HR: 13:45h
AN: H53L-01 INVITED    [Abstracts]
TI: Persistence and Transience in Bed Surface Texture
AU: * Dietrich, W E
EM: bill@eps.berkeley.edu
AF: University of California, Department of Earth and Planetary Science, Berkeley, CA 94720,
AU: Nelson, P A
EM: pnelson@berkeley.edu
AF: University of California, Department of Earth and Planetary Science, Berkeley, CA 94720,
AU: Yager, E M
EM: eyager@uidaho.edu
AF: University of Idaho, Center for Ecohydraulics Research Department of Civil Engineering, Boise, ID 83702,
AU: Lamb, M P
EM: mpl@berkeley.edu
AF: University of California, Department of Earth and Planetary Science, Berkeley, CA 94720,
AU: Venditti, J
EM: jgvenditti@yahoo.ca
AF: Simon Fraser University, Department of Geography 8888 University Drive, Burnaby, BC V5A 1S6,
AB: The grain size distribution on the surface of stream-channel beds typically displays significant spatial structure. Variations occur at all scales, but once they reach mappable domains they are often referred to as patches or facies of common size distributions. Here we report results of various field and experimental investigations that seek to explain the origin and dynamics of this patchiness. Our observations demonstrate that patches can be persistent through significant flow and sediment transport events, and transient, in that they either migrate downstream or are simply swept away or buried. The persistent patches can be thought of as "fixed" while the moving patches are "free." It appears that fixed patches arise from the interaction of the spatial structure of boundary shear stress and bed topography. For example, in both sand and gravel-bed rivers there can be persistent patterns of coarsening in pools and fining in the downstream tails of bars. Persistence seems tied to stability of channel bed topography. Fixed patches can remain constant in grain-size distribution despite complete particle exchange and large transport rates of dissimilar particle sizes across them. Small, finer- particle patches in coarse-bedded streams can persist during modest sediment transport events. These fine patches, however, may grow, or shrink and disappear depending on sediment supply. These changes in extent have large effects on rates of bedload transport. Free, moving patches emerge from grain interactions, and create a self-propagating perturbation in local boundary shear stress and sediment transport fields. Modeling efforts are underway to explore the predictability of fixed, free and locally transient patches.
UR: http://eps.berkeley.edu/~bill/papers/PatchesRCEM2005Dietrich_134.pdf
DE: 1825 Geomorphology: fluvial (1625)
DE: 1862 Sediment transport (4558)
SC: Hydrology [H]
MN: 2007 Fall Meeting