Influence of the Uncertainty in the Dam‐Breach Hydrograph on the Flood Hazard Assessment in a Valley Area

ABSTRACT The reliability of flood event simulations is a crucial aspect in terms of saving lives. The worst flood scenarios derive from possible dam failures. For earthen dams, the breaching mechanism, triggered by overtopping or piping, is affected by several modelling uncertainties, which propagate downstream and may influence flood hazard mapping. In this work, the hypothetical failure of a real earthen dam was simulated. Two hypothetical dam‐breach hydrographs were computed using a simplified physically based model and propagated downstream, showing that the peak discharge undergoes an attenuation process which causes the differences between the two scenarios to progressively decrease with increasing distance from the dam. Beyond a certain distance, the attenuation of these differences is such that a large portion of the flooded area falls into the same hazard classes, even though the hydraulic parameters of the two different scenarios do not completely coincide. Therefore, this result is important for its practical implications for hazard assessment. For the analysed case study, uncertainties in the dam‐breach hydrograph had little influence in terms of downstream hazard mapping, because most of the exposed area was located beyond this distance. In similar cases, uncertainties in the hydrograph peak have a limited effect on hazard assessment.