Dams and weirs are some of the barriers which when construct across the rivers and streams, cause accumulation of water behind them.
The water thus accumulat in form of an artificial lake is know reservoir.
In broad sense, any collected water in form of a pool or lake, may be termed as reservoir.
Dams and reservoirs are the most important elements of any multipurpose river basin development.
River water may be used for generation of hydroelectric power, irrigation, and water supply source for some town or city.
All these uses require a constant or almost constant supply of water.
But we know that discharge in rivers and streams remains fluctuating.
During rains, the water in the river may be more than the requirements and during dry period the discharge in the river may become less than the minimum requirements.
Thus to store the excess water, flowing during floods, dams are constructed across the rivers.
This stored water is use to augment the supplies of the river during dry weather.
By this arrangement it is possible to generate hydroelectric power, provide irrigation facilities and make available drinking water for whole of the year.
Actually dams and reservoirs are complementary to each other.
Reservoir can be develop only by constructing dam, conversely when dam is construct reservoir is bound to develop.
Both dams and reservoirs, being very important elements of any multipurpose irrigation project, have to be very carefully planned, designed and operated.
