Tidal Barrages

Top: the Dam for the tidal power plant on the estuary of the Rance River, Bretagne, France
Bottom: Artists impression of the Severn Barrage showing the built barrage deck

Tidal Barrages utilise the potential energy from the difference in height between high and low tides. A dam with a sluice is constructed spanning a tidal inlet, or a section of a tidal estuary creating a reservoir. At high tide sea water flows into the resevoir through a one way gate. The gate closes when the tide began to fall and when the tide is low enough, the stored water is released at pressure through turbines, back into the sea. The rotation of these turbines generates electricity.
The viability of Barrage systems has been questioned due to high civil infrastructure costs and environmental issues. There are only a few potential sites across the globe and there are only three functioning plants worldwide (Rance River, Bay of Fundy and Kislaya Guba).