Abstract
Numerical models provide considerable assistance in the investigation of complicated processes in natural rivers. In the present study, a physics-based two-dimensional model has been developed to simulate the braiding processes and morphodynamic changes in braided rivers. The model applies the basic hydrodynamic and sediment transport principles with bed morphology deformation and a TVD (Total Variation Diminishing) scheme to predict trans-critical flows and bed morphology deformation. The non-equilibrium transport process of graded bed load sediment is simulated, with non-uniform sediments, secondary flows, and sheltering effects being included. A multiple bed layer technique is adopted to represent the vertical sediment sorting process. The model has been applied to simulate the bed evolution process in an experimental river with bed load transport. Comparisons between the experimental river and predicted river are analysed, including their pattern evolution processes, important braiding phenomena, and statistical characteristics. Avulsion activities have been found in the braiding evolution process, representing the primary ways in which channels form and disappear in braided rivers. The increases in the active braiding intensity and total braiding intensity show similar trends to those observed in the experimental river. Statistical methods are applied to assess the scale-invariant topographic properties of the simulated river and real rivers. The model demonstrated its potential to predict the morphodynamics in natural rivers.
Highlights
Braided rivers are a distinctive river morphology with high flow energy and frequent channel changes
Braiding is one kind of fluvial pattern in these rivers characterized by complex dynamics, in which water and sediment flow are divided into multiple branches, joining and splitting at the nodes and shifting continuously in the floodplain [1]
The understanding of morphodynamics in braided rivers is especially important for managing engineering problems such as flood management, riverbank erosion, sedimentation in reservoirs and navigable waterways, and the design and construction of artificial channels and bridges
Summary
Braided rivers are a distinctive river morphology with high flow energy and frequent channel changes. Rivers) [18], depth-integrated Delft3D [14,19], and 2-D morphodynamic models [20,21] have been applied to simulate large sand-bed braided rivers and have produced morphological units with evolution mechanisms, the characteristic morphology of compound bars, and channels and statistical characteristics that are similar to those of natural sand-bed rivers Their development and application are still in an early stage [22], and quantitative analyses and comparisons between simulated and real rivers are still insufficient [14] especially for braided rivers dominated by bed-load sediment transport. The study aims to investigate the river morphodynamic processes and activities, analyse the statistical characteristics, compare them with the experimental river and natural rivers, and discuss the potential of the model for representing the morphodynamic processes in real rivers
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