Sensitivity of Italian dams' flood mitigation capacity to the combined effect of morphological and climatological factors

The management of reservoirs during flood events has been widely investigated to support real-time gates operation. However, there is still an insufficient elaboration of the assessment of average peak flow mitigation of dams to be used, for instance, in flood frequency analyses. Here the “natural” flood attenuation potential of 265 large reservoirs all over Italy is devised, in terms of the development of a Mitigation Efficiency Ranking (MER) based on just a few basin and dam essential factors. Simplified, yet rigorous and homogeneous assessment of MER can be used to prioritise the implementation of Dam Emergency Plans in Italy and to support similar initiatives worldwide. To maintain homogeneity in such a wide area, standardized hydrograph shapes are used and index-flood from the rational method is adopted as the incoming peak value, enhancing the results of a recent analysis of all Italian rainfall extremes. The attenuation index is computed by solving the differential equation of lakes. Twenty-four different design floods were derived adopting only two hydrograph shapes and minimal parameter options, i.e., the basin runoff coefficient, the time of concentration and the parameters of the Intensity-Duration-Frequency (IDF) curve. The MER results for the 265 dammed watersheds in all the tested configurations demonstrate to be strongly sensitive to the assumptions on the time of concentration and to some rainfall features, while, for instance, the hydrograph shape seems to exert much less influence on the ranking outcome. This analysis will be part of the research framework of the RETURN Extended Partnership Project.