Assessing volumetric and geomorphologic changes of terraces in Amalfi Coast using photogrammetric technique

Objectives Terraced landscapes are the most distinctive sign of human influence on territory modelling and a peculiar feature of cultural heritage worldwide. Indeed their construction has been essential to make mountain or steep slope areas habitable and arable, reducing the slope gradient and increasing soil permeability. Recently, they are barely sights and commonly abandoned due to their inadequate and insufficient competitiveness. This trend is causing serious problems of hydrogeological instability and, therefore, both European and Italian agricultural and environmental policy is focusing on the promotion of the protection of these areas. In particular, terraced landscapes wrap Amalfi Coast becoming a typical shape and enhancing its beauty. Moreover, they are a proof of the past and, for this reason, they are involved in UNESCO World Heritage List. In view of the above, the safeguard of this place and the development of a management and maintenance plan of these areas should be a priority. Understanding their evolution over the years is a prerequisite to implement a rescue plan suitable to the study area. Hence, the volumetric and geo-morphology changes of terraced landscapes in Amalfi Coast have been performed by analysing different photogrammetric Digital Elevation Models (DEMs), obtained by historical series of aerial photos. Methods The assessment of volumetric and geomorphologic changes have been implemented in Amalfi Coast, a stretch of coastline on the southern coast of Salerno Province in Southern Italy. To achieve this purpose, some historical series of aerial photos related to the area of interest over a fifty-year period have been taken into account and processed using Agisoft Photoscan Professional in order to generate a fine photogrammetric DEM for each year considered. Subsequently, the volumetric changes (m3) between the different DEMs have been evaluated by multiplying their horizontal grid resolution (m2) with their slope differences. Instead, also the slope degree differences have been analyzed. Eventually, the influence of terraces on the surface flow path have been estimated by the Relative Path Impact Index (RPII), computed on a smoothed DEM, purified of roads, trails and terraces. These indices have been computed using ArcGis. Results This research shows that the photogrammetric technique is a promising method to analyze the volumetric and geomorphological changes of terraced landscapes in Amalfi Coast. In particular, it allows to compare DEMs of different years and to quantify study area changes, which are significant because of the abandonment of this place and their insufficient maintenance.