Hydrology is the study of the occurrence, distribution, and movement of water on, in, and above the earth. As such, it is an earth science. The circle of motion between terrasphere, oceanosphere, and atmosphere is termed the hydrologic cycle.
There are two broad sub-disciplines within the science of hydrology. The first is surface-water hydrology[?] which focuses on water on and above the surface of the earth. Examples of applications of surface water hydrology is flooding and droughts. The second sub-discipline is ground-water hydrology[?], which focuses on the distribution and movement of water beneath the earth's surface. Ground-water hydrology is important for applications in water supply and irrigation.
Also included in hydrology is the study of motion of water and water-borne constituents[?]; materials carried either as dissolved quantities or in separate phases.
A related facet of hydrology is the determination of statistical flow prediction[?] in rivers and streams. This information is essential to design and evaluation of natural and man-made channels, bridge openings and dams. Stream gage data for this study has been collected and tabulated by the United States Geological Survey for many years and is available online for analyisis.
See also: water resources - virtual water
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