Page 6 - EAI-4_2015_48-59

:DYHFOLPDWHDQGFRDVWDO Research & development

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Incident offshore wave climate,

nearshore wave conditions and

wave-induced coastal circulation

at study areas were investigated

using available wave data and

mathematical models.

The offshore wave climate was

derived from historical data

measured from July 1989 to

March 2008 at Mazara del Vallo

recording station of the Italian

Sea Wave Measurement Network

FIGURE 4 Satellite view of Cala Azzurra and Lido Burrone sites and cross-shore [25]. Wave data were transferred
survey lines
to a virtual buoy located off
Cala Azzurra and Lido Burrone

sites, at 100 m depth. At this

to storm wave conditions associated to a given aim, a geographic transposition method [26] was

recurrence frequency or return period, based on the used, based on comparison among effective fetches

analysis of extreme events [23, 24]. In the present measured, respectively, at real and virtual station.

study, a 25 years return period was adopted and, Offshore wave data were processed to estimate mean

following Gumbel’s distribution, values of Hs=6.21 annual wave climate, in terms of joint occurrence
m, Ts=10.39 s were estimated, resulting in a depth of frequency of wave height and direction. A statistical
closure dc=11.66 m. analysis of extreme waves was also performed to
Based on the above considerations, survey lines were derive sea state parameters associated to different

extended in the offshore direction beyond a depth of values of the return periods, based on suitable

about 12 m, according to the available nautical charts probability distribution functions.

provided by the Hydrographic Institute of Italian Navy. Offshore wave conditions were transferred shoreward

In Figure 4, the navigation projects are shown for each using state-of-the-art numerical models. Namely,

site; survey lines are numbered from CA01 to CA030 different modules of MIKE 21 suite (DHI Water &

toward East for Cala Azzurra and from LB01 to LB30 Environment) were applied to simulate wave refraction,

toward South-East for Lido Burrone. The average length diffraction, breaking and to evaluate radiation stress

of the transects is 500 m at Cala Azzurra and 700 m at components [27, 28]; finally, using the two-dimensional,

Lido Burrone. depth-averaged hydrodynamic module [29],the surface

Bathymetric data were processed using BathyPro elevation and nearshore currents due to incident waves

and Surfer software. Post-processing tools and data were simulated.

filters were applied for error compensation and Numerical simulations were performed using

spike detection. Then, using algorithms for spatial interpolated bathymetric grids with different

interpolation, digital models of the sea bottom were resolutions, considering the model formulation,

built, with grid spacing consistent with spatial density spatial data density, required accuracy and

of data. Finally, beach profiles, contour maps and 3D computational effort. Offshore bathymetry was

surface were derived for presentation of data and derived by the official nautical charts provided by

further elaborations. the Hydrographic Institute of Italian Navy, whereas

All data were projected and presented in the UTM33N- survey data were used for detailed simulations in

WGS84 coordinate system. the nearshore shallow water zone.

51EAI Energia, Ambiente e Innovazione 4/2015