River Levee Overtopping: A Bivariate Methodology for Hydrological Characterization of Overtopping Failure: Fid-Bau Portal

River Levee Overtopping: A Bivariate Methodology for Hydrological Characterization of Overtopping Failure

Isola, Matteo / Caporali, Enrica / Garrote, Luis

This research presents a bivariate methodology for the hydrological characterization of the overtopping failure for an existing river levee. Conventional procedures usually consider only one variable for the hydrologic forcing (peak discharge, $Q$ ). Such an approach might fail if the volume of the hydrograph ( $V$ ) is also significant. The proposed methodology is based on the generation of a set of plausible inflow hydrographs characterized by their peaks and volumes in the $Q - V$ space. The shapes of the hydrographs are classified according to their tendency to produce overtopping, introducing a new index: the Overtopping Hydrograph Shape Index (OHSI). The levees in two river reaches located in Tuscany, Italy, were used as a case study. As a preliminary result, it was found that the hydrographs that produce overtopping failure in both cases lay on a zone in $Q - V$ space delimited by a curve, the Critical Overtopping Flood Hydrograph (COFH) curve. The existence of COFH demonstrates that overtopping failure is not determined by a unique variable ( $Q$ ) but rather by the combination of both $Q$ and $V$ . The limiting case corresponds to a family of hydrographs with varying $Q$ and $V$ values. The COFH allows dividing the $Q - V$ space into two zones, the no-failure zone and the failure zone, that simplify the evaluation of the failure probability for a river levee.