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Ocean & Coastal Management 80 (2013) 133e148

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Ocean & Coastal Management

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Anthropogenic influence on coastal evolution: A case history from theCatania Gulf shoreline (eastern Sicily, Italy)

Agata Di Stefano a,*, Roberto De Pietro b, Carmelo Monaco a, Angiola Zanini a

aDipartimento di Scienze Biologiche Geologiche e Ambientali, Sezione di Scienze della Terra, University of Catania, Corso Italia, 57, 95129 Catania, Italyb via Umberto, 311, 95129 Catania, Italy

a r t i c l e i n f o

Article history:Available online 2 April 2013

* Corresponding author.E-mail addresses: distefano.agata@libero.it, diste

rodepietro@libero.it (R. De Pietro), cmonaco@unict.it(A. Zanini).

0964-5691/$ e see front matter � 2013 Elsevier Ltd.http://dx.doi.org/10.1016/j.ocecoaman.2013.02.013

a b s t r a c t

We present the results of a study carried out on the littoral extending south of the Catania town (easternSicily) with the aim of identifying the causes responsible for the strong erosional processes, started afterthe 1950s and accentuated in the last decade. This shoreline, known as “La Plaja” beach, represents one ofthe unique areas of eastern Sicily, from geological, ecological and socio-economic point of views, and itsprogressive thinning has a strong impact especially for environmental as well as touristic aspects. Thevariations of shoreline evolution through time, as they are connected to the Simeto River mouth evo-lution, have been evaluated through the comparison of the available cartographic sources, whichcomprehend topographic maps, aerial photos and satellite images. Moreover, the retreating processoccurring in the last four decades has been quantitatively estimated along fourteen transects perpen-dicular to the shoreline direction. Our data point to more severe erosion close to the Simeto River mouthand in the southern tract of the shoreline (maximum retreat of about 204 m, with average rates of2.75 m/yr), and slower retreat in the northern one (maximum retreat of about 55 m, with average ratesof 0.74 m/yr). The analysis of the variations in the hydrological parameters occurring upstream withinthe Simeto River drainage basin, highlights a drastic reduction of the solid and liquid discharge, coin-ciding with the entry into operation of several hydraulic works, including dams, fluvial barrages andartificial embankments, after the 1950s. Such a reduction cannot be blamed on a variation in the plu-viometric regime of the area, as the statistical analysis of the rainfall data indicates an almost steadytrend during the last century which could not have produced any relevant effect. Neither could a vari-ation in the wave regime have triggered more intense erosional processes along the shoreline, as nosignificant change is observable in the wave parameters either. Thus, the sediment supply reduction andthe consequent coastline retreating, is mainly attributable to the installation of hydraulic works, coupledwith the progressive destruction of the coastal dune belt due to human building activities. In the absenceof suitable interventions, which should also consider the possibility of removing some of the existinghydraulic works, a further reduction, ranging from 20 to 100 m, of the coastline stretch is expected in thenext ten years.

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1. Introduction

In anthropogenically perturbated systems, the evolution of asandy coastal area through time is the result of a delicate balancebetween both natural (sediment supply, waves, currents, tides,winds, storms, rainfalls, tsunamis, etc.) and anthropic (dams,jetties, embankments, artificial channels) factors which may result

fan@unict.it (A. Di Stefano),(C. Monaco), zanini@unict.it

All rights reserved.

in advancing or retreating shorelines. The importance of preservingcoastal zones is self-evident as they perform important ecological,economic and societal functions, but in recent times human activityhas severelymodified the natural evolution of coastal areas and hasbecome the most important controlling factor.

Coastal retreat, defined as the landward displacement of ashoreline because of marine erosion or flooding (Bird, 1993), occurswhen the coastal erosional processes overcome the sedimentsupply, otherwise fundamental in maintaining beaches and near-shore bank systems. Several studies demonstrate that a decreasein sediment supply, transported to the sea by rivers, appears to be apivotal factor controlling coastal retreat. This may be caused by thepresence of man-made works which reduce the riverine sediment

A. Di Stefano et al. / Ocean & Coastal Management 80 (2013) 133e148134

fluxes and/or alter the normal sediment dispersal at the rivermouths. In addition, the occurrence of extremeweather events (e.g.damaging rain, wind events, higher rainfalls, greater wave energy)may lead to accelerated erosion of beaches or coastal margins.

The sandy coastline of the Catania Gulf (eastern Sicily, Italy), atthe Simeto River mouth, known as “La Plaja” beach, represents oneof the most unusual areas of eastern Sicily, from geological,ecological, environmental and socio-economic points of view. Yet,considerable changes are observable in the whole area and aninexorable retreat of the shoreline is occurring, enhanced overrecent decades.

In this paper we will examine all the available data concerningthe Simeto River drainage basin and the Catania Gulf shoreline in anattempt to quantitatively estimate the retreating rate and todiscriminate the influence of natural from human-induced factors.It’s worth to note that the availability of historical maps dating backabout 1000 years (almost unique in the world) allowed us to framethe recent (last 40 years) evolution of the system in a period of timesufficiently long to distinguish the causes of the processes.

In particularwewill focus our attention on the following aspects:

1) Historical and recent variations of the coastline position, withquantitative estimations of the coastal retreat and of thedisplacement velocities.

2) Variations of the hydrological characteristics of the drainagebasin (solid and liquid discharge).

3) Pluviometric data and wave parameters.

Finally, a predictive statistical analysis is provided, which sim-ulates the evolution in the next ten years, in the absence of changesaimed to arrest the retreating process. Our results will provide

Fig. 1. Simplified geo-dynamical scheme of eastern Sicily, illustrating the m

useful information in the perspective of future management plansof this coastal area which may undergo different typologies of riskconsidering the co-presence of a variety of geological processes(volcanism, seismicity, active tectonics, sea level rise) and whichinteract with an intense level of anthropogenic activity in the frameof a unique ecological system.

2. Geological setting

Our research has been focused on a 8 km long stretch of the NeSoriented sandy coastline, facing the Ionian Sea, extending south ofthe town of Catania and located between S. Francesco La Rena andVaccarizzo (Figs. 1 and 2). The study area falls along the coastalsector of the Catania Plain, a wide Holocene plain filled by thealluvial-coastal deposits of the Simeto River (Gemmellaro, 1839;Sciuto Patti, 1872; Accordi and Francaviglia, 1960; Francaviglia,1962; Longhitano and Colella, 2003). From a geological point ofview, the Catania Plain is part of the Gela-Catania foredeep(Di Geronimo et al., 1978; Lentini and Vezzani, 1978; Lentini, 1982),a tectonically controlled depression filled by Upper Pliocene toQuaternary marine sediments with volcanic intercalations (Bianchiet al., 1987; Finetti et al., 2005). The Gela-Catania foredeep sepa-rates the Hyblean Plateau, part of the emerged African forelanddomain, from the over-thrusting orogenic sectors (“Sicilian-Maghrebian Chain” Auct.), generated since Middle Miocene by thecontinental collision between the African and the European Plates(Ben-Avraham et al., 1990; Lentini et al., 1996; Finetti and Del Ben,1986; Adam et al., 2000; Finetti et al., 2005).

To the north, a belt of up to 300 m high hills (the “Terreforti”),constituted by a Pleistocene marine to continental terrigenoussuccession (Wezel, 1967; Lanzafame et al., 1997; Di Stefano and

ain orogenic domains, in the framework of the Central Mediterranean.

A. Di Stefano et al. / Ocean & Coastal Management 80 (2013) 133e148 135

Branca, 2002) separates the Catania Plain from the south-easternedge of the Mt. Etna volcanic edifice (Fig. 2). Southward it endsagainst the NEeSW oriented S. Demetrio Horst (Torelli et al., 1998),where Pleistocene shallow-water bioclastic sediments and UpperPliocene volcanics, belonging to the foreland domain, mainlyoutcrop (Pedley et al., 2001; Grasso et al., 2004; Carbone et al.,2009, 2011). The Pleistocene sediments of the Terreforti hillsform an asymmetric south-facing anticline, displaying a more orless EeWoriented axis (Bousquet et al., 1988; Labaume et al., 1990;Monaco et al., 1997; Ristuccia et al., 2013), grown during theMiddle-Late Pleistocene as a response to a NeS compressive tec-tonic regime related to the recent migration of the orogenic thrustfront (“Gela Nappe”, Beneo, 1958; Di Geronimo et al., 1978;Lickorish et al., 1999; Mattia et al., 2011). The compressive tectonicsoverlap an extensional regime, testified by WSWeENE strikingnormal faults, bounding the north-eastern margin of the HybleanPlateau (Catalano et al., 2010; Firetto Carlino et al., 2013). Towardthe Ionian Basin, the Catania Plain is bordered by an extensionalactive tectonic system, running parallel to the coast (Monaco et al.,1997; Bianca et al., 1999; Monaco and Tortorici, 2000, 2007). Activefaults have generated a Holocene regional uplift with rates of about1 mm/yr in the Catania Plain area (Spampinato et al., 2011) and areresponsible for the occurrence of destructive historical earthquakes(M� 7) which characterize this area (e.g. 1169 AD, 1693 AD events,Baratta, 1901; Postpischl, 1985; Boschi et al., 1995).

3. The Simeto River and its relation with the Catania coastline

The main means of sediment transport feeding the sandycoastline of the Gulf of Catania is the Simeto River, the largestdrainage basin of Sicily. The sediment discharge derived from theSimeto River constitutes the main source within the sedimentarybalance of the Gulf of Catania littoral, and sediment supply derivedfrom other streams flowing within the same coastal area can beconsidered negligible.

The 116 km long Simeto River rises in theNebrodiMts. (NE Sicily),flanks the western side of the Mt. Etna volcano making a large bendand crossing the Catania Plain before flowing into the Ionian Sea(Figs. 2 and3). It drains 4192.68 km2of central-easternSicily, crossingthe sedimentary successions of the Sicilian-Maghrebian Chain and

Fig. 2. Geological sketch-map of the study area, reporting the main stratigraphic andstructural features. The direction of the main sea-current along the offshore is alsoindicated.

over a lesser part of the catchment the volcanic rocks of Mt. Etna,before crossing the Holocene Catania Plain.

During the last 60 years, the Simeto River drainage basin hasundergone severe modifications due to the built of numerous man-made works which have strongly altered the normal erosionalprocesses (Amore et al., 1983; Amore and Giuffrida, 1985, 1996;Baglio et al., 1996). These include dams and artificial barrages,located as shown in Fig. 3 and whose main features are listed inTable 1, emplaced with the twin objective of regulating the hy-drological regime of the river and its tributaries, and of creating anumber of reservoirs.

The effects of these modifications to the drainage basin, affectedthe Simeto River delta and, in turn, the sediment budget of the Gulfof Catania shoreline. The Simeto River delta, building out into theIonian Sea, can be considered as a strongly asymmetric wave-dominated delta (Longhitano and Colella, 2007), whose asymme-try, due to the oblique wave approach, is emphasized by the pres-ence of an artificial embankment built at the end of 1950s and early1960s of last century, in order to achieve the alignment of the finalstretch of the river. The present morphological configuration of thedelta, evolving from an “open” to a “closed” morphology as afunction of wave energy and annual river discharge, is the result ofa complex evolution characterized by significant shifts of themouth through time (D’Arrigo,1950, 1953; Amore et al., 1990,1995;Longhitano and Colella, 2001a,b, 2007; Longhitano and Zanini,2002). Accordingly, the nearby sandy coast has undergone signifi-cant changes over recent decades, mainly characterized by pro-gressive, still ongoing, retreating processes.

4. Methods

Topographic changes of the Simeto deltaic area and of the Cat-ania Gulf shoreline (Figs. 4e6) were recorded through the analysesof the cartographic, ortho-photographic and satellite sources listedin Table 2. The past shoreline migrations were documented bycomparing the most recent position (year 2011) with those shownin the historical topographic maps, starting from the most ancient1154 Edrisi’s map reported in D’Arrigo (1949) up to the early ItalianMilitary Geographic Institute (IGM) topographic maps (1880 and1934).

The recent coastline variations were quantified through com-parison of topographic maps, orthophotos and satellite images(Table 2) digitized, rectified and geo-processed through AutoCAD3DMap, that allowed us to reconstruct not only the evolutionarytrend of the shoreline migration and the dynamics of the coastalprocesses, but also the variation in the morphological features ofthe Simeto River delta during the last 40 years. A number oflandmarks, mainly ancient buildings (Table 3), has been selected asdatum points with the objective of limiting the errors caused by thedifferent cartographic sources. In this case, the maximum error canbe attributed to the IGM cartography (scale 1:25,000) and corre-sponds to 5 m.

The 2011 coastline position has been reconstructed by GoogleMap and checked through a GPS survey (map datum WGS84 andUTM position) with an average range of error of about �3 m. Sucha range of errors is usually accepted in this kind of processing(Dolan et al., 1980), as it is comparable to the inherent errors ofmaps, aerial photos and satellite images or to the variability of thecoastline at the time of measurement, due to sea conditions ortides.

The quantitative estimation of the coastline variations has beencarried out discreetly by reconstructing fourteen WeE orientedtransects, represented by straight lines starting from the landmarkslisted in Table 3 and located as shown in Fig. 5. Distances betweenthe landmarks and the coastline were estimated relative to the

Fig. 3. Simeto River drainage basin and location of the hydraulic works listed in Table 1. The location of the hydrological and rainfall stations, whose data have been used for thepresent study, are also indicated.

A. Di Stefano et al. / Ocean & Coastal Management 80 (2013) 133e148136

reference datum measured in the 1969 Italian IGM map, whichrepresents the “zero point”. Based on the available cartographicsources (Table 2), thirteen measurements have been performedalong each transect (Table 4), subtracting each calculated distancefrom (or summing to) the previous. The data obtained have been

Table 1Location, year of entry into operation and principal characteristics of the water reservobarrages along the Simeto River is also reported. The latter were built after 1960, but an ofLentini dam is located outside the Simeto River drainage basin).

Reservoir/Dam Year River/Stream Cap

A Ogliastro 1966 Gornalunga R. 108B Nicoletti 1973 Bozzetta S. 17C Pozzillo 1958 Salso R. 140D Sciaguana 1992 Sciaguana S. 9E Ancipa 1953 Troina R. 2F Pietrarossa e Pietrarossa S. 30G Lentini* 1991 e 127Fluvial barragesH Ponte Barca e Simeto R. e

I Contrasto e Simeto R. e

J St. Domenica e Simeto R. e

K Simeto e Simeto R. e

L Dittaino e Dittaino S. e

M Cicogna e Cicogna S. e

N Cutò e Cutò S. e

O Finocchio e Finocchio S. e

P St. Elia e St. Elia S. e

reported in Fig. 7 (Fig. 7a and b respectively illustrates transectslocated north and south of the river mouth), in which each curverepresents the amount of the coastline shift along the corre-sponding transect, represented following interpolation of data re-ported in Table 4. As a regression curve, a cubic equation has been

irs/dams within the Simeto River drainage basin. The location of the main fluvialficial document attesting the exact year of entry into operation, is not available (* the

acity (Mm3) Catch basin (km2) Coordinates

.00 170.00 37.449205�N 14.574817�E

.40 49.50 37.607961�N 14.348002�E

.50 577.00 37.673510�N 14.610281�E

.90 64.89 37.599984�N 14.594516�E

.20 51.00 37.829494�N 14.574986�E

.00 256.56 37.366057�N 14.579495�E

.00 e 37.330954�N 14.971471�E

e 37.534377�N 14.872220�Ee 37.691089�N 14.800851�Ee 37.643807�N 14.809744�Ee 37.416288�N 15.022639�Ee 37.558515�N 14.502060�Ee 37.885505�N 14.688636�Ee 37.887874�N 14.688810�Ee 37.854127�N 14.651870�Ee 37.855600�N 14.595072�E

Fig. 4. Historical variations of the Gulf of Catania shoreline from 1154 to 1934(cartographic sources listed in Table 2), compared to the 2011 coastline position, andNeS oscillations of the Simeto River mouth.

A. Di Stefano et al. / Ocean & Coastal Management 80 (2013) 133e148 137

used. For each transect, the rate of the coastline shift has also beencalculated as interpolation of data reported in Table 4 (Fig. 8). Again,as a regression curve, a cubic equation has been used.

5. Variations of the Simeto River mouth and of the CataniaGulf shoreline

5.1. Historical and recent variations

Since the end of the 19th century many authors observed anddescribed the remarkable changes which characterized the SimetoRiver mouth and the associated coastal area through time(Marinelli, 1899; D’Arrigo, 1929, 1950, 1953; Amore et al., 1990,1995; Longhitano and Colella, 2007). The evolution of the CataniaGulf shoreline has been evaluated by comparing its presentmorphological configuration with the past coastal morphologiesobtained by historical cartographic sources and subsequently byaerial orthophotos and satellite images (Table 2).

The oldest cartographic sources (Fig. 4; Table 2) include a firstpioneering work compiled by the Arabian geographer Edrisi (1154,in D’Arrigo, 1949), the map of the Catania Gulf and Harbour (1784)redrawn from Zahra (in Amari, 1880), the 1836 survey of Gem-mellaro reported in D’Arrigo (1929) and the oldest topographicmaps from the IGM (1880 and 1934).

In spite of the discontinuous historical sources, the availablegeographic data document an oscillatory migratory pattern of

the Simeto mouth system from north to south and vice versa, over a4e5 km wide area, with a northern limit coinciding with the 1880position. The reconstruction of these migrations over the last threecenturies documents two main cycles, with alternating ascendantand descendant phases, that developed over intervals of at least 275years with an inferred rate of 20e30 m/yr (Longhitano and Colella,2007). At the same time a slight advancing tendency of the deltaand of the shoreline occurred, and the delta shape evolved fromarcuate to cuspate, reaching a peak of progradation in 1836 (Fig. 4).

Historical sources (Sciuto Patti, 1872; D’Arrigo, 1956) report theconfiguration of the Simeto River mouth and of the Catania Gulfshoreline, before the subsequent works made to align the lastfluvial segment. These authors provide an average accretion rateranging approximately from 0.20 to 0.25 m/yr.

A more modern dataset comprises a series of topographic maps,air- and orthophotos encompassing the time interval from 1969 to1999 (Fig. 5; Table 2). Before 1950 the last stretch of the riverformed a large meander before flowing into the Gulf of Catania,well evident in the 1934 map (Fig. 4), and the coastal area wascharacterized by a large coastal dune belt behind which lay wet-lands (D’Arrigo, 1956). The 1969 IGM map shows that the SimetoRiver mouth was artificially constrained and aligned by the con-struction of two training embankments (between the late 1950sand 1960s) flanking its lower course. The building of the northernembankment in basalt blocks with a clay core has prevented themigration of the mouth to the north, even though the mouth hastended to move toward that direction. This is evidenced by theerosion of the embankmentwhich started at the end of the 1980s ofthe last century. The comparison of the shoreline positions (Fig. 5)shows that the natural and gradual progradation process, docu-mented by D’Arrigo (1956), was abruptly interrupted as shown bythe 1976 position, which highlights a retreat of about 60 m, south ofthe river mouth compared to the 1969 shoreline position. Since theend of the 1980s, gradual erosion of the prominent sand bar hasoccurred. The coastal retreat process increased rapidly, mainly atthe river mouth, resulting in the collapse of the coastal defenses.

Themost recent variations of the CataniaGulf shoreline have beenrecorded through the comparison of the positions gained by aerial,ortho- and satellite photos covering the last decade (Fig. 6; Table 2).During recent years the sandy coastline to the north of the embank-ment has partially restored but the future trend is for progressivedestruction of the tip of the embankment as a result of the dispersionof its claycore and the settlementof theblocks of basalt into the sandybottom. In 2006 the sandy bar extending from the right bank of thedelta to the south was eroded, resulting in a considerable retreat ofthe river mouth and in the development of a small bay.

5.2. Quantitative estimation of the coastline retreat

The quantitative estimation of the Catania Gulf shoreline vari-ations, reported as a metric linear shift with respect to the 1969position (Fig. 7a and b; Table 4) and as movement rate (Fig. 8a andb; Table 4) highlights different values along the reconstructedtransects (Fig. 5; Table 3).

The most significant variations are represented by the position ofthe Simeto River mouth (Fig. 9a). In fact, the curve representing thetransect from Foce landmark (reported both in Figs. 7 and 8 asreference curve), located at the sand bar extending from the rightbank, documents a shoreline retreat of more than 80 m in thetime interval from 1969 to 1980 (average retreat rate of more than5 m/yr). In the subsequent 30 years the retreat rate decreased to aconstant value of less than 5 m/yr. At the beginning of 2000 the totalretreating amount was about 100 m. In the last decade the processhas accelerated, leading to a total retreat of about 220 m, with anaverage retreat rate of about 5 m/yr over the entire time interval.

Fig. 5. Variations of the Gulf of Catania shoreline from 1969 to 2008 (cartographic sources are listed in Table 2), and detail of the Simeto River mouth and of the southern tract (a),where the strongest erosional phenomena occur. Location of the landmarks (listed in Table 3) and traces of the correlated transects are also reported.

A. Di Stefano et al. / Ocean & Coastal Management 80 (2013) 133e148138

Fig. 6. Variations of the Gulf of Catania shoreline in the last decade (cartographic sources are listed in Table 2), and detail of the Simeto River mouth (a).

A. Di Stefano et al. / Ocean & Coastal Management 80 (2013) 133e148 139

Table 2List of the cartographic source used in the present study.

Year Source Scale

1154 Edrisi, in D’Arrigo (1949)1784 Zahra, in Amari (1880)1836 Gemmellaro in D’Arrigo (1929)1880 F 270 IGM (Italian Military Geographic Institute) 1:100,0001934 F 270 IIISO-IIINO IGM 1:25,0001969 F 270 IIISO-IIINO IGM 1:25,0001976 Aerial photo “Comune di Catania”1987 Aerial photo “Assessorato Territorio e Ambiente Sicilia”1990 Catania technical map 1:50001999 Map of Catania regional province 1:10,0002000 Orthophoto-SITR (Information System of Sicily)2002 Aerial photo “Comune di Catania”2003 Satellite image (Google Earth)2006 Satellite image (Google Earth)2007 Orthophoto-SITR2008 Satellite image (Google Earth)2009 Satellite image (Google Earth)2010 Satellite image (Google Earth)2011 Satellite image (Google Earth)

Table 3Location of the landmarks used to trace the transects employed to evaluate thevariations of the Gulf of Catania shoreline through time.

Landmarks Coordinates

1 La Rena 37�26025.4800N 15�04041.5800E2 Specchio 37�25056.4700N 15�04055.1900E3 Allegra 37�25031.7200N 15�04015.3200E4 Salatelle 37�24056.2500N 15�04024.2300E5 Vecchia Ansa 37�24029.4200N 15�05004.7800E6 Castello 37�24015.9500N 15�04052.3900E7 Foce 37�23058.0500N 15�03054.1900E8 Argine sud 37�23054.4700N 15�03054.0500E9 Gurnazza 37�23042.0600N 15�05005.0800E10 Trigona 37�23025.9400N 15�04055.4400E11 Gornalunga N 37�23011.2300N 15�04025.4200E12 Gornalunga S 37�22053.2200N 15�04052.4700E13 Aurora 37�22034.2100N 15�05007.1500E14 Vaccarizzo 37�22020.0200N 15�04056.9500E

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The curves representing the transects north of the river mouth(Figs. 7a and 9bed) document that the corresponding section ofcoastline has retreated more slowly in the last 40 years at value of30 m and an average rate of about 0.7 m/yr (Fig. 7b). Transect 5(from the Vecchia Ansa landmark), even records a slight pro-gradational trend between 1975 and 2005.

The curve representing transect 6 (from Castello landmark),shows a trend that departs from the others, illustrating an initial

Table 4Values of movement and variation rate calculated for each considered year, along the tra

Year 1 La Rena 2 Specchio 3 Allegra 4 Salate

m m/yr m m/yr m m/yr m

1969 0 e 0 e 0 e 01976 �7.05 �1.01 4.66 0.67 �14.26 �2.04 �11.831987 �11.60 �0.64 �16.82 �0.93 �27.12 �1.51 �30.401990 �6.47 �0.31 �7.74 �0.37 �20.65 �0.98 �7.931999 �16.74 �0.56 �13.16 �0.44 �36.02 �1.20 �26.702000 �0.45 �0.01 �12.49 �0.40 �36.68 �1.18 �19.592002 �6.92 �0.21 �20.29 �0.61 �19.09 �0.58 �19.182003 �8.89 �0.26 �20.15 �0.59 �27.88 �0.82 �16.692006 �4.83 �0.13 �15.59 �0.42 �23.37 �0.63 �24.662007 �2.66 �0.07 �13.82 �0.36 �30.72 �0.81 �13.582008 �5.58 �0.14 �4.90 �0.13 �35.97 �0.92 �15.342009 �15.47 �0.39 �32.75 �0.82 �25.68 �0.64 �22.422010 �7.89 �0.19 �21.12 �0.52 �25.68 �0.63 �31.282011 �10.15 �0.24 �24.83 �0.59 �44.47 �1.06 �32.72

retreating trend (up to 1980) followed by an advancing phase (up to2000). This unusual behavior is probably related to the position ofthe transect, lying at the mouth between the abandoned meanderand the present northern bank; this configuration has favoredtrapping the sediment, preventing coastal retreat. During the lastdecade a more rapid phase of retreat occurs, with respect to othertransects located north of the present mouth (average retreat rateof about 1.3 m/yr) and a total retreat of about 60 m (with respect to1969) being recorded.

Transects located south of the river mouth (Figs. 7b, 8b and 9eand f) show higher retreat values with respect to the northern ones,although values steadily decreasing southwards. The highest valuesare observed along transects from Gurnazza to Trigona, which re-cord a very rapid retreat of the shoreline, which reaches values of130 and 150 m in the 1990s (average rates of 6.3 and 7.0 m/yr,respectively). The coastline positions remained almost stable orretreated very slowly up to 2000. In the last decade the coastalretreat at these two transects has experienced a drastic increase,exhibiting total retreat values of 194 and 175 m, respectively, withaverage rates of 4.6 and 4.2 m/yr over the entire time interval.

Similar trends are displayed by the curves representing tran-sects from Argine Sud and GornalungaN landmarks. In both, the firsttwo decades are characterized by a more rapid phase of retreat,assuming more steady trends in the last two; the recorded totalretreats are of 116 and 136 m, respectively, with average rates of 2.7and 3.2 m/yr over the entire time interval considered.

The retreat values further decrease at southerly transects (fromGornalunga S and Aurora landmarks) where total retreat values of68 and 38 m are recorded, with average rates of 1.6 and 0.8 m/yrover the entire time period.

The southernmost transect (from Vaccarizzo landmark), high-lights an almost stable coastline, with slight advancing andretreating values in the order of few meters over the entire timeinterval monitored.

The weighted average retreat value of the entire stretch ofcoastline south of the river mouth in 2011, compared to 1969, is ofabout 100 m, with an average rate of about 2.4 m/yr.

6. Data analysis

6.1. Variations of solid and liquid discharge of the Simeto Riverdrainage basin

Hydrological data for the Simeto River drainage basin wereobtained from the archive of the Regional Hydrographic Service ofSicily (MLP-SI, 1925e1986). This reports information recorded bythe hydrometric stations of Biscari and Giarretta, located along the

nsects listed in Table 3, with respect to the 1969 coastline position.

lle 5 Vecchia Ansa 6 Castello 7 Foce

m/yr m m/yr m m/yr m m/yr

e 0 e 0 e 0 e

�1.69 1.26 0.18 �4.16 �0.59 �61.88 �8.84�1.69 16.80 0.93 �7.96 �0.44 �86.45 �4.80�0.38 2.95 0.14 2.04 0.10 �58.36 �2.78�0.89 �3.19 �0.11 �9.58 �0.32 �84.84 �2.83�0.63 8.38 0.27 �12.24 �0.39 �82.17 �2.65�0.58 9.84 0.30 �0.63 �0.02 �87.40 �2.65�0.49 5.20 0.15 4.40 0.13 �104.41 �3.07�0.67 �10.14 �0.27 2.67 0.07 �165.21 �4.47�0.36 �13.35 �0.35 �9.29 �0.24 �205.38 �5.40�0.39 1.57 0.04 �7.75 �0.20 �193.86 �4.97�0.56 �13.44 �0.34 �28.18 �0.70 �207.13 �5.18�0.76 �21.91 �0.53 �38.17 �0.93 �219.00 �5.34�0.78 �20.60 �0.49 �54.44 �1.30 �203.83 �4.85

Fig. 7. Diagrams of the Gulf of Catania shoreline movements (in m), expressed through interpolated curves, recorded from 1969 to 2011 along the transects (Table 3) located north(a) and south (b) of the Simeto River mouth. The curve corresponding to the Foce transect (Foce¼Mouth) has been reported in both diagrams as reference. We also reported thevalue points listed in Table 4 and used for the interpolation.

Fig. 8. Diagrams of the Gulf of Catania shoreline variation rates (m/yr), expressed through interpolated curves, recorded from 1969 to 2011 along the transects (Table 3) locatednorth (a) and south (b) of the Simeto River mouth. The curve corresponding to the Foce transect (Foce¼Mouth) has been reported in both diagrams as reference. We also reportedthe value points listed in Table 4 and used for the interpolation.

8 Argine sud 9 Gurnazza 10 Trigona 11 Gornalunga N 12 Gornalunga S 13 Aurora 14 Vaccarizzo

m m/yr m m/yr m m/yr m m/yr m m/yr m m/yr m m/yr

0 e 0 e 0 e 0 e 0 e 0 e 0 e

�65.44 �9.35 �53.83 �7.69 �92.23 �13.18 �44.36 �6.34 �35.99 �5.14 �5.22 �0.75 �0.18 �0.03�102.49 �5.69 �143.76 �7.99 �129.46 �7.19 �79.32 �4.41 �42.19 �2.34 �7.75 �0.43 �0.26 �0.01�26.16 �1.25 �132.89 �6.33 �147.00 �7.00 �107.96 �5.14 �39.35 �1.87 �5.90 �0.28 8.80 0.42�44.93 �1.50 �116.63 �3.89 �140.94 �4.7 �132.34 �4.41 �63.75 �2.13 �42.35 �1.41 �9.22 �0.31�96.41 �3.11 �115.86 �3.74 �152.52 �4.92 �103.42 �3.34 �54.10 �1.75 �20.54 �0.66 �7.71 �0.25

�126.86 �3.84 �136.37 �4.13 �157.61 �4.78 �116.96 �3.54 �51.64 �1.56 �24.89 �0.75 �4.23 �0.13�117.15 �3.45 �143.68 �4.23 �153.25 �4.51 �115.07 �3.38 �67.91 �2.00 �25.16 �0.74 �15.56 �0.46�135.10 �3.65 �129.24 �3.49 �168.64 �4.56 �118.03 �3.19 �67.8 �1.83 �18.10 �0.49 �3.12 �0.08�139.05 �3.66 �150.28 �3.95 �173.54 �4.57 �126.93 �3.34 �60.51 �1.59 �28.11 �0.74 �10.36 �0.27�179.09 �4.59 �169.19 �4.34 �156.51 �4.01 �120.79 �3.10 �64.66 �1.66 �40.55 �1.04 0.34 0.01�143.26 �3.58 �182.14 �4.55 �170.4 �4.26 �121.52 �3.04 �62.16 �1.55 �33.99 �0.85 2.53 0.06�146.24 �3.57 �177.6 �4.33 �174.23 �4.25 �131.01 �3.20 �67.07 �1.64 �23.70 �0.58 0.73 0.02�116.49 �2.77 �194.22 �4.62 �174.76 �4.16 �135.79 �3.23 �68.13 �1.62 �38.61 �0.92 �10.92 �0.26

A. Di Stefano et al. / Ocean & Coastal Management 80 (2013) 133e148 141

Fig. 9. (a) Aerial view of the Simeto River mouth (photo taken on April 24th, 2010). (b) Aerial panoramic view of the northern littoral stretch (photo taken on March 1st, 2011). (c)Littoral sector between the Allegra and Specchio transects along the northern section, in the background the Mt. Etna volcano (photo taken on February 27th, 2010). (d). Erosionalscarp at the Salatelle transect along the northern littoral stretch (photo taken on March 1st, 2011). (e) Aerial panoramic view of the southern littoral stretch (photo taken on March1st, 2011). (f) Gurnazza transect along the southern littoral stretch (photo taken on February 19th, 2010).

A. Di Stefano et al. / Ocean & Coastal Management 80 (2013) 133e148142

Fig. 10. Average monthly values of the liquid discharge (Table 5) recorded by theGiarretta (a) and Biscari (b) hydrological stations, in the 1931e1952/1959e1967 and1925e1950/1961e1986 time intervals respectively. Data of 1997 and 1998 years fromthe Giarretta station by personal measurements of the Authors. (c) Average monthlyvalues of the solid discharge (Table 5) recorded by the Giarretta hydrological station, inthe 1936e1958 and 1959e1967 time intervals.

A. Di Stefano et al. / Ocean & Coastal Management 80 (2013) 133e148 143

river (Fig. 3), about 70 and 22 km upstream from the mouth,respectively. Both stations documented the basin hydrologicalregime before and after the installation of the hydraulic works (RSP,2007; Fig. 3; Table 1).

The liquid discharge trend is illustratedby Fig.10a (Giarretta) andb (Biscari), which reports the average monthly values, respectivelyin the 1931e1952/1959e1967 and 1925e1950/1961e1986 time

intervals (Table 5). As regards the Giarretta station, data collected in1997 and 1998 derives from personal measurements of the Authors.

Maxima values have been recorded during the autumnewinterperiod of 1931e1952 at the Giarretta station (45 m3/s in February)which drastically reduce from 1959 on (maximum of 34 m3/s inJanuary) after the construction of the Ancipa and Pozzillo Dams. Asone expects, minimavalues are recorded during the vernal-summerperiod, even if a sensible increase of the water discharge isobservable over the 1959e1967 time interval. This was due to theextra discharge into the river of storedwater, designed to irrigation,but not yet usable. After this period, water was not discharged intothe river anymore, reaching the present configuration, as depictedby the 1997e1998 data. At the present time, the hydrological settingof the Simeto River drainage basin is further altered since 1991 bythe start of operations of the Lentini reservoir (De Pietro et al.,1998).Also the Biscari station records an evident decrease of the waterdischarge (Fig.10b) after the completion, in 1953, of theAncipaDam.

In the period from 1936 to 1967, Giarretta also acted as turbi-dometric station. Fig. 10c illustrates the monthly solid load duringthe 1936e1958 and the 1959e1967 time intervals, indicating a closerelationship between the water and the solid discharges. Bothcurves highlight a drastic reduction of the solids load during thevernal-summer months (from March to August). In fact, the mostremarkable changes are recorded in the fall-winter values (fromNovember to January) between the first (1936e1958) and the sec-ond (1959e1967) period. In particular, the annual average solidsload reduces from a value of 177 kg/s to a value of 44.01 kg/s, cor-responding to only 24.8% of the initial amount (MLP-SI, 1925e1986).

6.2. Rainfall regime

Analysis of pluviometric data between 1924 and 2011 was car-ried out in order to evaluate if significant variations of the rainfallregime have occurred within the drainage basin, which might haveinfluenced the hydrological parameters in the Simeto River. Weanalyzed the rainfall data recorded by the Bronte station (Fig. 3) andreported by the data archive of the Regional Hydrological Obser-vatory of Sicily (MLP-SI, 1925e2011).

Through a linear regression analysis of the data, a slightdecrease of the annual amount of rainfall is recorded (Fig. 11a),highlighted by a slope of �1.196 mm/yr. In the same time interval,the variation of the rainy days in relevant year has been considered(Fig. 11b). In this case, the linear regression analysis shows a slopeof �0.105 days/yr, indicating that, during the time intervalconsidered, the area didn’t undergo any significant variation.

We also tried to ascertain whether the rainfall, though notexperiencing significant mean changes, could have experiencedany variations in its frequency distribution. Thus, we determinedthe frequency distribution of daily precipitation the pluviometricstation, subdividing the considered period (1924e2011) into twotime intervals, namely 1924e1960 and 1961e2011, before and afterthe full entry into operation of the various hydraulic works(Fig. 11c). Size classes of 2 mm have been considered. The histo-grams regarding the two different intervals show that anyremarkable difference between the two periods is evident. Excep-tional events (daily rain > than 50 mm) are rare in the 1924e1969period, and decrease further in the last 40 years.

6.3. Coastal dynamics

Retreating or advancing trends of a sandy shoreline also dependon the dynamic processes occurring along the coastal area, namelyon the action of waves and littoral currents.

The analysed coastal stretch falls within the Ionian Sea, which canbe considered a micro-tidal zone (the alternating high- and low-

Table 5Averagemonthly liquid discharge recorded in the Biscari station in the 1925e1959 and 1961e1989 periods, and in the Giarretta station in the 1931e1952 and 1959e1967 ones.Measurements in 1997 and 1998 from the Authors. Average monthly solid discharge recorded in the Giarretta station in the 1936e1958 and 1959e1967 time intervals.

Month Average monthly liquid discharge Average monthly solid discharge

Biscari station Giarretta station Giarretta station

1925e1950 1961e1989 1931e1952 1959e1967 1997 1998 1936e1958 1959e1967

m3/s m3/s m3/s m3/s m3/s m3/s kg/s kg/s

January 17.40 11.56 44.00 34.00 534.00 155.25February 21.40 10.01 45.00 22.50 24.70 163.00 33.47March 19.30 8.95 40.00 20.00 4.16 8.34 63.70 54.00April 10.90 5.38 18.50 18.00 5.68 3.42 42.90 19.81May 4.94 2.21 8.00 14.00 0.84 1.23 8.85 13.56June 2.60 0.76 5.20 10.00 1.19 0.98 49.50 4.27July 1.52 0.78 3.00 9.80 0.60 0.90 0.16 2.78August 1.38 0.79 2.80 10.00 0.92 2.00 2.78September 1.71 0.74 4.90 10.20 0.95 107.00 10.62October 2.43 2.39 11.00 13.50 1.60 160.00 77.67November 8.13 2.60 19.50 10.00 523.00 86.77December 16.40 10.79 30.00 17.50 466.00 61.75

A. Di Stefano et al. / Ocean & Coastal Management 80 (2013) 133e148144

tides occur in at least 6 h per day, with a 20 cm range) dominated bywave action (Longhitano and Colella, 2007). Considering the verylow tidal range and the morphology of the submerged areas, verticalmovements related to tidal fluctuations cannot have a role in thecoastal erosional processes (Longhitano and Colella, 2007). The wa-ter movements in the Gulf of Catania are influenced by the westernIonian Sea circulation, where an anti-clockwise gyre forms (with0.21 m/s speed current) and interacts with the southerly-directedcurrent deriving from the Straits of Messina (Fig. 2b).

The dynamic processes observed and documented for theSimeto River delta (Longhitano and Colella, 2007) are typical of awave-dominated system, with water and sediment inputs from alarge, low-gradient drainage area having a single fluvial channel. Inan idealized situation, a condition of “quasi-equilibrium” is real-ized, inwhich the fluvial sedimentary supply equals the amounts ofsediment removed by wave action, which act as a dispersal agent.

To complete the present study, the analysis of available dataconcerning the wave parameters characterizing the Gulf of Cataniahave been considered, namely height and direction, in order toevaluate if any significant change in the wave energy through timecould have triggered enhanced erosional processes in the coastalarea. The datawere acquired by the nearest station belonging to theRON (Catania meteo-marine buoy, position: WGS84 e 37.43444e15.14667, 5 km offshore east of the Simeto River mouth; ReteOndametrica Nazionale, Italian Sea Wave network, www.idromare.it), active since 1989, consisting of eight directional type pitch-roll

Table 6Equations used in the regression model of Fig. 13. For each transect the used regression

Transect Regression curve Equation

1 La Rena Linear y¼�0.1042 Specchio Linear y¼�0.5543 Allegra Linear y¼�0.6304 Salatelle Linear y¼�0.4435 Vecchia Ansa Parabolic y¼�0.0506 Castello Parabolic y¼�0.0527 Foce Parabolic y¼�0.1558 Argine sud Parabolic y¼�0.04x9 Gurnazza Linear y¼�3.52010 Trigona Linear y¼�3.23011 Gornalunga N Cubic y¼�0.00112 Gornalunga S Linear y¼�1.33813 Aurora Linear y¼�0.85614 Vaccarizzo Parabolic y¼ 0.0006

buoys, equippedwith a satellite positioning system (ARGOS) for thecontinuous control of the location.

The available data, from 1989 to 2009, have been subdividedinto two sets, the first representing the 1989e1999 time interval(Fig. 12a) and the second 2000e2006 (Fig. 12b).

The northesouth oriented coastline is consequently exposed tometeo-marine events from I and II Quadrants. Diagrams for bothperiods indicate that the waves come predominantly from the eastand northeeast, more frequently from the sector between 30� and120� N, with the most intense events coming from the sector be-tween 75� and 120� N.

Taking into account that breaking wave heights are slightlyhigher (Sunamura and Horikawa, 1974; Scicchitano et al., 2007)than those obtained by 20 years buoy measurements, we can as-sume that these data are also representative of the near-shoreprocesses. Thus, the comparison between the two consideredtime intervals highlights the absence of significant variations of thewave parameters; rather, a detectable decrease of the higher waves(>5 m) is recorded in the last decade.

7. Evolution of the Catania Gulf shoreline

7.1. Causes of the coastal retreat

The analysis of the Gulf of Catania shoreline evolution docu-ments the abrupt interruption of a natural cyclic pattern with

and the error of estimate are specified.

SEE ¼ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiPn

i¼1 ðri � piÞ2n

s

Standard Error oF Estimate

5x� 4.3081 4.578xþ 2.6303 6.487x� 7.1096 7.028x� 5.9778 7.142x2þ 1.886x� 5.6149 6.518x2þ 1.8273x� 10.074 12.317x2þ 2.6031x� 36.439 27.072� 1.2739x� 20.807 28.696x� 24.958 22.109x� 44.138 18.568x3þ 0.1926x2� 8.228xþ 9.0834 7.884x� 12.6 6.883xþ 3.5065 7.75x2� 0.2019xþ 1.9387 5.89

Fig. 11. Analyses of rainfall data from the Bronte station. Linear regression of theannual amount of rainfall variations (a) and of rainy days per year (b). Histograms (c)showing the frequencies distribution of daily precipitations in the 1924e1960 and the1961e2011 time intervals.

Fig. 12. Wave parameters (height, direction) recorded by the Catania meteo-marinebuoy, in the 1989e1999 (a) and 2000e2006 (b) time intervals.

A. Di Stefano et al. / Ocean & Coastal Management 80 (2013) 133e148 145

accreting and retreating phases, since the 1950s, with the estab-lishment of a dramatic retreating trend.

Our results show that the retreating phase of the Catania Gulfshoreline has been triggered by the variation of the upstream hy-drological parameters of the Simeto drainage basin, clearly con-nected with bringing into operation, from 1952 to 1972, of fourmain water reservoirs (Fig. 3, Table 1) (Amore and Giuffrida, 1985;RSP, 2007), namely Ancipa, Pozzillo, Ogliastro and Nicoletti and

more recently the smaller Sciaguana. Overall, these reservoirs,which dominate about 30% of the total catchment area of theSimeto River, captures over one million cubic meters of sedimentper year. These artificial barrages and the consequent entrapmentof sediment in the artificial lakes, have strongly reduced theamount of water discharge and sediment load.

The reduction of the river load has also been promoted by theconstruction of several fluvial groynes, built with the aim ofreducing flow velocity during flood seasons, such as the PonteBarca barrage (Fig. 3; Table 1), built about 35 km from the mouth,which permit an off-take of 5 m3/s of water for agricultural use andan additional withdrawal of up to 23.7 m3/s for the reservoirof Lentini (Fig. 3). Minor hydraulic layout works (sills, weirs,embankments) along the Simeto River and its tributariesfurther contribute to reducing the sediment volumes carried to themouth.

The observed different behavior of the coastal stretch north ofthe river compared to the southern one, is linked to the presence ofthe artificial embankments, built up at the end of the 1950s in orderto stabilize the final reach of the river. They reduced the retreating

A. Di Stefano et al. / Ocean & Coastal Management 80 (2013) 133e148146

trend northward up to 2000, when a small bay formed and the barsouth of the river mouth started to be eroded and completely dis-appeared in the last few years (Fig. 6).

The analysis of the hydrological and rainfall data clearly indicatethat the drastic reduction of the solid and water discharge cannotbe influenced by climatic changes, as no significant variation in thepluviometric regime has been recorded over the last century.Neither could an increased intensity of the waves activity havetriggered more intense erosional processes along the shoreline,as no significant change is observable in the wave parameterseither.

Also the changes of the vegetation cover characterizing theSimeto River basin cannot have a role in the retreating processesoccurring along the shoreline. Indeed, the present vegetation coverof the basin has undergone a slight increase in its extent, attributableto the anthropogenic reforestation carried out after the 1950s, or torenewal of natural vegetation as a result of the abandonment ofagricultural activities. On the contrary, some areas must be morevulnerable to soil erosion due to recent fires. In total, available dataon the forest cover and land use (Baglio et al., 1996) point to a slightincrease of the vegetation cover, which at the present represents abare 5.5% of the entire catchment area of the Simeto basin (RSP,2007). This should imply a modest decrease of the erosional pro-cesses and in turn of the sediment supply at the mouth.

Yet, models of soil erodibility demonstrate that variation of theerosion rate related to the increase of the vegetation cover occur-ring in the Simeto basin during the last century can be consideredas negligible, being only a small part in comparison to the totalsurface (Cannata, 1996).

Rather, the retreating processes, related to this strongly reducedsediment supply, could have been accelerated by the narrowing ofthe formerly wide coastal dune-field, between Catania and Agnone,which occurred since the 1970s (Longhitano and Colella, 2007). Thecoastal dune belt, which represents a very important ecosystem andacts as a sea defense and represents a large sand reservoir for naturalbeach nourishment, has been strongly reduced or destroyed due tothe sand withdrawal for quarrying, building and touristic activities.At the current time, onlya fewdiscontinuous portions is still presentas part of the Natural Reserve “Oasi del Simeto”.

Fig. 13. Simulation of the Gulf of Catania coastline movements along the northern (a) and soTable 6); it represents the best-fit curve among three possible (linear, parabolic, cubic).

7.2. Simulation of the future coastline trend

On the basis of the available data we can conclude that the Gulfof Catania shoreline is not in an equilibrium state. For this reasonwe have performed a simulation of the coastal changes over thenext tenyears, assuming the persistence of these retreat factors andan unchanged scenario. For this purpose we have constructed, forthe selected transects, three possible regression curves (linear,parabolic, cubic), choosing the one that provides the mean value in2022 (Fig. 13a and b). According to this model, the highestretreating values are expected for the Foce, Trigona and Gurnazzatransects, respectively of 100, 40 and 20 m, with respect to the 2011coastal position.

This situation is likely to worsen further with the entry intooperation of new reservoirs, such as the Pietrarossa Dam (underconstruction, with planned useful capacity of 30 Mm3) which willdrain a catchment area of 256.56 km2.

7.3. Possible interventions

In such a rapidly evolving situation, it is of fundamentalimportance to itemize possible interventions aimed at reversingthe effects of the coastal retreat process. The building of artificialbars or breakwaters is unsuitable to the purpose, as, due to thecurrent deficit in sediment supply, they would trigger erosionprocesses at the margins of the coastal stretch, causing further lossof sections of shoreline.

The introduction of works to control the coastal erosion pro-cesses without being combined with greater sediment supply,would generate a progressive further narrowing of the coastalstretch in the “Oasi del Simeto” area. Furthermore, a fresh onset ofthe retreat processes will occur in the southernmost sector of theshoreline, which is the most stable at the present, causing thealteration, if not the total destruction, of the best preserved duneremnants, and a drastic reduction of the related biodiversity.

In our opinion, the best solution is to restore the hydrologicaland sedimentological regimes of the Simeto River drainage basin,loss of which has been totally responsible for the degradation ofthe Gulf of Catania shoreline, restabilising the parameters

uthern tracts (b) up to 2022. For each transect a regression curve has been reported (see

A. Di Stefano et al. / Ocean & Coastal Management 80 (2013) 133e148 147

characterizing the basin before the fully entry into operation of thehydraulic works. Moreover, the planning of future water reservoirsshould be abandoned.

Rather, the possibility of removing some of the existing hy-draulic works, as is happening in other countries, such as the UnitedStates (e.g. Graf, 2002; http://www.americanrivers.org/our-work/restoring-rivers/dams/) should be seriously considered.

8. Conclusions

A quantitative estimation of the coastal retreat of the Gulf ofCatania shoreline (eastern Sicily) over the last four decades hasbeen provided. Higher values have been measured in the southernstretch and at the Simeto River mouth (maximum retreat of about204 m, with average rates of 2.75 m/yr), compared to the northernone (maximum retreat of about 55 m, with average rates of 0.74 m/yr). The variations of the examined shoreline through time havebeen proved to be strictly governed by the hydrological parametersof the Simeto River, which have a deterministic role in the amountof sediment supply reaching at the mouth, and in turn on theshoreline evolution. Available data shows that the hydrologicalparameters (solid and water discharge) underwent a dramaticreduction with the construction of several hydraulic works,including dams and fluvial barrages, since the second half of the lastcentury. Moreover, the presence of artificial embankments at theriver mouth favored the differential retreat process between thetwo coastal stretches.

The variation of other parameters such as pluviometric regime,wave intensities or vegetation cover can be considered negligible inthe coastline retreat process. Thus, the reduction in sediment supplyand the consequent coastline retreat is mainly attributable to theinstallation of the hydraulic works, coupled with the progressivedestruction of the coastal dune belt due to human building activities.

In the absence of suitable intervention, which should alsoconsider the possibility of removing some of the existing hydraulicworks, a further reduction, ranging from 20 to 100 m, of thecoastline is expected in the next ten years.

These results, which regard a strategic region from socio-economic and ecological points of view, should be taken into ac-count from the perspective of its future management plans, alsoconsidering the variety of environmental risks (volcanic, seismic,industrial pollution) which lay heavily on this highly populatedcoastal area.

Acknowledgments

The authors are indebted to Dr. F. Panzera for his kind help in thefigures preparation, and to two anonymous reviewers for theirfruitful suggestions. Dr. C. Martino realized Figs. 3 and 12, and therainfall dataset. The study has been founded by PRA2008 (“FondiAteneo”) grants to ADS and CM.

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