The forebay is a regulating reservoir which stores water under reduced load conditions and provides water when the load increases.
Details and Construction
The forebay is a wide water body whose major function is storage of water. Depending on low, medium, or high heads its construction and working can be different. Its design and location also depends on various circumstances and can be different under different conditions.
In Low head plants
Usually, a dam is constructed on the river and a canal is constructed for diverting water to a forebay. The water is then sent from forebay to the turbines.
In Medium Head Plants
Here the water from the river is tapped off to the forebay from which it proceeds to penstock and then moves to turbines. In medium dams, the forebay serves as another surge tank.
Similar to read: Role of the Surge tank in close conduit dams
Forebay in High Head Power Plants
In high head plants, the powerhouses are located far away from the storage reservoir. In such cases, forebay is another smaller reservoir constructed downstream of the main reservoir. The powerhouse takes water from it
The above cases are general cases, depending on local conditions the construction of the structure and its application might vary and should be decided by power crew on that station.