Developing Fragility Curves for Overtopping-Caused Dam Breaching

The increasing frequency of intense rainfall heightens the susceptibility of earthen embankments to breaching by overflow. Deterministic models for assessing dam breaches often overlook uncertainties in applied and critical shear stresses. This study introduces a fragility framework that addresses these uncertainties, demonstrated using a hypothetical case of dam breach initiation. Uncertainty in applied shear stress arises from hydraulic parameters, such as the weir coefficient and Manning’s roughness coefficient, while critical shear stress uncertainty is influenced by sediment density. Sediment transport principles are used to establish a probabilistic breach initiation criterion, with hydraulic analysis linking overflow characteristics to applied shear stress. Hydraulic parameters and material properties are treated as random variables, with potential values generated using probability density functions. Monte Carlo simulations are conducted to capture a wide range of applied and critical shear stress combinations. Results showed that for a fixed discharge scenario, an increase in the weir coefficient led to higher probabilities of breach initiation by reducing overtopping depths and accelerating flow, thereby increasing applied shear stress. Similarly, an increase in Manning’s roughness coefficient resulted in a higher applied shear stress, thus increasing the probability of breach initiation. Conversely, higher sediment density enhanced erosion resistance and decreased breach initiation probability. Fragility curves are developed to represent breach initiation probabilities across wide ranges of applied shear stresses and overtopping depths. The proposed framework offers the potential to improve dam safety practices by predicting breach initiation.