A barrage is a barrier across a river intended to control the flow of water and perhaps provide hydro-electric power.

A diagram showing how a barrage works.

A barrage on the Ohio River.

A barrage is made out of concrete with gates that are made of steel. The gates are lowered or raised to allow more or less water to flow through them. Gates are managed to keep the water above the barrage deep enough for boats to navigate, but they are kept low enough to allow water to pass down river and flood the valley above the barrage.