Prediction of Sand Transport over Immobile Gravel from Supply-Limited to Capacity Conditions

Successful sediment management of streams and rivers downstream of dams requires a method for predicting sand transport across a range of conditions that can include sand transported below the top of an armored gravel layer through complete burial of the coarse substrate. Previous studies have shown that the elevation of sand relative to gravel along with shear stress at the elevation of the sand are needed to successfully predict sand transport. Experiments were conducted in a laboratory flume channel with increasing sand elevations to document the transition from supply-limited sand transport over gravel to capacity-sand transport. A modified Engelund-Hansen sand transport relation was developed by adding terms to scale the fraction of the bed covered with sand and to reduce the bed shear stress acting on the sand. This modified relation yielded good predictions for the range of conditions from very low rates of sand transport over an immobile gravel bed to 100% sand bed conditions for the data from this and two previous studies. (C) 2017 American Society of Civil Engineers.