spillways

Spillways are hydraulic structures that carry away excess water from a dam or reservoir to prevent overtopping. They provide a controlled discharge during floods and help protect the dam, downstream areas, and infrastructure. Spillways may be built into the dam crest or located downstream as a separate channel, tunnel, or shaft.

Spillway types include ogee crest spillways, chute spillways, side-channel spillways, and shaft or siphon spillways. They can be uncontrolled, allowing water to flow over the crest, or controlled, using gates such as radial, tainter, or vertical lift gates to regulate discharge.

Key components are the inlet or crest, the spillway channel, gates or valves, and an energy-dissipation system such as a stilling basin or plunge pool. Downstream features may include outlet works and tailwater controls. Operation involves monitoring inflow and reservoir level, then opening gates or permitting crest overflow to maintain safe storage while meeting downstream flow needs.

Design considerations include hydraulic capacity, head, flow velocity, cavitation risk, erosion and scour, debris management, and structural and seismic safety. Environmental and socio-economic impacts on downstream areas are also evaluated. Regular inspection, maintenance of gates and energy-dissipation devices, and debris removal are essential.

Prominent examples include spillways associated with large dams such as the Hoover Dam and Three Gorges Dam. The 2017 Oroville Dam incident highlighted the importance of maintenance and monitoring of spillway structures to prevent failures during extreme floods.