Analysis of the interactions between coastal morphodynamic processes and Beach Litter distribution.

Beach litter (BL) poses a constant threat to coastal areas and related ecosystems. Standard monitoring techniques used so far for the identification and classification of BL items consist of in situ visual surveys, which are time-consuming and only allow to cover limited coastal stretches. Recently, innovative and multi-disciplinary approaches have attempted to limit these logistic and practical issues. In this context, a growing number of studies are exploiting the use of aero-photogrammetric surveys, coupled with GIS software post-processing tools, for the monitoring of BL-related pollution. To this purpose, Unmanned Aerial Vehicles (UAVs) are often used to acquire images that can be used to evaluate the BL items' density and the relationships between coastal morphodynamic processes and BL distribution along the beach profile. In this study, carried out in the frame of the RETURN Extended Partnership and RiPARTI Project, the results obtained from a monitoring survey carried out along the Torre Guaceto beach (Apulia region, Italy) are shown. In particular, aero-photogrammetric flights were conducted to obtain RGB georeferenced orthomosaics on which manual image screening and morphodynamic analysis were performed to define the recent shoreline evolution and analyze the potential influence of coastal processes in the dispersion and accumulation of BL along the beach profile. The visual screening process was carried out in QGIS software and 382 BL items were identified and categorized. Artificial polymers/plastic (88%) turned out to be the most frequently represented object, followed by glass and textiles (3.4%). Coastal evolution trends were estimated using a specific GIS tool. Results highlighted a general retreat trend of the shoreline, with erosion rates ranging from 1.4 m/yr to 0.18 m/yr. The limit of the fixed vegetation has also been affected by recent retreat processes, up to 3 m. The zone between the embryo dune and the foredune limit, corresponding to the inner section of the investigated beach, gathered the highest density of BL items (1.24 items/m²). This zone is relatively far from marine or aeolic processes along the shoreline so, objects tend to lay for a longer period of time. These can constitute accretion cores for small embryo dunes that, in turn, will tend to increase the risk of burial for BL items. In conclusion, this study highlights that the exploitation of UAV systems facilitates the monitoring of wide coastal sectors and the analysis of beach morphodynamic trends, supporting the identification of hotspot areas for BL accumulation and the definition and planning of tailored clean-up activities.