REVISITING THE JONSWAP BOTTOM FRICTION FORMULATION

Abstract

The derivation of the JONSWAP bottom friction for wind-driven seas is revisited. This is motivated by the fact that in the literature two different values for the corresponding coefficient are recommended, one value applicable for swell conditions and a significantly higher value for wind-driven sea conditions. The value applicable for winddriven seas was originally determined by Bouws and Komen (1983) who studied the source term balance of a remarkably stationary storm in shallow water. We used a more accurate interpretation of these observations by hindcasting this storm with the third-generation wave model SWAN. In addition, we compare wave model results with measurements in the Wadden Sea and with parametric growth curves, some of which were obtained in Lake George, Australia. The results strongly suggest that the lower bottom friction value of Cb=0.038 m2s-3 is applicable for both wind-sea and swell conditions.