NATURAL EVOLUTIONARY TREND IN TWO POCKET BEACH OF CALABRIA (SOUTHERN ITALY)

Transcription

1 NATURAL EVOLUTIONARY TREND IN TWO POCKET BEACH OF CALABRIA (SOUTHERN ITALY) Maurizio Alessio Baldassarre, Piero Bellotti, Lina Davoli & Sabrina Vella Department of Earth Sciences, Sapienza University of Rome, Piazzale A. Moro 5, Rome, Italy, Tel , Fax , Abstract Pocket beaches are small stretches of coastline confined between two headlands and with very poor or none sediment inter-changes with adjacent coastal sectors. Sediments in these beaches vary from gravel to sands and generally derive from local rivers, cliff erosion and material carried on the coast at the end of the last transgression. Even if the pocket beaches are very common around the world, literature is not quite exhaustive about their hydrodynamic, morpho-sedimentary processes and natural evolutionary tendencies. The study focuses on two pocket beaches of the Calabria coast, which differentiate for exposure to the sea, coastal setting, sediment characteristics, and drainage basin of the rivers that feed them [1] [2] [3]. All these aspects were analyzed in the present study, which aims to identify the evolutionary coastal trends and related environmental drivers, particularly those playing an important role in the past, today and probably in the future. Data used concern: (a) climate time-series recorded by dozens of meteorological stations distributed in the drainage basins; (b) orthophotos and topographic maps dated back to different periods, by which rates of shoreline changes and related sediment imbalances were estimated; (c) multi-temporal DGPS data recorded during two-years in order to ascertain the short-term beach variations; (d) bathymetric measures supported by scuba diving observations; (e) beach-shoreface sediment grainsize data. Introduction The aim of this work is to estimate pocket beach dynamics by means of the study of morphometric, sedimentological and climate characteristics. The study area coincides with two pocket beaches of Calabria (Fig. 1). The pocket beach of Cala Janculla faces Tyrrhenian Sea, whereas Caminia di Stalettì faces Ionian Sea. The pocket beaches differ from each other for exposure to the sea, coastal setting, sediment characteristics, drainage basin of the rivers that feed them and for a different anthropic forcing. The Italian pocket beaches are very important as a tourist attraction and so as also a relevant social-economic source for populations that live near these beaches [4]. Although pocket beaches dynamics have been study extensively, no specific data exist to estimate the relationship of erosive processes with the factors that cause it [5]. So, in this study, characteristics of fluvial environmental, sedimentological and morphometric parameters and climate factors have been considered all together to understand, if it is possible, if and how much they influence pocket beaches dynamics. 189

2 CALA JANCULLA BEACH CAMINIA DI STALETTI BEACH Exposure: WNW Cord lenght: 360 m Exposure: SE Cord lenght: 1232 m Embayment: 120 m Beach lenght: 360 m Embayment: 287 m Beach lenght: 946 m Lithology: metamorphic rocks Sediment input: fluvial, gravitative phenomena Relief slope: high Anthropic impact: very low Lithology: metamorphic and intrusive rocks Sediment input: mainly fluvial Relief slope: high Anthropic impact: high Closure Depth [6] [7]: 10.3 m Depth of closure [6] [7]: 10.2 m Figure 1 Location map of the study area and beaches morphometric characteristics. Data and methodology - Climate data Rainfall and temperature data used for this study have been registred in Palmi (Tyrrhenian side) and Soverato Marina (Ionian side) stations (Table 1). Data were provided by Centro Funzionale della Calabria. The analysis was performed on daily records and no treatments were undertaken to correct for missing observations in the series. Table 1 Characteristics of meteorological stations. Latitude N Longitude E Meteorological Elevation (Gauss (Gauss Station (m) Boaga) Boaga) Soverato Marina (CZ) Palmi (RC) Data P T Missing data Period

3 - Morphometric data Some morphometric parameters of two drainage basin have been considered: the length and the hierarchical order of the streams [4]. Basin networks are digitalized in GIS platform, using topographic basemap (1:25.000). On this basis, parameters are calculated for each beach. - Sediment grainsize Sedimentological analysis were conducted on samples (submerged and emerged) collected for both beaches compared. The observations for Cala Janculla are only qualitative and relate to samples taken along the shore through underwater diving. - Bathimetric data Single-Beam sounder surveys were conducted for both beaches in November 2010 and GIS Tool was used to manage bathymetric data. - Shoreline variations Changes in shoreline have been measured for both beaches using aerial photographs. DGPS surveys carried out mainly over period and only for Caminia di Stalettì because Cala Janculla is not easily accessible. Results Climate analysis Annual precipitations for periods and stations have been considered (Fig. 2 and 3). Both stations show a diminution of annual precipitation values. Figure 2 Total annual precipitation, average precipitation and linear trend observed in the Soverato Marina meteorological station. 191

4 Figure 3 Total annual precipitation, average precipitation and linear trend observed in the Palmi meteorological station. In Table 2 are reported the descriptive indicators of the climate. The extreme rainfall events also have been calculated. They were defined as those exceeding 95 th percentile of data serie (P = 13 mm for Soverato Marina and P = 16.8 mm for Palmi). These values (13.0 mm for Soverato Marina and 16.8 mm for Palmi) are not usable to estimate temporal variations of extreme rainfall events, because they are very low. Table 2 Descriptive indicators of the climate data. Meteorological Station P Mean (mm) T max ( C) T min ( C) T Mean ( C) 95 th Percentile Soverato Marina (CZ) Palmi (RC) Morphometric analysis In Figure 4 drainage basins and networks for both beach are reported, whereas tables 3 and 4 show the number of segments calculated for each order, for Cala Janculla and Caminia di Stalettì. 192

5 Figure 4 Drainage basins and networks of Cala Ianculla basin and Caminia di Stalettì basin. Table 3 Stream order for Cala Janculla basin (a) and Caminia di Stalettì basin (b). Order Nu Length (m) Order Nu Length (m) (a) (b) I I II II II III IV The analysis shows that hydrographic basin of Caminia di Stalettì (2.4 km 2 ) is wider than basin of Cala Janculla (1.8 km 2 ). The maximum stream order also is higher in Caminia di Stalettì. Sedimentological analysis As shown in Figure 5a, the submerged beach of Cala Janculla shows variations also very evident about the particle size distribution of sediments along the various portions of the beach. There is alternation of sediments characterized by predominantly coarse material, most likely resulting from the material to fall from the cliff behind, with mediumfine-grained sediments, with a high sand component linked forms with evidence of the influence of wave action. Figure 5b shows the situation relative to Caminia di Stalettì beach, for which laboratory tests have involved samples from the beach submerged and emerged. The analysis of grain size distribution shows a gradient characterized by a Mz decrease [8] going to off shore and from southwest to northeast. In the latter case, the gradient might be related to the influence of a long-shore current that moves northward into the bay. 193

6 (a) (b) Figure 5 Sedimentological characteristics of two submerged beaches: (a) Cala Janculla; (b) Caminia di Stalettì. Bathymetric analysis The figure 6 shows the results obtained by the bathymetric survey conducted. The submerged morphology appears to be characterized by a fairly regular bathymetric gradient in both beaches. A higher morphologic variability in Cala Janculla might be explained by the action of the waves and the rock falls from headlands and reliefs that border this coast. Figure 6 Bathymetric characteristics of Cala Janculla and Caminia di Stalettì. 194

7 Morphologic variations Figure 7a shows the comparison between the shorelines on the beach of Cala Janculla. The available data show no significant changes from 1954 to The situation highlighted for Caminia di Stalettì is similar (Fig. 7b); in fact, the available data, although coating the same period ( ), show very small variations of the shoreline. (a) (b) Figure 7 Shorelines comparison: a) from 1954 to 2009 for Cala Janculla; whereas b) for Caminia di Stalettì from 1954 to Final remarks According with Köppen Climate System, the climate of Calabria belongs to the Humid mesothermal climate (C), Mediterranean type with very hot summer (Csa) [9] [10] [11]. At Soverato Marina, mean annual temperature is 18.6 C ( period) and mean annual precipitation is mm ( ). At Palmi, mean annual temperature is 12.0 C ( period) and mean annual precipitation is mm ( period). The analysis shows decreasing trend, for all climatic parameters calculated, except for temperature, in both stations. These variations don t seem to influence the coastline position. In fact, the pocket beaches seem to remain stable for period considered. Caminia di Stalettì shows minimal rotation (advancing at N and retreating at S). Probably, ongoing work about anemometric data might explain that rotation. The high anthropic impact, at Caminia di Stalettì, don t seem to influence the natural equilibrium of beach. References [1] D Alessandro L., Davoli L., Lupia Palmieri E., Raffi R. - Natural and anthropogenic factors affecting the recent evolution of beaches in Calabria (Italy), Appl. Geomorph.: Theory and Practice. Ed. By R.J.Allison (2002). John Wiley & Sons, Ltd,

8 [2] Davoli L., Baldassarre M.A. Le pocket beach della Calabria. Progetto di ricerca riguardante i processi evolutivi delle pocket beach con riferimento agli obiettivi del protocollo Integrated Coastal Zone Management (ICZM) della Convenzione di Barcellona. Convenzione tra il Ministero dell Ambiente e della Tutela del Territorio e del Mare Direzione per la Ricerca Ambientale e lo Sviluppo ed il CURSA. Relazione Tecnica, Primo Stato di avanzamento lavori, pp , (2009) [3] Evangelista S., Baldassarre M.A., Le pocket beach del Lazio. Progetto di ricerca riguardante i processi evolutivi delle pocket beach con riferimento agli obiettivi del protocollo Integrated Coastal Zone Management (ICZM) della Convenzione di Barcellona. Convenzione tra il Ministero dell Ambiente e della Tutela del Territorio e del Mare Direzione per la Ricerca Ambientale e lo Sviluppo ed il CURSA. Relazione Tecnica, Primo Stato di avanzamento lavori, pp , (2009) [4] Simeoni U., Corbau C., Pranzini E., Ginesu S. Le pocket beaches Dinamica e gestione delle piccole spiagge, Ed. by Franco Angeli s.r.l., Milano (2012) [5] Pranzini E., Rosas V. Pocket beach response to high magnitude-low frequency floods, Journal of Coastal Reserch (2007), SI50 (Proceedings of the 9 th International Coastal Symposium), [6] Hallemeyer R.J. - Uses for a Calculated Limit Depth to Beach Erosion, Proc. coastal Eng. Conf., 16th, Hamburg, Germany, (1977) pp [7] Nicholls R.J., Birkemeier W., Hallemeyer.J. - Application of the Depth of Closure Concept. 245th Castal Engineering. Conf., (1996), pp [8] Folk R.L., Ward W.C. Brazos river bar: a study in the significance of grain size parameters, Journal of Sedimentary Petrology, 27: [9] Brunetti M., Buffoni L., Mangianti F., Maugeri M., Nanni T. - Temperature, precipitation and extreme events during the last century in Italy, Glob. Planet. Change (2004) 40, [10] Brunetti M., Maugeri M., Monti F., Nanni T. - Temperature and precipitation variability in Italy in the last two centuries from homogenised instrumental time series, Int. J. Climatol. (2006) 26, [11] Brunetti M., Caloiero M., Coscarelli R., Gullà G., Nannia T., Simolo C. - Precipitation variability and change in the Calabria region (Italy) from a high resolution daily dataset, Int. J. Climatol. (2012) 32,