Assessing the Potential Sediment-Related Impacts of Hydropower Development in the Mekong River Basin

Abstract

Hydropower potential has remained mostly untapped for many years in the Mekong/Lancang River Basin, which drains land in China, Myanmar, Thailand, Laos, Cambodia and Vietnam. Currently the basin is undergoing extensive hydropower development that will likely result in altering its natural flow and sediment regimes. This in turn could significantly disrupt as many as 32 delicate and productive ecosystems throughout the region. Within the Mekong basin, the Se San, Sre Pok and Se Kong sub-basins (collectively called the “3S” basin) are a particularly important set of adjacent, transboundary watersheds with respect to biodiversity and ecological productivity, and serve as an important source of flow and sediment to the lower mainstream Mekong River. Currently, 19 hydropower projects are in operation or are under construction in the 3S basin, but this number could reach 41 by 2020 (with an installed capacity of just over 6,300 MW). Studies on potential impacts of reservoirs in the 3S basin are limited, and extensive research is still required to better understand the potential disruption of the sediment regime, which will impact (1) hydropower output and reliability; (2) the geomorphologic makeup of the system, and (3) the health and productivity of the region’s exceptionally biodiverse ecosystems. The work to be presented includes the development of a sediment accounting tool for the Mekong basin applied to the 3S basin. This tool is a daily time-step mass-balance simulation model of flow and sediment to predict in relative terms the spatial and temporal accumulation and depletion of sediment in tributary reaches and in reservoirs under different operating policies. Discussion will include use of the model to identify reservoirs that could significantly alter the natural sediment regime, and for which improved sediment and flow management practices could have a positive impact. Relative tradeoffs between hydropower production and sediment regime alteration will be discussed for different operating policies.