Vietnam, located in the lower course of Mekong, is at a disadvantageous position as more and more dams have arisen on the upper course of the river.
In July, Xe Pian – Xe Nam Noy, a dam on a Mekong’s branch in Laos, collapsed, causing severe damage to the surrounding area.
Prior to that, in May 2018, the concern about the building of Sekong1 dam on Sekong River was voiced by Gregory A. Thomas from the Natural Heritage Institute (NHI) and Jake Brunner from IUCN Indo-Burma Group.
Sekong is the only Mekong branch which has not been hindered by hydropower dam. It has become the only route still open for fish to migrate to the riverhead to breed before reaching Tonle Sap Lake in Cambodia to seek food and develop into commercial fisheries.
The blocking of Sekong River would lead to the reduction of 20 percent of total fish output of the entire basin because half of the fish caught in the Mekong River Basin are long-distance migratory species.
Plains will sink naturally and can only stay above sea level if they are constantly filled with silt, especially sand. Sekong River is also the last remaining sediment source from the 3S basins (formed by the Se Kong, Srepok and Se San rivers) to the Mekong Delta. Thus, blocking the natural flow of river is a threat to the survival of the delta.
Sekong1 has the designed capacity of 76 MW, or just equal to 1/10 of Yali, very small to contribute to the regional electricity output. The benefits expected from electricity generation are small if compared with the costs, including opportunity costs.
In 2012, scientists from Princeton University and fisheries centers in Cambodia carried out a research work to quantify the impacts of the dams on Mekong on biodiversity and food security.
Scientists found that if building all 78 dams on tributaries, not including ones on mainstream, this will produce less electricity and lead to greater environmental risks than building only six dams on the mainstream.
The dams found having the biggest impact on fish output were Lower Se San 2 which could lead to the reduction of 9.3 percent of total fish output, Sekong3d (2.3 percent), Sekong3u (0.9 percent) and Sekong4 (0.75 percent).
The increase of one terawatt hour electricity per year (TWh/y) was estimated to cause the decrease of 0.3 percent, or 1,700 tons of fish each year.
If the decrease is higher than 14 TWh/y, dams on Sekong would cause a yield loss of 1.3 percent, or 8,200 tons a year on each added TWh/y.