Influence of Bottom Friction on Sea Surface Roughness and Its Impact on Shallow Water Wind Wave Modeling

Abstract

Abstract Using a selected subset of the measured data obtained in shallow waters near Vindeby, Denmark, during RASEX (Riso Air–Sea Experiment), the role of bottom friction dissipation in predicting wind waves (not swell) is assessed with a third-generation numerical wind wave model. The RASEX measurement site is located in relatively shallow waters (depths of about 3 to 4 m) in an area where the waves are predominantly fetch limited (i.e., maximum fetch of about 20 km). The bottom friction dissipation source term is modeled using the linearized bottom friction formulation. This formulation contains a dissipation coefficient, Cf, which depends on wave and sediment properties. In the numerical investigations, we considered three cases: (i) a constant value for Cf as obtained in the JONSWAP Experiment, (ii) a constant geometric roughness kN, and (iii) a constant median sediment size, d50. In the latter case, the bed is treated as a mobile bed and the geometric roughness is related to the dimensions of wave-f...