Evolution Mechanism of Meandering River Downstream Gigantic Hydraulic Project I: Hydrodynamic Models and Verification

Abstract

The evolution mechanism of meandering river is one of essential references to predict the evolution disciplines of meandering river. Jingjiang curved reaches are the typical meandering river; more specifically, they are located downstream the gigantic hydraulic project named Three Gorge Project (TGP). Because the incoming water and sediment condition have been changed by the gigantic project, the evolution behavior of Jingjiang curved reaches changes a lot, making the evolution behavior unpredictable. However, traditional two-dimensional (2D) hydrodynamic model could not simulate the transportation characteristics of unbalanced and suspended sediment, leading the predict results of 2D model are far from the measured data. This paper presents a theoretical and numerical approach that explores the evolution mechanism of meandering river downstream gigantic hydraulic project. Firstly, the evolution behavior and evolution disciplines of Jingjiang curved reaches were classified before and after the hydraulic project implement respectively. Secondly, a 2D hydrodynamic model was set up and verified according to the measured data. And then a superior three-dimensional (3D) numerical model, whose boundary conditions were simulated by the results of the 2D numerical model, considering the unbalanced water and sediment transportation properties, was developed and verified by the measured data. Research results show that the 2D model displayed a reasonable accuracy in predicting the water level, branch diversion ratio, and flow velocity; the 3D model displayed a better accuracy in predicting the water lever, vertical flow velocity, longitudinal flow velocity, sediment concentration, and sediment variable quantity. Both 2D and 3D models could be applied to study the evolution mechanism of meandering river; especially the proposed 3D model considering the sediment transport in longitudinal, transverse, and vertical directions will improve the accuracy of behavior prediction and will help decision-making for the river regulation.

A Numerical Expedition through the Mathematical Representation of Complex Braided Morphometry—A Case Study of Brahmaputra River in India

“…Several attempts ha been made to simulate the realistic flow field, including transverse components in co plex geometry like bends and curves [5,[7][8][9][10]. More recently, the hydrodynamic mo has been used to represent the evolution mechanism of a meandering river [11]. Howev the assessment of flow fields in braided rivers with 'secondary flow correction' in comp Two sets of Survey of India toposheets (1914 and 1975) and a set of IRS satellite photos encompassed the cloud-free time to study a portion of the Brahmaputra's reach [2].…”

“…After computing → T φ and → T ψ , one can compute α from Equation (10b) and ∆M n from Equation (11). Using the value of ∆S 1 from Equation ( 15), ∆N n is computed.…”

Analysis of the evolution pattern and causes of downstream gigantic hydraulic projects

“…The previous paper (Liu et al 2018) has studied that the evolution behaviors of the Jingjiang reach can be divided into two types. In Type-A, before TGR impoundment, the concave bank was scoured, while the convex bank was deposited; after the impoundment, the reverse happened, namely, the concave bank was deposited, while the convex bank was scoured.…”

“…The setup and verification method of the numerical model were provided by the previous paper (Liu et al 2018), and then the model was used to analyze the change disciplines of the mainstream line, the flow velocity and the shear stress of the river. The measured topographic data of February 2012 were chosen as the original boundary condition of the 2D numerical model.…”

“…Under natural conditions in a CR, the main stream will pass along the river bank during a low water period, while going downstream directly during a high water period. In the long term, the concave bank will be scoured, while convex bank will be deposited (Liu et al 2018). The Jingjiang CR mainly followed the evolution disciplines of concave bank scouring and convex bank depositing (Yu 2006;Jia et al 2010;Lu et al 2011).…”