Modelling the impact of consecutive dry and wet events on levee failure and flooding

Prolonged droughts followed by high river flows can weaken earthen levees before they are hydraulically loaded. Desiccated soils may develop cracks, lower resistance to shear stress and increase susceptibility to concentrated erosion, yet antecedent soil conditions are rarely represented explicitly in flood-risk assessments. This study examines how consecutive dry-wet conditions may affect levee-failure probability and breach-induced flood dynamics. We combine a crack-widening erosion-swelling model with a probabilistic reliability framework and a 1D-2D hydraulic model for a representative reach of the Po River in Italy. The analysis shows that drier antecedent soil conditions increase the probability of failure and shift failure to earlier stages of the flood hydrograph. Earlier failure influences maximum inundation to a limited extent, but it accelerates flood propagation and reduces the available warning time by several hours. The scenario-based results highlight the need to account for antecedent drought effects in dynamic flood-risk management.