Definizione di scenari e analisi delle condizioni di rischio geologico-idraulico derivanti da una possibile occlusione d'alveo per frana nel T. Reggia (bacino del Tevere--Umbria settentrionale)

Landslide dams form when a landslide reaches the bottom of a river valley causing the blockage (partial or total) of the water course. The first effect of such a dam is the formation of a backwater lake and the submersion of the areas upstream, while the possibility of a sudden dam collapse, with a quick release of the impounded waters, produces a high flood risk to the downstream areas. In this work we have carried out an analysis of a dormant landslide situated on the left slope of Reggia Creek, 800 m upstream of Umbertide (Northern Umbria): the huge extension of the area involved in the landslide (85000 m2 ) and the peculiarities of the river valley makes highly probable the blockage of the river, as a consequence of the landslide reactivation. The procedure proposed consists of quantifying the volume of the displaced material through a slope stability analysis, defining dam geometry in conformity with the involved volume, simulating the dam failure through the "BREACH" code, verifying the hydraulic risks both in the downstream and upstream areas. This method, clearly schematic because of the congenital phenomena complexity, is based on the evaluation of a reduced number of variables and, for this reason, it can be particularly suitable for a preliminary characterization of the risk condition.