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

A subgrid moveable-bed bottom friction model is developed for use in l arge-scale wind wave models. This model defines a representative botto m roughness based on the local application of a discontinuous roughnes s model and a statistical description of depth, sediment and wave para meters for a finite area within the model (i.e., a grid box). The mode l reproduces the discontinuous attenuation behavior of swell in condit ions of initial ripple formation as predicted by a small-scale model. It furthermore suppresses non-physical oscillations of swell energy an d unrealistically strong dependencies of depth-limited wave heights on sediment parameters. An alternative interpretation of the model expla ins the (continuous) transition between the no-ripple and ripple regim es as sometimes observed in nature.