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. 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
- 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. Environmental flows in the Mekong
- 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. 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. 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
- 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. Hydropower development on the Sesan River Planned Sesan 1
- 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. 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. FLOW SCENARIO IMPACT ASSESSMENT
- 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. 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. Hydrological impacts below the planned Sesan 1
- 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. 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. 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. 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. 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. 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. 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
Notas do Editor
- Many views so first defineDirty word – could be integrated flow managementConcept not just cover the flows but also the assessment to reach the flow agreementToday focussing on the technical studies but should also remember the need for consultation and negotationMany views on what e-flows are so want to start with a definition:t he provision of water for freshwater dependent ecosystems to maintain their integrity, productivity, services and benefits.But the concept does not just cover the flows themselves it also refers to the technical studies and consultative approach needed to define and implement them. A good environmental flows assessment that will have long term outcomes will engage all the water users and setup the institutional context for an informed trade-offwhich limits negative environmental and social impacts while maximizing the opportunity for further development.Discussing and setting E-flows regimes require the integration of a range of disciplines from across the social, political and natural sciences. Today will be introducing some of the more technical initial work required for e-flows, to provide an idea of the technical start needed but recognizing the need for broad consultation and further work before any decisions could possibly be made.Doesn’t need to be called E-FLOWs, can be a dirty word – can call it integrated flow management
- People in the basin depend on environmentalresources so eflows are an important approach in the current context of increasing dams and other water demands. MRC Integrated Basin Flow Management program (2003-2007) – under the Mekong agreement the procedures to agreeing flows specifies minimum flows so focussed on minimum flows. As part of the new proposed council study the MRC will be seeking to apply the DRIFT model for environmental flows – i.e. so it has returned under a new nameTwo excellent examples like to highlight – supported by IUCNHuong River Basin, rapid eflows assessment (2003-2004) – supported by IUCN - outside the basin but a excellent example of holistic but rapid eflows assessmentNam Songkhram River Basin, 2006 – 2007 – supported by IUCN – slightly more complex intermediate eflows approachKey difficulty for all the assessments is linking hydro changes to ecological impacts. E-flows processes have substantial potential in the Mekong Basinto assist river basin managers as they grapple with competing demands, including the need for environmental sustainability.At present, however, the tool has only been used in academic or technical settings
- Illustration of technical study needed to development environmental flows
- Relies on hydrological analysis to calculate indicators of flow health. The indicators used in the program have been chosen to characterise attributes of the flow regime in terms of the main ecologically relevant flow components –they are necessarily general and direct links between the hydrological indicators and ecological impacts are not defined within the program. Linking of the flow indicators to particular risks to the downstream ecosystems must be interpreted by the user.
- Study of the geomorphological character and habitats of the Sesan and their importance for fish identified the eight distinct geomorphological zones of the river For example below the planned Sesan 1:
- The first large hydropower project to be built on the Sesan river was built at Yali Falls,begun in 1993 and sealed in 1996, fully operational in 2001. Since then a total of six other large hydropower projects have been constructed in the Upper Sesan in Vietnam. The total installed capacity of hydropower in Vietnam is 1,829 MWNo dams have yet been built on the Sesan in Cambodia, although Lower Sesan 2 has been approved and is waiting for construction. Plans for another 2 the mainstream on the Sesan, namely Sesan 1/5 which is located on the border and would be a joint project between Vietnam and Cambodia, Lower Sesan 3 which has a very large reservoir areas. If all the projects are built, the total installed capacity of hydropower in Cambodia would be 873 MWNote Sesan 1 at the border of Vietnam and Cambodia, at the bottom of the 8 dam cascade
- Since construction of the Yali falls dam began there is a clear decrease in the seasonality flow shifts sub-indicator at all sites. Closer analysis of the time series shows that the month of lowest flow is shifting back from April to March and occasionally to February. The highest flow month is also tending to occur earlier, shifting from September to August. The change in seasonality is important because it can disrupt the natural timing of flow pulses and baseflows that stimulate the behavior of aquatic organisms whose life cycle has adapted to a particular seasonal flow pattern (Gippel et al, 2012).At all three sites the persistently higher sub-indicator has shown a marked decrease since the sealing of the Yali falls dam in 1996. This is particularly noticeable for the years 2000-2001 where the indicator dropped to almost zero at all sites. The sub-indicator reflects the period of time when the flow is persistently (i.e. for two or more consecutive months) notably higher than expected in the low flow period (i.e. exceeding the 75th percentile of the reference period). The sharp decrease in the sub-indicator since the sealing of the Yali falls dam indicates a smoothing out of the low flows by the removal of natural high flow pulses that are regulated by the dam.
- Since construction of the Yali falls dam began there is a clear decrease in the seasonality flow shifts sub-indicator at all sites. Closer analysis of the time series shows that the month of lowest flow is shifting back from April to March and occasionally to February. The highest flow month is also tending to occur earlier, shifting from September to August. The change in seasonality is important because it can disrupt the natural timing of flow pulses and baseflows that stimulate the behavior of aquatic organisms whose life cycle has adapted to a particular seasonal flow pattern (Gippel et al, 2012).At all three sites the persistently higher sub-indicator has shown a marked decrease since the sealing of the Yali falls dam in 1996. This is particularly noticeable for the years 2000-2001 where the indicator dropped to almost zero at all sites. The sub-indicator reflects the period of time when the flow is persistently (i.e. for two or more consecutive months) notably higher than expected in the low flow period (i.e. exceeding the 75th percentile of the reference period). The sharp decrease in the sub-indicator since the sealing of the Yali falls dam indicates a smoothing out of the low flows by the removal of natural high flow pulses that are regulated by the dam.
- Reduction in Vietnam of about 1000GWHReduction in Camodia of about 500GWHTotal 13% reduction in electricity production
- Sesan 1 on the VN/Cam borderSimulated downstream discharges of Sesan 1 under scenarios A. Full regulation and B. No regulation Note that no regulation close to matches the natural flowFull regulation – reduced peak, delayed peak and high dry season flowsAverage over the 6 years modelled – put the full time series into the Flow Health software
- Used flow health software to assess impact on the hydrological regime. Software provides indicator scores for impacts on hydrology.Put up quickly to show all indicators but focus on key changes
- Flood frequency is decreasing due to regulation of water by the dams. The flood flow interval steadily decreases from the start of the test period indicating that major floods may not ever occur if the system is fully regulated. Reduced flood frequency may mean that flows that overtop the banks and inundate floodplain wetlands will occur less often which would severely impact on the floodplain ecosystem health. Contraction of the river channel may occur because not receiving high and scouring flowsIncreased sedimentation particularly at tributary confluencesSediment tends to aggrade raising the level of the river bed, reducing overall capacity of the river and therefore easier occurrence of floodplain flooding
- There is a sharp decrease in the persistently higher sub-indicator under fully regulated conditions. This result indicates that there will be an increase in the period of time when the flow is persistently (i.e. for two or more consecutive months) notably higher than the expected range in the low flow period (i.e. exceeding the 75th percentile of flow in the low flow period). The increase in flow volume during the low flow period is likely to be due to the storage of water during the high flow period for release during the low flow periods. Increasing time when flow is higher than normal for more than two months in the low flow period Parts of the channel which are used to being exposed during last 2-3 months of dry season will no longer be exposed In-channel wetlands used to the variation will no longer be exposed Wetland plants typically depend on having their roots exposed during the dry season so will be less productive and some of the vegetation may die out