A forebay is an artificial pool of water in front of a larger body of water. The larger body of water may be natural or man-made.
at www.wisegeek.com. Retrieved on 13 Jun 2013 Forebays have a number of functions. They are used in

flood control Flood control methods are used to reduce or prevent the detrimental effects of flood waters."Flood Control", MSN Encarta, 2008 (see below: Further reading). Flood relief methods are used to reduce the effects of flood waters or high water level ...

to act as a buffer during

flooding A flood is an overflow of water ( or rarely other fluids) that submerges land that is usually dry. In the sense of "flowing water", the word may also be applied to the inflow of the tide. Floods are an area of study of the discipline hydrolog ...

storm surge A storm surge, storm flood, tidal surge, or storm tide is a coastal flood or tsunami-like phenomenon of rising water commonly associated with low-pressure weather systems, such as cyclones. It is measured as the rise in water level above the n ...

s, impounding water and releasing in a controlled way into the larger waterbody. They may be used upstream of

reservoir A reservoir (; from French ''réservoir'' ) is an enlarged lake behind a dam. Such a dam may be either artificial, built to store fresh water or it may be a natural formation. Reservoirs can be created in a number of ways, including contro ...

s to trap sediment and debris (sometimes called a sediment forebay) in order to keep the reservoir clean. This entails the use of a

dam A dam is a barrier that stops or restricts the flow of surface water or underground streams. Reservoirs created by dams not only suppress floods but also provide water for activities such as irrigation, human consumption, industrial use ...

built upstream of the main reservoir, called a forebay dam or pre-dam. Forebays may also be used upstream of

lake A lake is an area filled with water, localized in a basin, surrounded by land, and distinct from any river or other outlet that serves to feed or drain the lake. Lakes lie on land and are not part of the ocean, although, like the much large ...

s to prevent

siltation Siltation, is water pollution caused by particulate terrestrial clastic material, with a particle size dominated by silt or clay. It refers both to the increased concentration of suspended sediments and to the increased accumulation (temporary or ...

. Some forebays are used simply to create a natural habitat for flora and fauna, to counterbalance the environmental impact of a dam or reservoir. Forebays vary greatly in size depending on their situation and purpose. A forebay can also be a reservoir from which water is taken to run machinery such as turbines.

References

Artificial lakes Reservoirs {{Geo-term-stub