HR: 17:40h
AN: H54E-07 INVITED    [Abstracts]
TI: Downstream Sediment Sorting as a Fractionation Process
AU: * Paola, C
EM: cpaola@umn.edu
AF: AU: Fedele, J J
EM: jjfedele@stcloudstate.edu
AF: Department of Earth & Atmospheric Sciences, St Cloud State University, St Cloud, MN 56301, United States
AB: Downstream size segregation in net depositional systems can be thought of as a fractination process in which a well mixed, heterogeneous input is unmixed based on its relative mobility. Although we are accustomed to thinking of the segregation process as hydraulically driven and rather complex, we argue that at large time and length scales size segregation can be substantially simplified. The main controls are the downstream distribution of sediment extraction, which is typically controlled externally (e.g. by subsidence) and the size distribution of the sediment supply. Hydraulics plays a secondary role because of the tendency for river channels to self organize to a shape that maintains a limited range of dimensionless shear stress on the channel bed. The end result of this line of reasoning is a simple method for calculating downstream size segregation in depositional systems that is in good agreement with the limited data available. In terms of local dynamics, we introduce evidence that topographic roughness plays an important role. This is not explicitly incorporated in our analysis, and the best ways to characterize roughness for this purpose are yet to be determined. Finally, to estimate the importance of abrasion effects at large scales, we re-introduce a dimensionless parameter to describe the relative importance of abrasion, which sorts material by durability, and selective transport, which sorts by transportability.
DE: 1815 Erosion
DE: 1825 Geomorphology: fluvial (1625)
DE: 1861 Sedimentation (4863)
SC: Hydrology [H]
MN: 2007 Fall Meeting