The model is applied to three representative locations in the V enice lagoon (Figure 2). The locations were chosen to describe different substrate characteristics and hydrodynamic conditions. The characteristics of each location are reported in Table 1. Location 1 is near the lagoon inlet, and it is characterized by a sandy substrate. Locations 2 and 3 are instead near the basin boundaries and have a bottom composed of clay and silt [Amos et al., 2004].

The temporal evolution of the tidal flat elevation is studied by simulating long-term wind conditions under different scenarios of sediment input and output. At the beginning of the simulation, a value for the sediment-input rate Mand sediment lossfare chosen in equation (14). The model simulation procedure consists of nine steps that are repeated every temporal interval: (1) two random numbers r1 andr2 are drawn from a random uniform distribution defined between 0 and 1 and then used in equation (11) to calculate the wind speed and duration; (2) the tidal elevation and velocity are calculated for the duration of the wind every 30 min from equations (2) and (3); (3) given the wind intensity and the water depth, the wave height is computed from equation (6) for fully developed sea and from equation (8) for fetch limited conditions; (4) given the wave height, the bottom shear stresses are computed from equation (7); (5) the wave shear stresses and the tidal current shear stresses are combined to determine the total shear stress in equation (1); (6) the erosion is calculated from equation (15) for noncohesive and from equation (17) for cohesive sediments; (7) the deposition rate is calculated from equation (16) for noncohesive and from equation (18) for cohesive sediments; (8) the sediment concentration is computed with equations (13) and (14); (9) the bottom elevation is updated in equation (12). A temporal step of 30 min was chosen to resolve in detail the tidal oscillations without compromising computational speed.

An example of model results for location 2 is presented in Figure 8 with M = 2?10?5kg/m2/s. The temporal series of wind intensity produce waves of elevation up to 0.4 m. Only wind speeds exceeding 3 m/s produce significant waves, and the tidal elevation has a marginal effect on modulating the wave height (but the tidal effect becomes important in shallow tidal flats). The wave shear stress is then added to the tidal current shear stresses (Figure 8f) to produce the total shear stress (Figure 8g) responsible for the resuspension of sediments in the water column (Figure 8i) and bottom erosion (Figure 8j). Sediment input (Figure 8h) is on average higher than sediment output during normal wind conditions (small waves), but, when wind waves resuspend a consistent volume of sediments, the tide exports part of this material to the ocean (sediment output, Figure 8h). Superimposition of tidal shear stress to wave shear stress appears to be crucial for bottom erosion. Short wind events of few hours produce erosion when they occur during ebb or flood but are not effective during slack water. Prolonged wind durations spanning at least half a tidal cycle are more effective in eroding the tidal flat bottom, since they are always combined with peak tidal discharges.   

Quoted from: Wind waves in shallow microtidal basins and the dynamic equilibrium of tidal flats