Maritime and geotechnical modeling of the stability of coastal dikes in the Po river Delta lagoons.

The Po Delta region is characterized by a great value from an environmental and economic point of view but also by a huge hydrogeological fragility and a high hydraulic risk. These will increase due to the effects of climate change, the consequent sea level rise and the increase in the frequency with which extreme events occur. This fragility affects the development of the area, with the possible loss of landscape and economic resources such as fishing, shellfish farming and tourism. This work aims to analyze the coastal dikes stability in the Po River Delta region, studying the main meteo-marine forcings and the geotechnical characteristics, to identify the critical sections, in a current scenario (2020) and in a future one (2070). The data used for this purpose regards the mean sea level rise, the wave set-up, the subsidence, and the geotechnical characteristics. The data related to the mean sea level rise come from the studies conducted by the IPCC, updated to the latest report provided (SROCC, 2019). While the geotechnical data are referred to the boreholes conducted by the AIPO in 2021. Thanks to the in situ and laboratory tests it was possible to characterize the soil and starting from these data perform the geotechnical modelling in PLAXIS 2D. The result is the identification of the most critical areas but also the possible design interventions that must consider a series of elements, such as hydraulic-maritime (tidal level, wave run-up and overflow), geotechnical (seepage, piping and erosion) and socio-economic (maintenance and costs) aspects. The need to raise the coastal dikes is also demonstrated considering the effect of subsidence and the sea level rise. This is required to obtain a sufficient freeboard and guarantee a safety condition. It will be necessary also to proceed with a more detailed analysis especially in the lagoons where this has not been done in the past and where the geotechnical safety coefficient is higher than the limit indicated by law.