RIACON: Risk analysis of coastal nourishment techniques in the Netherlands

Circa 75% of the coastline in The Netherlands is formed by dunes and beaches. This coastline is constantly moving because ofaccretion and erosion. Sand nourishments are used to prevent coastal erosion and have been carried out along the Dutch coast since the 1970's. As alternative to the common used dune and beach nourishment, a recent development in coastal protection is application of shoreface nourishment (VAN HEUVEL & HILLEN 1991). Shoreface nourishment implies the deposition of a buffer ofsand on the sea floor at ca. 5 m depth in front of the beach. This buffer is intended a) to provide the beach with sand through natural onshore transport and b) to reduce erosion by dissipating wave action. Shoreface nourishment is designed to conserve the coastline for several years. Apart from being cheaper than beach nourishment, shoreface nourishment has the advantage ofminimal interference with recreational activities on the beach. Large scale nourishments will confront the benthic community with environmental changes including increased sedimentation and changes in sediment structure. Benthic fauna is able to survive a sudden coverage with sediment to a certain extent. This ability, however, varies from species to species, being dependent on the type of material, the thickness of the sediment deposited and the deposition velocity (BrJKERK 1988). To study the response of the benthic community to shoreface nourishment and the accompanying subaqueous sand extraction, the RIACON program was initiated. RIACON is co-sponsored by the MAST II (Marine Science & Technology) program of the Commission of the European Communities and evaluates the ecological risk of shoreface nourishment and subaqueous sand extraction at sites in Denmark, Germany, The Netherlands, Belgium and Spain (Catalonia).