School of Geographical Sciences and Urban Planning, Arizona State University, Tempe, Arizona, USA
Received: 02 Jul 2014 – Discussion started: 17 Jul 2014
Abstract. Bed load transport over ripples and dunes in rivers exhibits strong spatial and temporal variability due to the complex turbulence field caused by flow separation at bedform crests. A turbulence-resolving flow model downstream of a backward-facing step, coupled with a model integrating the equations of motion of individual sand grains, is used to investigate the physical interaction between bed load motion and turbulence downstream of separated flow. Large bed load transport events are found to correspond to low-frequency positive pressure fluctuations. Episodic penetration of fluid into the bed increases the bed stress and moves grains. Fluid penetration events are larger in magnitude near the point of reattachment than farther downstream. Models of bed load transport over ripples and dunes must incorporate the effects of these penetration events of high stress and sediment flux.
Revised: 15 Jan 2015 – Accepted: 26 Jan 2015 – Published: 09 Feb 2015
Schmeeckle, M. W.: The role of velocity, pressure, and bed stress fluctuations in bed load transport over bed forms: numerical simulation downstream of a backward-facing step, Earth Surf. Dynam., 3, 105-112, doi:10.5194/esurf-3-105-2015, 2015.