Since 1993, China has built six dams in the mainstream on the Upper Mekong Basin, known as the Lancang in China.
Operations of these dams have stirred many concerns from the Lower Mekong Basin communities on how these dams will impact the river and their livelihoods.
The impacts of the two biggest storage dams of the cascade, Xiaowan and Nuozhadu, have often been in the news. The concerns include how changes in water flow (discharge) impacy fisheries, sediments, and downstream community livelihoods.
While the picture of the impacts is incomplete, the Mekong River Commission’s (MRC) river monitoring arm points out that these Chinese dams do affect water flows in the Lower Mekong Basin, generally reducing water flow during the wet season and increasing it during the dry season.
Downstream water flow in the dry season increased, easing the effects of droughts. Storage dams can contribute to increased flow during the dry season as they discharge water for energy production.
For example, the release of supplemental water from the Lancang dams eased the regional drought of 2016.
The drought resulted in 16 percent less flow compared to the long term average. However, because of the emergency water releases from the Chinese dams upstream, the increased dry season flows ultimately helped to mitigate potential impacts of the drought.
A total of 12.65 billion cubic meters of water was discharged from the Jinghong hydropower reservoir during the period of March to May 2016. These releases amounted to between 40 � 89 percent of flow along various sections of the Mekong River.
The emergency supplemental water increased water level or discharge along the Mekong mainstream to an overall extent of 0.18-1.53m or 602-1,010m3/s.
If these emergency releases did not occur, flows would have been 47 percent lower at Jinghong, 44 percent lower at Chiang Saen, 38 percent lower at Nong Khai and 22 percent lower at Stung Treng. This additional flow has also alleviated salinity intrusion in the Mekong Delta.
Downstream water flow in the wet season is reduced. Conversely, in the figure below, we see a clear downward trend in wet season flows at Chiang Saen, less pronounced at Kratie, which is likely to be a result of dam operators storing water in the wet seasons and possibly an increase in extractions of wet season flows for production purposes.
In short, while the Mekong communities should be concerned about the adverse effects of Chinese dams on issues such as sediments and fisheries, these dams have not reduced downstream flows during the dry season.
Source: Lao News Agency