Also found in: Dictionary, Thesaurus, Medical, Legal, Financial, Acronyms, Wikipedia.
in rivers and lakes, the position of the free water surface referred to some horizontal surface of constant elevation. The surface of reference may be either relative or absolute, that is, either some plane of arbitrary elevation (the plane is the datum level) or the surface corresponding to the mean water level of the ocean at the shores of the continents.
Variations of the water level in a river occur primarily because of changes in flow rate, warping of the channel, or the backwater effect. In an inland body of water, variations of the water level may result from a change in the ratio of the elements in the water balance, surges, or seiches. Annual water level variations depend on climatic conditions and range from a few centimeters to 2–3 m in lakes and up to 5–12 m in large rivers.
Water level observations are made at water level measuring stations.