# Hydrodynamic Modelling in a Mediterranean Coastal Lagoon--The Case of the Stagnone Lagoon, Marsala
## 3 Results and Discussion
### Calibration with 2006 Data
The evolution and the complexity of the hydrodynamic circulation inside the lagoon is represented in Figure 10. The north mouth appears to work as a funnel with strong differences between the two velocity components due to the Venturi effect. It is possible to observe how the outgoing flux corresponds to the ebb tide phase, as on 7 July 2007 at 12:00 p.m. (Figure 10d). Figure 9: Behaviour of simulated variables against the recorded data of Val_06, related to water depth (a) and horizontal velocities northward and eastward, (b) and (c) respectively. The south mouth is characterized by a higher hydrodynamic circulation and complexity. Wider width and deeper water allow the fluid to develop velocities where there is a combination of the tide and large eddy effects (Figure 11a). Large eddies could be caused by wind blowing and site morphology (Figure 11c). As shown in the north mouth, even in this case, the flux corresponds to the ebb tide phase (Figure 11f). Figure 10: Graphical maps of hydrodynamic circulation. A whole tidal cycle is reported. A strong Venturi effect can be observed in when the flow is outgoing **(a,b,d)**, caused by the falling tide. A modest eddy is simulated in (c). Is also possible to appreciate **(d–f)** the tide evolution with 6 h period. Comparing the simulations against the recorded data, the NSE parameter is used to compare the prediction capability of different model set-ups. The predictivity capacity is dependent on the differences between the recorded time series and the simulated one. Starting from the comparisons of the simulations showed above, for the two stations Vec_06 and Adv_06 in the centre of the lagoon, it was possible to obtain, in Vec06 for the water depth, a value of NSE = 0.77, and for the Vy and Vx velocity components, respectively, NSE = 0.13 and NSE = \(-\)2.63 (Table 2). In Adv_06, we found NSE = 0.67 and NSE = \(-\)18.37 for the Vy and Vx velocity components, respectively, considering the longest recording period between the 8 th at 08:46 a.m. and the 9 th at midnight, as can be seen in Figure 8.  
Figure 11: Hydrodynamic circulation in the lagoon’s southern region. Is possible to appreciate how the circulation follows the tides (**a**,**c**,**f**). Lower hydrodynamism is simulated in the coastal part of the lagoon (**b**,**d**). Is possible to appreciate the 6 h tide evolution (**e**,**f**). In Val_06, the northernmost station, the obtained values are NSE = 0.50, NSE = \(-\)0.62, and NSE = \(-\)3.37 for water depth, Vy, and Vx variables, respectively (Table 2). The positive values of NSE for water depth mean that the model acceptably reproduces the water level oscillation. The positive values of NSE for the velocity in the north-south components are acceptable from the south mouth up to the centre of the lagoon. The simulated Vy is not acceptable in the northern part of the lagoon (NSE < 0 in Val_06, Table 2). Finally, the simulated east-west component Vx is not acceptable (NSE < 0 in all the three stations). To increase the model reliability, different values of bed roughness Ks were tested: from 20 m\({}^{1/3}\)/s to 35 m\({}^{1/3}\)/s. The NSE values for the water depth are always positive (0.42 < NSE < 0.79) for the Vec_06 and Val_06 stations (Figure 12a). For the Vy velocity, the NSE is positive (0.13 < NS < 0.67) in the Vec_06 and Adv_06 stations. But in Val_06, the furthest station from the southern mouth, the NSE for the Vy velocity is negative under almost any tested roughness condition, probably because the simulation does not adequately predict the velocities in the northern part of the lagoon (Figure 12b). For the Vx component, the NSE is always negative in the three stations for the different roughness values tested (Figure 12c). It is possible to underline how the predictive ability of the model varies in different lagoon areas, appearing to be better close to the Vec_06 and Adv_06 location, the stations closer to the south mouth and close to the southern boundary input.