Anticipated geomorphic impacts from Mekong basin dam construction

ABSTRACT

The Mekong River is undergoing rapid dam construction. Seven mainstem dams are completed or under construction in China and 133 completed or proposed for the Lower Mekong River basin. We combined geomorphic assessments of the Mekong channel and delta with models of sediment trapping by reservoirs to forecast geomorphic change. We expect the biggest changes to occur along alluvial reaches, though stripping of thin sediment deposits in bedrock reaches may also have significant consequences for benthic invertebrates, fishes, and other aquatic organisms dependent on the presence of alluvium in the channel. If all dams are built as proposed, the resulting 96% reduction in sediment supply would have profound consequences on productivity of the river and persistence of the delta landform itself. Strategies to pass sediment past dams should be implemented to reduce the magnitude of sediment starvation and resulting impacts.

Keywords:

• Mekong River
• sediment load
• reservoir sedimentation
• channel change
• dam construction

Acknowledgements

Tim Burnhill and George Annandale provided helpful background information and insightful comments. We also thank Tom Wild, Matti Kummu, Jorma Koponen, Chris Alford, and Steve Darby for helpful discussions and background information.

Funding

This research was performed in conjunction with the Natural Heritage Institute (San Francisco), partially funded by a grant from the U.S. Agency for International Development (USAID) under Cooperative Agreement AID-486-A-11-00002 for the project ‘A Climate-Resilient Mekong: Preserving the Flows that Nourish Life’, the Mekong River Commission, and the Beatrix Farrand Endowment of the Department of Landscape Architecture at the University of California Berkeley.