Half of Viet Nam’s agricultural land would be drowned under sea water if global warming raises the surrounding ocean-level by a metre, flooding the Red River and Mekong River deltas.

Ninety per cent of the Mekong River Delta and 35 per cent of the Red River Delta and could be soaked in salt water, Deputy Minister of Agriculture and Rural Development Dao Xuan Hoc told a conference held in Ha Noi on Wednesday.

"The flooding in Mekong Delta would last for four to five months during the rainy season and 70 per cent of its area would be affected by salt water in dry season," he said. The Mekong Delta is 4,060,400ha wide.

The most vulnerable localities in the Mekong region include Can Tho, Long An, Soc Trang, Ca Mau, and HCM City, with the flooding occupying from a quarter to half of each locality’s area.

Though 78 per cent of Red River Delta’s 1,486,000ha are protected by a dyke system, there are worries about how well the dykes will hold once the sea level reaches one-metre, equal to the dykes’ pitch.

In addition to forestation to protect the existing dyke, the ministry is planning to create new agricultural and aquaculture areas that would escape the intrusion of salt water.

The ministry also plans to speed up the construction timeline for a coastal dyke system from northern province of Quang Ninh to Quang Nam Province in the central region.

And plans for an attached set of dykes, stretching from the adjacent central province of Quang Ngai to Kien Giang in Mekong Delta, has been submitted to the Prime Minister for approval.

Experts in irrigation suggested building a 3-metre-high dam system, blocking half of the estuaries along the region’s 700km.

Pollution threat

But this solution could have unintended consequences. Dams built along the Mekong Delta coast to keep out rising seas could instead flood the region with pollution from industrial zones, other experts warned.

The dams would hinder flow of the rivers that carry the region’s waste water, slowing their self-cleaning processes.

"Huge losses could occur if a third of the region flooded [with sea water]," said Dr Vo Hung Dung, director of the Viet Nam Chamber of Commerce and Industry’s Can Tho chapter, "but to have the entire region soaked in waste and polluted water is more serious."

With water flows already weakened by hydro-electricity works in the upper Mekong River, dams on sea mouths would prevent the region’s main rivers from maintaining a minimum speed of 2,000cu.m in dry season – which is necessary for self-cleaning, Dung said.

Death zones

And if the Tien and Hau rivers are no longer able to self-clean, enormous amounts of waste and contaminants from industry, agriculture, aquaculture and daily activities will turn 30,000km of rivers and canals into death zones.

That’s because industries in the region’s 200 zones discharge 50 million cubic metres of waste water every year. A further 500 million cubic metres are generated by aquaculture, and 600,000 tonnes by households.

The volume of industrial effluents could double by 2020 when industries are predicted to occupy 50,000ha, said Dr Nguyen Thanh Chuong of the Party Central Committee‘s Commission for Popularisation and Training.

The most important task in building the dams was to ensure an outlet for the waste, Chuong said.

Dam pollution

Single dams to block salt water were built in many coastal parts of the region without such forethought, to unfortunate results.

In Tien Giang Province’s Go Cong Peninsula and Ca Mau Province’s Ca Mau Town, for example, heavy pollution has taken place during dry seasons. Residents near the Maspero River and a Hau River section in Soc Trang Province have complained of the pollution on the rivers.

The province’s Department of Natural Resources and Environment last week discovered and fined 11 seafood processing factories for violating environment protection law.

Those companies released untreated waste water to the Hau River with content of BOD5 and COD over the allowed level of 28.29 to 78.03 times, the department said.

(Source:VNS)