Spatial Approach to Medium-Term Coastal Evolution in South Sicily
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View metadata, citation and similar papers at core.ac.uk brought to you by CORE provided by Digital.CSIC Journal of Coastal Research 24 1 33–42 West Palm Beach, Florida January 2008 Spatial Approach to Medium-term Coastal Evolution in South Sicily (Italy): Implications for Coastal Erosion Management Jose´A´ ngel Martı´nez del Pozo and Giorgio Anfuso* Departmento de Geologı´a Facultad de Ciencias del Mar y Ambientales Polı´gono Rı´o San Pedro s/n 11510 Puerto Real Ca´diz, Spain [email protected] ABSTRACT MARTI´NEZ DEL POZO, J.A´ . and ANFUSO, G., 2008. Spatial approach to medium-term coastal evolution in south Sicily (Italy): implications for coastal erosion management. Journal of Coastal Research, 24(1), 33–42. West Palm Beach (Florida), ISSN 0749-0208. Four sets of maps and aerial photographs have been integrated into a Geographic Information System (GIS) project to investigate coastal changes along a 60-km-long littoral sector in south Sicily, Italy. The beaches studied recorded significant morphological changes essentially related to the presence of human structures that interrupted littoral drift. Most of the investigated beaches experienced progressive erosion because of sediments being trapped by human structures resulting in the formation of wide beaches on the updrift side and erosion downdrift. The latter has often been counteracted by the construction of breakwaters. However, local planning authorities did not carry out an as- sessment of the impacts related to the construction of harbours and ports and their successive enlargement. This article proposes alternative actions concerning the possible future erosion management of the studied littoral. ADDITIONAL INDEX WORDS: Shoreline trend, erosion, human impacts, management. INTRODUCTION 1983; MRIDE et al., 1991; TANEY 1961). Recently, the use of these different documents has been improved with Geograph- Corresponding with globally rising sea levels, coastal ero- ic Information Systems (GISs) and computer-assisted multi- sion problems have been growing during past decades be- variate analysis (COOPER and MCLAUGHLIN, 1998; KELLY, cause human activities and constructions are exceedingly 2000). close to the shoreline (BIRD, 1996). This has enhanced sci- In this work, aerial photographs integrated into a GIS pro- entific interest in coastal erosion processes, which have been ject, have been used to reconstruct the coastline evolution investigated over various timescales using a variety of meth- during a 32-year period in the area between Punta Secca and ods and data sets (KOMAR, 1998; SHORT, 1999). Punta Castellazzo (south of Sicily, Italy). The studied coastal Satellite images, vertical aerial photographs, and other sector experienced significant erosion problems related to the techniques have been used to study changes at weekly, large developments built during recent decades, primarily monthly, and seasonal periods (CROWELL,LEATHERMAN, and the construction of ports, harbours, breakwaters, summer- BUCKLEY, 1991, 1993; DOLAN,FESTER, and HOLME, 1991; houses, and littoral roads. This has had a great impact on EL-ASMAR, 2002; GORMAN,MORANG, and LARSON, 1998; the littoral drift, justifying a need for Integrated Coastal Zone JIME´ NEZ and SHA´ NCHEZ-ARCILLA, 1993; JIME´ NEZ et al., Management (CLARK, 1996). Additionally, quantification of 1997; SMITH and ZARILLO, 1990). erosion rate in the studied area is very important because Moreover, aerial photographs, maps, charts, and satellite shoreline retreat takes place over a human timescale. Con- images are especially useful in the reconstruction of coastline sequently, the recorded data can be used to determine safe changes over time periods from years to decades and over construction setbacks, to evaluate the efficiency of coastal medium spatial scales (from 1:18,000 to 1:30,000) and in ob- protection structures, and to elaborate coastal erosion man- serving the distribution of coastal types, land uses and the agement and land use plans (BERLANGA and RUIZ, 2002; evolution of dune fields (DOLAN et al., 1980; DOM´ıNGUEZ,AN- BUSH,RICHARD, and NEAL, 1996; FISCHER and ARREDONDO, FUSO, and GARCIA, 2005; FISHER and OVERTON, 1994; 1999; LIZA´ RRAGA,APPENDINI, and FISCHER, 2001; SA´ NCHEZ- FORBES et al., 2004; JIME´ NEZ et al., 1997; LEATHERMAN, ARCILLA,JIMENEZ, and VALDEMORO, 1998). DOI:10.2112/05-0598.1 received 30 September 2005; accepted in re- vision 27 February 2006. STUDIED ZONE This work was partially funded by the Provincia Regionale di Ra- gusa Administration (Sicily, Italy), and it is a contribution to the The length of the studied area is about 60 km and is located Andalusia P.A.I. Research Group RNM-328. between Punta Secca and Punta Castellazzo, in the southern * Corresponding author. littoral of Sicily, Italy. Coastal orientation varies from WNW– 34 Martı´nez del Pozo and Anfuso Figure 1. Location map with distribution of human structures along the studied coast. ESE in the northern sector between Point Secca and Cava 40 cm, usually in the order of 10 cm. The coast is principally d’Aliga, to E–W in the southern sector from Cava d’Aliga to affected by winds blowing from the third quadrant; winds Point Castellazzo (Figure 1). The littoral is composed of sandy from the second quadrant achieve greater importance during beaches of different widths, which are rich in quartz (ഡ65%), the autumn and spring. Unfortunately, no wave-gauges exist carbonates (ഡ30%) and which also contain feldspars and in the area, and information about wave climate was ob- heavy minerals (ANFUSO 1999; AMORE and RANDAZZO, tained from the Littoral Environment Observation (LEO) 1993). The nearshore zone is very smooth (average slope 1– measurement system, based on visual wave observations in 2%), and large surf zones are observed, especially in the the open sea. Major storms hit the coast most frequently from southern sector. the third quadrant, with significant deep-water wave heights The beaches are backed by dune ridges and cliffs cut in (Hs) of 8 m and periods (T) of 11 seconds. Minor storms ap- ϭ ϭ sandstones, marls, and limestones. According to AMORE and proach from the second quadrant, with Hs 5.5 m and T RANDAZZO (1997) and ANFUSO (1999), no significant sedi- 10.5 seconds. mentary inputs to the littoral budget are derived from either cliff retreat, because eroded sediments are generally too fine, METHODS or from fluvial inputs. In fact, rivers originate predominantly To characterize the coastal environment, detailed field ob- from chalk catchments, and their sedimentary supplies have servations have been carried out several times over recent been greatly restricted because of the construction of weirs, years (i.e., from 2000 to the present), during both winter and dams, and artificial canalization to avoid flooding in urban- summer conditions. These observations enabled the evalua- ized areas. tion of the morphodynamic state and the behaviour of the In terms of marine climate, the zone is a microtidal envi- investigated beaches, as well as the presence of longshore bar ronment characterized by maximum tidal variations of about and dune dynamics. On the other hand, the distribution of human structures and their characteristics have been de- scribed by ANFUSO (1993, 1999) and ANFUSO and MARTı´NEZ Table 1. Documents used in study of coastal evolution over 32 years in southern Sicily, Italy. (2005). Also, a range of aerial photographs and maps from differ- Type Year Scale Notes ent years and timescales have been used to reconstruct and Topographic map 1967 1:25,000 quantify shoreline evolution over a period of 32 years accord- Aerial photographs 1977 1:17,000 B&W1 ing to STAFFORD (1971), DOLAN et al. (1980, 1991), LEATH- Aerial photographs 1987 1:12,500 Colour ERMAN (1983), JIME´ NEZ et al. (1997), and PAJAK and LEATH- Orthophotographs 1999 1:12,500 Colour ERMAN (2002) (Table 1). 1 Abbreviations: B&W ϭ black and white. These documents have been scanned, geo-referenced, and Journal of Coastal Research, Vol. 24, No. 1, 2008 Coastal Trend and Management Problems 35 computer-rectified to eliminate effects of scale and distortion ther, the 1977 coastline has been compared with that of the (CROWELL,LEATHERMAN, and BUCKLEY, 1991; LILLESAND 1999 one to obtain a perspective on the overall evolution of and KIEFER, 1987; MOORE, 2000). Ground Control Points the littoral over a time span of 22 years, referred to as me- (GCPs) for photo registration have been obtained from the dium-term time fame (CROWELL,LEATHERMAN, and BUCK- geo-referenced orthophotographs of 1999, and all the infor- LEY, 1993). It is important to note that the 1977 geo-refer- mation has been presented in Gauss-Boaga Coordinates (zone enced photographs were preferred to the 1967 geo-referenced 2). Taking into account the smooth topography of the studied map (1:25,000) and were used as the reference data because area, a polynomial transformation has been applied in the of their superior resolution. In the obtained figures, shoreline registration process (CHUVIECO, 2000). The number of GCPs variations lower than Ϯ10 m were not displayed, according used varied from one photograph to another (from 9 to 15 to the previous assumptions about the shoreline mapping er- units), and their position has been located in unequivocal ror. places (THIELER and DANFORTH, 1994). The error related to the distortion of the photographs (AN- RESULTS DERS and BYRNES, 1991; CROWELL,LEATHERMAN, and Areas of Accreting Shoreline BUCKLEY, 1991; DOLAN et al., 1980; MOORE, 2000) has been solved and controlled in the geo-referenced