Chapter 19 - Damming the Mekong: Impacts in Vietnam and Solutions

Abstract

The Mekong River delta, the third largest delta in the world, is presently shifting from growing to shrinking, with its ecosystem and environment seriously degraded. These changes are due to several factors including ill-planned water management schemes, hydropower dams in the river basin, sediment starvation, increased nutrient inflows, in combination with other human activities that include infrastructural extension, riverbed mining, delta subsidence, climate change and sea level rise, degradation of the coastal mangrove belt, and gaps in governance in the whole Mekong basin. The delta is now shrinking and the rate of shrinking will increase markedly this century. The chapter compiles new data together with recent key studies implying that much of the degradation in the Vietnamese Mekong delta is due to hydropower dams in the entire Mekong river basin but particularly the big dams in China in the Upper Mekong basin (known as the Lancang basin). By comparison with the period before 1990s (when there were no big dams), the natural regime here has changed as most of the Mekong River water is now trapped in these big dams and the annual sediment load to the delta has decreased by 50%–60%, the flood discharges have also decreased, low flow events are now common, the hydrological seasonal regime has shifted resulting in earlier and more severe salinity intrusion into the delta as well as flooding from storms at sea are now not blocked by the river discharge. Further, the riverbed is on the average deeper by 1.3m, to which riverbed mining also contributes. There has been a recent increase of erosion of riverbanks (400 locations) and coasts (66% of the foreshore is eroding) and their occurrence is increasing. If all the proposed mainstream hydropower dams in the Lower Mekong Basin were built, then the Vietnamese Mekong delta with its ecosystems and about 18 million people face critical issues of sustainability. The chapter also focuses on some remedial solutions that may decrease, but not eliminate, the negative impacts of these dams for the Vietnamese Mekong delta. Nonengineering solutions have the highest propriety, but engineering solutions are needed for protecting eroded coastal foreshore, riverbanks, and the mangrove belt. However, a long-term solution requires China adapting the use of its dams to accommodate the concerns of Vietnam.