Flood hazard assessment due to dam breaching considering river morphodynamics

Abstract The failure of a dam is a catastrophic event, which is expected to induce drastic changes to the downstream bed morphology. However, knowledge about channel response due to dam-breach flood wave and its impact on flood hydrodynamics and hazard assessment is still poor. Therefore, we studied the river morphodynamics associated with dam-breach floods, in order to understand the possible extent and distribution of the erosion depths and deposition heights, as well as the consequences of these changes on the flood hydrodynamics and, above all, on the hazard assessment. In this work, these impacts were investigated by simulating the hypothetical failure of a real embankment dam, using a simplified physically based model for the computation of the dam-breach hydrograph, and a two-dimensional morphodynamic model for the downstream wave propagation. To account for some of the uncertainties related to both models, two breach shape scenarios and three mobile bed configurations were considered. It was found that bed erodibility affected the flood hazard much more than the breach shape. Furthermore, the mobile bed configuration significantly affected river morphology in the narrow and steep part of the river, where both erosion depths and deposition heights were very high, while bed elevation changes in the downstream plain part of the river were significantly less. Finally, consideration of river morphodynamics in dam-breach flood wave propagation has been shown to shorten the arrival times of the flood wave and lead to more intense flood hazard due to a remarkable increase in the unit discharge.