Water level in lakes and reservoirs, water storage

Abstract

Lakes level is a complex index of natural water exchange within their watersheds. Therefore, longterm level fluctuations in natural (unregulated) lakes also reflect climate changes occurring in the region. On the other hand, lake water storage, which depends on water level, is an easily available source of water for many sectors of economy such as agriculture, domestic and industrial water supply, hydropower, water transport and others. The World Meteorological Organization’s ( WMO) International Glossary of Hydrology defines lakes as an inland body of water of considerable size while reservoirs are natural or man-made water bodies used for storage, regulation and control of water resources. Gauges on lakes and reservoirs are normally located near their outlets, but sufficiently upstream to avoid the influence of drawdown (WMO-No.168, 1994). Hydrological information obtained by groundbased gauge instruments is limited due to the sparse distribution of gauge stations. An alternative is to use radar altimetry to measure surface water height of large lakes which has an accuracy of within two centimetres and is available in near-real time. Water level in lakes and reservoirs is measured in centimetres against the national reference plane or against some adopted plane (so called “zeroâ€Â graph). Surface area of a lake or reservoir is measured in m2 or km2 depending on their size. Lake or reservoir storage (volume) is measured in m3 or km3 depending on their size.