Geometry characterization of sediment particles from the primary source region of the Yangtze River

Sediment particle geometry is fundamental in governing sediment transport and thus fluvial morpho-dynamics. This work aims to unravel the geometrical features of fluvial sediment particles from the primary source region of the Yangtze River (SRYR), while also focusing on the role of maximum projection in quantifying particle geometry.

Sediment particle images and mesh surfaces were acquired through scanning electron microscope and microfocus X-ray computed tomography. 2D geometrical descriptors were statistically examined based on particle outline reconstruction using Fourier analysis. 3D particle surfaces were reconstructed using spherical harmonic functions. Numerical all-around projection was undertaken to probe into the interrelationships between geometrical descriptors derived from 3D particles and their 2D projections.

Fine sand particles exhibit relatively low 2D convexity values, while coarse gravel particles exhibit low 2D aspect ratios. The 2D angularity index increases with particle size. Measurement based on maximum projection underestimates the sphericity of prolate particles and overestimates that of other types of particles when compared to all-around projections. Concurrently, such measurement tends to overestimate particle roundness. 3D shape descriptors are weakly correlated to their 2D counterparts from maximum projection.

Shape characteristics of sediment samples from the SRYR are influenced by particle size and show variations across different size categories. Estimating average 2D or 3D geometrical features from the maximum projection bears considerable uncertainties. This work facilitates the basis for further investigating fluvial sediment transport mechanics and morpho-dynamics in the SRYR in line with the climate change-induced sediment flux surges.