Spillway
Reviewed • Standard Hydrology Definition • WaterLakeLevel
# Spillway
A spillway is a critical safety structure built into or alongside a dam to release floodwater that exceeds the storage capacity of the reservoir. Without a spillway, extreme floodwaters would overtop earthen or concrete dam embankments, causing catastrophic dam failure.
- Controlled (Gated) Spillways: Equipped with large radial or taintor gates that operators raise to regulate discharge.
- Uncontrolled (Service) Spillways: Fixed concrete crests where water automatically spills once elevation exceeds the crest.
- Morning Glory (Bell-Mouth) Spillways: Large inverted funnel drains, such as the famous Monticello Dam Glory Hole on Lake Berryessa.
A engineered structural passage designed to release floodwaters safely over or around a dam.
What Is a Dam Spillway?
A spillway is a critical safety structure built into or alongside a dam to release floodwater that exceeds the storage capacity of the reservoir. Without a spillway, extreme floodwaters would overtop earthen or concrete dam embankments, causing catastrophic dam failure.
Types of Spillways:
- Controlled (Gated) Spillways: Equipped with large radial or taintor gates that operators raise to regulate discharge.
- Uncontrolled (Service) Spillways: Fixed concrete crests where water automatically spills once elevation exceeds the crest.
- Morning Glory (Bell-Mouth) Spillways: Large inverted funnel drains, such as the famous Monticello Dam Glory Hole on Lake Berryessa.
Explore Other Hydrology & Boating Terms
Acre-Foot
A volumetric water unit representing the amount of water required to cover one acre of land to a depth of one foot.
Conservation Pool
The volume of water stored in a reservoir dedicated to beneficial uses such as drinking water, power, and recreation.
Datum
A reference surface or mathematical baseline from which vertical elevations or geographic coordinates are reckoned.
Dead Pool
The critical low-water elevation below which water cannot flow downstream through gravity outlets.
Drawdown
The deliberate or natural reduction of a lake or reservoir water surface elevation.
Evaporation Loss
The invisible volumetric loss of water from a lake surface into the atmosphere caused by heat, sun, and dry winds.