Main aim is to reduce likelihood of flooding. In some cases, however, it can increase the risk.
In Bangladesh embankments have been built along the river channels in some places. These are designed to increase river capacity, but at the same time prevent flood water draining back into rivers.
The Farakka dam lies on the upper reaches of the River Ganges in northern India. In 1988, the Indian government allows the floodgates of the dam to be opened during the rainy season, because the reservoir behind the dam was at risk of flooding.
This saved the land surrounding the dam but downstream in Bangladesh it was a different matter. The extra discharge in the river coincided with the normal floods expected at that time of year and greatly increased their severity.
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