# Hydrodynamic Modelling in a Mediterranean Coastal Lagoon--The Case of the Stagnone Lagoon, Marsala
## 3 Results and Discussion
### Validation with 2007 Data  
After the calibration with 2006 data, a validation process was conducted for the 2007 campaign. Starting from the optimum set-up model found during the calibration, the simulation of the 2007 field campaign was tested using the following parameters: Strickler \(\text{K}_{\text{s}}=20\)\(\frac{\text{m}^{\frac{1}{3}}}{\text{s}}\) and wind friction factor \(f\) = 0.0020, neglecting the eddy viscosity term. Again, instrumentation was deployed in the most representative areas of the lagoon, and the following time series show the model attempts replicating the behaviour of the lagoon. Starting from the south side, the times series will be described below. Starting from Vec_07, the closest station to the south mouth, it is possible to underline a better evolution, with respect to 2006 data, of the water depth and Vy velocities. The  
Figure 13: NSE values obtained by the comparison of Vec_06 (**a**), Adv_06 (**b**), and Val_06 (**c**) recorded values and simulated ones, depending on the friction factor f.  
results show NSE = 0.92 for water depth and NSE = 0.72 for Vy. The Vx components remain badly simulated, resulting in an NSE = \(-\)0.32 for Vx, and the seiches are poorly replicated as well (Figure 14). Moving to the centre of the lagoon, in the ADV_07 station, there is some agreement between the simulated values of Vy and the recorded values; NSE = 0.50 for Vy. For the Vx component, there is disagreement; the filtered recorded Vx is generally negative, while the simulated values are generally lower than the recorded ones. In fact, NSE = \(-\)10.57 (Figure 15). These rates of accordance between recorded and simulated data can also be estimated from Appendix A (Table A1), where RMSE and R\({}^{2}\) are reported. Figure 14: Behaviour of simulated variables (water level, Vy, and Vx velocity components, respectively, in (**a**–**c**)) against the recorded data of Vec_07. The northernmost measurement was recorded in Val_07, and from the time series reported in Figure 16, it is possible to see how the simulation had some difficulty replicating the considered variables. The simulated water depth anticipates the recorded one; then, the NSE = 0.28 approaches zero. For the Vy velocity component, the simulation fails in replicating the recorded values simulating generally negative velocities and missing the tidal accelerations and decelerations; NSE = \(-\)6.27 for Vy. The Vx velocity component is poorly replicated, mismatching all the hydrodynamic phenomena; NSE = \(-\)47.21. Seiches depend on the combination of the intensity and direction of wind blowing, morphology, and the penetration of another lagoon's external seiches. These phenomena can induce fluid to move even in antiphase with the wind direction, as can be seen in Figure 16, where the recorded and the simulated Vy velocities and wind vector are reported. At 20:00 on 25 July and at 18:00 on 26 July, the recorded Vy velocity component was about +0.08 m/s, while the simulated one was 7-0.03 m/s; at the same time, the wind was directed southward with a speed of 8 m/s. This is probably because during the day, the tidal movement from the south mouth was predominant over the effect of the wind. The model appears not to replicate this phenomenon, and this affects its predictivity capacity, generating lower values of NSE. It seems that the main effect of the wind is to create wind waves, rather than generating motion in the north-south direction. In fact, when the wind is absent, the unfiltered water level and velocity Vy do not show noise in the signal. Meanwhile, the wind blows the unfiltered water level, and Vy velocity shows the effect of the orbital motion due to the wind wave (Figure 16). The flow in the north-south direction is mainly due to the tidal motion from the south mouth. In this area, the model seems to account greater importance to wind-induced effects to the motion field, underestimating the effect produced by tidal variations.