Numerical prediction of the drying-wetting process in a river levee and floodplain

One third of the economic losses due to natural disasters in the last century has been caused by floods. Today the flood hazard is increasing due to more frequent extreme hydrological events, caused by climate change, and to the land use change and urbanization, that reduce the water storage capacity of the subsoil and the floodplain areas. An appropriate planning of river levees and floodplains is required to protect inhabited areas and infrastructures. At the same time, an efficient management, assisted by effective monitoring and prediction tools, ensures the performance of the defence systems. In this context, a land reprofiling was designed for river Secchia in Northern Italy, to widen the natural floodplain. In the paper the response of the new system to flood events is assessed by finite element analyses able to describe the soil-water-atmosphere interaction. The reliability of the numerical prediction relies on a proper description of both the hydraulic behaviour of the unsaturated soil, i.e. the water retention curve and the permeability function, and the external load history, established from the hydraulic and atmospheric boundary conditions. Indirect methods for the estimation of the Soil Water Retention Curve may involve significant limits if not combined with a laboratory information on the soil nature and state. Moreover, the numerical results show that the drying-wetting process is highly dependent on the initial saturation conditions of the subsoil, thus making it essential to simulate a sufficiently long load history.