Stanford computer models show that small dams on Mekong River tributaries could have catastrophic impact on fish and people

Planned dams in Southeast Asia would affect fish productivity and biodiversity in the world's largest inland fishery, says Stanford researcher Guy Ziv.

Pianporn Deetes / Creative Commons A bend in the Mekong River at the site of the proposed Xayaburi Dam in the Xayaburi province of Northern Laos.

A bend in the Mekong River at the site of the proposed Xayaburi Dam in the Xayaburi province of Northern Laos.

New dams planned for tributaries of the Mekong River in Southeast Asia will be more environmentally destructive and will produce less energy than the dams in the main river, according to Stanford researcher Guy Ziv.

"You can get the same energy production with very different environmental impact, depending on which dams you build," said Ziv, the lead author of a study recently published in Proceedings of the National Academy of Sciences.

The study looked at 27 tributary dams planned for construction between 2015 and 2030. The future of those dams is still to be decided, but if built they would significantly affect fishing. Laos plans to build 26 of the 27 dams, but the most significant effects will be felt in the fisheries of neighboring Cambodia.

Dams block fish from migrating, and more than a million tons of freshwater fish are harvested in Vietnam and Cambodia annually.

"The revenue will come to Laos, by exporting energy to Thailand and Vietnam," Ziv said, "and the fish will be lost in the floodplains of Cambodia and Vietnam, but mainly in Cambodia."

"[The loss of fish] translates to a big impact on food security of a very poor population," he said. "There is a huge population that relies on a cheap food supply from fish, and their livelihood will be impacted."

Tributary dams

The international Mekong River Commission, a coalition of Laos, Cambodia, Vietnam and Thailand, regulates the dams in the main stream of the Mekong River. However, the individual nations regulate the offshoot tributary dams and only need to notify the commission, rather than seek its approval. Ziv's study focused mainly on tributary dams, an often-overlooked area of environmental impact, he said.

The commission is considering scenarios including these 27 tributary dams, and up to 11 mainstream dams in the lower Mekong River Basin.

If only the planned tributary dams are built, the migratory fish population in the Mekong will decline by 19 percent, according to Ziv's computer projections. If, however, six of the mainstream dams are built, the fish population will decline by only 7 percent, while the dams will produce 49 percent more power.

Using the computer models, Ziv and his collaborators calculated the energy production and the loss of fish if certain dams were built. They used that model on every configuration of building or not building any of the 27 dams, resulting in more than 130 million scenarios. This data allows planners to quickly identify which scenarios produce the best results.

"If you want a certain amount of energy, [our calculations showed] which dams you should build to minimize the impacts on food production," Ziv said.


Cambodia's only planned tributary dam of the 27, the Lower Se San 2 Dam, is the most disruptive. "Lower Se San 2 Dam is probably good to be avoided, unless you need all the energy you can supply," Ziv said. The Cambodian government approved the dam last year, although construction has yet to begin.

The next most damaging dams would be those built in Sekong Province in Laos. "The benefits are questionable, unless you really need more than 15 terawatt hours per year," said Ziv.

"Our results really suggest that some dams can and should be avoided," Ziv said. "It calls for some change in the international agreement in the area."

Furthermore the amount of fish lost correlates with the number of endangered species affected. Biodiversity provides a role in supporting the ecosystem, although that role is vague, underestimated and hard to give an economic value, Ziv said.

"This is a first step," he said. "Getting a more complete picture requires getting the impact on sediments and the social costs. We hope something along this line can be done [in the future] in collaboration with the stakeholders."

Stephen Tung is an intern at the Stanford News Service.

Dan Stober, Stanford News Service: (650) 721-6965,