Spillway

A spillway is a structure incorporated into a dam or embankment to safely convey water from the reservoir to a downstream area. It is designed to release inflows that exceed the normal operating capacity of the dam, preventing overtopping, reducing hydraulic pressure on the structure, and supporting flood control and reservoir level management.

Spillways can be fixed-crest or gated. Ungated (fixed) crests pass water when the reservoir level rises to the crest, while gated spillways use gates to regulate discharge. Gates commonly used include radial gates, tainter gates, and sluice gates. Crest shapes vary, with the ogee crest being a widely used form that shapes the flow over the top of the structure.

Flow paths for spillways include chute spillways, where water descends a sloped channel into a stilling basin; tunnel spillways that convey water through a buried conduit; and side-channel spillways that route flow along the dam face. Siphon spillways use a siphon principle to lift water over the crest under certain reservoir levels. An emergency spillway provides an additional, normally ungated route for extreme flood events when the main spillway capacity is exceeded.

Energy dissipation is a central design concern, typically achieved with stilling basins, flip buckets, or baffle blocks to reduce downstream velocity and erosion. Spillway design considers factors such as design flood capacity, tailwater conditions, sediment transport, seismic loads, and maintenance needs.

Spillways are essential for dam safety and flood management, and they are subject to regular inspection, testing, and upkeep to ensure reliable operation during extreme events.