A 2D hydrodynamic (labeled as CAR) model has been proposed in a rectangular Cartesian coordinate system with two axes within the horizontal plane and one axis along the vertical direction (global coordinates), considering the effects of bed slope on both pressure distribution and bed shear stresses. The CAR model satisfactorily reproduces the analytical solutions of dam-break flow over a steep slope, while the traditional Saint-Venant Equations (labeled as SVE) significantly overestimate the flow velocity. For flood events with long duration and large mean slope, the CAR and the SVE models present distinguishable discrepancies. Therefore, the proposed CAR model is recommended for applications to real floods for its facility of extending from 1D to 2D version and ability to model shallow-water flows on steep slopes.

Flash flooding is one of the most severe natural hazards and commonly occurs in mountainous and hilly areas. Due to the rapid onset of flash floods, early warnings are critical for disaster mitigation and adaptation. In this paper, a flash flood warning scheme is proposed based on hydrodynamic modelling and critical rainfall. Hydrodynamic modelling considers different rainfall and initial soil moisture conditions. The critical rainfall is calculated from the critical hazard, which is based on the flood flow depth and velocity. After the critical rainfall is calculated for each cell in the catchment, a critical rainfall database is built for flash flood warning. Finally, a case study is presented to show the operating procedure of the new flash flood warning scheme.

Shallow water hydro‐sediment‐morphodynamic (SHSM) models have been applied increasingly widely in hydraulic engineering and geomorphological studies over the past few decades. Analytical and approximate solutions are usually sought to verify such models and therefore confirm their credibility. Dam‐break flows are often evoked because such flows normally feature shock waves and contact discontinuities that warrant refined numerical schemes to solve. While analytical and approximate solutions to clear‐water dam‐break flows have been available for some time, such solutions are rare for sediment transport in dam‐break flows. Here we aim to derive approximate solutions for ideal dam‐break sediment‐laden flows resulting from the sudden release of a finite volume of frictionless, incompressible water‐sediment mixture on a uniform slope. The approximate solutions are presented for three typical sediment transport scenarios, i.e., pure advection, pure sedimentation, and concurrent entrainment and deposition. Although the cases considered in this paper are not real, the approximate solutions derived facilitate suitable benchmark tests for evaluating SHSM models, especially presently when shock waves can be numerically resolved accurately with a suite of finite volume methods, while the accuracy of the numerical solutions of contact discontinuities in sediment transport remains generally poorer.

As different from traditional large dams, the hydraulic lifting dam is a kind of low-head movable weir, which can be partly lifted to impede water while the rest part of the weir collapsed to surpass water, resulting in a rather complicated terrain. Therefore, the flow structure around a hydraulic lifting dam might become complex and highly three-dimensional (3D). Generally, depth-averaged two-dimensional (2D) models are employed in the prediction of riverine morphodynamic processes. However, in the vicinity of a hydraulic lifting dam, the 2D models not only lose the turbulence details, but also neglect the impacts of turbulence on sediment transport and hence bed deformation. Here, a comparison study is conducted by using a 2D and a 3D model, respectively. The 2D model is a validated depth-averaged hydro-sediment-morphodynamic model using Finite Volume Method on unstructured meshes. The 3D model adopts a Reynolds-averaged Navier-Stokes (RANS) based turbulence model or a delay detached eddy simulation (DDES) model under the framework of OpenFOAM. The results show that the flow details, which cannot be reproduced by a 2D model, have a great potential of modifying the morphodynamic processes, so a 3D model is desperately required for resolving flow structure as well as sediment transport and morphological changes in the vicinity of a hydraulic lifting dam.