What is a Forebay?

Mary McMahon
Mary McMahon

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.

Hydroelectric dams can benefit from a forebay to trap sediment and debris and keep them from passing through their turbines.
Hydroelectric dams can benefit from a forebay to trap sediment and debris and keep them from passing through their turbines.

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.

Mary McMahon
Mary McMahon

Ever since she began contributing to the site several years ago, Mary has embraced the exciting challenge of being a wiseGEEK researcher and writer. Mary has a liberal arts degree from Goddard College and spends her free time reading, cooking, and exploring the great outdoors.

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Discussion Comments


My dad frequently takes me out to Halsey Forebay in Placer County, California, near our home. This small forebay is fed by the Bear River Canal, and only the locals who keep up with trout stocks know about it.

Halsey Forebay is in the hills at 1,800 feet. We can find some pretty large trout here, from 10 to 12 inches on average. However, our luck at this forebay is confined to the few days after it is stocked.

The lake is replenished with rainbow trout around the time spring is becoming summer. I guess the locals really snap up the trout quickly, because after those first few days following the restocking, we can hardly catch a bite.


I have a cousin in Colorado, who I visited this past summer. He took me to Mount Elbert Forebay. This forebay was built in the 1970s, and it has an outstanding view of the mountains.

The forebay covers 210 acres and is popular with fishermen. It is known as a great spot to fish for rainbow trout, brown trout, lake trout, cutthroat trout, and cutbow trout. My uncle took my cousin here every weekend while teaching him how to fish.

Fishermen can catch fish up to 40 inches long in this forebay. My cousin caught one 38 inches long! The lake is restocked with rainbow trout regularly, and the fishermen just keep on coming.


The forebay at my local man-made lake provides for some interesting photography and observation of nature. I have seen many types of birds here, from cranes to what surely appear to be seagulls, even though we are hundreds of miles from any ocean.

The area is covered with reed-like grass. This grass is a great hiding spot for the birds, which often fly out of it alarmingly when you get too close.

I never knew that forebays keeps water cleaner, but I guess it makes sense, because since it's just a giant mud puddle. I love to swim in the lake, so I am glad they built one in my lake!

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