On the Role of Wood and Seagrass Rests in Coastal Flooding Events in Mediterranean Microtidal Beaches

Trogu, D.; Simeone, S.; Usai, A.; Porta, M., and De Muro, S., 2024. On the role of wood and seagrass rests in coastal flooding events in Mediterranean microtidal beaches. In: Phillips, M.R.; Al-Naemi, S., and Duarte, C.M. (eds.), Coastlines under Global Change: Proceedings from the International Coastal Symposium (ICS) 2024 (Doha, Qatar). Journal of Coastal Research, Special Issue No. 113, pp. 115-119. Charlotte (North Carolina), ISSN 0749-0208. In December 2019, following intense rainfall, the riverbeds of the rivers flowing into the Gulf of Cagliari (Sardinia, Italy, western Mediterranean Sea) dumped a large quantity of river reeds attributed to the species Arundo donax (Poaceae) into the sea. The concomitance of a sea storm event acting in the waters of the Gulf of Cagliari transported and allowed the deposition and sedimentation of reeds and other seagrass rests (mostly P. oceanica) on the Poetto beach (an urban microtidal beach located in the Gulf of Cagliari), for an estimated mass of over 85 tonnes. The subsequent lock-down given by the Covid-19 pandemic, and thus the absence of anthropogenic interferences, allowed the almost undisturbed interaction of beach processes with these wood and seagrass rests. This paper will describe the sedimentary structures formed on the berm, generated by the interaction between reeds, Posidonia and sediment. Subsequently, it will be analysed how these sedimentary structures protected the beach from coastal flooding during storm events which were characterised by wave parameters (significant wave height and wave peak period) with greater values than those recorded during other storm events that led to beach inundation. In detail, analyses were carried out comparing the wave data with images acquired by a coastal video monitoring system. However, this storm event caused the reeds to redistribute along the emerged beach, generating new sedimentary structures that, as a result of successive storm events from different directions, became stratified in the beach increasing its permeability. Although the beach cleaning operations often carried out with a removal of vegetal berms, the results of this study highlighted that the non-removal strategies along the foreshore and the backshore can increase the whole beach system resilience and protect the anthropic structures built in and behind the beach.