Floods Glossary

polder

A mostly low-lying area artificially protected from surrounding water and within which the water table can be controlled. A kind of retention area. A piece of ground lying adjacent to a stream that is separated from it by dykes and can be inundated in a controlled operation during a flood in order to retain the water and to lower the flood crest. Once the water has fallen below the critical discharge level, the polder is emptied again. For this purpose, pumps must be used if the base of the polder is lower than the surface of the river. In times when it is not needed for retention, a polder can be used for agricultural or other purposes, but only on the condition that it is not ploughed up. The danger with polders that are seldom needed is that their value for other uses gradually increases in the course of time and this may even result in them no longer being suitable for their original purpose.