Standing on his land next to the Mekong River, Tran Van Cung of Vietnam can see his rice farm wash away right in front of him.
The farm’s edge is falling into the river delta.
Just 15 years ago, the river carried 143 million metric tons of sediment through the Mekong River Delta every year. The process carried essential nutrients along the river’s edge that helped keep tens of thousands of farms productive.
But Chinese-built hydroelectric dams have caused the river to spread out. Much of that sediment is now being blocked. That information is based on a study of satellite imagery by the German remote sensing company EOMAP and the news agency Reuters.
The study supports earlier estimates by the Mekong River Commission that, in 2020, only about one-third of those river soils would reach the floodplains in Vietnam.
The commission also estimated that less than five million metric tonnes of sediment will be reaching the delta each year by 2040.
The Mekong River is a farming and fishing lifeline for tens of millions of people. The river stretches nearly 5,000 kilometers. It flows through China, Laos, Myanmar, Thailand and Cambodia before reaching Vietnam.
Cung, the Vietnamese farmer, has grown rice at his family’s 10-hectare farm for more than 40 years.
“Without sediment, we are done,” he said. His yearly harvest brings in less than half the money that he earned only a few years ago. His two children and several of his neighbors have left the area in search of more dependable work.
For many years, scientists and others have warned that upstream dam projects would have serious and harmful effects on the rice-growing industry. The area’s rice market is worth $10.5 billion. Rice is a major source of food for up to 200 million people across Asia.
Because of these worries, Cambodia has temporarily halted its plans for building two dams on the river.
But in China and Laos, the dam-building continues. Seven new dams are planned in Laos. At least four are co-financed by Chinese companies, the Mekong Dam Monitor says.
Using data from thousands of satellite images, EOMAP and Reuters examined sediment levels around four major dams on the Mekong – two in China and two in Laos.
The analysis showed the presence of each dam greatly reduced the sediment that should have flowed through the river.
Farmers in the Vietnamese Mekong River Delta were not prepared for the speed at which their land has changed.
The area where rice farming takes place has shrunk by five percent in the last five years alone.
Many rice farmers have been forced to do shrimp farming in salty seawater instead. Yearly earnings in this once-booming area are now among Vietnam’s lowest.
EOMAP and Reuters studied satellite images taken over 30 years around four major dams in China and Laos. The examination found evidence that the dams are greatly reducing sediment flow.
The study used measurements of the amount of light scattered by solid particles suspended in water as a way to estimate sediment levels. Sediment clouds the water as it flows. The cloudier the water, the more sediment it is likely carrying.
Scientists not involved in the examination agreed that the findings made clear that the dams were a major reason for the delta’s sediment loss.