Page 11 - EAI-4_2015_48-59

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
on the direction of annual wave energy flux, the above
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
Burrone site. Bathymetry was derived by available
nautical charts. Considering the spatial resolution
of data and the formulation of the model, rectangular
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simulations, with x-axis directed shoreward.
For example purpose, Figure 16 illustrates one of the
simulations performed for offshore wave direction
260°N. It can be observed that the wave fronts rotate due
to refraction. Results of all simulations are condensed in
the rose plots of wave climate at 15 m reference depth,
shown in Figure 15. Consistently with wave refraction
and with coastline and bathymetry configuration, a
general wave height reduction and rotation of wave
direction southward are noticed; the sheltering effects
of headlands for waves propagating from the western
quadrant is also evident, especially at Lido Burrone.
FIGURE 16 Example of wave propagation from deep water toward
study areas. Vectors indicate the wave direction. The radiation stress components derived by PMS
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56 EAI Energia, Ambiente e Innovazione 4/2015
TABLE 2 Main results of wave propagation at Cala Azzurra site
(15 m depth)
TABLE 3 Main results of wave propagation at Lido Burrone site
(15 m depth)
As a general observation, compared to Lido Burrone
more intense wave conditions can be estimated at Cala
Azzurra.
For each sector of offshore wave direction, resultant
vectors of mean annual wave energy flux at 15 m
depth were calculated. Significant heights (Hm) and
periods (Tm) of the ideal waves representative of the
annual wave climate in terms of wave energy flux and
steepness, i.e. the so-called “morphological waves”,
were also estimated. Results are summarized in Table
2 and Table 3.
Waves) was used to simulate wave propagation and
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
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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.
module results were used as input in the HD module to
simulate nearshore hydrodynamics induced by incident
morphological waves. Results of HD simulations are