# Hydrodynamic Modelling in a Mediterranean Coastal Lagoon--The Case of the Stagnone Lagoon, Marsala
## 3 Results and Discussion  
### Calibration with 2006 Data  
Initially, the Gauckler-Strickler coefficient \(\mathrm{Ks}=20\) m\({}^{1/3}\)/s was set as constant in the whole area, and the wind friction factor coefficient was set as \(f=0.0010\), similarly to the value found by [25], who used f = 0.0014 for W \(<\) 10 m/s, and as it was recognized as more reasonable for running the model. The default coefficient suggested by MIKE21 (f = 0.0026) returns values strongly conflicting with the recorded ones. Finally, the effects of the eddy viscosity parameter did not modify the lagoon behaviour when imposed as a constant eddy  
Figure 6: Evolution of water levels recorded in both mouths. formulation, starting from \(\
u=0.0\) m\({}^{2}\)/s, until values of \(\
u=1.2\) m\({}^{2}\)/s. By default, MIKE21 suggests a constant value of \(\
u=0.002\). Furthermore, for eddy viscosity, the Smagorinsky formulation was imposed, with a range of specific k coefficients from k = 0.25 to k = 1.00 following [21], but no change in simulated water level and velocities was detected. It was then decided to neglect the simulation of the eddy viscosity. The numerical model can reproduce the dominant effects of winds and tides, as can be seen in the following figures where it is possible to appreciate the comparisons between the recorded and the simulated evolution of target variables in all the stations. In Figure 7, it is possible to compare the evolution of water elevation and the Vy and Vx velocity components recorded in Vec_06. Starting from the comparisons between recorded and simulated time series for Vec_06, it is possible to appreciate that the general hydrodynamic behaviour of the lagoon is  
Figure 7: Decoupling of recorded and simulated data on Vec_06, related to water depth (**a**) and horizontal velocities northward and eastward, (**b**) and (**c**) respectively. replicated even if some difficulties are present. Although the simulated water depth evolution is in accordance with the recorded ones, the Vy velocity component is sometimes in antiphase with the recorded values, as at midnight of 6 July, when the recorded velocities were northward (positive values), but the simulated ones are southward (negative values) (Figure 7b). The worst agreement was found considering the Vx velocity component, especially during the night of 8 July (Figure 7c). These rates of accordance can be estimated from Appendix A (Table A1), where RMSE and R\({}^{2}\) are reported. Even if Adv_06 had technical problems related to a battery failure during the 2006 campaign, it is possible to appreciate that the general behaviour is replicated, especially for the Vy velocity component (Figure 8a). The Vx component has a bad agreement during the night of 9 July (Figure 8b), when a strong acceleration recorded in the velocities, due to seiches, is not reproduced by the simulation. Finally, in Figure 9, it is possible to appreciate the evolution of the simulated and recorded water level values, as well as the Vy and Vx velocity components of Val_06, in the northern part of the lagoon. In some moments, the simulated water depth anticipates the recorded one. The range of the simulated Vy is lower with respect to the recorded values. This is particularly the case on the night of 8 July, when the simulated Vy is close zero, but the recorded values reached \(-\)0.03 m/s southwards and +0.04 m/s northwards. At 9:00 a.m. of 5 July, the recorded Vy is positive (northward), while the simulated Vy is negative (southward) (Figure 9b). Figure 8: Behaviour of the Vy and Vx velocity components recorded and simulated in Adv_06, related to horizontal velocities northward and eastward, (**a**) and (**b**) respectively. Looking at global simulation, the hydrodynamic circulation inside the lagoon follows peculiar pattern strongly related to tide and wind variability, as shown in the figure below representing a tidal cycle between 6 and 7 of July 2006.