Flood control areas as an opportunity to restore estuarine habitat

Intertidal areas in estuaries play a multi-functional role, from energy dissipation and mitigation of floods over provision of natural habitat to a contribution in the cycling and recycling of nutrients. Many of these intertidal areas have been claimed for urban, agricultural or industrial expansion. When considering restoration in a land-scarce environment, managed realignment is not always an option and thus other approaches need to be considered. In this paper we investigate the possibility to combine the concept of a flood control area (FCA) with nature development and the functions of intertidal areas, by use of simple sluice constructions to introduce a controlled reduced tide (CRT). Model results show the possibility to introduce acceptable tidal influence in FCAs. Nevertheless there are major differences with tidal characteristics of natural outer dike marshes: the spring-neap tidal range is strongly reduced, the tidal curve flattened. Also the relation between inundation time (IT) and inundation frequency (IF) shows strong distortion compared to the natural situation, with roughly doubled inundation times as compared with a natural outer dike marsh. This has important implications for nature and vegetation development. Further research and monitoring of test sites is necessary to conclude about the desirability of the implementation on larger scale of this concept.