Tailrace

A tailrace is the channel, tunnel, or conduit that carries water away from the outlet of a dam, hydroelectric turbine, or other hydraulic structure back into the downstream watercourse or lower reservoir. It follows the turbine or outlet structure and returns the discharged water to the river or reservoir, completing the hydraulic cycle. Tailraces are designed to convey flow at controlled depths and velocities while minimizing erosion and ensuring safe operation of the facility.

In hydroelectric facilities, water passes through the turbine to generate power and then flows through the tailrace, which directs the discharged water toward the downstream river or reintroduction point. Tailraces can be open channels, lined canals, or submerged tunnels, depending on site conditions and design. The geometry of the tailrace, including cross-section, slope, and energy-dissipation devices, influences tailwater depth, velocity, mixing, and potential impacts on downstream hydraulics.

Key design considerations include energy dissipation at the outlet (often achieved with a stilling basin, baffles, or other structures to prevent strong jet impacts and erosion), sediment transport, ice and debris management, and maintenance access. Environmental and ecological factors are also important: rapid tailwater changes can affect aquatic habitats and fish, so some projects incorporate features to mitigate ecological impacts and maintain minimum downstream flows.

Tailrace configurations vary with project scale and objectives, but all serve to safely and efficiently remove turbine discharge and stabilize the downstream water conditions after generation.