Project part-financed by the European Union (European Regional Development Fund)

The Interreg IVB North Sea Region Programme

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Walsoorden pilot part A (2004): relocation of dredged sediment to a shallow water area at the edge of the Walsoorden sandbar


The experiment was thoroughly monitored between November 2004 and January 2006, morphologically as well as ecologically. Five criteria (2 for morphology and 3 for ecology) were defined on beforehand to judge the success of the test (see Fout! Verwijzingsbron niet gevonden.).

The morphological criteria were related to the stability of the relocated material and to the sedimentation in the “Schaar van Valkenisse”, the flood channel next to the Walsoorden sandbar. In order to be able to follow the morphological developments (topographic and bathymetric monitoring), high resolution multibeam surveys were executed on and around the relocation area at a regular basis (in the beginning weekly, after a while monthly). Additional, the altitude of the Walsoorden sandbar was measured twice from an airplane (LIDAR technique). Sediment transport was also monitored with a measurement campaign (before, during and after the relocation test), as well as with a sediment tracing test after the relocation.

The ecological criteria were related to the elevation of the Walsoorden sandbar, change in percentage intertidal mud and change in intertidal macrobenthos. The ecological monitoring consisted of an intertidal (Walsoorden sandbar) and subtidal part (shallow water around the Walsoorden sandbar, i.e. impact area Figure 4: I1). To analyse significant changes, a number of control areas were defined (Figure 4: C1-4). First the consistency of the soil (grain size and mud-percentage) was determined for the different areas in different seasons. Samples were also taken to analyse macrobenthos (biomass, diversity and density). At three locations, the elevation was observed in detail. To observe the developments of the Walsoorden sandbar as a whole, a flight was executed while using remote sensing and hyperspectral analysis. The goal of this extensive ecological monitoring program was to see whether the in situ relocation test caused a significant effect on all measured parameters, thus affecting the local ecology.

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