Coastal vulnerability assessment through complementary monitoring technologies: The case of riccione

Monitoring is known to be the basis for coastal planning and management studies, for verifying the interventions effects and for forecasting the future state of beaches. There are several proxies that must be considered in the definition of a monitoring plan, such as the spatial and temporal extension of the monitoring activities, the types of data and their required accuracy values, the acquisition frequency of the data and perhaps the available budget to invest are among the most important aspects. The present paper presents the first results of the monitoring activity with integrated and complementary techniques applied to a stretch of coast near the city of Riccione, North Italy, within the framework of the research project STIMARE, financed by the MATTM and of the project POR FESR TAO. The site is protected by non-traditional defense works, and the on-going activities aim to monitor the shoreline evolution by using videocameras, with a low-cost hardware system, based on Raspberry Pi components, and the development of on-site software for the survey, correction and georeferencing of data. The monitoring of the emergence and submerged beach is carried out by means of topographic and bathymetric surveys (terrestrial laser scanner, UAV photogrammetry, ASV multibeam), allowing a very high-resolution digital terrain model (DTM) to be obtained. The comparison between successive surveys acquired with different techniques provides information on the response of the coastal stretch to the local regime of waves and currents and on the effects of the defense structures on the seabed, both in the nearfield and in the farfield, with the possibility of quantifying the volumes of eroded or accumulated sand. Finally, the two monitoring approaches are shown to be complementary in terms of time and precision: direct surveys provide data with high spatial precision but not continuous acquisition due to budget and logistics reasons, while video monitoring provides only information on the shoreline, (used as a proxy for the description of coastal dynamics) but with data continuously acquired. The project aims to verify the complementarity and integration of the different techniques adopted in monitoring, and the possible feasibility in other coastal stretches with the purpose of assessing vulnerability.