Recent Researches in Information Science and Applications

Erosion Hazard Assessment of the Coastal Stretch (Southern )

PAOLO BUDETTA Department of Civil, Architectural and Environmental Engineering University of Piazzale Tecchio, 80 – 80125 Napoli ITALY [email protected]

Abstract: - This paper deals with natural and human causes giving rise to the coastal erosion of the Cilento shoreline. It is predictable that, in 2100, along the coasts of the a sea level rise varying between 9 and 30 cm will be attained. This increase will cause also a marked rise in the coastal erosion of beaches and rocky coasts of the studied area. The current state of knowledge about erosion processes affecting beaches and cliffs of the Cilento shoreline was shown. Finally, a hazard zonation of potential beach erosions and landslides also was proposed.

Key-Words: - Sea level rise, erosion, sandy beaches, rocky coasts, hazard zonation, Cilento, .

1 Introduction The aim of this paper is to show the current state Although still controversial, the gradual increase in of knowledge about erosion processes affecting the mean global warming, probably induced in part by Cilento shoreline. This stretch of coast is crossed by human activities, will among other things lead to a some important transportation corridors (state roads rise in the sea level. In the last 2,000 years the sea and the Tyrrhenian railway) linking famous tourist level has risen about 1.30 metres, in tectonically resorts such as , Casalvelino, , and stable areas of the central Mediterranean Sea. Due . Furthermore, during the summer the whole to a probable effect of the anthropic global coast stretch is intensely inhabited and exploited for warming, the sea level has risen about 12 cm during bathing purposes. Consequently, risk conditions the last 100 years [1]. It is predictable that, in 2100, considerably increase. a global rise of about 0.18 – 0.59 metres will be attained [2]. Due to the weather conditions 2 Geologic and neotectonic setting characterizing an inland sea and heavy evaporation The Cilento shoreline extends for about 118 km not compensated for river discharges, a rise in the between Agropoli and Sapri (Fig. 1), being included sea level of the Mediterranean Sea varying between in the physiographic unit of the Cilento Coast as 50% and 100% of the global scale value can be well as partly in the Gulf of and in the Gulf expected [1]. This increase will cause a marked rise of Policastro units. Along this coast the combined in the coastal erosion of beaches and rocky coasts. effects of sea level rise, man-made alteration and As a result, more and more new human settlements reduced solid discharge coming from rivers cause and infrastructures along the coast will be exposed heavy coastal erosion. The resident population in the to high marine erosion risk. For purposes of coastal 15 coastal Municipalities totals about 76,500 planning and engineering mitigation, it is therefore inhabitants, with a mean density of 179 inhabitants necessary to assess the potential increase in erosion per km2. Transportation corridors run for about 115 processes due to wave action, particularly if they are kilometres. able to accelerate basal erosion and mass The shoreline between Punta and Capo movements on rocky coasts. The basic factors Palinuro is affected by a maximum fetch of about controlling marine erosion are well-known: the 530 nautical miles, coming from the strike N230°. force of waves against the beaches and bases of According to wave motion data recorded by the cliffs, as well as the lithology of exposed rock Italian Ondametric Network (time span July 1989 - masses. Additional factors are reduction in rock December 2003), the most frequent provenance of strength owing to weathering by sea spray, rock wave motion is included in the sector comprised mass removal, tidal action, and material fatigue between N210° and N330°. The maximum recorded caused by cyclic loading of the wave action. wave height (Hs) is about 7 m, coming from the strike N270° [3]. The Italian Ondametric Network

ISBN: 978-1-61804-150-0 207 Recent Researches in Information Science and Applications

Figure 1: Coastal dynamic and landslide density map of the Cilento shoreline. recorded 52 sea storms which lengths of time belonging to flysch formations cropping out in the between approx. seven days (Ponza 24/12/1999) and inner part of the Cilento region. Almost all of these a few hours, during the time span March 1999 - shorelines are eroded beaches with a mean December 2003. Very often the wave motion is in withdrawal of about 8 - 10 m (in the last 50 years). the West sector with prevailing strike N270°. These It should be noted that the widest withdrawal was waves cause a longshore drift from NW towards SE, near harbor works, mostly built in the 60s and 70s whereas the prevailing drift is in the direction W – E of the last century. This confirms the strong in the Gulf of Policastro. In order to protect the influence of human causes. shoreline, several sea works (such as artificial reefs, Solid discharges furnishing beaches coming from and shelters) are present, whereas quay walls and the nine main rivers of the area total about 11 jetties constitute the main harbor works located millions of T/year. As these sediments show a between Agropoli and Sapri. In total, the granulometric sorting mainly towards fine sands and anthropized shoreline extends for about 14 km. silts, they are not suitable for the beach- The coastal stretch consists of sandy and pebbled nourishment. Furthermore, beach erosion is beaches (sometimes pocket beaches), alternating worsened by the sand and gravel drawing from river with high cliffs and steep slopes. Sandy shorelines beds and sediment trapping in reservoirs. With have considerable lengths just to the north of reference to the sediment drawing, an amount of Agropoli, Santa Maria di , between allowed withdrawals of about 13,400 m3 per year, Casalvelino Marina and , north and south of during the time span 1979 – 1999, was calculated. Capo Palinuro and between As this amount does not take into account illegal and . These beaches are nourished by withdrawals it is a rounded down value. The “Piano weathering and landform erosion processes della Rocca” dam and other reservoirs located in the affecting sandstones and pelitic limestones river basin detain about 19,600 m3 per year

ISBN: 978-1-61804-150-0 208 Recent Researches in Information Science and Applications

Figure 2: Beach zoning: (a) erosion effects in the immediate future (high hazard zone, P3); (b) erosion

effects at longer-term (medium hazard zone, P2); (c) indirect effects affecting constructions and

infrastructures (low hazard zone, P1) (after [4] modified). of sediments. It was calculated that the total amount eruptions or catastrophic landslides, and coastal of sediments that don’t reach the shoreline (due to landslides. For this area, the hazard exposure is the sediment drawing from river beds and trapping lower than that affecting Southern Calabrian, the in reservoirs) is about 2.5% of the total theoretical Straits of and Eastern . With solid discharge [4]. reference to the Lower between the The rocky coast extends for about 62 km. This region and Sicily, the Italian Tsunami coastal type is made of steep slopes and cliffs with Catalogue edited by INGV (Istituto Nazionale di outcropping arenaceous-conglomeratic strata Geofisica e Vulcanologia) reports 72 tsunami events alternating with silty-marly or calcilutitic ones during the time span 79 ad - 2004 [6]. Furthermore, belonging to the Cilento Flysch Units [5]. the coast is more exposed to anomalous waves Subordinately limestones, cherty-limestones and caused by submerged volcanic eruptions from the dolomites belonging to the Alburno-Cervati and Aeolian or Marsili seamounts. Waves coming from Mount Bulgheria Units, as well as Quaternary the Island (during the December 2002 polygenic conglomerates, and cemented Aeolian eruption) reached the shoreline in the Policastro Bay sands outcrop. causing slight damages. With reference to sea level The whole shoreline is exposed to the tsunami changes caused by recent tectonic movements, hazard caused by earthquakes, submerged volcanic stationary conditions or only a slight uplift (lower

ISBN: 978-1-61804-150-0 209 Recent Researches in Information Science and Applications

than 0.07 mm per year) were established [7]. This basis of a landslide inventory map was carried out. was stated on the basis of several geologic and Furthermore, data regarding failure mechanisms, biological leading indicators dating back to the landslide mobility as well as run out distances of the Tyrrhenian period (about 125,000 years ago). A landslide debris also were collected. Special maximum ground lowering of about 0.03 mm per attention was paid to the study of rock falls because year only for the shoreline belonging to the Mount they are usually sudden and happen without any Bulgheria sector has been recorded. apparent warning signs. The major geomorphological, geological and 3 Coastal erosion hazard structural features of about 161 slopes and cliffs in In order to evaluate hazard levels due to beach carbonatic rocks and flysch have been analyzed and erosion a zoning of sandy shorelines according to several parameters affecting rock masses were the ability of the wave motion to cause flooding and detected and measured. These parameters deal with beach profiles erosion during storm surges has been topographical, geological, geomechanical, proposed [4]. For sea storms, with a return period environmental and wave hydraulic characteristics of (Tr) that occurs every fifty years, three areas of low, the studied area. medium and high hazard (P1, P2, and P3) have been In order to perform a heuristic approach based on mapped (Fig. 2). It turned out that, with reference to the Rock Engineering Systems (RES) proposed by a total of 180 beaches, an area of about 1.4 km2 falls Hudson, several steps were performed [8, 9]. The into class P3, about 0.23 km2 are mapped as medium main steps were: (1) the choice of parameters hazard (P2) and 1.84 km2 were in the low hazard relevant to landslide hazard zonation, (2) the (P1). analysis of binary interaction between parameters, With reference to rocky coasts, about 228 (3) the weighting of interaction importance, (4) the landslides directly or indirectly triggered by the rating assignment to different classes of parameter wave motion were mapped (Fig. 3). Most of these values and (5) the final computation of an landslides are dormant rotational slides (affecting “Instability Index” (I.I.). A database containing the about 28% of the studied area), followed by measured parameters was prepared, and using an suspended rotational slides, complex landslides (slide - flow) and rock falls. Although the latter represent only 3% of the total landslide area (1.78 km2), they frequently occur along both active and fossil cliffs. Landslides mainly affect the municipalities of , Agropoli and followed by Castellabate, and S. Giovanni a Piro. Using landslide data by the IFFI Catalogue (Inventario Fenomeni Franosi Italiani), a Coastal Landslide Density Map was drawn (Fig. 1). The map displays landslide density areas varying Figure 3: Frequency of typologies and areas of the 2 landslides affecting the studied coast. Key: A = between 2 and 10 landslides per km . The greater active debris flows; B = inactive slow earth flows; C landslide concentration is found along the coastal = active slow earth flows; D = dormant slow earth stretches between Agropoli and Punta Licosa, flows; E = rock-falls; F = active rotational slides; G Montecorice and , Ascea and Pisciotta, as = suspended rotational slides; H = dormant well and . In these areas arenaceous- rotational slides; I = active complex slide-flows; L = pelitic and marly-calcareous strata which are dormant complex slide-flows; M = active ascribed to the so-called "structurally complex translational slides. formations" crop out. This confirms the important ---- role in the landslide triggering played by lithology interaction matrix, the outputs were linked into a and geotechnical properties of rocks, compared to Geographic Information System (GIS). Values of wave energy and climate. the I.I. (%) were grouped into 3 classes marking In order to zone the variable degree of landslide low, medium and high landslide hazard (S1, S2 and hazard of the rocky coasts, an in-depth study on the S3). Both carbonate cliffs and flysch slopes were

ISBN: 978-1-61804-150-0 210 Recent Researches in Information Science and Applications

distinguished with respect to I.I. values to show the costiere italiane, Quaderni Società Geologica differences in landslide hazard (Table 1). In fact, Italiana, Vol. 2, 2007, In Italian. Available on rapid but small rock falls can cause more damages web site: http://www.socgeol.it or casualties than large slides at moderate speed. [2] Intergovernmental Panel on Climate Change – High landslide hazard affects about 33% of IPCC, Climate Change 2007: Synthesis Report, carbonate cliffs and about 54% of slopes in Contribution of Working Groups I, II and III to arenaceous-marly flysch. the Fourth Assessment Report of the Intergovernmental Panel on Climate Change, Rocky cliffs 2007. Available on web site: Class I.I. ranges No. of cliffs Cliff http://www.ipcc.ch/ percentage [3] Istituto Superiore Protezione e Ricerca S1 26 – 40 % 40 41 Ambientale – ISPRA, Atlante delle coste “Il S2 41 – 60 % 25 26 moto ondoso a largo delle coste italiane”, S3 61 – 83 % 32 33 APAT Agenzia per la protezione dell’ambiente Flysch slopes e per i servizi tecnici - Dipartimento Tutela Class I.I. ranges No. of Slope slopes percentage delle Acque Interne e Marine Servizio Difesa S1 32 – 40 % 5 9 delle Coste, 2011, In Italian. Available on web S2 41 – 60 % 21 37 site: http://www.apat.gov.it/site/it- S3 61 – 79 % 31 54 IT/Servizi_per_l'Ambiente/Stato_delle_coste/A Table 1: Distribution of cliffs and slopes tlante_delle_coste/ outcropping along the coast with different landslide [4] Budetta P., Calabrese M., Pianese D., Approcci hazard classes. metodologici per la valutazione della pericolosità da erosione costiera e dell’apporto 4 Conclusion solido ai litorali, Cilentum, No. I, 2006, pp. 18- The studied shoreline shows an environmental 28. In Italian. setting produced by combination and interaction of [5] Bonardi G., Ciarcia S., Di Nocera S., Matano many complex, natural causes. Some are "long- F., Sgrosso I., Torre M., Carta delle principali term" causes, as they are related to geological unità cinematiche dell’Appennino meridionale. phenomena the effects of which, are appreciated Nota illustrative, International Journal of over time (e.g., Neotectonics) or located away from Geoscience, Vol. 128, No. 1, 2009, pp. 47-60. the area most directly affected (e.g., tidal waves In Italian. generated by a tsunami). Other causes are structural [6] Tinti S., Maramai A., Graziani L., The new as they are linked to the geomechanical properties of Catalogue of Italian Tsunamis, Natural outcropping rock-masses. Hazards, Vol. 33, No. 3, 2004, pp. 439-465. There are also occasional factors which originate Available on web site: from the offshore wave motion and that, in turn, http://roma2.rm.ingv.it/it/risorse/banche_dati/2 determine the magnitude of the wave energy 7/il_catalogo_dei_maremoti_italiani transfer to the shoreline, the sediment drift, as well [7] Ferranti L., Monaco C., Antonioli F., Maschio as beach and cliff erosion. In recent decades, man- L., Kershaw S., Verrubbi V., The contribution made actions have added to natural factors. Their of regional uplift and coseismic slip to the effects propagate both at the global scale (e.g., the vertical crustal motion in the Messina Straits, global warming and consequent sea level rise) and Southern Italy: evidence from raised Late local one (e.g., the human settlement, poorly Holocene shorelines, Journal of Geophysical designed coastal defenses, reduced solid discharges Research, Vol. 112, B06401, 2007, pp. 234- coming from rivers). Unfortunately, the emerging 256. overall negative outline is no different from that [8] Budetta P., Santo A., Vivenzio F., Landslide characterizing other Mediterranean coastal areas. hazard mapping along the coastline of the This outline is characterized by increasing erosion Cilento region (Italy) by means of a GIS-based processes that give rise to serious environmental and parameter rating approach, Geomorphology, economic consequences. Vol. 94, 2008, pp. 340-352. [9] Budetta P., Stability of an undercut sea-cliff References: along a Cilento coastal stretch (Campania, [1] Antonioli F., Silenzi S., Variazioni relative del Southern Italy), Natural Hazards, Vol. 56, livello del mare e vulnerabilità delle pianure 2011, pp. 233-250.

ISBN: 978-1-61804-150-0 211