Landslide dam failure and flood hydraulics. Part II: coupled mathematical modelling

A coupled 2D mathematical modelling study of landslide dam failure and flood is presented, complementing our experimental investigation presented in the companion paper. The model is built upon the shallow water hydrodynamic equations. The governing equations are numerically solved using the total-variation-diminishing version of the second-order weighted-average-flux method along with the HLLC (Harten, Lax and van Leer with Contact wave restored) approximate Riemann solver. Two parameters related to bed-load sediment transport and critical slope stability are calibrated using the measured stage hydrographs from two runs of the flume experiments. The calibrated model is then applied to other independent runs of the experiments featuring different inflow discharges, dam geometry, dam composition and initial breach dimensions. It is found to be able to satisfactorily reproduce the measured stage hydrographs and the widening of initial breach. The experimental observation of the prime role of the inflow discharge and initial breach in dictating the dam failure process and flood is unequivocally resolved, along with the impacts of dam geometry as well the content of cohesive clay and gravel in the dam. Interestingly, the downstream peak discharge and stage of the flood are substantially reduced by initial breach, which clearly exemplifies its role in modulating the flooding.