulation simulation only allowed max. 3 Mm3 regulation capacity for each reservoir • No impact on Flow Health Parameters
  21. 21. Impacts summary The No regulation scenario optimises flow and ecosystem health but causes a 13.3% decrease in overall energy production compared to the full regulation scenario The Full regulation scenario optimises the production of energy but will have significant impacts on downstream channel morphology and inchannel wetlands
  22. 22. Reaching a comprise The No regulation scenario optimises flow and ecosystem health but causes a 13.3% decrease in overall energy production compared to the full regulation scenario The Full regulation scenario optimises the production of energy but will have significant impacts on downstream channel morphology and inchannel wetlands
  23. 23. E flows challenges in the Sesan and the basin Environmental flows Consultation & negotiation Environmental demands Nonenvironmental demands 1. Technical challenges: Linking hydrological changes to complex geomorphological and ecological impacts in the Basin 2. Institutional context: Key to good consultation and negotiation

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