Towards the assessment of the flood attenuation potential of italian dams: first steps and sensitivity to basic model features

The effect of reservoirs on downstream flood regime has been largely investigated in the literature worldwide, but there is, to date, still an insufficient elaboration on the “natural” flood peak mitigation exerted by dams. In this work, the attenuation potential of flood peaks by the main Italian reservoirs is devised, based on a small number of objective factors that concur to the implementation of a ranking method. This can be used to select priorities in the implementation of Dam Emergency Plans in Italy, according to a legislation act of 2004. The attenuation potential is estimated here by means of a very simple procedure, that does not require the definition a priori of a hydrograph shape and the mitigation effect is computed assuming that the dam operates as a linear reservoir, meaning that the stored volume and the outflow are linked by a linear relationship. A realistic average annual design flood peak has been estimated for each basin upstream the dams through the rational method, using for the first time the results of a countrywide analysis of rainfall extremes. The study has been carried out using 265 dams and related watersheds throughout Italy. Results were examined in terms of both magnitude and order position of the attenuation coefficient: a strong sensitivity to the time of concentration is apparent.