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Research & development

waves sub-sectors, namely the sector 120-180°N, with
30% relative occurrence frequency, and the sector
190-300°N, with 70% relative occurrence frequency.
For both the complete sector and each sub-sector, the
resultant vector of offshore annual wave energy flux
was evaluated; results are summarized in Table 1. Based TABLE 2 Main results of wave propagation at Cala Azzurra site
on the direction of annual wave energy flux, the above (15 m depth)
directional sub-sectors were referred to as SE sector
and SW sector, respectively.
Offshore waves were transferred shoreward using
different numerical models. First, MIKE 21 NSW
(Nearshore Spectral Waves) module was applied
to simulate wave propagation from deep water to
intermediate depth off the Cala Azzurra and Lido TABLE 3 Main results of wave propagation at Lido Burrone site
Burrone site. Bathymetry was derived by available (15 m depth)
nautical charts. Considering the spatial resolution
of data and the formulation of the model, rectangular As a general observation, compared to Lido Burrone
grids with Δx=30 m and Δy=100 m were adopted for more intense wave conditions can be estimated at Cala
simulations, with x-axis directed shoreward. Azzurra.
For example purpose, Figure 16 illustrates one of the For each sector of offshore wave direction, resultant
simulations performed for offshore wave direction vectors of mean annual wave energy flux at 15 m
260°N. It can be observed that the wave fronts rotate due depth were calculated. Significant heights (H m ) and
to refraction. Results of all simulations are condensed in periods (T m ) of the ideal waves representative of the
the rose plots of wave climate at 15 m reference depth, annual wave climate in terms of wave energy flux and
shown in Figure 15. Consistently with wave refraction steepness, i.e. the so-called “morphological waves”,
and with coastline and bathymetry configuration, a were also estimated. Results are summarized in Table
general wave height reduction and rotation of wave 2 and Table 3.
direction southward are noticed; the sheltering effects At both sites, MIKE 21 PMS (Parabolic Mild Slope
of headlands for waves propagating from the western Waves) was used to simulate wave propagation and
quadrant is also evident, especially at Lido Burrone. breaking from 15 m depth to the shore and to calculate
the radiation stress components. Finally, MIKE 21 HD
(Hydrodynamic) module was used to simulate the
wave-induced currents in the nearshore, based on
results from previous simulations. Bathymetric survey
data were used for simulations with PMS and HD
modules, and finer bathymetric grids (Δx=Δy=5 m)
were adopted. Wave conditions used for simulations
corresponds to morphological waves representative of
SE and SW sectors, as reported in Table 2 and 3.
Figure 17 and Figure 18 illustrate results of nearshore
wave propagation provided by PMS module, described
by directional wave vectors.
The radiation stress components derived by PMS
module results were used as input in the HD module to
FIGURE 16 Example of wave propagation from deep water toward simulate nearshore hydrodynamics induced by incident
study areas. Vectors indicate the wave direction.
Offshore wave direction is 260°N morphological waves. Results of HD simulations are

EAI Energia, Ambiente e Innovazione 4/2015
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