A dam or barrier built across a tidal channel to allow a power-generating plant to operate. The siting of the barrage requires there to be a large tidal range, in excess of 5 m, and a large water body open to the sea, with a narrow entrance. One barrage and generating plant in operation since 1960 is on the Rance Estuary in Brittany, France. It generates electricity by the use of two-way turbines, as water flows in and out of the estuary through the barrage. The Severn Estuary and Morecambe Bay are potential sites for tidal barrages in the British Isles.