Tidal barrage systems work on the principle that ebb and flow at sea cause a water level difference across a dam or flood defence structure. This potential energy can be harvested with turbines (Witteveen+Bos & CE Delft, 2019). In addition to bi-directional low-head turbines, free-flow turbines can also be used. There are a number of locations where bi-directional low-head turbines are in the picture for possible projects, partly due to a possible dual role as pump and turbine. That is why tidal barrage at dams has been included in a separate fact sheet, despite the overlap with the tidal stream category.