Mainstream Dams Threaten the Mother of all Rivers

by Shannon Lawrence and Carl Middleton
Friday, June 1, 2007

While China is midway through the construction of a controversial cascade of major dam projects on the Upper Mekong mainstream, the lower stretch of the river shared by Thailand, Cambodia, Laos and Vietnam has so far escaped hydropower development. For the 60 million people who depend on the lower Mekong for food, income, transportation and other services, that has been good news. But now there are troubling signs that the tide is turning, as Laos and Cambodia offer up stretches of the mighty Mekong to dam builders.
In 1994, the Mekong Secretariat (the precursor to the Mekong River Commission, or MRC) produced a study of “run-of-river” hydropower schemes for the lower Mekong. The study proposed nine projects that would produce a total of 13,350 megawatts of electricity (most of which would be exported to Thailand) and displace an estimated 57,413 people. IRN responded then with an analysis that stated: “The report attempts to give the impression that these projects are small dams without storage reservoirs. In fact, what is proposed is a staircase of dams 30 to 60 meters high with reservoirs covering more than 600 kilometers of the 1,800 kilometers studied. The six dams and reservoirs recommended are on a comparable scale to the Bonneville Dam on the Columbia River in the US Northwest. Such massive dams cannot be considered ‘run-of-river’ projects.”

The Mekong Secretariat study failed to adequately consider the significant impacts the proposed dams would have on fisheries throughout the Mekong River basin, such as blocking migration routes and inundating spawning grounds. According to IRN’s review, the study also ignored the downstream impacts on the Mekong Delta, failed to assess the water quality impacts of the dam cascade, and included inaccurate resettlement estimates.

Fortunately, none of these schemes got off the ground in the late 1990s. The 2001 Mekong River Commission’s Hydropower Development Strategy attributed the failure to develop mainstream Mekong dams to four factors: riparian countries’ focus on tributary projects within their national borders; the unfavorable political situation in the region; the significant costs of the projects; and the “formidable” fisheries and resettlement impacts of the mainstream dams.

The MRC Hydropower Strategy went on to note, however, that conditions were beginning to change. With increasing power demand in Thailand and Vietnam and a move away from thermal power plants, renewed interest from private developers and state-owned utilities with financial and managerial “spare capacity,” and the rising price of energy alternatives, riparian countries began to look again at damming the lower Mekong. By mid-2007, Laos and Cambodia had signed agreements for the development of four mainstream Mekong dams.

Laos’ planned dams  

The mainstream Mekong dam at the most advanced stage of consideration is Don Sahong in the Khone Falls area of Laos. Mega First Corporation Berhard from Malaysia is conducting a feasibility study on Don Sahong that is expected to be completed shortly. The 240 megawatt (MW) dam would generate power for export to either Thailand, Cambodia or Vietnam. Although little information is available about Don Sahong, news reports estimate the project cost to be $300 million.  

Khone Falls is the only waterfall on the lower Mekong and is a key area for Mekong fisheries. The Don Sahong Dam, located less than one kilometer upstream of the Cambodia border, would block the sole channel that fish migrating up from Cambodia can easily pass, known as Hoo Sahong in Laos. As a result, the dam could prevent fish migrations up the Mekong River from Cambodia and Vietnam to Laos and Thailand, ultimately undermining fisheries-based livelihoods in all four countries. In fact, a Mekong River Commission 1996 newsletter noted: “The blocking of Hoo Sahong could devastate much of the most important Mekong River fisheries in Laos.”   

In May, more than 30 scientists sent a letter to Mekong-region government officials expressing concern about the proposed dam’s impacts on fisheries. The letter states: “The location of this proposed dam is probably the worst possible place to site a 240 MW project since it is the point of maximum concentration of fish migration in the river that supports the world’s largest freshwater fishery.” The scientists’ letter cites a 2002 fisheries review commissioned by the MRC which determined that the construction of fish passages to mitigate impacts on fish migrations is “simply not valid for larger projects.”