Quantifying the Dynamic Evolution of Graded Gravel Beds Using Particle Tracking Velocimetry

Abstract

The motion of graded gravels under steady and spatially uniform turbulent flow is investigated in laboratory conditions using particle tracking velocimetry (PTV). The gravel bed is subjected to flows approaching critical armor velocity, and water worked until static armor is reached. A digital particle tracking (DPT) algorithm, based on image subtraction between subsequent frames, is developed and applied on the particle scale as the graded gravel bed is water-worked. The dynamic evolution of graded gravels is quantified continuously for up to 8 h. Characteristics of particle motion are identified, and movement patterns under complex flow conditions are analyzed. Particle tracking is applied to low-frequency (0.67-fps) and high-frequency (30-fps) data. This study provides a new perspective on gravel particle transport distances, trajectory sinuosity, sediment transport rate, fractional sediment transport rates, particle movement patterns, and instantaneous particle velocities.