Resistance to overland flow due to bed‐load transport on plane mobile beds

During bed-load transport by overland flow, momentum is transferred from the flow to the bed via grain collisions, resulting in a decrease in flow velocity and an increase in flow resistance, herein termed bed-load transport resistance. In overland flow on mobile plane beds, total flow resistance f consists of grain resistance fg and bed-load transport resistance fbt. In order to identify and evaluate the relative importance of the factors controlling fbt, 38 flume experiments were performed on slopes of 2·7 and 5·5° using sediment with median diameters of 0·74 and 1·16 mm. All flows were supercritical and turbulent. This study is an extension of a recent study by Gao and Abrahams (Earth Surface Processes and Landforms 2004, vol. 29, pp. 423–435). These authors found that fbt is controlled by three factors: sediment concentration C, dimensionless sediment diameter D*, and relative submergence h/D, where h is flow depth, D is median sediment diameter. However, a new dimensional analysis identifies two additional factors: Froude number F and slope S. Multiple regression analyses reveal (1) that these five factors together explain 97 per cent of the variance of fbt, and (2) that S controls fbt entirely through C. The variable C is therefore redundant, and a new functional equation relating fbt to D*, h/D, S and F is developed. This equation may be used to predict fbt. An advantage of this equation is that it may be used to predict fbt without measuring bed-load transport rate. Copyright © 2004 John Wiley & Sons, Ltd.