Geomorphological Environment: Dunes in Agrigento Coast Vincenzo Liguori Dipartimento di Ingegneria Strutturale e Geotecnica Facoltà di Ingegneria Università degli Studi di Palermo [email protected] Giorgio Manno Dipartimento di Ingegneria Strutturale e Geotecnica Facoltà di Ingegneria Università degli Studi di Palermo Francesco Caruso Dipartimento di Ingegneria Strutturale e Geotecnica Facoltà di Ingegneria Università degli Studi di Palermo Territoris (2007-2008), 7: 157-173 Territoris Universitat de les Illes Balears 2007-2008. Núm. 7. pp. 157-173 ISSN: 1139-2169 GEOMORPHOLOGICAL ENVIRONMENT: DUNES IN AGRIGENTO COAST Vincenzo Liguori Giorgio Manno Francesco Caruso RIASSUNTO: La fascia costiera di San Leone (Agrigento-Siclia). è costituita da una spiaggia sabbiosa delimítala verso terra da un complesso dunale di particolare pregio. L'assetto geomorfologico di questo litorale è stato inlluenzato dal forte grado di antropizzazione del luogo. La fascia costiera nel tempo ha súbito degli avanzamenti e arreiramenti. Sono stati quindi analizzati e proposti alcuni rimedi. mirali alia ricostruzione. al mantenimenlo e alia diíesa della duna. ABSTRACT: The coastline ol'San Leone (Agrigento) is characterised by sandy beaches delimited on the interior by a particular dunal complex. The geomorphological aspects of this coast nave been influenced by a high degree of site anthropization and undergone advances and regressions over time. Several recommendations for reconslructing. maintaining and defending the dunes are proposed and analysed. KEY WORDS: Coastal environmeiit. dunes, coastal geomorphology. 1. Physical environment Behind the coastline. from west to east. we find the seaside resort of San Leone, San Leone (Agrigento) coastline is in- which extends from the mouth of the cluded between the mouth of the Akragas Akragas River until the so-called zone river (also known as San Leone river) and «Ragno d'oro». where the «Viale delle the mouth of the Naro river. San Leone dune» originates. path that skirts almost the coastline belongs to the physiographic unit whole shoreline taken into consideration and 10. This área has a hilly morphology and it that ends. in its turn. in the called área «Le is localized in south-west Sicily. confining Dune». This zone is adjacent to the Lido with the Mediterranean Sea. The coastline is Cannatello (bathing place), near to the long approximately 5.6 Km and its géo• mouth of the Naro river. graphie disposition is in the direction San Leone coastline is well linked up NW/SE. with the chief town Agrigento. The roads Liguori, V.. Manno. G. y Caruso F. Geomorphological Environment: Dunes in. that link up Agrigento with San Leone are: physiographic units. Thanks to this scale, it Francesco Crispi street, provincial road N°4 is possible to analyse in detail the and Emporium avenue. In this treatment. the development effects of the dynamics coastal. coastal physiographic unit has been chosen In the figure 1 there are shown the 21 as temtorial level of analysis. or rather that physiographic units into which the Sicilian littoral strip in which the movements of shorelines has been divided. figure 2 sediments are delimited and where there are describes the studied area. no exchanges with other adjacent Figura 1: The 21 physiographic units: 1) Milazzo - Capo Peloro: 2) Capo Peloro - Scaletta Zanglea: 3) Scaletta Zanglea - Giardini: 4) Giardini - Porto di Catania: 5) Porto di Catania - Punta Castelluzzo; 6) Punta Casteliuzzo - I. delle Correnti: 7) I. delle Correnli - Punta Braccetto: 8) Punta Braccetto - Licata: 9) Licata -Punta Bianca; 10) Punta Bianca - Capo Rosselló; 11) Capo Rosselló - Capo San Marco; 12) Capo San Marco -Punta Granitola; 13) Punta Granitola - Capo Feto; 14) Capo Feto - Capo San Vito: 15) Capo San Vito - Capo Rama; 16) Capo Rama - Capo Gallo; 17) Capo Gallo - Capo Mongerbino; 18) Capo Mongerbino - Cefalü: 19) Cefalü - Capo D'Orlando; 20) Capo D'Orlando - Capo Calava; 21) Capo Calava - Milazzo. 160 Territoris, núm. 7. 2007-2008 Geomorphological Environment: Dunes in. Liguori, V.. Manno. G. y Caruso F. Figura 2. The San Leone coastline (Agrigento) 2. San Leone (Agrigento) geology to «marine terrace» and dune shorelines. The geològic context is invariable also towards The arca is characterized by Plio- cast. in C.da Cannatello. where the area Pleistocene lands with different features occupied from the dunal sandy sediments (incoherent, pseudo-coherent and lithoid). becomes really denser. These sediments arc Among the genètic mechanisms that have overlapped lo the alluvium typical of the determined their formation, a very important Naro River's mouth. The nature of the role has been played by the processes of sea sediments, after flowing into the sea. is advance and regression that has produced the strictly linked up with the petrography sedimentation of sand stone and sand in characteristics of the rocks outcropping. heteropy with marly clays (Fm of Agrigento). inside the river basins. The superficial wàters These genètic mechanisms have brought transport sediments into the sea. allowing to the formation of lands clayey. slimy and of their distribution along the coast. It can be conglomerates pertaining at the marine affirmed that the lithological successions terrace. This tenace is wide inside in outcrop typical of the basins of Agrakas river and in the coastal area of Agrigento. In particular, Naro river, are constituted of clayey for• the coast that precedes the inhàbils place of mation (Tertiary). These sediments are co- San Leone and Cannatello is characterized vered in some parts from lands of the geologically by incoherent lands pertaining evaporitic series («Gypseous Sulphurous Territoris, mim. 7. 2007-2008 161 Liguori, V.. Manno, G. y Caruso F. Geomorphological Environment: Dimes in. Serie» -middle- upper Messinian). We nave from the shoreline and 30 cm deep) and the executed drawing of samples of sediments submerged shore (through 5 m deep both from the emerged shore (to 5 meters submersion). The depth valué has been chosen equal Figure 3b and 4b ¡Ilústrate the to 5 m because that valué is equal to the granulometric curves of the samples drawn «depth of closing». Beyond this valué the near the «Third beach» (fig. 3a) and offshore samplings. repeated year after year. do not (fig. 4a) being considered as representative show variations in the bathymetric. of the average shoreline conditions. 162 Territoris, núm. 7. 2007-2008 Geomorphologicaí Environment: Dunes in. Liguori. V.. Manno. G. y Caruso F. From the granulometric curves that have Images of the samples previously men- been made. il luis emerged that the I),, ol'lhe tioned have been aequired (besides fig. 5a samples drawn on land is on average of and 5b) through electrònic microscope and 0.4mm, while which one of the samples aequired through digital telecamera, drawn on the submerged shore is of allowing to analyze the geomètric aspeets of 0,13mm. In both cases the curves indícate the shape of elàstic elements. that drawn samples are sand. From the analysis of these images. it has 3. Geomorphologicaí environment emerged that the elàstic clements which form the samples have mostly spherical The coast consists of sandy beaches li- shape and they show an elevated degree of mited in the inner side by rock slopes or rounding. The superficial weaving of grains al·luvial plains. Morphologically. the te- is glittery. opaque and carved. Yellow ochre. rritory along the coast area is characterized white and the grey are the principal colours. by a landscape with very soft and bland The granular components are calcite and shapes. imposed by the presence of Plio- quartz (in traces). Fossiliferous microfauna Pleistocene outcropping sedimentan1 lands is absent both in the samples drawn on the with clayey-arenaceous matrix. It is possible emerged shore and on the sunken one. This to fïnd the presence of remarkable sub-level study shows how the fundamental difference surfaces produced by the erosi ve-sedi- between the samples drawn on the emerged mentary processes dues to the sea beach and on the submerged one is almost transgressions in the hinterland. which have exclusively a dimensional difference. strongly moulded the country plain. The Territoris, núm. 7. 2007-2008 163 Liguori, V.. Manno, G. y Caroso F. Geomorphological Environment: Dimes in. coastal dunes that we meet along this shore the shoreline. can grow up to constitute a are formed by the sand transported by the real dune (foredune). In this process. Ihe wind from the surface of the beach. They vegetation. which keeps on growing above, constitute an element of transition between has a decisive role as it always remains a the beach and the hinterland. In the backing semi-permeable barrier. shores the eolic deposits can miss or if not. As it is shown in figure 6b. the beach they show signs of erosión at the basis and vegetation has a parallel course with the the vegetation on the external side results shore. It is possible to observe an arca often with the roots exposed. as it happened without vegetation and an área of plants along the coastline subject of the study. (which survive in an environment rich in precisely along «Terza Spiaggia» (fig. 6a), sodium chloride) that progressively covers and the «Spiaggia delle dune». with shrubby and arboreal dune vegetation. Well defined geomètric elements as In this coast. the dune disposition is enclosures or buildings along St. Leone always parallel to the shore, independenlly coastline. provoke often an accumulation of from the direction from which the wind sand on the windward side. The vegetation blows, so that the geometry of the dunes represents a less rigid obstacle and it reduces system cannot be used as palaeoclimatic gradually the wind speed. indicative to recognise those anemologic Where vegetation is present the dune is conditions of the age of their formation. softly joined with the beach (fig. 6b) as it The reason for that has to be found in the occurs along the shore área sheltered from fact that vegetation can grow at a much the emerged breakwater barriers in pro- defined distance from the sea.