Depth-Averaged Two-Dimensional Model of Unsteady Flow and Sediment Transport due to Noncohesive Embankment Break/Breaching

Abstract

A depth-averaged two-dimensional model has been developed in this study to simulate the unsteady flow and noncohesive sediment transport due to embankment break and overtopping breaching. The model adopts the generalized shallow-water equations that consider the effects of sediment transport and bed change on the flow, thus leading to coupled calculations of these processes. It computes the non-equilibrium total-load sediment transport and considers the noncohesive embankment slope avalanching. The model solves the governing equations using an explicit finite-volume method on a rectangular grid, with the Harten, Lax and van Leer (HLL) approximate Riemann solver to handle the mixed-regime flows generated by embankment break/breaching and the monotonic upstream scheme for conservation laws (MUSCL) piecewise reconstruction method to reach second-order accuracy in space. It uses a varying time step length that satisfies both the Courant-Friedrichs-Lewy condition and the limitation that the bed change is less than about ten percent of the local flow depth at each time step. Validations using laboratory and field experiments showed that the developed model generally predicts well the embankment-break wave propagation over movable beds, the induced sediment transport and bed changes, and the temporal evolution of noncohesive embankment breach.