Modelling of hyperconcentrated flow in steep-sloped channels

Abstract

An unsteady two-dimensional depth-averaged numerical model for hyperconcentrated flows in steep-sloped alluvial channels is developed and applied to the Zhuoshui River in Central Taiwan. In this model, the suspended load and bed load are both included to reproduce actual sediment transport characteristics of steep-sloped channels in the chosen study river reaches. A rheological relationship for Bingham fluid and the formula for the sediment carrying capacity, established through laboratory experiments, are used to describe the hyperconcentrated flow behaviour in the model. At peak discharge during Typhoon Morakot, bed shear stress from the hyperconcentrated flow model can be 150% larger than that from the clear water model. According to the simulation for Tung-Pu-Rey Creek, an upstream tributary of Zhuoshui River, the temporal evolution of bed changes obtained from the model can be used to provide plausible explanations for the reasons behind levee failure during Typhoon Toraji.