This work aims to assess the role played by a beach berm, reinforced by the accumulation of reed and seagrass wracks, on coastal protection against storm-induced floodings. A huge depositional event, mostly consisting of Arundo donax reeds from nearby river systems and Posidonia oceanica wracks, happened in December 2019 in Poetto beach (southern Sardinia, western Mediterranean). Following the concerns that this event raised among local tourism service providers, the municipal authorities decided to remove the reed wracks. In support of coastal management, a scientific inquiry was commissioned to the Coastal and Marine Geomorphology Group (CMGG), belonging to the Department of Chemical and Geological Sciences of the University of Cagliari (Italy) for the assessment of the berm processes before the removal of the reed wracks. Within the five months between the reed deposition and removal, a video monitoring system collected runup and flooding data during storm wave conditions. These data were integrated by five topographic, three bathymetric and two drone surveys. The presence of the reeds intertwined with seagrass wracks, seems to strengthen the berm, making it more resilient to wave action, eventually offering additional protection against overwash and flooding. These results are supported by a numerical model chain, with the nesting of a phase-resolving model into a phase-averaged model, providing a characterization of wave runup dynamics.

Assessing the role of reed and seagrass wracks in coastal protection. An example with numerical modelling integrated with videomonitoring system data in a southern Sardinia beach

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.

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


<i>**Session Chairs: **Clara Armaroli (Istituto Universitario di Studi Superiori (IUSS)), Renata Archetti (University of Bologna), Duccio Bertoni (University of Pisa), Simone Simeone (CNR - IAS)</i><br><br>


S15. Coastal erosion

technical paper

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With the motto "Geology Without Borders" this event aims to promote Earth Sciences as a scientific discipline projected into the future, beyond geographical, political and disciplinary boundaries, to better understand the interior of Planet Earth and the structure of the subsurface, defend society from dangerous geological events, better understand climatic variability, plan the use of geo-resources in an ethical way and respecting the environment.


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Earth Sciences should be understood not only as necessary for a better understanding of the interior of the planet Earth, but also as a defense of society from dangerous geological events, for the understanding of climatic variations, for the planning and use of georesources in a ethical and respecting and protecting the environment.

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Assessing the role of reed and seagrass wracks in coastal protection. An example with numerical modelling integrated with videomonitoring system data in a southern Sardinia beach

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

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