Interesting. Thanks
A number of estuarine sites, including the Severn and the Mersey have been examined around the UK. The Severn Estuary proposal consists of a single basin barrage designed to operate on the tide’s ebb. This system allows for the rising tide to flow in through the sluice gates and turbines. After high tide, these are closed until the tide has ebbed sufficiently for the difference in water level between the sea and the barrage basin to drive the turbines. This continues until the water level is too low for the turbines to operate and they are then closed down.
Same principle.