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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
MK3: Optimizing cascades or systems of reservoirs in small catchments
Jeremy Carew-Reid, Tarek Ketelsen, Peter-John Meynell, Timo A. Räsänen and Simon Tilleard
ENVIRONMENTAL FLOWS
Environmental flowsEnvironmental flows: the provision of water for freshwater dependent ecosystems to maintain
their integrity, productivity, services and benefits
Broad consultation and negotiation
Non-environmental sector water
demands
Multidisciplinary technical studies to
define environmental water demands
Environmental flows in the Mekong
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
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
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
THE SESAN RIVER
Geomorphological character of the Sesan River
• Eight distinct geomorphological zones
Zone 4
Zone 5
• 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
Planned Sesan 1
Hydropower development on the Sesan River
Planned Sesan 1
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1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004Sub-
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Persistently higher (PH)
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1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004Sub-
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Seasonality flow shift (SFS)
Flow Health analysis - Modification of flow regime by existing dams
Construction Yali Falls dam Yali Falls dam fully operational
•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
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1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004Sub-
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Persistently higher (PH)
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1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004Sub-
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Year
Seasonality flow shift (SFS)
Flow Health analysis - Modification of flow regime by existing dams
Sealing of Yali Falls dam Yali Falls dam fully operational
•Decrease in 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•Change in channel morphology
FLOW SCENARIO IMPACT ASSESSMENT
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.
Impacts on energy productionFull
regulation[GWh]No
regulation[GWh] Reduction[%]
Upper Kontum 998 820 17.9Plei Krong 470 473 -0.6Yali 3,721 3,202 14.0Sesan 3 1,184 1,011 14.7Sesan 3A 439 374 14.6Sesan 4 1,425 1,304 8.5Sesan 1 638 512 19.8VIETNAM TOTAL 8,875 7,695 13.3Prek Liang 2 238 166 30.2Prek Liang 1 313 211 32.6Lower Sesan 3 1,626 1,323 18.6Lower Sesan 2 2,196 2,086 5.0CAMBODIA TOTAL 4,373 3,786 13.4
TOTAL OF 11 13,248 11,481 13.3
Hydrological impacts below the planned Sesan 1
Flow Health analysis– Fully regulated
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Flood flow interval (FFI)
Seasonality flow shift (SFS)
Persistently very low (PVL)
Persistently higher (PH)
Low flow (LF)
High flow (HF)
Reference period Test period
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Flood flow interval (FFI)
Flow Health analysis– Fully regulated geomorphic implications
Decreasing occurrence of 2-3 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
Flow Health analysis– Fully regulated ecological implications
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Persistently higher (PH)
Increasing period when flow is higher than normal for more than two months in the low flow period •Change of regime for in-channel 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
Pre-dams
Post-dams
Flow Health analysis– No regulation
• Minor difference between the no-regulation and natural scenarios because the no-regulation simulation only allowed max. 3 Mm3 regulation capacity for each reservoir
• No impact on Flow Health Parameters
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
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
Reaching a comprise
Environmental flows in the Sesan need to reach
a compromise between the two
E flows challenges in the Sesan and the basin
1. Technical challenges: Linking hydrological changes to complex geomorphological and ecological impacts in the Basin
2. Institutional context: Key to good consultation and negotiation
Environmental flows
Consultation &
negotiation
Non-environm
ental demands
Environmental
demands
