Modelling Inner Surf Zone Hydrodynamics at Egmond (NL)

Abstract

This paper presents the numerical hindcasting of the first eleven days of the main experiment of the Coast3D project, carried out near Egmond (the Netherlands) in the autumn of 1998. In this period a rip channel develops with an orientation correlated with the wave direction. Hindcasting the wave height and velocity measurements with a numerical model resulted in an increasing underestimation of wave breaking going closer to the shore. Consequently, there is good agreement between the computed and measured longshore velocities on the seaward slope of the inner breaker bar (Station lA), but less so for these velocities on the shoreward slope of the inner breaker bar (Station 1D). We expect this to be due to the inability of the wave model to predict rapid decrease of the wave height across the inner bar. Crossshore velocities in the main transect are dominated by rip currents and wave breaking-induced return flow. Qualitative agreement is fairly good but quantitative agreement between the measurements and the model results is only reasonable, probably caused by the application of a 2DH mode, inaccurate prediction of the location of rip currents and differences in the bathymetry. INTRODUCTION The COAST3D measurement campaigns near the town of Egmond, the Netherlands, resulted in two extensive data sets. Data of the first (pilot) field campaign was used to 1) Researcher, Section of Hydraulic Engineering, Delft University of Technology, P.O.Box 5048, 2600 GA Delft, The Netherlands. m.d.klein@ct.tudelft.nl 2) Researcher, Section of Hydraulic Engineering, Delft University of Technology, P.O.Box 5048, 2600 GA Delft, The Netherlands. e.p.l.elias@ct.tudelft.nl 3) Professor, WLJDelft Hydraulics, P.O. Box 177, 2600 MH Delft, The Netherlands. marcel.stive@wldelft.nl 4) Senior Researcher, WLlDelft Hydraulics, P.O. Box 177, 2600 MH Delft, The Netherlands. dirkj an.walstra@wldel ft.nl