Mitigating Dam Conflicts in the Mekong River Basin

Abstract

The Mekong/Lancang River Basin is undergoing a period of rapid hydropower development, with plans to construct over 100 dams in the next several decades. These dams may alter the river’s natural flow and sediment regimes, which could significantly degrade the exceptional biodiversity and productivity of the basin’s ecosystems. Sediment that is trapped in reservoirs will be unavailable to support the basin’s geomorphology and habitats, and by reducing reservoir water storage capacity may decrease hydropower output and reliability. This paper illustrates how alternative dam location, design and operation may have the potential to reduce reservoir sediment trapping. This paper describes the simulation model used to identify alternative siting, design and operating options for two planned dams in Cambodia: Sambor on the Mekong River and Lower Se San 2 on a tributary of the River. Lower Se San 2 Dam is particularly important with respect to biodiversity and ecological productivity. Sambor Dam could prevent significant quantities of sediment from reaching Tonle Sap Lake and the Vietnam Delta, two critically important features of the river basin. Results from daily simulations of water and sediment flows show the extent to which sediment management practices could reduce the adverse impacts of reservoir sediment trapping if conducted in an environmentally friendly manner, as well as the loss in hydropower production resulting from those practices.