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- Title
Quantitative Analysis of Grain Orientation as a Proxy for Historical Flow Dynamics.
- Authors
Qin, Jie; Li, Qiran; Wu, Teng; Ding, Huimin
- Abstract
The spatial arrangement of grains in gravel‐bed rivers significantly influences sediment transport, flow resistance, and ecological conditions. Inferring historical flow information from spatial grain arrangements has garnered considerable interest among researchers. This study presents a robust and feasible method for such inference, focusing on quantitative approaches to estimate grain arrangement through inclination analysis. Two parameters based on inclination analysis are proposed for estimating grain arrangement. Quantitative relationships between these parameters and grain arrangements are established using artificially generated grain surfaces with predefined grain features. Additionally, the degree of imbrication, represented by the standard deviation of inclination curves, is examined using these generated surfaces. At the macroscopic level, the irregular inclination curve of a riverbed arises from the spatial variability of local hydrodynamic processes, leading to different local grain arrangements. Leveraging this feature at the microscopic level, the spatial distribution of grain orientation, or the grain azimuth field, is obtained using the proposed quantitative relationship. To explore the relationship between this grain azimuth field and flow velocity directions, a three‐dimensional turbulent model based on Detached Eddy Simulation is deployed to simulate the detailed flow field near a gravel bed surface. Comparisons between the grain azimuth field and the flow velocity field highlight similarities, affirming that historical flow direction can be inferred from grain arrangement information. This study contributes to advancing the understanding of the intricate connections between grain arrangements and historical flow dynamics in gravel‐bed rivers. Plain Language Summary: In gravel riverbeds, the particles are often arranged into specific structures or oriented in particular directions under the influence of flow processes. This feature exerts an influence on water flow, sediment transport, and ecological conditions in rivers. Researchers have long been interested in inferring historical flow information through particle orientation. This study aims to develop quantitative methods for estimating gravel azimuth and exploring the interconnection between gravel arrangement and flow velocity near the surface. Two parameters are proposed to describe gravel arrangement. The quantitative relationships between these parameters and orientation features are established using artificial grain surfaces generated with known arrangement features. In addition, flow velocity near a gravel surface is estimated using a numerical model, and the interconnection between the velocity field and particle azimuth is investigated. This research contributes valuable insights into the understanding of gravel orientation and its relationship with flow processes in rivers. Key Points: Quantitative relationships are proposed to estimate the azimuth of gravelsThe proposed equations facilitate the generation of a 2D grain azimuthal field on gravel surfaces, offering insights into the spatial distribution of flow velocity directionsThe magnitude of bottom flow velocity is positively correlated with the imbrication degree, as expressed by the standard deviation of inclination curves
- Subjects
FLOW velocity; QUANTITATIVE research; SPATIAL arrangement; SEDIMENT transport; RESEARCH personnel; GRAIN
- Publication
Journal of Geophysical Research. Earth Surface, 2024, Vol 129, Issue 5, p1
- ISSN
2169-9003
- Publication type
Article
- DOI
10.1029/2023JF007480