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Coupling a hydro-maritime model and remotely sensed techniques to
assess the shoreline positioning uncertainty:

the Marsala coast study case.

Giorgio Manno*, Carlo Lo Re, Giuseppe Ciraolo, Antonino Maltese
Department of Hydraulic Engineering and Environmental Applications (DIIAA), Università degli
Studi di Palermo, Viale delle Scienze Bldg. 8, Palermo, Italy

ABSTRACT

The severe erosion phenomena affecting the Mediterranean coasts are strictly related to geophysical characteristics and
socio-economic pressures. This suggests the need of monitoring and modelling the phenomenon in order to quantify its
strength. In fact, the shoreline position, as well as its temporal evolution, provides important information for designing
defence structures and for the development of a coastal management plan. The shoreline has a dynamic nature as it
changes both in the short and long period. Those changes are caused by geo-morphological (e.g. bars and barrier island
development etc.) and hydrodynamic (wave motion, tides and flows) processes, as well as by sudden and fast events
[1]
such as sea storms, earthquakes and tsunamis . The research examines the uncertainty in positioning the shoreline
coupling remotely sensed images and a hydro-maritime model. Although the assessment accuracy strongly relies on data
availability and consistency, the resulting assessment of the shoreline erosion and accretion is crucial for an overall
understanding of the hydro-maritime geo-morphological interaction. The study case is the Marsala coastline (western
th
coast of Sicily, Italy), named 12 island physiographic unit. It is characterized by a low coast with sandy sediments from
Holocene age. These sediments are in continuity of sedimentation on whitish debris composed by organogenic limestone
from Pleistocene age. The diachronic analysis was carried out on both emerged and submerged parts of the beach and
involves two distinct phases. In the first phase, geo-morphological in situ data have been compared with maps and
georeferenced remote sensing images referred to the period 1994-2006. It allowed the identification of shoreline
[2]
indicators such as the beach cross-section and the shoreline positioning including its spatial and temporal variations. It
should be noted that the comparison between EO (Earth Observation) images and cartographic maps is subjected to
several uncertainties, due to graphic error, geo-referencing accuracy and spatial resolution. Moreover tidal and climate
waves data refer to an acquisition time different to that of the EO images. In the second phase, a maritime hydraulic
modelling accounting for sea fluctuations has been performed. The run-up is related to wave’s amplitude and phase, as
[3]
well as to the composition and particle size of the beach sediments determining the beach slope . Prior to run-up
calculation, an investigation aiming to evaluate how the waves propagate from offshore to inshore (a third-generation
spectral wave numerical model, SWAN - Simulating WAves Nearshore), has been carried out. Wave data have been
acquired by a buoy belonging to the National Network Waves Data, located at the SW of the Mazara del Vallo harbour
(Trapani), while tide data were recorded by the national marigraph of Porto Empedocle (Agrigento). The results allowed
assessing the uncertainty and the consequent accuracy in the shoreline positioning for given slope, highlighting that it is
not always possible to assess the shoreline rise and fall, for values lower than 10-15 m.
Keywords: coast, sandy beach, shoreline motion, waves run-up, tides.

1. INTRODUCTION

The shoreline erosion has direct consequences on geomorphological and ecological systems of the environment, since
these are fragile systems, and extremely vulnerable to the antrophic impact. The shoreline is defined as the intersection
[1]
between low sea tide and land surfaces, and spatially divides maritime and terrestrial water bodies . A long time deficit
of sediment income causes the regression of the shoreline, highlighting a local equilibrium rate of sediment and
[4]
consequently the dynamical nature of the beach . An accurate diachronic analysis requires the knowledge of the
uncertainties in the shoreline positioning, which are both of hydraulic and remote sensing typologies. To detect the
shoreline a variety of remote sensing operational methodologies can be used, working on images acquired in different
parts of the electromagnetic spectrum. Remote sensing techniques include: aerial photography; shortwave or longwave

*manno@unipa.it; phone: +39 091 23896517; fax +39 091 6657749
Remote Sensing for Agriculture, Ecosystems, and Hydrology XII, edited by Christopher M. U. Neale, Antonino Maltese,
Proc. of SPIE Vol. 7824, 78241Z · © 2010 SPIE · CCC code: 0277-786X/10/$18 · doi: 10.1117/12.865000

Proc. of SPIE Vol. 7824 78241Z-1

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