Basic Information | International Commission on Irrigation & Drainage (ICID)

Dams and Reservoirs

A reservoir,an artificial lakeorimpoundmentis created in river valleys by the construction of adamto storewater.

A dam constructed in a valley relies on the naturaltopographyto provide most of the basin of the reservoir. Dams are typically located at a narrow part of a valley downstream of a natural basin to provide strength and the lowest practical cost of construction. From a water budget point of view, large reservoirs are hydrologically most efficient. Large reservoirs, through their carry over capacity, and informed reservoir operation can serve as a preventive tool against droughts.

In addition to diverting water for irrigation, large reservoirs often serve multiple purposes such as meeting drinking water needs, flood control, hydro-power generation, fish breeding and recreation activities such as boating and water-sports.They form the unique source of raw water for drinking purposes to serve the needs of large urban centres.

For irrigation purposes, water is released into networks ofcanalsfor use infarmlandsor secondary water systems and can irrigate far off fertile lands, away from the lands adjacent to rivers, providing opportunity for development to those not favourably located and across to other basins based on the demand. In most of the cases the water flows under gravity thereby helping reduce carbon foot prints of agriculture. The quality of water in the reservoirs depends on the land-use in its watershed.

All reservoirs will have a monetary cost/benefit assessment and environment, social and cultural impact assessment. In many reservoir construction projects people have to be re-located and rehabilitated, historical artefacts moved or rare environments relocated.