Citation:
Abstract:
The aim of this study is to calculate the displacement rates of the coastline at the western part of the island, which is characterized of the escarpment coast. The shape of this coastal zone is caused mainly by tectonism which is very frequent in this wider area (Valkaniotis et al., 2018). The western coast of the island from Cape Agios Ioannis (NW) to the southernmost point of the peninsula, Cape Doukato is steep and precipitous, as a result of the high seismicity of the Ionian Sea area (Bornovas, 1964). Along this side of the island, several landslides and rock falls are observed. The situation changes only at the northern part of the island, with a distinctive coastal landform over the narrow zone called "Zostiras" (Leivaditis & Verikiou - Papaspyridakou, 1986).
This work was conducted using two different types of data. Historical analogue panchromatic aerial images of high resolution (Zuidam and Van Zuidam-Cancelado, 1979) and contemporary digital high resolution multi-spectral satellite images were combined for extracting the coastline at the time period of acquisition. The acquisition of the aerial photographs took place during 1945 and 2010, while the satellite images where acquired during 2016, 2017 and 2018 (Figure 1). In all cases the images were digitally processed and optically optimized in order to produce a highly accurate representation of the shoreline at each time period. All the data were imported in a Geographic Information System platform, where they were subjected into comparison and geo-statistical analysis (Tsokos et al., 2018). Several transects were drawn normally to the coast and the distance between them was set at every 200 m as the relative displacement of the coastline was calculated for each one of them.
In a way to achieve this, an extension of the ESRI ArcGIS v.10.6.1 software was employed as published by USGS and named Digital Shoreline Analysis System v.5 (DSAS). The DSAS extension (Thieler et al., 2009) lets the user define a constant straight line in a specific distance from the shoreline and take transects perpendicular to it among the evolving coastlines. The measurements give quantitative information on the change of the position of the shoreline, as well as more useful statistical data. Even if this seems to be an arbitrary value, it worked rather sufficiently at this almost 12 km long segment of the shoreline as it can be characterized as rather curvy and either a smaller value would result an oversampled area with transects intersect each other mixing the calculations or a larger value would result quite sparse transect locations without any representative outcome.