Despite the completion of lower cascade of six hydropower dams on the Lancang River (Upper Mekong) in 2014, little is known about the environmental impacts of the Lancang Dams. To better understand the environmental impacts, over the past two and a half years, International Rivers has travelled the length of the Lancang River in China, reviewed Chinese and English research literature on the Lancang dams and collected hydrological data from Lower Mekong countries. International Rivers has prepared a research brief examining the impacts of the Lancang dam cascade on hydrology, fisheries and sedimentation.
We found that the dams’ impacts are extensive with significant implications for the millions of people who rely directly on the lower Mekong river for their livelihoods. Fish are the main source of protein for many people throughout the Lower Mekong basin, with the hydrological and sedimentation schemes fundamental for the habitat where fish live and reproduce. One report we examined found that the operation of the Lancang dams is altering flow by as much as 49% during the dry season and can be felt as far as Kratie in Cambodia. Altering the hydrological and sedimentation schemes and blocking fish migration will potentially reduce fish stocks and change fish composition in the Mekong River, and lead to food security and livelihood risks. Another study we examined found that in the first ten years of the operation of Manwan Dam alone, it was estimated that 35% of the total sediment transported from the Lancang River to the Lower Mekong was trapped. The impacts of an altered hydrological regime and sediment flow goes beyond food security. The the reduction of sedimentation deposit and associated seawater intrusion in the Mekong delta will affect the highly productive agricultural and rice fields in the region, which depend on the nutrients that the Mekong River transports in its sediment, and therefore create even bigger challenges in food and livelihoods.
With another seven dams, now under construction on the middle Lancang (Miaowei, Dahuaqiao, Huangdeng, Tuoba, Lidi, Wunonglong, Gushui), International Rivers expects to see further impacts to come on the Lower Mekong from further hydropower development of the Lancang River.