ARS | Publication request: OPTIMAL MODE OF SEDIMENT TRANSPORT BY SHALLOW FLOWS IN UPLAND AREAS

Submitted to: International Journal of Sediment Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: October 1, 2000
Publication Date: March 1, 2001

Interpretive Summary: Of the many constituent processes in soil erosion, sediment transport by overland flow, especially shallow flow, is one of the most vexing problems to quantify. Many sediment transport relationships have been proposed. Almost all of them apply for channel flow, where flow depth is large relative to the thickness of the flow zone near the boundary, the boundary layer. These relationships are not suitable to describe sediment transport in shallow, overland flow since they do not take into account the micro-mechanical effect of interactions of sediment particles in motion. It has been observed that sediment, and granular movement as well, on slopes is often associated with the development of waves which are expressions of particle interactions. This paper documents and discusses the development of those sediment waves as well as the self-organizing phenomenon of granular flow.

Technical Abstract: Soil erosion and sediment movement are serious problems of upland areas of a watershed. In these areas, most of the eroded sediment is transported in overland flows; either in shallow or in concentrated flow situations. These flows are usually associated with nonlinear waves, generally known as "roll waves" in the hydraulic engineering literature. Under suitable hydraulic conditions, these waves contain a significant fraction of the total kinetic energy of the flow regime. Hence, the waves act as the primary energy source in transporting eroded sediment in shallow flows on steep slopes. Our laboratory experiments under controlled condition suggest that modulation of the roll waves is effected by the addition of increasing amounts of sediment in the flow. The optimal condition in the sediment transport rate is reached when most of the available wave energy is consumed in carrying the sediment. A related set of experiments on gravitational flows of dry granular material show that the evolving scales of sediment waves are intrinsic to the transport mechanism of the solid phase.