UAV application for monitoring the annual geomorphic evolution of a coastal dune in Punta Marina (Italy)

Unmanned Aerial Vehicles (UAV) allow to gather detailed topographic data at low cost over large survey areas. The study site, located in Punta Marina (Emilia-Romagna), is one of the few regional coastal locations still characterized by “natural” dunes; in 2015 a preservation scheme was realized to protect the dune system and reduce the erosion and vegetation degradation generated by beach users. Four UAV surveys were performed using a commercial DJI Phantom 3 Professional, a quadcopter equipped with the standard digital camera of 12 megapixels (3.6 mm focal length). Drone surveys were supported by a RTK-GNSS, both for GCP measurements and drone-derived DSM validation. Orthophotos were obtained through photogrammetry processing with a geometric resolution of about 3 cm, generating a DEMs with a cell size of 5 cm. Dune morphology was compared by means of DoD processing to understand the geomorphological evolution and quantify the volume of sediments displaced. The most evident result is related to the growth of a small incipient dune fed by aeolian processes and enhanced by preservation measures (planted vegetation and wooden fence). A cumulative vertical growth of 0.5 m was locally measured after the monitoring period. The role played by the growth of pioneer plants in overestimating volume changes was quantified as +11%. The use of drone-derived images, combined with SfM algorithms, allowed to achieve a centimetric accuracy in the incipient dune analysis. This methodological approach can represent an efficient tool for coastal and landscape managers, both for mapping and risk assessment purposes at small spatio-temporal scales.