Flow structure around a hydraulic lifting dam and its implication for sediment transport and morphological changes

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.