Keep the River Free-Flowing Through Cambodia to the Sea by Redesigning the Sambor Dam:
The Sambor dam, proposed by the Government of Cambodia, is probably the largest and most destructive dam in the Mekong River Basin. It is slated to be located on the mainstream between the confluence with the 3-S basin, which is where migratory fish reproduction takes place, and the Tonle Sap Great Lake, the most productive freshwater lake fishery in the world. The original Sambor project proposed a dam 56 meters high and 18 kilometers wide that would result in a 82 km reservoir all the way up to the confluence of the 3-S tributaries at Stung Treng. It would create a complete barrier to fish and would trap 50% of the sediments and nutrients needed to nourish Tonle Sap and replenish the delta. Some 20,000 people are expected to be displaced according to the Mekong River Commission’s (MRC) 2010 Strategic Environmental Assessment (SEA) on Mekong mainstream dams.
Replacing the dams slated for the Xe Kong mainstream will keep the intact portion of the Mekong River System free-flowing all way to the sea if, but only if, the Sambor Hydropower Project on the mainstream is redesigned. This dam could literally kill the Mekong River and devastate Cambodia’s economy and food security.
NHI is working under a formal agreement with the Ministry of Mines and Energy of the Kingdom of Cambodia to assess alternatives to the Sambor Dam that will keep the river free-flowing, maintain 95% survival of fish moving upstream and downstream through that corridor, and discharge virtually all of the sediments and nutrients into the Tonle Sap Great Lake and the Vietnam delta.
NHI project has now investigated 10 alternative designs to ameliorate the horrific impacts of this dam. The designs for the two best performing finalists are now being completed. One would locate a much smaller dam on the main channel, leaving all of the side channels free-flowing. The other would locate an even smaller dam on the side channels, leaving the mainstream free flowing.
A preliminary paper on principles and concepts for the design of the fish passage facilities at the Sambor alternative proposed by NHI has been produced by Dr. Martin Mallen-Cooper, a NHI project’s team member. Entitled “Fish Passage at Sambor Dam: Preliminary Design Criteria and Concepts,” the approach of the paper is to base the design and operational parameters on the key aspects of the life history of the migratory fish that pass the Sambor site, both upstream and downstream. It has been used to inform the discussions with the Cambodian counterparts.
In addition, a study on “Operating Policies to Improve Sediment and Fish Passage, and Implications for Energy Production” has been conducted by NHI’s technical team to serve the purpose of comparing energy production at the original Sambor plan to the alternative concept with 3 measures for maximizing (i) sediment passage, (ii) upstream/downstream fish passage, and (iii) downstream egg/larvae passage implemented. Preliminary results show the optimal sediment passage policy is by bypassing sediment during monsoon, sluicing non-bypassed sediment during monsoon and flushing every 15 years. The analysis concludes that sediment management and fish passage will not significantly reduce mean annual energy production.
It is prudent to assume that some version of the Sambor Dam will be constructed, and soon. The question is which one, and when. This project is on the official water resources plan of the Government of Cambodia, and it a top priority after completion of the Lower Se San 2 dam. It is imperative that this work be completed so that the government will be well apprised of the best option for keeping the river alive.
- Expected output: Comparative assessment of alternatives for Sambor, showing tradeoffs between hydropower production and fish survival.
- Outcome: Adoption of the least impactful alternative as the project for which the Government of Cambodia will entertain competitive proposals for hydropower development.
- 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)