Modeling Breach Evolution in Noncohesive Earthen Dams by Overtopping

A two-dimensional, finite-difference numerical model is developed to simulate the breach evolution of noncohesive optimally compacted earthen dams. The main feature of the model is the inclusion of a source term in the sediment mass conservation equation that explicitly describes breach widening due to mass slumping of the breach sides. Model results are compared against experimental measurements of time variation of breach width and depth, breach discharge, and reservoir water depth for embankments of different sizes, sediment median grain sizes, inflow discharges, and reservoir volumes. The numerical model successfully captures the two stages of failure, namely, prewidening and widening. Then, the model is applied to simulate the overtopping failure of an earthen dam that occurred due to Hurricane Joaquin in October 2015 in Lexington, South Carolina. A sensitivity analysis is conducted to assess the effect of the main model parameters on the prediction of breach evolution. This analysis shows that breaching is affected more by tailwater depth than the soil failure angle and inlet discharge.