Section Cartography and GIS SPATIAL DISTRIBUTION OF EROSION AND DEPOSITION ZONES AS A RESULT OF SURFACE RUNOFF BASED ON A PROBABILITY MODEL. A CASE STUDY IN THE ISLAND OF SAMOS. Kotinas V. 1* Gournelos T. 1 Evelpidou N. 1 Vlachogiorgou M. 1 1 Department of Geography and Climatology, Faculty of Geology and Geoenvironment, University of Athens, Panepistimioupoli, Zografou, Athens, GREECE *Corresponding Author ABSTRACT: In this paper we attempt to map erosion and deposition zones in the island of Samos (Greece). The relief of Samos is characterized by hilly and mountainous geomorphology mantled by surface sediments and soils. The processes of erosion depends mainly on the frequency and magnitude of precipitation, surface water flow, slope characteristics, rock s susceptibilitiy to erosion, vegetation and human impacts. The aim of this paper is to study these dynamic processes using easily updated spatial mapping processes in order to design structures to minimize erosion. Keywords: Erosion, G.I.S., Natural Hazards INTRODUCTION Erosion, the result of surface water flow, is a very complicated process. Prior to the erosional stage, a physical or chemical rock alteration takes place, a process called weathering. This process produces the soil and the weathered mantle. Since the beginning of erosion studies, five variables have been recognized as of major importance for weathering: climate, biological activity, topography, parent material and time. The erosion process carries away the soil and weathered material and thus deposition takes place. There are many factors that control these processes such as: rainfall volume and intensity, morphology, lithological properties, type of land cover and human interventions. The above factors define the region s flow regime, the Hortonian or not runoff, and finally the critical time and the amount of erosion and deposition. The main purpose of this paper is to study these dynamic processes using easily updated spatial mapping processes in order to design structures to minimize erosion. Similar erosional problems, may be treated by using different methodologies [1], [5]. METHODOLOGY The identification of erosion and deposition zones involves a series of different stages, as field work, satellite images and air photo interpretation, digitization of topographical, geological and drainage system maps, definition of the input and output variables. The main steps of the procedure which is based on a G.I.S. platform are (Fig. 1): 1. The definition of the input variables (altitude, morphological slopes, vegetation land use, lithology, upslope area). 1087
15 th International Multidisciplinary Scientific GeoConferences SGEM2015 2. The development of a simple probability model to transform the input variables to the output ones (zones of erosion and deposition). 3. The spatial characterization of the output variables. Topographic maps, the geological and land use map were digitized and imported into a G.I.S. environment (ArcGIS 10.1). The elevation data were processed using a data aggregation algorithm and Delaunay triangulation interpolation to construct a digital elevation model (DEM) of the island of Samos. The resolution of the Grid input data is 10 meters. The probability model consists of five input variables which correspond to: 1. Slope (x1) 2. Altitude (x2) 3. Upslope area (x3) 4. Lithology (x4) 5. Land use (x5). Thus if X=(x1, x2, x3, x4, x5) the vector of the input variables we define the conditional probability Then the inner product is formed with where are the coefficients which we estimate, from the input data. These coefficients are related to the input variables. Their values depend on the relative impact of each variable to erosion and deposition processes. Finally the probability of erosion - deposition is considered as a function of S (the result of the above inner product) and so the final equation of probability of erosion - deposition is given by: where Lower values indicate deposition zones while higher values are classified as areas where erosion occurs with different intensity depending on the calculated P value. Input data Topographical Geological Vegetation Input Variables 1. Slope 2. Altitude 3. Upslope Area 4. Lithology 5. Land Use Probability Model G.I.S. Processing Probability of Erosion- Deposition Classific ation Erosion- Deposition Map Figure 1: Flow diagram of the main steps to produce the final output map 1088
Section Cartography and GIS EROSION AND DEPOSITION PROCESS IN SAMOS ISLAND Samos island, situated in the eastern part of the Aegean Sea (Fig. 2) is one of the biggest and most important Greek islands in the Aegean Sea. It covers an area of 476 km 2. The topography of the island is characterized by an alternation of mountainous areas and low basins of North-South direction. The western part of Samos Island hosts the highest mountain of all the Aegean islands, the Kerkis Mountain with an altitude of 1434 m. Samos Island belongs to the geotectonic unit known as Aegean crystalline-schist zone, which is impeded between Atticocycladic complex and Menderes crystalline-schist zone (W.Turkey). The geology of Samos consists of a pre-neogene complicate substratum of gneiss, schists, marbles and a non metamorphic unit [3], [4], [6], [7], [8], [10], [11]. Figure 2: Study area The neogene sediments are mainly located in two neotectonic basins in the island, the Karlovasi and Mytilinii basins, and consist of marls, conglomerates, limestone and tuffs [9]. Recent sediments overlay the pre-neogene and neogene formations and are mainly alluvial formations. 1089
15 th International Multidisciplinary Scientific GeoConferences SGEM2015 The presence of neogene and recent sediments and the relatively high morphological slopes favor the erosional processes in the island of Samos. As mentioned, land use is one of the most significant factors that affect erosion. In Samos Island we have a mixture of areas covered with forests, bushes, fruit trees and vineyards that show lower susceptibility to erosion. Barren land and especially recently burnt areas (like in the area of Zoodoxos Pigi, NE of Samos) are more susceptible to erosional phenomena especially when lithology and slope is propitious. The processes of erosion in the island of Samos have been studied before [2] using fuzzy sets. The creation of erosion deposition map of Samos is the result of the above mentioned procedures and of the probability model. The workflow created for the implementation of these procedures in a G.I.S environment (ArcMap 10.1) is shown in Figure 3. Figure 3: Work flow created using Model builder application (ArcGis 10.1), for the production of the final Erosion-Deposition Map. The proposed probability model transforms the five above mentioned input variables, to the output one which is the probability of erosion deposition for the Samos island. Figure 4 shows the distribution of the output variable and consequently maps the probability of erosion - deposition for the entire island. It is observed that the areas with medium and high probability values of erosion are located mainly in the central part of the island where lithology and relatively high slope favors the denundation processes. The depositional zones are located near the coast and in the internal basins of the island. 1090
Section Cartography and GIS Figure 4: Erosion Deposition Map of Samos Island CONCLUSION It is obvious that the island of Samos is affected greatly by erosion processes. Lithology plays a great role in defining the most susceptible areas for erosion. Also high morphological slopes favor the process. Upslope area defines the amount of water that flows through an area, and when this is combined with high morphological slopes the erosional processes are magnified. Extensive burning of the vegetation cover over the years have resulted in significant erosional processes. Finally the product of the erosional processes accumulates to depositional zones which are located to the coastal areas and to the internal basins of the island ACKNOWLEDGEMENTS This work is supported by the project ECOFLOW (11SYN_8_917) that is funded by the Action Cooperation 2011-2015 of the Operational Programme Competitiveness and Entepreneurship co-funded by the European Regional Development Fund (ERDF) and the General Secretariat for Research and Technology (Hellenic Ministry of Education). 1091
15 th International Multidisciplinary Scientific GeoConferences SGEM2015 REFERENCES [1] Carrara, A., Multivariate models for landslides hazard enaluation, Math.Geol. 15(3), 1983, pp. 403-427. [2] Gournelos Th., Vassilopoulos A., Evelpidou N., An erosion risk study on Samos Island, based on fuzzy models, taking into consideration landuse situation after the fire of July 2000, 7th International Conference on Environmental Science and Technology Ermoupolis, Syros island, Greece, 2000, pp. 284-290. [3] Guernet C., Le "cristallin" de l'eubee du Sud et se problemes. Comparaisons avec le "cristallin" du Laurium et de Samos. Z. Deutsch. Geol. Ges., t.123, 1972, pp. 353-364. [4] Okrusch, M., Richter, P., Katsikatsos, G., High-pressure rocks on Samos, Greece. In: The Geological Evolution of the Eastern Mediterranean (Dixon J.E., Robertson, A.H.F., eds.). Geol. Soc. Spec. Publ. 17, 1984, pp. 529-536. [5] Malgot, J., Mahr T., Engineering geological mapping of the West Carpathian landslide areas, Bull. Int. Ass. Eng. Geol., 19, 1979, pp. 116-121. [6] Mezger K. and Okrusch M., Metamorphism of the Variated Sequence at Kallithea, Samos, Greece, TMPM Tschermaks in. Petr. Mitt. 34, Wurzburg, 1985, pp. 67-82. [7] Papanikolaou D., Unites tectoniques and phases de deformation dans l'ile de Samos, Mer Egee, Grece. Bull. Soc. Geol De France, XXI, no: 6, 1979, pp. 745-752. [8] Philippson A., Die griechischen Landschaften. Eine Landeskunde: IV, Das Aegaische Meer und seine Inseln, 1959, pp. 412. [9] Stamatakis, M., Authigenic silicates and silica polymorphs in the Miocene saline-alkaline deposits of the Karlovassi basin, Samos Island, Greece, Economic Geology Vol. 84, 1989, pp.788-798. [10] Theodoropoulos, D., Geological map of Greece 1:50,000, sheet Neon Karlovassi. IGME publication, Athens, 1979. [11] Theodoropoulos D., Geological map of Greece 1:50000, sheet Vathi port, IGME publication, Athens, 1979. 1092