Effect of seepage on sediment transport

Abstract

This study presents the experimental results and theoretical analyses of seepage effects on sediment transport. A total of 529 experiments grouped under four different series of tests were conducted in a laboratory flume with a permeable sediment boundary to investigate the effect of seepage, the length of the suction zone and time on bedload transport rate. Two different types of cohesionless sand particles with diameters = 0.9 mm and 0.48 mm were used in the study.

Three dimensionless groups, viz. Einstein’s parameter Φ, Shields’ parameter without seepage τ*o and modified densimetric Froude number Ω are chosen to examine how seepage affects bedload transport rate. Eleven undisturbed flow conditions were tested, five under clear water and six in live-bed condition. No bedforms with significant height were observed during the experiments. The results show that an increase in suction rate causes an increase in shear velocity excess, which is defined as the difference between the bed and critical shear velocities, leading to an increase in bedload transport rate. The experimental data also show that for the same undisturbed flow conditions, the dimensionless bedload transport rate increases linearly (in semi-logarithmic scale) with increasing suction rates. The equations for predicting bedload transport rate under suction are derived empirically; the predicted results using these empirical equations compared well with measured data, with an accuracy of 20%. Published results from other researchers are used to compare with results obtained and inference drawn from the present study. The similarities and differences of these studies are highlighted.