The use of UAV images to assess preliminary relationships between spatial litter distribution and beach morphodynamic trends: the case study of Torre Guaceto beach (Apulia Region, southern Italy)

Abstract

Beach litter (BL) represents one of the major threats to coastal areas and related ecosystems. Monitoring programs based on in situ visual surveys allow the identification and classification of BL items. Nevertheless, such activities are time-consuming and only cover limited coastal stretches. Due to the above limitations, recent studies are exploiting the use of Unmanned Aerial Vehicles (UAV) to collect photogrammetric images for the monitoring of litter-related pollution. In this study, the BL spatial distribution along the Torre Guaceto beach (southern Italy) is assessed by mapping macro (> 2.5 cm) items on the orthomosaic obtained through the post-processing of UAV images. Furthermore, in order to define the recent morphodynamic evolution and analyze the potential influence of coastal process in the dispersion and accumulation of BL along the beach profile, morphological changes that occurred in the last 20 years have been estimated in the GIS environment. From the manual image screening process, a total number of 382 items BL are identified. The highest number of items are composed of artificial polymers/plastic (88%), followed by glass and textiles (3.4%). What concern the morphodynamic evolution, the central part of the investigated sector has been interested by a general retreat trend, especially in the last two years. Recent erosion processes affected mostly the fixed vegetation, whose limit has been affected by a retreat up to 3 m. The highest density of BL has been estimated for the inner part of the investigated beach, which corresponds to the area from the embryo dune to the foredune limit. In conclusion, this study highlights how the use of UAV systems enhances the monitoring of wide coastal sectors and the analysis of beach morphodynamic characteristics, this way supporting the easy identification of hotspot areas for BL accumulation as well as the establishment of appropriate clean-ups works.