Forebay (reservoir)

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The Schleusegrund forebay and pre-dam, part of the Schönbrunn Dam system

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.[1]

Forebays have a number of functions. They are used in flood control to act as a buffer during flooding or storm surges, impounding water and releasing in a controlled way into the larger waterbody. They may be used upstream of reservoirs to trap sediment and debris (sometimes called a sediment forebay[2]) in order to keep the reservoir clean. This entails the use of a dam built upstream of the main reservoir, called a forebay dam or pre-dam. Forebays may also be used upstream of lakes to prevent siltation. 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.[1]

A forebay can also be a reservoir from which water is taken to run machinery such as turbines.[3]


  1. ^ a b What is a Forebay? at Retrieved on 13 Jun 2013
  2. ^ Sediment Forebays Archived 2012-06-23 at the Wayback Machine at Accessed on 14 Jun 2013
  3. ^ "Definition of Forebay". Retrieved 2020-06-24.