Some like it salty, some like it not
Plants and animals, including humans, are very finely attuned to the saltiness of water and cannot adjust to an alien environment. Most water resources can be clearly defined as saline or fresh, and that is how they remain year in and year out. Estuaries and deltas, and the land through which they flow, may change according to season especially in those regions that experience a monsoon. The people who live and farm in these regions learn to make the best of it but most would be much better off if the salinity could be controlled. Or would they? This was the assumption in the Bac Lieu province south of the Mekong delta in Vietnam. Surprising, therefore, to find that some people were very unhappy about the way their lives were being changed.
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| Credit: IRRI |
Bac Lieu province is flat. The tide inundates vast areas of land and the salt seawater builds up salinity in the soil for many kilometres inland. The east of the region has good soil, suitable for rice production. Traditionally farmers grew one crop of rice during the rainy season when the monsoon and the Mekong flushed out the salt. To the west of the region, where the soil is acid and unsuitable for rice, people harvested wild fish from the brackish water in the rivers, ditches and channels that abound. Others raised brackish water shrimp in ponds.
In the late '80s and early '90s, the Vietnamese government was keen to increase rice production to reduce the need for imports and earn foreign exchange from exports. The Bac Lieu province had the potential, provided that the principal constraint to increased production - salinity - could be resolved. The authorities decided to make use of the national highway that runs along a high bank, skirting the province on the seaward side and forming an effective barrier against the South China Sea. The many channels bridged by the road that had allowed free flow of water were blocked with sluices designed to close against incoming saline seawater. The effect was amazing. The saline/fresh interface moved steadily westwards (away from the Mekong) and farmers to the east of the interface were able to grow two or even three crops of rice each year instead of only one, and yields were much higher. The area under rice doubled and everyone was delighted.
The shrimp farmers in the west did not share the general delight. Their land remained too acid for rice, and shrimp catches declined as the water became less brackish. Could the needs of both rice and shrimp farmers be satisfied? This was the challenge presented to IRRI and partners* with the goal of providing the provincial government with the necessary information on which to base a new water management strategy.
The area, some 200,000 hectares and home to a few hundred thousand people, the majority of whom are very poor, was divided into zones. To the east, the plan was to ensure that the land was suitable for two or three crops of rice per year. Slightly further west, farmers would be able to grow one crop of rice during the rainy season and raise shrimp in the dry season. In the west, shrimp farming would predominate. By using a simulation model, scientists were able to test what would happen to the salinity of the water in a particular channel if, for example, a specific sluice were opened for x number of days. The model showed that it would be possible to achieve the desired freshwater, salinity balance at the correct levels for the farming activities in any particular area.
2001 saw the first full practical run of the system and reality was found to match theory very well. District level officers control the sluices but the whole system is coordinated by the provincial hydrology service. Constant monitoring of the water is essential and radio and mobile phones help to keep each monitoring station in touch. The data can be fed back to refine the model. Now everyone is delighted. Rice farmers are entirely satisfied with the freshwater they now enjoy year round. Shrimp farmers are pleased to return to their previous means of earning a living. And the authorities are grateful for a solution to what had been a major source of dissatisfaction.
* The project is being implemented by the International Rice Research Institute, in collaboration with University of Newcastle upon Tyne, ICLARM - The World Fish Center, Cantho University, Department of Agriculture and Rural Development of Bac Lieu Province, Sub-Institute of Water Resources Planning, and the Integrated Resources Mapping Center. The UK Department for International Development is contributing to the costs.
