Experimental Investigation of Effects of Unsteady Flow on Bed-Load Transport Process

Abstract

In this study, the dynamic behavior of bed-load sediments under unsteady flow conditions is experimentally investigated and discussed. A series of experiments were conducted in a 6-m-long laboratory flume with naturally shaped hydrographs, and a video technique was applied to simultaneously monitor the bed-load motion and variations in the water level. Analysis of the experimental results demonstrated that the flow unsteadiness contributes to easier entrainment of the bed load, and the effect on the bed-load behavior decreases with an increase in the hydrograph duration. A further analysis revealed that the time lag between the occurrence of the peak discharge and that of the peak sediment transport rate is related to the base flow, and the bed-shear-stress peak triggers the bed-load transport peak. An unsteadiness parameter is proposed to account for the influence of the bed-load incipient. The regression analysis indicates a strong linear relationship between the bed-load transport and the unsteadiness parameters, which can be used for the estimation of the bed-load motion in the unsteady flow.