Page 4 - LoRe_Musumeci_alii_2014

C. Lo Re et al. / Procedia Engineering 70 ( 2014 ) 1046 – 1054 1049

dξ = u
dt s (1)

Such a relation states that the fluid particles at the shoreline remain along the shoreline (Prasad and Svendsen
2001). Moreover the momentum equation at the shoreline must be also considered in order to close the problem; in
dimensional form such a shoreline equation reads:

du ∂ζ
s = − g + F (2)
dt x ∂ fric
s
where ∂ζ/∂x| s is the derivative of the surface elevation evaluated at the shoreline, F fric is the bottom friction force
evaluates as follow:

f
F fric = − ⋅ u⋅ u
h +ζ (3)
in which h is the local depth, f is the bottom friction coefficient. When the value of F fric becomes too large, due to
the small value of the total water depth, a threshold is used. In such a case, the dependency on the water depth has
been eliminated and the bottom friction is assumed to be only a quadratic function of the depth-averaged velocity:

F fric = − C ⋅ u ⋅ u (4)
f

−1
where C f is a coefficient that was assumed equal to 5.0 m in the present work, such a value is based on the work
of Lo Re et al. (2012).
3. Study area and field measurements

The beach considered in the present work is known as Lido Signorino and is located in the western part of
Sicily (Fig. 2a). The Lido Signorino beach has a mild slope, being essentially a dissipative beach with beach face
slopes varying from 1.5 to 10.8°. It extends in the N-S direction, for about 3.5 km, between the two headlands
called Torre Tunna (325°N - 37°45'32.26''N; 12°27'40.00''E) and Torre Sibilliana (185°N - 37°43'36.31''N;
12°28'11.23''E). The sector from which waves can arrive has an amplitude of 140°. Note that, because of the
presence of the Egadi archipelago, the beach is screened marginally by the Favignana Island, located along the
320°N direction.
The beach is made up by very fine Holocene sand with sub-rounded grains constituted by lithic and fossil shell
fragments with a carbonate composition. The granulometric analysis gave a mean value of D 50 ~ 0.55 mm and
mean granulometric fractions of 0.4% of silt, 0.6% of clay and 99% of sand.
The dominant wind diagram (Fig. 2a), obtained from measurements of the nearby meteorological station of
Trapani in the period 2004-2008, shows that the winds which can mainly model the beach have NW-SE and W-E
directions. The beach tends toward erosion, with much of the natural dune ridge having been overtaken by urban
development. The dunes remain only in the southern part, where the human activity is less intense. At such a
location, the dunes are only 2.5 m high on average.

3.1. Wave and topographic data

Offshore wave data were provided by a wave rider buoy offshore Mazara del Vallo, deployed offshore the
beach, less than 30 km far from field site and at about 100 m water depth. Such a buoy is managed by the ISPRA -
Institute for Environmental Protection and Research of the Italian Government (www.idromare.it).