GIS applications to support coastal erosion analysis: the case study of the Domitian littoral

Coastal erosion is one of the problems that most afflicts coasts around the world, therefore, a thorough knowledge of this phenomenon and its evolution over time in each area is necessary to guide action planning. To reconstruct the morphological variations over time, at least as regards the position of the coastline, maps and remotely sensed images can be used and compared in GIS environment. The spatial analysis of the changes induced in an area requires the perfect overlay of all compared layers: we can reach this condition only carrying out georeferencing operations in accurate way and reporting all data to the same cartographic projection and datum. The aim of this work is to provide a method to measure the effects of coastal erosion and nourishment in terms of retreats and advances of the coastline and estimate the result accuracy. The attention is focused on Domitian coast (Italy), a prime example of areas that have been heavily affected by erosion in the past so as to require the construction of important defense works. Maps and remotely sensed images, in different cartographic datums, concerning this area and covering a time interval of 39 years (from 1974 to 2013), are analysed and harmonized using Quantum GIS software. The coastlines extracted from these layers are compared to define in quantitative way the coastline changes in the considered period. The experiments detect retreats and advancements reaching a few tens of meters; the results present different level of accuracy.