Designing fish passage facilities at Lower Se San 2 Dam – Cambodia:
Lower Se San 2 hydropower dam is being constructed just below the confluence of the Sre Pok and Se San (3-S tributaries) in Cambodia. This dam is now 70% complete, and the scale of the dam poses an absolute barrier to both upstream and downstream fish migration, yet until NHI’s involvement, it was being built without any means of passing migratory fish.
The Environmental Impact Assessment for the Lower Se San 2 Hydropower Dam (ECC1 & Key Consultants Cambodia Oct. 2008) concludes at page S-4/5:
“Impacts on fish will be severe as many species are migratory (around 66%) and their passageway through the project area will be blocked by the dam. This will also have impact downstream of the dam into the Mekong River and potentially also the Tonle Sap Lake as this is where some fish migrate to/from. The impacts will occur whatever the dam size as it will block fish passage through the dam site, some species may disappear of change and there shall be potentiality of natural fish yield’s reduction.”
A report in the Proceedings of the National Academy of Science estimates that 9.3% of the fisheries biomass of the entire river will be lost due to this dam.
Fish and other aquatic animals are crucial for food and nutritional security and provide more than 76% of the total animal protein and much of essential minerals and vitamins in the diet of the Cambodian people. From a nutritional point of view, fish are a rich source of protein, fatty acids, and essential vitamins and minerals such as Vitamin A, calcium, iron, zinc, and iodine. Therefore, a diet rich in fish protein can be used to alleviate micronutrient malnutrition that is widespread particularly among preschool-aged children and lactating women in Cambodia.
Avoiding a devastating loss in the Mekong fishery, with subsequent impacts on food security and livelihoods, depends on devising feasible measures to aid migration of fishes around the dam and through the reservoir, both upstream and downstream, to connect appropriate habitats to complete the life cycles of these species.
Interacting with the Cambodia Ministry of Mines and Energy, and through NHI’s constructive working relationship with Hydrolancang International Energy (HIE), the developer of Lower Se San 2, NHI has been able to get HIE to agree to incorporate a fish by-pass into the construction of the dam (on the right bank). NHI is working to remedy the design flaws in the proposed right bank fish pass facility, design a left bank and downstream migration solution, and devise a financing strategy to get these improvements implemented. The NHI technical team has already produced an initial report on “Fish Passage at Lower Se San 2 Dam: Design Principles, Preliminary Criteria and Concepts,” and also provided a critique of the HIE’s fish by-pass design and proposed solutions to make it effective.
- Outputs: Improved design of fish passage facilities at LSS2.
- Outcome: Greatly improved survival of migratory fish past the dam and through the reservoir.
- Ministry of Water Resources and Meteorology (MOWRAM)
- Ministry of Mines and Energy (MME)
- Ministry of Environment (MOE)
- Inland Fisheries Research and Development Institute (Fisheries Administration of Ministry of Agriculture) (IFREDI)
 Ziv, G., Baran, E., Nam, S., Rodriguez-Iturbe, I. and S. Levin. 2012. Trading-off fish biodiversity, food security, and hydropower in the Mekong River Basin. Proceedings in the National Academy of Sciences. 109, 5609-5614.