Author(s): Alessandro Masoero; Daniele Ganora; Pierluigi Claps; Alberto Petaccia
Linked Author(s): Claps Pierluigi
Keywords: Flood Frequency Curves; Reservoirs; Flood Attenuation; Hydrologic Safety
Abstract: Along with other risk mitigation measures, artificial flood storage has been considered as a smart way to tackle the problem, since it help reducing flood peaks. Dams embedded into the river network are able to modulate the flood wave propagation, given their’natural’flood attenuation potential driven by the portion of volume available above the spillway crest level. Usually the‘natural’effects that these dams exercise on the flood peak values is not considered when assessing the Flood Frequency Curves (FFCs) of the river reaches downstream. This can become a significant issue in areas where the presence of relatively large reservoirs must be taken into account to provide a correct Flood Hazard estimation. In this study we first use a regional statistical method for flood frequency estimation to assess the‘undisturbed’FFCs at the cross section of several dams in the North West of Italy. The procedure adopted here does not require the definition a priori of an analytic form of the FFC, because the regionalization applies on the three first L-moments, that are allowed to smoothly varying in the space. Then, we correct the‘original’FFCs taking into account the presence of reservoirs. The correction proposed is based on the assessment of the reservoir attenuation effect that has been computed, on all dams, with two different methods: i) by using a simplified and constant attenuation index named SFA (Synthetic Flood Attenuation) and ii) by solving numerically the continuity equation to compute the maximum outgoing peak discharge. Results are examined and compared, first to assess if a single index can be useful to this goal and, secondly, to look for factors responsible of the variability of the actual attenuation effect with the return period. The study has been carried out using all 57 large artificial reservoirs located in the Northwestern part of Italy, for which a comprehensive set of hydrological and structural data has been collected, also with the help of the Italian Dams Authority (Registro Italiano Dighe, RID).
Year: 2014