Weak wind-wave/tide interaction over a moveable bottom: results of numerical experiments in Cádiz Bay

Abstract

The formulation of weak wind-wave/low-frequency current interaction is extended to the moveable rough bottom case using the bottom roughness predictors of Nielsen (Coastal Eng. 7 (1983) 233) and Tolman (J. Phys. Oceanogr. 24 (1994) 994). This “extended” formulation is then implemented in a 2D non-linear, high-resolution hydrodynamic model and the modified model is applied to study the changes in the tidal dynamics of Cádiz Bay due to wind-wave/tide interaction and bottom mobility. It is shown that an agreement between the observed and predicted tidal elevation amplitudes and phases at the tide-gauge and bottom-pressure measurement locations within the bay tend to be improved if both of these factors are accounted for. Distinctions between the solutions derived when employing Nielsen's and Tolman's bottom roughness predictors are considerable though not so much as might be expected. The sensitivity of the solution to the mean sediment grain size turns out to be either moderate or low depending on which of the above-mentioned bottom roughness predictors is adopted and much less than the sensitivity to the tidal reference bottom roughness length. Accordingly, if the wave and tidal reference bottom roughness lengths are set equal to each other, the changes in the fields of tidal characteristics become unreasonable, thereby eliminating the possibility of prescribing a single reference bottom roughness length.