SEDIMENT TRANSPORT AND BUDGET OF THE CENTRAL COASTAL ZONE OF HOLLAND

Based on the available short-term morphological data (1964-1992), the net yearly-averaged sand volume change in the surfzone (3/-8 m NAP; to local datum approximately mean sea level) along the coast of Holland was found to be 125,000 m(3)/year (sedimentation), including beach nou rishments. A sand budget model has been developed, which describes the sand volume change (in m(3)/year) in each compartment of the coastal area given known gradients of the computed longshore and cross-shore t ransport rates and known source/sink terms (nourishment, dumping and d redging). The model area extends in cross-shore direction from the +3 m NAP contour to the -20 m NAP contour. The sand budget model has been calibrated (hindcast study) using the yearly-averaged sand volume cha nges derived from bathymetry data (Jarkus-data base) collected during the period 1964-1992. Input data are the gradients of the yearly-avera ged longshore and cross-shore transport rates at the boundaries of the compartments and the available data of beach nourishment, dumping and dredging in the same period. A 2DV-mathematical model representing th e hydrodynamic (waves and currents) and sand transport processes in a cross-shore profile was applied to compute the yearly-averaged transpo rt rates in various profiles along the coast at depths of 20 and 8 m a nd in the surf zone. A detailed sensitivity study was performed to det ermine the variation ranges of the transport rates. (C) 1997 Elsevier Science B.V.