OFFSHORE SAND EXTRACTION AND NEARSHORE PROFILE NOURISHMENT

Jos S.L.J. van Alphen, Frank P. Hallic, Jan S. Ribberink, J.A. Roelvink, Cees J. Louisse

Abstract


Because of the increasing need of sand for use on land and coastal protection, offshore sand extraction has become commonplace. On the other hand, the practice of beach nourishment has become a common method to combat beach erosion. Here, economic and other interests may be served by dumping the sand not directly onto the beaches, but nearshore. Within the framework of the Coastal Defence Study for the Dutch coast and the preparation of a Marine Aggregate Extraction Plan model studies were performed in order to obtain indications and quantitative estimates of the morphological effects of offshore sand extraction and nearshore profile nourishment. The major results of the model computations are: - offshore sand extraction landward of the 16 m isobath may affect the coastline within a century. - nearshore nourishments landward of the 7 m isobath have positive effects on the coastline. The model computations could not be validated in the field. Due to the relatively large margins of inaccuracy the political implication of this study is that sand extraction landward of the 20 m. isobath is not licensed.

Keywords


offshore sediment; sediment extraction; nearshore profile; beach nourishment

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