Author(s): Zhixian Cao; Zhiyuan Yue; Xin Li; Tao Che
Linked Author(s): Xin Li
Keywords: Mathematical modelling; Shallow water hydrodynamics; Sediment transport; Dambreak flood; Glacier-lake outburst flood (GLOF); Debris flow
Abstract: A two-dimensional coupled mathematical model is developed for free surface flow, sediment transport and morphological evolution. The governing equations of the model comprise the complete shallow water hydrodynamic equations closed with Manning roughness for boundary resistance and empirical relationships for sediment exchange with erodible bed. The second-order Total-Variation-Diminishing version of the WeightedAverage-Flux method, along with the HLLC approximate Riemann Solver, is adapted to solve the governing equations, which can properly resolve shock waves and contact discontinuities. Of verified accuracy for idealized cases with known analytical and independent numerical solutions, the model is applied to the pilot study of the flooding due to sudden outburst of a real glacial-lake. Numerical modelling is carried out respectively with erodible and nonerodible beds. In the case of erodible bed, a heavily concentrated flood wave front is built up, which propagates appreciably faster than the clear-water flood wave front over non-erodible bed. This is because the gravitational role on the steep channel is enhanced due to sediment, and uniformly overwhelms over the effect of bed deformation, in contrast to the case with mild bed slope. The fast propagation of the subaerial debris flood wave front over erodible bed phenomenally echoes that for subaqueous debris flow, and yet it remains to be identified if it features a mechanism similar to hydroplaning for subaqueous debris flow and thus reduced resistance that should be incorporated in the modelling. The present model delivers a useful framework for quantitative analysis of a hierarchy of flood processes, which may involve intense sediment transport and rapid morphological evolution.
Year: 2007