Ecological Impacts of the Construction of Dams in an Estuary

To reduce flooding in coastal regions of the Netherlands, the Delta plan was established, which required that 5 of the 7 estuaries in the southwest of the country should be closed off by dams between the islands, with additional barriers on the landward side where necessary. A map showing the location of the dams is included. Two methods of constructing the barriers, using concrete blocks and rubble, and using sand alone, were investigated. Although sand had certain advantages, its use required low current velocities during the final closing period of the dam. The effects of reducing either tidal amplitude or tidal frequency on the natural ecosystems and fisheries are discussed.