Bedload sheets are subtle bedforms, different from other previously described bedforms in form, structure, and kinematics, that appear during transport of mixed-grain-size sediments by flowing water. They are very low relief, transverse accumula- tions of grains, coarser toward the front and only a few grain diameters thick, that migrate downstream by deposition toward the front and erosion toward the rear, like ripples and dunes, but at faster speeds. The first visible sign of a newly-forming bedload sheet is the appearance of the zone of coarser grains at its front. The bedload-transport rate varies from essentially zero just in front of a bedload sheet to a broad maximum over the middle of one. Moreover, the peak in transport rate is significantly closer to the front for the coarser grains than for the finer, so that the coarser and finer size fractions continually leapfrog one another. Thus, bedload sheets, when present, markedly affect the processes of bedload transport and sorting . Their possible presence, therefore, must be taken into account in future observational and theoretical research on bedload transport and also must be considered in the statistical design of bedload sampling programs. The proposed research is part of a long-term study of the physics of bedload transport. It will investigate bedload sheets in Muddy Creek. Wyoming, which actually is clear, and at a comparative site elsewhere by means of both high-speed and time-lapse 16-mm motion-picture photography. It will provide a detailed, quantitative picture of (a) bedload transport mechanics in the presence of bedload sheets, (b) the mechanisms by which bedload sheets form, grow, and migrate, (c) the conditions for their growth, stability, and decay, (d) whether they vary continuously into other bedforms, such as dunes or ripples, and, if so, how, and (e) how they interact with dunes with which they may be associated.
