Hydro-sedimentological modelling of the ’96 Versilia extreme flood

The mitigation of the risk connected with sediment dynamic and not only with flood propagation is an important purpose of the actual hydrological-hydraulic research. The authors propose here a study of the spatio-temporal heterogeneity of sediment routing processes and his interactions with rainfall and catchment characteristics. The aim is to quantify the amount of the sediment load and to characterize the dynamic of the mud wave, reproducing the sedigraph, during an extreme event. To achieve this task, a conceptual sediment transport model, based on linear reservoir cascades, coupled with sediment deposition and degradation, has been applied. The evaluation of the sediment transport and the hydro-sedimentological dynamic has been performed for the disastrous flash floods on 19 June 1996 which occurred in the Versilia mountain river basin of the Apuanian Alps in Central Italy. The event has recorded exceptional amounts of rainfall (i.e. peaks of more than 100 mm/hour), similar to the most intense tropical storm. The hydro-geological consequences of the flood have strongly impacted the infrastructures and the population, several causalities have been recorded. A complete analysis of the modeling results is illustrated and a first attempt to describe the evolution of the sediment routing event has been achieved. The sediment routing assessment,especially during the most intense events, is important to predict the amount of the soil material involved and to define different protection strategies. A better knowledge of this phenomenon is very useful to undertake the appropriate response measures.