## 6 Sea Storm Effect Analysis  
### Local Scale Interactions between Wave Motion and Coastal Features  
The stretch of Via Partenope near Castel dell'Ovo has suffered from the heaviest effects during sea storms coming from S to SW directions. The vulnerability of this stretch of coast depends on a number of local factors (Figure 3). Particularly, the presence of Castel dell'Ovo bastion, given the relatively high-water depth to the SW of the structure, causes a \"wall effect\" and a significant reflection of the incoming waves towards the coastline. In Figure 17, a set of four pictures has been collected, showing wave fronts propagating from SSW to NNE during the phase of maximum intensity of the swell and the interaction with the seawall protecting Via Partenope. The complex scenario of wave motion in front of Via Partenope, due to the reflection of incident waves on the western bastion of Castel dell'Ovo is shown in Figure 18.  
The western bastion of the Castel dell'Ovo reflects the incident waves (wave fronts 1-2-3), creating reflected wave trains (wave fronts 1'-2'-3') that propagate along ESE-WNW direction. Reflected waves have a limited extension, as the interaction of waves with the Castel dell'Ovo western bastion is relatively limited in time (yellow line in Figure 18a). The reflected waves interact with the incident waves causing a superposition of effects. This leads to marked undulations of the sea surface (Figure 17) due to the composition of the two different wave motions (incident and reflected). Figure 18a indicates the points where the incoming and reflected waves combine. The dynamics of waves interaction leads to a chaotic scenario where the incoming waves prevail, and rogue waves may also form.  
Photos and video images from the evening of 28 December 2020, show that the wave crests in front of Via Partenope were diffusely breaking (see Figure 17) due to the progressive shallowing of the seafloor. The merging of the incident waves with reflected waves results in an overall deviation to the NW from the direction of the incoming waves.  
The combined analysis of available photographic and video images in the phase of maximum wave development allowed for the estimation of the wavelength L as distance between the major wave crests and, therefore, the evaluation of the period T characterizing  
Figure 17: Photos taken from the buildings along Via Partenope, showing the waves scenario during the phase of maximum intensity of the swell.  
Figure 18: Complex scenario of wave motion in front of Via Partenope, due to the reflection of incident waves on the western bastion of Castel dell’Ovo. Reflected waves are indicated with dotted light blue lines 1’-2’-3’ (**a**). (**b**) The energy flux reflected by Castel dell’Ovo, enhances the wave energy impacting Via Partenope. Equation indications are from Equation (20).  
the main wave motion. This analysis led to establish a value of about 100 m for the wavelength. To obtain the period, we use the following relation existing between L and T:  
\[\text{L}=1.5\text{T}^{2}=>\text{T}=\sqrt{\left(\frac{\text{L}}{1.5}\right)}=8.2 \text{ s}. \tag{15}\]  
This value is significantly higher than the maximum observed at the wave buoy of the Parthenope University, equal to 6.6 s (Table 5), which corresponds to a wave motion with a wavelength equal to 65 m. This value is also higher with respect to the one extracted by Groen-Dorrestein nomogram for H\({}_{\text{C}}\) (7.3 s) and almost equal to the one relative to H\({}_{\text{max}}\), thus confirming the assumption that wave enhancing factors are present, at local scale, in the area.