Experimental Study of the Coarse Surface Development Effect on the Bimodal Bed-Load Transport under Unsteady Flow Conditions
Publication: Journal of Hydraulic Engineering
Volume 139, Issue 1
Abstract
Gravel-bed rivers display a surface layer that is coarser than the substrate lining below this armored surface. The armored layer that is developed under certain flow conditions may be attributed as water-worked sediment bed. Both the threshold of incipient motion and the bed-load transport are affected by the presence of this layer. In this study, the coarse surface development and its effect on the sediment transport were investigated experimentally in a rectangular flume. Four antecedent flow rates were combined with an input hydrograph, without sediment feeding. The reference shear stress of individual fractions and the grain-size distribution were determined after the development of the coarse surface due to the antecedent flow. Then a triangular-shaped hydrograph was generated for both the intact surface and the coarse surface cases. It was seen that the maximum bed-load transport values obtained in unsteady flow experiments were highly dependent on the coarse surface formed by the antecedent flow. The interrelation between the armor ratio and the total bed load was also sought. It was revealed that there existed a nearly linear relation between the armor ratio and the dimensionless total bed load with a correlation coefficient of 0.99. This strong interdependence implies that the knowledge of the armor ratio is of basic and utmost importance to predict accurately the bed load to be transported. The values of the Einstein bed-load transport parameter were plotted versus those of the dimensionless shear stress. When the global sediment transport was considered, a clockwise hysteresis appeared in the case of the initial intact bed surface, whereas a counterclockwise hysteresis arose when the coarse surface was developed. As for the fractional sediment transport, in the case of the intact initial surface the clockwise hysteresis was encountered more frequently, but for the armored bed experiments the coarser the bed surface, the more dominant was the counterclockwise hysteresis, meaning that the quantity transported during the falling limb of the hydrograph was higher than that transported during the rising limb.
Get full access to this article
View all available purchase options and get full access to this article.
Acknowledgments
The authors would like to acknowledege the financial support of TUBITAK through the Projects No: 106M274 and 109M637.
References
Bombar, G., Elçi, Ş., Tayfur, G., Güney, M. Ş., and Bor, A. (2011). “Experimental and numerical investigation of bedload transport under unsteady flows.” J. Hydraul. Eng., 137(10), 1276–1282.
Bunte, K., and Abt, S. R. (2001). “Sampling surface and subsurface particle-size distributions in wadable gravel- and cobble-bed streams for analyses in sediment transport, hydraulics, and streambed monitoring.”, U.S. Dept. of Agriculture Forest Service Rocky Mountain Research Station, Fort Collins, CO.
Einstein, H. A. (1950). “The bed load function for sediment transportation in open channel flows.”, U.S. Dept. of Agriculture, Washington, DC.
Fripp, J. B., and Diplas, P. (1993). “Surface sampling in gravel streams.” J. Hydraul. Eng., 119(4), 473–490.
Graf, W. H. (1998). Fluvial hydraulics: Flow and transport processes in channels of simple geometry, Altinakar, M. S., ed., John Wiley and Sons, England, 681.
Hassan, M. A., Egozi, R., and Parker, G. (2006). “Experiments on the effect of hydrograph characteristics on vertical grain sorting in gravel bed rivers.” Water Resour. Res., 42(9), W09408.
Kellerhals, R., and Bray, D. I. (1971). “Sampling procedures for coarse fluvial sediments.” J. Hydraul. Div., 97(8), 1165–1180.
Lee, K. T., Liu, Y. L., and Cheng, K. H. (2004). “Experimental investigation of bedload transport processes under unsteady flow conditions.” Hydrol. Processes, 18(13), 2439–2454.
Mao, L., Cooper, J. R., and Frostick, L. E. (2011). “Grain size and topographical differences between static and mobile armour layers.” Earth Surf. Processes Landforms, 36(10), 1321–1334.
Parker, G. (1979). “Hydraulic geometry of active gravel rivers.” J. Hydraul. Eng., 105(9), 1185–1201.
Parker, G., and Wilcock, P. R. (1993). “Sediment feed and recirculating flumes: Fundamental differences.” J. Hydraul. Eng., 119(11), 1192–1204.
Pender, G., Hoey, T. B., Fuller, C., and McEwan, I. K. (2001). “Selective bedload transport during degradation of a well sorted graded sediment bed.” J. Hydraul. Res., 39(3), 269–277.
Powell, D. M., Reid, I., and Laronne, J. B. (2001). “Evolution of bed load grain size distribution with increasing flow strength and the effect of flow duration on the caliber of bed load sediment yield in ephemeral gravel bed rivers.” Water Resour. Res., 37(5), 1463–1474.
Qu, Z. (2002). “Unsteady open-channel flow over a mobile bed.” Ph.D. thesis, No. 2688, École Polytechnique Federale de Lausanne, Lausanne, Switzerland.
Saadi, Y. (2008). “Fractional critical shear stress at incipient motion in a bimodal sediment.” Civ. Eng. Dimension, 10(2), 89–98.
Shvidchenko, A. B., Pender, G., and Hoey, T. B. (2001). “Critical shear stress for incipient motion sand/gravel streambeds.” Water Resour. Res., 37(8), 2273–2283.
Smith, G. H. S. (1996). “Bimodal fluvial bed sediments: Origin, spatial extent and processes.” Prog. Phys. Geog., 20(4), 402–417.
Smith, G. H. S., Nicholas, A. P., and Ferguson, R. I. (1997). “Measuring and defining bimodal sediments: Problems and implications.” Water Resour. Res., 33(5), 1179–1185.
Song, T. (1995). “Velocity and turbulence distribution in non-uniform and unsteady open-channel flow.” Ph.D. 2thesis, No. 1324, École Polytechnique Federale de Lausanne, Lausanne, Switzerland.
Wilcock, P. R. (1988). “Methods for estimating the critical shear stress of individual fractions in mixed-size sediment.” Water Resour. Res., 24(7), 1127–1135.
Wilcock, P. R. (1993). “Critical shear stress of natural sediments.” J. Hydraul. Eng., 119(4), 491–505.
Wilcock, P. R., and Southard, J. B. (1988). “Experimental study of incipient motion in mixed-size sediment.” Water Resour. Res., 24(7), 1137–1151.
Information & Authors
Information
Published In
Copyright
© 2013 American Society of Civil Engineers.
History
Received: Apr 29, 2011
Accepted: Jun 6, 2012
Published online: Jul 23, 2012
Published in print: Jan 1, 2013
Authors
Metrics & Citations
Metrics
Citations
Download citation
If you have the appropriate software installed, you can download article citation data to the citation manager of your choice. Simply select your manager software from the list below and click Download.