Morphological development of a mega-nourishment; first observations at the sand engine

Abstract

Large (mega-scale) nourishments have been proposed as a promising alternative for traditional beach and shoreface nourishments, especially for locations with large structural erosion and sucient sediment to dredge. This paper examines the initial bathymetric evolution of the Sand Engine, a mega-nourishment of 17 million m3 protruding almost 1 km seaward from its surrounding coast. Topographic surveys show that, despite the blunt initial shape of the nourishment, the sediment is reworked into a nearly symmetrical (bell curve like) shape in less than 1.5 years. The cross-shore extent decreased by 150 m in this period which is a reduction of 15%of its original extent. Simultaneously, the alongshore size of the nourishment increased by 60 % as the sediment is redistributed to the adjacent coasts. This is also reflected in the large 1.6 million m3 loss of sediment on the peninsula. Almost 70 % of this volume is found to accrete in adjacent coastal sections. Although not all sediment loss from the peninsula could be relocated, the findings reveal that the Sand Engine mega nourishment is feeding its surrounding coast substantially.