World Water Storage in Man-Made Reservoirs
FR/R0012
April 2005

This review addresses man-made reservoirs that provide water storage and other benefits such as hydroelectric power, flood control and navigation. Although they only provide a proportion of the water required for domestic, industrial, agricultural and other purposes, man-made reservoirs play a particularly important role where natural precipitation is erratic or seasonal because they store water during wet periods to make it available during dry periods.

The focus is on large reservoirs where worldwide data is available. There are around 40,000 large reservoirs worldwide used for water supply, power generation, flood control, etc. Increasing populations and increasing consumption per capita mean that the demand for storage is rising inexorably despite the increasing use of alternative sources and the more efficient use of water.

The benefits attributable to dams and reservoirs, most of which have been built since 1950, are considerable and stored water in reservoirs has improved the quality of life worldwide. These benefits can be classified under three main headings: -

• Irrigation: About 20% of cultivated land worldwide is irrigated, some 300 million hectares. This irrigated land produces about 33% of the worldwide food supply. Irrigation accounts for about 75% of the world water consumption, far outweighing the domestic and industrial consumption of water.
• Hydropower: About 20% of the worldwide generation of electricity is attributable to hydroelectric schemes. This equates to about 7% of worldwide energy usage.
• Flood control and storage: Many dams have been built with flood control and storage as the main motivator e.g. the Hoover dam, the Tennessee Valley dams and some of the more recent dams in China.

In many areas of the world the life span of reservoirs is determined by the rate of sedimentation, which gradually reduces storage capacity and eventually destroys the ability to provide water and power. Many major reservoirs are approaching this stage in their life.

This ROCK reviews the world stock of reservoirs, considers the problem of sedimentation and possible measures to minimise the impact of sedimentation. But first, the contribution of reservoirs is put into context by considering overall water resources and water usage.

Copies of the full report are available from the Foundation, price £15.00, less 20% for FWR Members..