Nourishing intertidal foreshore

Improving safety and nature

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After extensive flooding in 1953, Deltaworks were constructed to protect the Southwest delta in the Netherlands. In the Eastern Scheldt the connection to the North Sea was regulated by an open storm surge barrier and two compartment dams. These decreased the tidal volume and consequently tidal flats are eroding and disappear under water. The intertidal flats and shoals have two important functions in the basin. Firstly, they are valuable habitat and foraging grounds for wading bird species. A second function of intertidal foreshores is to reduce the wave attack on surrounding water barriers. In front of the Oesterdam Rijkswaterstaat has started a pilot project called “the Oesterdam safety buffer? to find a solution to the erosion problems. This report investigates several solutions for this foreshore nourishment. In total seven different designs have been evaluated in this report. Four different design strategies have been found in a workshop namely, a high dune, a buffer, an equally spread flat nourishment and finally a wave breaking ridge. For all these strategies different profiles have been dimensioned. To model the morphological development of the profiles a 1D morphological model called XBeach has been used. A safety check for the design conditions (1/4000yr) has been done both for the initial profiles, as designed, and for the final profiles at the end of their 50years lifetime. To calculate the overtopping over the Oesterdam the program PC-Overslag has been used. Results showed that all nourishment designs give a smaller overtopping volume of the dam and thus create safety. Final evaluation of the designs showed that a Flat foreshore nourishment combines a solution for nature and safety.