Lower seasonal floods threaten Mekong Delta

In early September, fishermen gathered along a riverbank in Moc Hoa District of Long An Province to prepare for a new harvest season.

One of them is Nguyen Thi Phung, 49, who has been doing the job for almost 20 years now.

Residents of the delta, which is on the downstream reaches of the Mekong River, have for generations depended on the annual floodwaters to inundate their fields before sowing seeds, especially in the Plain of Reeds, a wetland straddling Long An and Dong Thap provinces.

Phung said that in the past, the floodwaters rose high and her family could catch 50-70 kg of fish per day.

"But this year the water is low and the output has dropped by half."

Fishermen in a flooded rice field in Long An Provnce, September 4, 2023. Photo by VnExpress/Hoang Nam

Lying 100 km away, rice fields in Hong Ngu District in Dong Thap Province have been prepared for the year's third crop.

Farmer Nguyen Van Thai said in previous years, those fields would be flooded, but in recent years, the floods have been absent, and therefore he and other farmers decided to grow different crops in between the winter-spring and summer-autumn rice.

For generations, floods have arrived in the delta in late July or early August and remained until November or even later, blessing the region with extraordinary fertility as they deposit silt from upstream areas.

The floodwater, especially overland water, provides migration routes and breeding sites for many species of fish, distributes sediment that retains nutrients for agriculture, recharges groundwater aquifers, and prevents salt intrusion, not to mention washing away chemical residues left from previous crops.

"For each hectare of rice field, it costs VND20 million (US$830) for fertilizers and pesticide. If the floodwaters are high, farmers could save 20-30% of that cost as the water washes away pests and brings along alluvia that is good for the soil," said Thai.

A rice field in Dong Thap Province is left with no floodwaters in early September. Photo by VnExpress/Ngoc Tai

Vo Kim Thuan, head of Long An’s Department of Agriculture Development and Irrigation, said the flooding season arrived in time this year but with lower water levels.

As of late last month, the water level in the Plain of Reeds ranged from 0.54 – 1.57 m, which is lower than last year and the last 20 years’ average by 0.02 – 1.69 m.

In An Giang Province, the water level is currently one meter lower than the average of previous years.

Nguyen Nghia Hung, deputy head of the Southern Institute of Water Resources Research (SIWRR), said the institute predicts that the seasonal flood levels this year in the Mekong Delta will be lower than previous years by 0.2 – 0.42 m.

Hung said part of the reason is impacts of El Nino, which causes less rain.

In addition, hydroelectric reservoirs upstream the Mekong have held back 13-29% of water, or 65 billion cubic meters.

"The abnormal flow of the Mekong has caused the flood levels in the Mekong Delta to drop in the past 20 years," he said.

According to SIWRR, with the low level of floodwaters, farms should be ready for salt intrusion that is likely to arrive sooner than usual once the dry season kicks in.