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VIETNAM: Saltwater Intrusion Adds to Water Woes

Tran Dinh Thanh Lam

MEKONG DELTA, Vietnam, Jun 12 2009 (IPS) - When they got out of bed one morning in April this year, the residents of Vi Thanh City here in southern Vietnam’s Mekong Delta were surprised to find that their water had become salty.

During the night, seawater had intruded into the Xa No canal, the main source of water for the city of 200,000 people.

“Never in my life have I seen the water at Vi Thanh become that salty,” said 76 year-old Nguyen Duc Bon, who was born in the city. “Our running water has become so salty that we could not use it for cooking or for washing.”

For daily use, inhabitants now have to buy fresh water supplied from the nearby regional centre of Can Tho at high prices.

A dam is being built to prevent the penetration of saltwater, but it will not be finished until 2011.

The area’s farmers also worry that their 37,000 hectares of paddies and aquaculture could be totally destroyed by the seawater intrusion.

Many factors are being blamed for the change in water quality – hydropower construction upstream on the Mekong River, global warming, and, ironically, the network of small dams build by local farmers themselves to protect their crops and aquaculture products.

There are two seasons in the Mekong Delta, the dry season, usually taking place from May to November; and the rainy season, from December to April.

During the dry season, the water level of the Mekong is very low, enabling the intrusion of saltwater.

During the rainy season, the Mekong overflows, flooding the delta but also washing out the areas recently invaded by seawater.

To fight these floods, local farmers have built a network of dams to protect their crops and aquaculture products – a method that in previous years was acclaimed as an innovation because it helped farmers continue producing even in the rainy season. Now, however, these dams have turned out to be one of the causes of saline intrusion.

“Because of these closed dams, the overwhelming quantity of flooding water is not retained [in the soil] and thus runs out into the sea,” said Le Van Banh, president of the Mekong Delta Institute of Rice. “When the dry season comes, the small quantity of underground water that remains is not enough to stem the invading seawater.”

With global warming, April and May have become the hottest months of the dry season -at a time when the Mekong’s level of water is at its lowest.

This has resulted in further seawater intrusion into the dried-out regions of the Delta.

According to experts, seawater intruded up to 70 kilometres into some parts of the Delta during the 2009 dry season – the farthest distance in the last 20 years. More than 20,000 hectares of crops throughout the Delta have been immersed in saltwater.

“The areas covered by sea water extend year by year,” Vu Anh Phap, of the Institute for the Development of the Mekong Delta, told Radio France International in an interview. “The salinity is also increasing.”

Phap said that due to intensive irrigation in the Mekong region in the past few years, especially by farmers in upstream countries like Laos and Cambodia, the water level downstream has gone lower and lower and allowed greater penetration of seawater.

Increasing dam construction projects upstream is also widely viewed as another major cause of the water shortages downstream.

“These dams have reduced the water flow of the Mekong significantly,” said Ky Quang Vinh, head of the Centre for Natural Resources and Environment in Can Tho.

“Water shortage has already occurred this year and will be more critical in the coming years,” added Vinh. “Even in time of floods, the water flow of the Mekong in downstream has also been reduced.”

In October, he said, it fell from 40,000 cubic metres a second to 28,000 cubic metres a second.

The shortage of water in the Mekong emerged as a matter of significant public concern in Vietnam in late May after the newspaper ‘Tuoi Tre’ cited a United Nations report saying that dams built by China on the upper reaches of the Mekong could have significant implications for Vietnam.

The report stated: “China’s extremely ambitious plan to build a massive cascade of eight dams on the upper half of the Mekong River, as it tumbles through the high gorges of Yunnan Province, may pose the single greatest threat to the river.” It went on to say the impacts of the proposed dam development could include “changes in river flow volume and timing, water quality, deterioration and loss of biodiversity.”

These dam developments include the recently completed Xiaowan dam, which at 292 metres is the world’s tallest and has a reservoir storage capacity equal to all the other Southeast Asia reservoirs combined.

It is part of China’s long-term plan to direct water for irrigation and hydropower to dry areas of the country.

“Dams are already big at heights of 15 metres, and 292 metres is unbelievable,” Vinh told ‘Tuoi Tre’.

“[Chinese] dam construction now joins hands with climate change to worsen droughts, salinity intrusion, landslides and land erosion,” Ngo Dinh Tuan, chair of the scientific council of the South-east Asia Institute of Water Resource and Environment, told ‘Tuoi Tre’.

“The Vietnamese government must create a national strategy for protecting the river downstream, not only for the Mekong but the Red River [in Vietnam’s north], as China has started to build dams on it as well,” Tuan added.

The U.N. report also found increasingly low water levels at several river basins such as Tonle Sap in Cambodia, Nam Khan in Laos and Sekong-Sesan in Cambodia and Vietnam.