Hydroelectric dam. Water flowing out of the base of the Rossens dam in Switzerland. This dam is on the Sarine river, forming the lake of Gruyere. The dam capacity (the amount of water that can pass through it) is 930 cubic metres per second. This water generates electricity as it falls through turbines. The dam (main wall off right of image, not seen) has a height of 83 metres, and was built in 1947.