Gerbrant van Vledder, Marcel Zijlema, Leo Holthuijsen


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.


Wave modelling; bottom friction; TMA scaling;SWAN; JONSWAP; North Sea

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