Bedload transport by a vertical jet impinging upon sediments

Abstract

Laboratory experiments are performed to examine the formation of a crater in sediment by an impinging vertical turbulent jet. Light attenuation and a "depositometer," which records conductivity through the bed from an array of electrodes, are used to measure the crater depth as a function of space and time. The onset of crater formation and deepening is best characterized in terms of the Rouse number, Rs (proportional to the particle settling speed divided by the centerline jet speed), rather than Shields number, Sh (proportional to the stress divided by the particle weight per unit area). The critical Rouse number, Rsc, is found to increase with the particle Reynolds number, Rep, as a power law with exponent 0.45 ± 0.03 for Rep ranging between 0.6 and 160. For smaller Rs, the crater is observed to deepen at a near-constant speed, while the crater radius remains constant. Bedload transport, measured in terms of the crater deepening speed, is determined to increase as Rep times the difference between Rsc and Rs. © 2014 AIP Publishing LLC.