Dottorato in INGEGNERIA AMBIENTALE E IDRAULICA

Titolo della tesi: A novel one-line model for long-term evolution of sandy beaches in presence of coastal defence measures

One-line numerical models represent one of the most robust and useful tools to simulate shoreline changes over long time scale (from one year to tens of years). Coastal zones, which have a significant environmental, touristic and economic value, are constantly exposed to natural (e.g. waves, tides, climate change) and human (e.g. over-exploitation by the construction of railways, roads, private buildings too close to the beach) hazards. Thus, for coastal planners is essential knowing and modeling the behaviour of coastal morphodynamics, in order to define effective coastal management strategies. This thesis deals with the description of a novel one-line model, devolped in order to deeply investigate some of the most important coastal mechanisms affecting long-tem shoreline evolution. The model solves the mass conservation equation and the long-shore sediment transport due to wave breaking, under the standard assumptions of one-line models. Firstly, the present research focused on the description and comparison of capabilities and limits of currently available shoreline models. Secondly, following the observations made in the above point, the proposed morfRESTORE model development is illustrated. In the study, particular attention was paid to the offshore/onshore wave transformation model, since the latter influences the breaking wave characteristics, required to estimate the long-shore sediment transport rate. As a matter of fact, several one-line models use internal wave propagation models or coupled with external models, with different levels of complexity (e.g from linear theory to complex wave averaged numerical models). The internal wave transformation model proposed herein is a one-dimensional model that allows to reliably simulate wave propagation across beaches of irregular profile and also in nearshore regions, where wave dissipation cannot be neglected. Special focus was also addressed to the impact of shore-normal coastal structures (e.g. groynes) on the long-shore sand transport. In order to solve this problem, a non-constant cross-shore distribution, which varies according to the forcing wave condition, of the long-shore sediment transport was formulated. Furthermore, some aspects related to the numerical implementation and stability of the model were investigated. A sensitivity analysis was carried out in order to verify the numerical stability and reliability of the model, varying some input parameters. Finally, the comparison between numerical and analytical results demonstrated that the proposed model successfully represents shoreline change both in absence and in presence of shore-normal coastal defence structures. The model was also applied to the coastal stretch of The Circeo National Park (Central Italy, Tyrrhenian Sea). The model demonstrated to be able to reproduce the long-term evolution (sixteen years) of shoreline.