SUBGRID MODELING OF MOVEABLE-BED BOTTOM FRICTION IN WIND-WAVE MODELS

A subgrid moveable-bed bottom friction model is developed for use in large-scale wind wave models. This model defines a representative bottom roughness based on the local application of a discontinuous roughness model and a statistical description of depth, sediment and wave parameters for a finite area within the model (i.e., a grid box). The model reproduces the discontinuous attenuation behavior of swell in conditions of initial ripple formation as predicted by a small-scale model. It furthermore suppresses non-physical oscillations of swell energy and unrealistically strong dependencies of depth-limited wave heights on sediment parameters. An alternative interpretation of the model explains the (continuous) transition between the no-ripple and ripple regimes as sometimes observed in nature.