In the 1980s there was a major effort to develop realistic parametrisations of all the source functions. The present version of the WAM model has an input source function which is based on Miles critical layer mechanism [3] (including the feedback of the wave stress on the wind profile [27]), the nonlinear interactions are represented by means of the direct-interaction approximation (DIA) of Hasselmann et al. [12] while the dissipation source function is based on the work of Hasselmann [28]. A first account of this is given by [14], while a more up to date account of the status of wave modelling can be found in [26].