Author(s): Yufang Ni; Wei Huang; Duan Chen
Linked Author(s): Duan Chen, Wei Po Huang
Keywords: Phosphorus transport modelling cascade movable weirs low-head dams bed deformation
Abstract: Last decades have witnessed wide applications of cascade low-head movable weirs for water storage and ecological restoration. Specifically, fifteen hydraulic lifting dams, a type of movable weir that can rotate about the river bottom, were constructed in cascade in the middle Fen River in China. These weirs disturb the prior equilibrium formed between fluvial flow, sediment transport and morphology, thereby modifying the processes of contaminant transport, all of which affect the riverine ecology. As the fluvial flow, sediment transport, bed deformation and contaminant transport are strongly coupled, especially after the construction and operation of hydraulic structures, a computationally efficient and fully coupled 2D model for sediment-borne contaminant transport is proposed here, with the effects of bed deformation on dissolved and adsorbed contaminant incorporated. Computational results show that collapse of all the dams (CA) results in an overall reduction of total amount of phosphorus both in the sediment-laden flow and saturated bed in the study river reach and a relatively high concentration of phosphorus in the sediment-laden flow compared with the scenarios under operation of all the dams (OA) and operation of the dams in the main channel only (OM). Operation of all the dams leads to an overall increase of total amount of phosphorus in the study river reach and a relatively low concentration of phosphorus compared with the other two scenarios. When only the dams in the main channel operate, the total amount of phosphorus in the study river reach decreases slightly, and phosphorus concentration in the sediment-laden flow is lower than that in the CA while higher than that in the OA modes. The variations of total amount of phosphorus in the sub-reaches are closely related to the bed deformation, i. e., the bed deposition tends to trap the adsorbed phosphorus over bed and the dissolved phosphorus in the pore of the bed, emphasizing the necessity of consideration of bed deformation impacts on the phosphorus transport modelling. These findings have important implications for the decision making of operation schemes of the cascade low-head movable weirs.
Year: 2025