Short-term effects of storm events on the coastline morphology of a Mediterranean microtidal wave-dominated beach (Piscinnì, SW Sardinia)

The Mediterranean coastal areas have been recognized as the most sensitive regions to actual climate and environmental changes. The increased frequency, intensity, spatial extent, duration, and timing of storm events due to climate change can increase the susceptibility of low-lying coastal areas to seawater flooding. The impact of climate change is expected to be strong in areas characterized by severe anthropogenic disturbances. In this context, the understanding of the interaction between beach dynamics, human impact, benthic marine habitat and climate forcing appears crucial for scientists and coastal planners to evaluate coastal risks and to develop the best measures to mitigate them. This work aims to improve the knowledge of the short-term effects of storm events on the coastline morphology of natural, microtidal, wave dominated beaches located in the western Mediterranean trough the images processing from the data of video monitoring system at Piscinnì beach (SW Sardinia). The morphodynamic states and the spatial shoreline variability of this natural beach has been assessed in our study, during two years of data acquisition, from August 2013 to August 2015 along a 0.3 km stretch of sandy beach. During this period severe storm events mainly related to south-westerly winds (about 50 km/h on average) were happened. For the evaluation of morphodynamic states we carried out forty-two time-exposure (timex) images from three hundred snapshot, with a frequency of 1Hz, of a single recording interval during the storm events, that allow us to understand the morphology of the shoreface (configuration of bars and troughs). For the spatial shoreline variability, we rectified and georeferenced a single snapshot from the day before, during, and two days after the storm event. These images has been loaded in a GIS software where the shoreline was mapped, and the results showed an erosion and a consequent accretion of the studied beach of about 20 m in two days after the event (SW wind and waves) as a result of the deposition of the Posidonia oceanica beach-cast litter. Another significant result is the clear reconfiguration of nearshore bars linked to the wave energy flux, calculated by the Copernicus Marine Environment Monitoring Service. A better knowledge of this morphological response induced by storm events is crucial for coastal managers to define beach management plans (for example beach cleaning practice), to prevent coastal risk and to understand the importance of seagrass berm deposition in the formation of natural Mediterranean beaches.