A forebay is a human-made pool of water in front of a larger body of water. The larger body of water may be natural or engineered. Forebays serve a number of functions in a variety of settings, and they can be found in many regions of the world. While constructing a forebay can add to the initial costs of water control and containment, it reduces maintenance costs in the long term, making it a cost effective move in many settings.
One major function of a forebay is to act as a buffer zone during flooding and storm surges. The small pool traps the excess water, releasing it in a controlled fashion into the larger body of water. This can increase safety and help with flood control and abatement measures. Forebays designed for this purpose may be deliberately kept shallow so that there is lots of room to accommodate a sudden surge of water.
Another purpose of a forebay is to trap sediment and debris. This keeps the larger body of water cleaner and clearer. For things like dams, which often become clogged with sediment, a forebay can extend the life of the dam and reduce maintenance costs. Trapping sediment is also useful for preserving natural bodies of water which would slowly fill in over time, if people want to keep a body of water clear for their use. In reservoirs used to store water for human uses, eliminating sediment with a forebay increases capacity, reduces maintenance, and cuts down on the need for filtering.
A forebay can also act as a natural habitat. Forebays may be appealing to fish, waterfowl, aquatic plants, and other members of the natural world. For this reason, they are sometimes established for the purpose of creating a more environmentally friendly water management project. Forebays can also be used in wetlands management and restoration, in which case the goal is usually to maintain or restore a wetland for flood control and environmental reasons with the assistance of the forebay.
The size and shape of a forebay can vary considerably. It may be immediately connected to a body of water, or linked with channels or piping which can be used to control the flow of water from the smaller pool to the larger body of water. For aesthetic and environmental reasons, the area around the forebay may also be landscaped with plants, which will also help to trap sediment and to prevent erosion.