January, 28 2013 09:19:00

Big dykes inflict major environmental damage

By Phuoc Buu

Farmers reinforce a dyke to protect rice fields in Hong Ngu District in the Mekong Delta province of Dong Thap. — VNA/VNS Photo Duy Khuong
DONG THAP (VNS)— Dykes that encircle large rice fields in the Cuu Long (Mekong) Delta could have negative environmental impacts in the long run and any economic benefits farmers get will be short-lived, experts warn.

They explain that while the dykes allow for the growing of more crops a year by keeping seasonal flooding at bay, this is causing severe degradation of soil that would hit farmers hard in the near future.

However, farmers in the area are happy with the dykes for now because they have boosted incomes sharply.

Just a decade or so ago, delta farmers could grow two rice crops a year, with the second crop normally ending in August to avoid flooding over the next three or four months as inflows increased from the upper reaches of the Mekong River.

The cultivation of two crops a year had been a tradition developed over more than 200 years since people started settling in the delta.

But occasionally, the flooding happened before August,inundating rice fields that had not been harvested. This prompted farmers to build earthen dykes and protect paddy that has not been harvested.

The earthen dykes, built whenever farmers needed to protect their rice from early flooding, were temporary and called "August dykes."

In the early 2000s, farmers in many localities started to make dykes that were much longer than the traditional August dykes to squeeze in an additional crop in the delta's two main rice growing areas - the Plain of Reeds and the Long Xuyen Quadrangle.

The longer dykes allowed farmers to cultivate rice during the flooding season and local authorities supported the move.

In 2007, two "circle dyke" systems were built to enclose the Plain of Reeds in Dong Thap Province and the Long Xuyen Quadrangle in An Giang and Kien Giang provinces.

Since then, farmers have been able to cultivate the third crop every year and earn higher incomes, but experts insist the dykes cause greater harm than farmers realise.

Dr Duong Van Ni of the Can Tho University says the dykes have blocked the inflow and outflow of flood waters into the Plain and the Quadrangle, and this will create serious problems.

"Naturally, floods bring alluvia to the soil, giving nutrition back to the land after crops," says Ni, a hydrology expert who has worked in the delta for decades.

The alluvia deposits during the flooding also help strengthen the weak stratum of the "young delta," he says.

Also, "after several months, when the flood gets out of the fields, it carries the waste of chemical fertilizers and pesticides out to the sea," he says. The flushing out operation freshens the fields for the new crop, which means less pests and diseases.

Another Can Tho University lecturer, Dr Le Anh Tuan, who is studying water management in the delta, says the dykes "have changed the nature of the delta."

"The Plain of Reed and the Long Xuyen Quadrangle serve as two reservoirs of water for the whole delta thanks to its sunken topography," he says. "The lower part of the Mekong River in Viet Nam receives an average of 400 billion cubic metres of water from the upper part annually. Ninety nine per cent of this arrives during the rainy season, and 10 per cent in the dry season.

"When floods enter the country, water pours into the Plain of Reeds and the Long Xuyen Quadrangle first, then flows to other areas of higher topography.

"So it is obvious that these two areas help reduce flooding in other areas in the delta while replenishing underground water supply for rivers and canals during the dry season," Tuan says, adding that this role has been curtailed by the dykes.

Studies done by Ni and Tuan have also shown that soil quality in rice fields has degraded strongly after five or six years of cultivating three crops each year.

Both experts express concern about the losses farmers face now and in the near future.

Farmers in the delta say they do recognise the degradation of soil and have also seen a fall in fresh water fish and other seafood for many years now.

However, high prices of rice from the third crop has significantly improved living standards for his family, says Huynh Van Minh, a farmer in Dong Thap Province's Tan Phuoc Commune, "In the commune, 90 per cent of the residents cultivate the third crop, which yields 10 bags (usually 50kg) of rice per cong (one tenth of a hectare). The first and second crops yield six bags," Minh says.

Nguyen Van Tang, another resident of the commune, says farmers do not seem to care about soil degradation or a sharp decrease in seafood resources. "They all seem to be happy as they can work and earn even during the flooding season," he says.

In the past, farmers could not work during the flooding season. Now, many farming households also say they feel safer with the protection that dykes offer from floods.

But experts insist that this is a short-sighted approach. They say the profit and other benefits from the encircling dykes cannot make up for the impacts on the environment, as well as long term socio-economic impacts.

They say authorities need to act urgently and spread awareness of the negative impacts among farmers to protect the nation's resources and ensure livelihood sustainability in rural areas. — VNS

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