Eco-geomorphological and hydrodynamic analysis of Mediterranean microtidal beaches in Southern Sardinia

Global climate change is increasingly having an impact on the marine and coastal environment, with rising sea levels and a growing frequency and intensity of extreme weather and marine events. These phenomena threaten the stability of coastal systems, accelerating beach erosion, damaging infrastructure and exposing ecosystems and economic activities to significant risks. In this context, integrated coastal management strategies become essential, as they play a key role in predicting, mitigating and adapting to potential impacts on coastal areas. Therefore, ensuring the long-term resilience of coastal systems requires strategic planning grounded in robust scientific knowledge. This thesis carries out a multidisciplinary study on the geomorphological, morphometric, hydrodynamic and ecological aspects of the microtidal beaches of Southern Sardinia, Italy (Western Mediterranean Sea). Given the geomorphological variability along this coastal stretch, as well as the differing wave conditions and exposures, an initial morphometric analysis and classification was carried out on 79 microtidal beaches (natural or influenced by the presence of artificial structures), providing an estimation of their level of embaymentisation and the prevailing hydrodynamic circulation in the surf zone. In addition, the spatio-temporal variation of the shorelines was investigated to estimate the accretion and retreat rates for each identified beach. The results highlighted that, over approximately 70 years, changes in shoreline position reflect dynamics associated with the levels of naturalness or human modification of the beach. In fact, some beaches exhibited more pronounced shoreline evolution trends, probably due in part to possible human influence (e.g., construction of artificial structures, damage to the Posidonia oceanica meadow, and others). From a hydrodynamic perspective, a further contribution of this thesis was the numerical modelling of currents circulation within the surf zone of embayed beaches (a common beach type along the studied coastlines). Numerical modelling highlighted that wind forcing on the sea surface plays a crucial role in the formation and location of rip currents, as well as in determining their intensity and their longshore and cross-shore extent. Finally, considering the widespread presence of Posidonia oceanica meadow along the entire coastline, the role of beach-cast in coastal flooding events was investigated. For this purpose, a coastal video monitoring system, located on a microtidal urban beach (Poetto), and numerical modelling were used to analyse two storm events and their effects on morphodynamic processes, such as the interaction between wave motion and beach-cast (mainly composed of Posidonia oceanica and Arundo donax remains).