Supervisors info:
Βασιλάκης Εμμανουήλ, Επίκ. Καθηγητής, Τμ. Γεωλογίας & Γεωπεριβάλλοντος, ΕΚΠΑ
Πούλος Σεραφείμ, Καθηγητής, Τμ. Γεωλογίας & Γεωπεριβάλλοντος, ΕΚΠΑ
Γεώργιος Παπαθανασίου, Επίκ. Καθηγητής, Τμ. Πολιτικών Μηχανικών, Δημοκρήτειο Παν/μιο Θράκης
Summary:
In this thesis intakes a standard methodology for assessing the displacement rates of the coastline from 1945 to 2018 in the western coastal zone of the island of Lefkada, from the north beach of Agios Ioannis to the Dukato cape, with a total length of approximately 118 km.
The basic functions of this application are related to digitisation, analysis of aerial photographs and satellite images, overlay analysis of thematic layers and the combination evaluation. This was accomplished with the use of software ArcGis10.2.2.
For the survey of the study area we used a rich cartographic material and specific topographic 1: 5000, 1: 50,000 maps of the Greek Army Map Service, aerial photos of the years 1945, 1971, 1996, 2010 and satellite images of the years 2016, 2017, 2018 for detailed visualization of terrain and landforms, geological maps and climatic features of the area.
Several transects were drawn normally to the coast and the distance between them was set at every 150 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 Isoftware was employed as published by USGS and named Digital Shoreline Analysis System v. 4_3 (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.
By employing the methodology described above, at the area of investigation we have calculated the displacement rate of the coastline position over the past 75 years. The rates of change that were calculated were not homogeneous along the full length of the coastline. Specifically, the average value of the rate of receding is 10 cm/year, while extreme values of order 1 m/year were also observed, increasing the riskiness of specific positions. In conclusion we calculated that the extreme coastline displacement values reach the 1.06 m/yr (erosion) and 0.59 m/yr (progradation). The combination of geological formations and intense seismicity seems to be the main factor leading to these results.
Keywords:
DSAS, Lefkada, Morphotectonics, coastal erosion
