Energy balance of wind waves as a function of the bottom friction formulation

Four different expressions for wave energy dissipation by bottom friction a re intercompared. For this purpose, the SWAN wave model and the wave data s et of Lake George (Australia) are used. Three formulations are already pres ent in SWAN (ver. 40.01): the JONSWAP expression, the drag law friction mod el of Collins and the eddy-viscosity model of Madsen. The eddy-viscosity mo del of Weber was incorporated into the SWAN code. Using Collins' and Weber' s expressions, the depth- and fetch-limited wave growth laws obtained in th e nearly idealized situation of Lake George can be reproduced. The wave mod el has shown the best performance using the formulation of Weber. This form ula has some advantages over the other formulations. The expression is base d on theoretical and physical principles. The wave height and the peak freq uency obtained from the SWAN runs using Weber's bottom friction expression are more consistent with the measurements. The formula of Weber should ther efore be preferred when modelling waves in very shallow water. (C) 2001 Els evier Science B.V. All rights reserved.