Fusegate Operation

Shongweni Dam in South Africa
Shongweni Dam in South Africa,
equipped with fusegates,
during a flood event.
The flood discharge is below the level,
as defined by the client,
at which the first fusegate overturns.

Under normal conditions, fusegates increase the dam’s live storage capacity. For all floods below the first fusegate tipping level (which is set by the client, usually well above the one in 100year flood), the fusegates act as an ungated spillway.

Fonctionnement de la hausse fusible
Overturning mecanism
during very exceptional floods

In the case of very exceptional floods, water rises to the level at which the first fusegate tips off the spillway sill. Water enters the inlet well and floods the base chamber, creating uplift pressure that forces the fusegate to rotate up and overturn. Fusegate tipping points are set at different levels to ensure that units overturn progressively. The sequential tipping of fusegates creates an ever-increasing opening along the spillway for the flood discharge, thereby protecting the dam from floods and possible overtopping. The progressive, accurate and carefully controlled, overturning of fusegates is the mechanism that limits the effects of major floods on the downstream riverine environment.

Spillway on the McClure Dam in the U.S.
Spillway on the McClure Dam in the U.S.
An 8-unit fusegate rotation sequenc
has been set for extreme floods.

It’s important to note that fusegates only begin to overturn in the event of exceptional floods with a very low probability of occurrence. Depending on the project, the flood recurrence interval for the first Fusegate rotation could be between one in 100 and one in 10,000 years or more.

Fusegate rotation frequency can be cost-effectively adjusted in accordance with storage capacity gains and operational shortfalls related to fusegate tipping probability