HR: 1340h
AN: H53C-1263    [Abstracts]
TI: Turbulent flow over an evolving gravel bed
AU: * Venditti, J G
EM: jgvenditti@yahoo.ca
AF: Stillwater Sciences, 2855 Telegraph Ave #400, Berkeley, CA 94705 United States
AU: Egozi, R
EM: regozi@uwo.ca
AF: University of Western Ontario, Department of Geography , London, ON N6A 5C2 Canada
AU: Hassan, M A
EM: mhassan@geog.ubc.ca
AF: University of British Columbia, Department of Geography, Vancouver, BC V6T 1Z2 Canada
AB: There is a growing literature on bedforms developed in gravel bedded streams such as clusters, cells, bedload sheets, imbrications and a variety of coarse surface layers. In particular, clusters, cells and imbrications tend to stabilize the bed by providing structural integrity and thereby reducing the transport rate. It has also been suggested in the literature that these features increase flow resistance based on laboratory studies with high-relief clusters on fixed beds but, these high relief forms may not have a natural analogue. This poster reports on a series of experiments undertaken to examine turbulent flow over a gravel bed as cluster and cellular structures develop through time. The experiments were conducted in a 0.5 m deep, 1 m wide and 9 m long flume with a sediment feed. Flow depths ranged between 0.05 and 0.10 m and bulk mean shear stresses ranged between 0.9 and 4.4 Pa. Measurements of velocity were made at a sampling rate of 25 Hz using an acoustic Doppler velocimeter at 8 to 15 points in each of three velocity profiles separated by 0.5 m in the along stream direction. Bed sediment was well mixed at the beginning of the experiments and low-relief gravel clusters and cellular structures developed, generally increasing in density with time. Profiles were obtained after a coarse surface layer had developed at 2, 4, 8, 16, 32, 40, 70 hours from the beginning of the experiments. Shear stress estimates are made based on the Law of the Wall and Reynolds stress profiles and compared to structure type and density. The results suggest that the low relief clusters and cellular structures commonly observed in nature may not have as strong an effect on flow resistance as previously thought. Rather, the first order effect on flow resistance is derived from the development of the coarse surface layer and not its organization into clusters and cells.
DE: 4568 Turbulence, diffusion, and mixing processes
DE: 1815 Erosion and sedimentation
DE: 1824 Geomorphology (1625)
SC: Hydrology [H]
MN: 2004 AGU Fall Meeting