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.
The Mississippi River in the southern states of the USA is one of the most managed rivers in the world. Artificial embankments (levees) have been built along the lower reaches of the channel to protect the heavily settled floodplain.
The city of New Orleans lies below sea level on the banks of the Mississippi and is at particular risk of flooding but is protected by levees and diversion channels, built by the government.
In August 2005, devastating floods occurred, submerging the city as the levees were breached. A storm surge, brought by Hurricane Katrina, gushed up the river from the coast. This, coupled with heavy rainfall brought by the storm, caused the river to rise dramatically. Major damage to the embankments resulted as they were breached in several places.