Modelling granular sediment transport over water-worked gravels

Abstract

This paper reports a numerical model that calculates the transport paths of individual granular particles over a natural water-worked gravel surface. Surface topography is measured using digital photogrammetry and incorporated into a computational fluid dynamics (CFD) scheme by the application of a porosity algorithm. The predicted hydraulics determine the forces acting on each particle enabling the particle trajectory to be solved by Langrangian transport equations. The methodology demonstrates the importance of including complex topography in the numerical scheme as topographically induced hydraulic acceleration and deceleration affect both the transport mechanism and subsequent trajectory of the particle. Hydraulically induced hops, where the particle is entrained into a localized shear layer around a bed particle, are demonstrated to be important in transporting granular sediment across the bed and in re-starting sediment transport if the particle has fallen into a hydraulically sheltered region.