Simulation of wind waves in shallow microtidal basins: Application to the Venice Lagoon, Italy

A number of studies and field observations have demonstrated the crucial role of wind waves on sediment resuspension in shallow microtidal basins, where tidal fluxes alone prove unable to produce the bottom shear stresses necessary to mobilize tidal-flat sediments. Tidal currents, in fact, are seen as the main process governing the morphological evolution of the system in proximity of the inlets and within the chan-nels, whereas, in shallow unchanneled areas, tidal currents mainly act enhancing wind-wave bottom shear stress and redistributing sediments within the system. We recently developed numerical model combining wind-wave effects with the influence of tidal fluxes, in a shallow basin (Carniello et al., 2005). The highly irregular bathymetry and morphological features usually characterizing shallow tidal environments with deep channels, emergent salt marshes, and extensive tidal flats, suggested the introduction of specific hypotheses while solving the wave-action conservation equation to describe wind-wave generation and propagation. In particular we considered a monochromatic wave and assumed that the direction of wave propagation instan-taneously adjusts to the wind direction. The wave period characterizing the monochromatic wave reproduced by the model was assumed to be constant in space and time. In the present contribution we present a reconsideration of the above model, by relaxing some of the previous assumptions, in particular by assuming a variable wave period. Wind-wave data collected in the Venice Lagoon, are used to test and modify the relationship between wave period, wind speed and local water depth suggested by Breugem and Holthuijsen (2007). The improvement in the wind-wave field description obtained by introducing such an estimation of the local wave period reveals to be noteworthy. The results of a number of simulations carried out by considering different storm events support our claims.