Modelling of hyperconcentrated flood routing and channel evolution in the lower Weihe River

Hyperconcentrated floods with sediment concentrations higher than 300 kg/m3 often occur in the lower Weihe River. These floods result in extremely high water levels and severe channel evolution and may pose a threat to people and property in certain reaches. Therefore, it is necessary to accurately simulate hyperconcentrated flood routing processes and the associated channel evolution in the lower Weihe River. A one-dimensional (1D) coupled morphodynamic model was developed to simulate the 1978 hyperconcentrated flood in the lower reach between Lintong and Huayin, and the effects of sediment concentration and bed evolution on flood routing were considered in this model. The calculated hydrographs of the discharge and sediment concentration agreed well with the data observed at hydrometric sections, with corresponding correlation coefficients higher than 0.93. The calculated channel evolution amount in the lower Weihe River was 0.14 × 108 t based on the 1D numerical model, which was lower than the observed value (0.22 × 108 t). In addition, we investigated the effects of the thickness of the active layer and the size distribution of the incoming suspended load on the model results. The maximum sediment concentrations at hydrometric sections and the cumulative channel evolution volume of the study reach increased with an increasing active layer thickness, and with a decreasing mean median diameter of the suspended load. Two metres is a reasonable active layer thickness for simulations of hyperconcentrated flood events in the lower Weihe River.