Caratterizzazione geologica e geomorfologica del settore litoraneo della Piana del F. Sele (Campania, Italia) e considerazioni circa la sua vulnerabilità costiera

In 1990 in the Mediterranean zone there was a coastal population of 146 million; some authors, in 1998, estimated the urban coastal population growth at least of further 30 million by 2025 with 350 million of tourists (Hinrichsen, 1998). In 2005 the dossier edited by UEP/MAP (Plan Bleu, 2005) rescaled these values: by 2025 population will increase of 20 million people, and the tourists will be 137 million more compared to the 176 million already present mainly on littorals. The analysis of data shows, moreover, that 75% of mediterranean population lives in coastal zones (in Italy the value varies from 60% to 70%). Italian coastal zone, more of 7500 km long, in addition to the several beauties of landscape, has a substantial part of the national economic resources, with important urban and industrial centers, infrastructures and touristic activities. These circumstances, especially after the recent reports about climate change (IPCC, 2007), cause heavy problems in coastal resource handling and in connected risk assessing. It’s therefore of primary importance to realize how the coast will develop. Interdisciplinary researches of the last 20 years highlight how many world coastal plains (Italian too) are subject to erosion and flooding risk by sea ingression due to natural (global and local) and anthropic elements. Among these studies we point out to the readers VECTOR project (Vulnerability of the Italian coastal area and marine ecosystems to climatic changes and their role in the Mediterranean carbon cycles) from which the subject of this PhD thesis originates. In this work has been analyzed in detail the littoral Sele river Plain (Campania, Italy) extremely interesting zone in order to realize the evolution of a low and sandy coast with concentration important built-up area (Salerno), great touristic places (archeological site of Paestum, Capaccio-Paestum littoral, Eboli beaches) and morphological conditions which make the area open to developments of coastal system. In the last six millennia this plain and all plains in the southern Italian region of Campania have experienced coastal progradation amply documented by several dune systems. Since the 20th century this trend has been interrupted and many stretches of the coastline are now affected by erosion, at times severe. This has serious implications both for public safety and of a socio-economic nature. The causes are essentially to be sought in the decrease in sedimentary discharge due to forest hydraulic engineering works but especially to the construction of many artificial lakes along the main water courses. Clear evidence of this is the transformation of the mouths of the main water courses from fluvial-dominated to wave-dominated. A further factor is intense urbanization, which took place especially after World War II in the wake of tourist development. Starting from these assumptions the aim of this work is the determination of the morphological and sedimentological characterizations and the evolution dynamics of sandy coastal sector between the Solofrone and Picentino mouths in order to estimate the state of coastal vulnerability. The first stage of the study provides an in-depth search of bibliographic, cartographic and photogrammetric data concerning the study area. Bibliographic analysis specifies the salient points of geomorphological evolution, that is essential requirement to realize the morphogenetic events and recent coast dynamics. Cartographic and photogrammetric analysis, essentially founded on finding documents about the last century, outlines the historical evolution of shoreline. In particular have been used historical maps by IGMI (Istituto Geografico Militare Italiano) on 1870, 1908 and 1954, the cartography CasMez (Cassa del Mezzogiorno) on 1975, the CTR (Carta Tecnica Regionale) by Campania Region on 2004, the aerial-photos on 1944, 1954, 1984, 1998 and 2004. The documents collected have been organized, rectified and adapted by a GIS software (ArcGis rel. 9.2). In particular, for the aerial-photos has been used a software (Erdas rel. 9.1) to orthorectify them before the employment. The second phase consisted in collecting original data through a campaign work, during which, with the use of a DGPS positioning system (GNSS R6) has identified the shoreline in 2009 and the topography of various longitudinal profiles of beach. It was also made a study in order to define the sedimentological aspects characterizing the different geomorphological contexts recognized for the profiles examined: 48 samples were collected along the coast of the Salerno Gulf, on each of whom is performed a particle size analysis, with relative statistical interpretation. The topographical surveys were then linked to the textural characteristics of sediments as this critical step and preparatory to the understanding of geo-morphological phenomena of the coast: sediments that form the beach are affected by coastal dynamics because, along the transit longitudinal and transversal axes, granulometric tend to converge towards the bottom where they are on average in equilibrium under the action of waves. An important stage of work was the evaluation of wave climate both off and along the coast, through the application of physical models. It was back to the type of wave climate on the Sele Plain, as well as the assessment of the effects of it on the beaches with the calculation of specific parameters, such as the run-up and set-up. The information collected gave a clear reading and a detailed characterization of the entire coastal strip between Salerno and Agropoli (SA) and especially were the basis for implementing a new method of analysis for the assessment of coastal vulnerability. The method gave the possibility to create a map of potential coastal vulnerability, as well as to carry out evaluation and maps on wider range of time: in fact, considering the scenarios predicted by the IPCC (2007) on 25 and 50 years, it was possible to introduce these parameters and construct maps of coastal vulnerability projected onto these years. The following is an overview of operations and the results obtained by running the individual phases of work. The comparative analysis of coastlines taken from cartographic and photogrammetric survey showed clear evidence that during the 20th century, it’s possible to identify at least three evolutionary phases. The first, from 1870 to 1908, shows a progradational phase, especially at the mouths of Sele, Tusciano and Picentino rivers with trend reaching 5.50 m/y. This phase is reversed completely during the chronological period between 1908 and 1984, with values of backing down that tend to increase between 1975 and 1985 (notice that the mouth of river Sele retreated at a rate of 7.7 m /y). The last phase goes from 1984 to 2009 (and likely continues today). In fact the littoral is in equilibrium: there are areas that show little progradation, while not much beaches are in retreat (near the mouth of Sele river). This analysis shows that the evolution of the coastal strip of the Piana del Sele is closely linked to the river inputs, just note that areas strongly influenced by erosion are exactly the ones facing areas of mouth. This is certainly to correlate to the drastic reduction of contributions sedimentary caused by removing sediment on the river bed and construction of crosspieces and dams. The analysis conducted in 140 years showed that on the coastal area of Sele Plain insists a trend erosive very marked, localized especially near the mouth of Picentino river and Sele river, with values of retreat respectively 0,4 m/y and 1,3 m/y. To characterize the morphology and the morphometry of backshore and nearshore, and the sedimentological aspects, 12 profiles have been traced, transversal to the coast line on prominent parts of the waterside. Morpho-sedimentary analysis of the shore has shown that the entire sector is morphologically characterized by shores whose extent goes from 20 m to a maximum of 80 m. The nearshore sector is characterized by the existence of a big bar with its trough, while the slope of the intertidal zone is considerable along the mouth of the Sele river, with a mean of 13%, and it reduces to a slope of about 10% on the rest of the coast. Regarding the zones on the southern side of the mouth of the Sele river, the foreshore slope is constant along the whole line, with a mean of about 11%. On the inspected sector of the shore there is a foreshore step located in the range -0.5 m to -0,4 m. Along the whole coast the berm is very evident, reaching the height of 0.6 m with very evident slope contrasts between the beach-face and the berm. This is not the case of the storm berm, which are often erased by the anthropic action and, where visible, they are not always definite. The dunal system is preserved in the most part, but it is not always in good condition. In fact, in some cases (concentrated in the southern portion of the system and in its central part) it is possible to notice the existence of at least, very wide at South and very cut near the mouth of the Sele river, while in the region between the mouth of the Tusciano river and Salerno the dune has almost completely disappeared and/or is extremely urbanized. Granulometric analysis carried out on the samples collected on the foreshore show that the grain sizes between 0.39 mm and 0.45 mm (medium sand) are predominant in the sectors nearer to the mouth of the Sele river, while towards North gravel sediment has been revealed: in fact the sizes go from 0.69 mm and 0.97 mm (coarse sand) in the stretch of central shore from Campolongo to the mouth of Asa stream. The part nearer to Salerno is instead characterized by a type of gravel sediment. In the southern and central sectors it reaches values of 0.55 mm (coarse sand). An anomalous datum, which shows how this coast can be locally influenced by the contribution of external sediment, is the maximum of the Kurtosis index which reaches the value of 10.63 (a really high value, considering that Folk & Ward, 1957 suggest a maximum limit of 3 for this index). With the studies carried out on the condition of the wave climate it has been possible to evaluate the prevalent wave climate with the relative wave heights and average period. Analyzing the series obtained at the Ponza buoy it has been possible to notice that the significant wave height average is 4.34 m, with a period of 7.76 s. In addition, it has been evaluated the effected of the maximum sea storm from the analyzed series, dating to 26/12/1999, with wave height of 6.9 m and a period of 11.94 s. The prevalent direction is SSW-NNW. Such values have been used to evaluate some parameters strictly related to them, like the closure depth, equal to 7.714 m (11.191 m for the maximum sea storm detected). Furthermore the set-up and the run-up of the incident waves have been evaluated for every investigated profile, with a mean value along the entire coast of the Sele Plain of 0.05 m for the former and 1.65 m for the latter. In this case as well we can notice the presence of sectors with energy characteristics very different: in fact, the run-up goes from a minimum of 0.91 m to a maximum of 2.07 m, which means that an wave climate can flood the emerged shore for values between 24% and 101%. On the analyzed shore profiles it has been possible to estimate the evolution trend of the coast, as a consequence of the expected increase in sea level (IPCC, 2007), using mathematical and morphological models capable to evaluate the expected retreat. For the examined case the parameters needed for this evaluation have been measured analyzing the wave climate for the period between the years 1989 and 2008, and the individual topographic profiles of the shore. In particular, the SLR retreat has been evaluated using two morphologic methods and using the sea level increment calculated by Antonioli & Leoni (2007) on the basis of data published by IPCC (2007). The retreat for this has been estimated to a value of 0,16 m/y (using Bruun, 1964) or a value of 0,23 m/y (Davidson-Arnot, 2005). The data obtained with this study have been used to derive a model addressed to the coastal vulnerability determination along the coastal areas that have been analyzed. The coastal vulnerability, which is intended as the susceptibility of a determined coastal area to be affected either by flooding or erosion, is linked to several parameters that can be grouped into three main categories: erosion, permanent inundation and episodic inundation. There are several models for the vulnerability evaluation and comparison among different coastal areas, models that are both qualitative and quantitative. The model proposed by Gornitz et al. (1997), suggest the determination of a coastal vulnerability index (CVI) through the determination of several parameters which can be considered representative of the considered coastal area, and by applying a linear regression to these parameters. This method, which has been largely applied, has the limit that it can be just used for large areas. In my case, I have tried to use this method by applying some modifications that could make it useful also for the study of small coastal environment by improving the number of parameters to calculate and by using a GIS software (ArcGis 9.2). I was so able to propose a new index of vulnerability (IVC) which is based on the evaluation of the Potential Erosion and the Potential Flooding and two more index of coastal vulnerability, (IVC25 e IVC50), which consider the Sea Level Rise (SLR) at 25 and 50 years. The final correlation of the described indexes is obtained trough a multiple linear regression, and the final index value is derived by the expression , which was already used by Goritz et al. (1994). In Fig. 1 it is reported the case study of the coastal areas of the Sele Plain, with the individuation and the representation of the different classes. The areas with the highest values in the IVC are comprised between the Campolongo Hospital and Molo Sirena, an area which include the Sele river mouth. The use of a new model addressed to small areas has allowed to the determination of the main features of the littoral portion of the Sele plain system, with a particular attention to the potential erodibility and to the susceptibility to the flooding and so the determination of the coastal vulnerability. It seems to be a simple a detailed method, which can be used for preliminary studies of all the coastal systems and it is so an instrument useful to the coastal planning.