Tidal energy

A tidal barrage may be built across the River Severn estuary between England and Wales. One of the possible designs is shown below.

A tidal barrage harnesses the powerful surge of tide as it comes in, by holding back the sea, which makes a difference in the levels of water on each side of it.

The tide flows out on the outgoing (ebb) tide, the barrage holds back the river again, making a difference in the levels of water on each side once more. This time as the water goes through the tunnels, the turbine is turned the other way.

For maintenance of the turbines, lock gates are lowered at either outlet to seal off the water.