Caratterizzazione morfodinamica della spiaggia del Poetto

The impact of storms on a sandy coast can drastically modify the geomorphological aspect of beaches, including along the coastal zone where beach front intense human activities cause coastal damage, as well as civil protection issues. This factor is particularly relevant along urban beaches, where managing coastal erosion and maintaining beaches are the most important forms of defence against flooding and storms. In Sardinia (western Mediterranean), the most important urban beach, Poetto, is a wide, semi-enclosed beach that is about 8 km in length and fronts the city of Cagliari. Poetto Beach is a wave-dominated urbanized sandy beach that is characterized by an inner shelf with large seagrass (Posidonia oceanica) meadows that are mainly developed on the eastern side of the submerged beach. The aim of this study is to investigate the morphodynamic behaviour of a Mediterranean urban beach using a multidisciplinary approach that includes remote sensing, field surveys and numerical models. In particular, the use of video monitoring techniques and numerical modelling provides a low cost and very reproducible methodology for: evaluating urban beach processes, including the effects of storms and human stressors; and helping local managers to properly manage the beach space. Wave data, beach profiling, sediment sampling and analyses, low-cost video monitoring techniques and numerical modelling were used to investigate the beach dynamics. A multidisciplinary methodology coupling wave data, sediment sampling and analyses, beach profiling, video monitoring techniques and numerical modelling was used to investigate the Poetto Beach dynamics. On the basis of the data obtained it was possible to apply the morphodynamic classification method of Short (1999). The classification is based on the dimensionless fall velocity Ω. The climate data (wave and wind) and morphodynamic and sedimentological characteristics of the study area were utilized to set up the numerical model. Both the Delft3D-FLOW (Lesser et al., 2004) and Delft3D-WAVE models were used to simulate the hydrodynamics and waves forcing on to Poetto Beach. The main hydrodynamic scenario identified in the area of Poetto Beach was simulated. The results derived from the wave data and sediment and beach profile analyses were coupled with a video monitoring analysis to classify Poetto Beach’s morphodynamic state. The morphodynamic classification results (Short, 1999) are compatible with morphologies detected with a coastal video monitoring system. The numerical simulation (Delft3D) showed good agreement with the field data and video image analyses for the distribution and direction of the rip and longshore currents. Finally, this study highlighted that the application of a low cost and easily reproducible methodology (video monitoring) can be very useful for investigating the dynamics of an urban beach, and can provide a helpful tool for beach managers to plan how to prevent and minimize the effects of storms and flooding.