Modelling of annual sand transports at the Dutch lower shoreface

Dutch coastal policy aims for a safe, economically strong and attractive coast. This is achieved by maintaining the part of the coast that support these functions; the coastal foundation. The coastal foundation is maintained by means of sand nourishments. Up to now, it has been assumed that net transports across the coastal foundation's offshore boundary at the 20 m depth contour are negligibly small. In the framework of the Coastal Genesis 2.0 program we investigate sand transports across this boundary and across other depth contours at the lower shoreface. The purpose of this paper is to provide knowledge for a well-founded choice of the seaward boundary of the coastal foundation. The lower shoreface is the zone where the mixed action of shoreface currents (tide-, wind- and density gradient driven) and shoaling and refracting waves is predominant. Transport rates are relatively small and hence the bed levels in the lower shoreface undergo relatively slow changes.