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Back to spillwaysSpillways & Outlets - Shaft spillways

Top of a shaft spillway

The top of the shaft spillway
at Llyn Pontsticill in Wales

A shaft spillway is sometimes called a "morning glory" spillway. It is a hollow tower or shaft, usually circular, which has a funnel at its top. The tower sits in the reservoir near the dam.

Shaft Spillway

Shaft Spillway at Ladybower
Dam in England

When the reservoir level rises above the top of the spillway, the water flows over its sides and down into the shaft. At the bottom of the shaft, it enters a tunnel. The tunnel usually runs under the dam, and diverts the water to join the river downstream.