The influences of the hydropower dams on the Mekong River on Vietnamese farmers are becoming more apparent: floods and salinity have penetrated rice fields, aquatic resources have decreased, and alluvium cannot reach the delta.

Farmers attending a seminar held in Can Tho City on August 21-22, on the threshold of consultation among Mekong region countries about the Donsahong hydropower plant on the Mekong’s main stream, all expressed their worries about the possible impact of the dam.

“In the past, we could easily predict the weather conditions based on the natural water flow, and cope with natural calamities, including floods. But now we cannot respond to emergencies because the river current has changed a lot,” said Nguyen Van Hiep, a farmer from Tam Nong District in Dong Thap Province.

According to Hiep, farmers now find it hard to draw up their production plans, because floods come in rainy season, while the river gets exhausted in dry season, paving the way for salinity to penetrate more deeply into the mainland.

“The aquatic resources are on the decline, while alluvium has been blocked and cannot go to the delta. As a result, we have to spend more money on fertilizer to enrich the soil,” he said. “The hydropower dams on Mekong River have deprived us of our livelihood.”

Researchers found that Donsahong dam would lead to a 50 percent decrease in the volume of water to be provided to the lowlands in the dry season, because the Mekong overall flow (this comprises 17 branches) collects water for Housahong, which is blocked by Donsahong dam.

Research works have found that 75 percent of the fish on the Mekong’s main stream go through Housahong branch as there is no waterfall.

So, when Housahong’s current is blocked, the natural migration of the fish would not be possible, which can cause big changes to the region’s ecosystem.

According to Dr. Le Anh Tuan from the Climate Change Research Institute of Can Tho University, Donsahong is the second hydropower dam to be built on the Mekong’s main stream located in Lao territory.

This would be a hydropower dam with no storage reservoir, 32 meters in height and designed capacity of 260 MW. 

Meanwhile, it is expected that another 19 hydropower dams would also be built on the Mekong’s main stream. China has four operational, while it is planning to build four more. Laos is building Xayabury and is going to build Donsahong; it is also planning to build seven more. Cambodia is also going to build two dams.

The hydropower potential of the Mekong River, by international scientists’ estimates, is about 54,000 MW. However, Tuan said, the hydropower plants on the main stream would lead to the extermination of many catfish and other migrating fish species.

Meanwhile, Dr. Duong Van Ni from Can Tho University fears that in the context of  climate change, the hydropower plants on Mekong would also pave the way for salinity to encroach on the delta in the rainy season.