Headrace

Headrace refers to the hydraulic conduit that conveys water from an upstream reservoir or forebay to the turbine in a hydroelectric facility. It is a key part of the plant’s water conveyance system and, together with the tailrace, helps determine the plant’s available head and flow. The term encompasses both open-channel structures (such as canals) and closed conduits (such as tunnels or pressurized pipes), with the choice driven by head, distance, geology, and cost.

Common components of a headrace include the intake structure with screens or trash racks for debris removal, velocity control gates, and sometimes surge tanks or air-release devices. The route may be an open canal, a covered channel, a tunnel, or a pipe, and is designed to minimize head losses from friction, fittings, and transitions while allowing access for maintenance. In long or highly pressurized installations, surge protection is used to mitigate water hammer during startup and load changes.

Functionally, the headrace delivers the required water flow to the turbine; the turbine extracts energy and the spent water continues to the tailrace and back to the river. The efficiency of the headrace affects overall plant performance, as head losses reduce the effective head available to the turbine. Environmental considerations, such as fish passage and intake screening, may influence headrace design and placement.

In relation to other plant components, the net available head is the vertical difference between the upstream water surface and the turbine inlet, minus head losses in the headrace.