Flood hazard evaluation downstream of Ceppo Morelli dam.

Ceppo Morelli dam is a particular case study since the sediments transport and the periodic interventions carried out by dam owners in order to restore the dam's initial conditions continuously alter the storage capacity of the reservoir, leading to rising needs for periodic flood hazard assessments. This report describes the development of 1D and 2D hydrodynamic models for hazard assessment, obtained through DEM generated cross sections of the river downstream Ceppo Morelli dam, by considering not only dam-break induced floods, but also synthetic hydrographs given by a hydrological model. ORSADEM 1D was used to simulate a 1000-years return period storm over a length of 21km downstream of the dam and the long duration of the events has led to the elimination of flood routing, resulting in a very peculiar behaviour of the river. Two different hydrodynamic models were considered for the 2D simulations: HEC-RAS and ORSA2D were used to simulate the dam break event for a smaller reach of 6km, using data from a recent bathymetric survey for an accurate storage estimation, by considering an instantaneous dam break. A comparative analysis was carried out starting from the results given by each model and results obtained through a previous 1D simulations of the same dam, with an equal stored volume that dates back to 2015, with the aim of evaluating the reliability of 1D models to solve dam break problems. It was found out that hydraulic results varied significantly for each model, but the flood hazard seemed to be equivalent for certain water depth levels, due to the particular morphology of Anzasca valley.