THE ROLE OF SURFACE ROLLERS ON THE FORMATION OF SURFZONE TRANSVERSE SAND BARS

A morphodynamic model has been developed to gain more fundamental knowledge about the formation of transverse finger sand bars. The model describes the feedback between waves, rollers, depth-averaged currents and bed evolution, so that self-organized processes can develop. The wave and bathymetric conditions measured at Egmond site are firstly applied and the modeled longshore current and wave height are compared with field data of that beach. Subsequently, the wave and bathymetric conditions measured at Noordwijk site are used to compare model results with the up-current oriented bars observed there. Realistic positive feedback leading to formation of the observed bars only occurs if the resuspension of sediment due to bore turbulence is included in the model. The modeled wavelength, crest orientation and growth rate agree with data but the model overestimates the migration rates.