HR: 16:00h
AN: H54A-01    [Abstracts]
TI: Morphology and Hydraulics of Nine Sand-bed Fluvial Bifurcations from the Mossy Delta, SK: Implications for Their Stability
AU: * Slingerland, R
EM: sling@geosc.psu.edu
AF: The Pennsylvania State University, Department of Geosciences, 513A Deike Bldg, University Park, PA 16802, United States
AU: Klein, F E
AF: The Pennsylvania State University, Department of Geosciences, 513A Deike Bldg, University Park, PA 16802, United States
AU: Edmonds, D A
AF: The Pennsylvania State University, Department of Geosciences, 513A Deike Bldg, University Park, PA 16802, United States
AU: Best, J L
AF: University of Illinois at Urbana-Champaign, Departments of Geology and Geography and Ven Te Chow Hydrosystems Laboratory, 1301 W. Green St., Urbana, IL 61801-2939, United States
AU: Parsons, D R
AF: University of Leeds, School of Earth and Environment, Leeds, LS2 9JT, United Kingdom
AU: Bridge, J S
AF: University of Binghamton, Department of Geological Sciences and Environmental Studies, PO BOX 6000, Binghamton, NY 13902-6000, United States
AU: Janesko, D
AF: University of Binghamton, Department of Geological Sciences and Environmental Studies, PO BOX 6000, Binghamton, NY 13902-6000, United States
AU: Smith, N D
AF: Department of Geosciences, 214 Bessey Hall, P.O. Box 880340, Lincoln, NE 68588-0340,
AB: The distributary channel network of the Mossy Delta, SK consists of ~25 presently-active bifurcations created by channel splitting around river mouth bars during a 70 year history of delta growth. Detailed morphologic and hydraulic data from nine bifurcations are analyzed here to define the processes that determine their stability. Processes considered include bedload steering by adverse bed slopes, sediment and flow steering by secondary circulation, flow steering by inherited channel planform, and gradient advantage due to external boundary conditions. Stability of the bifurcations was determined from serial aerial photo analysis. Results indicate that the net topology and planforms of the bifurcations were set early during deposition of river mouth bars. Inherited alignment of a bifurcate channel thalweg with the main stem does not play a large role in subsequent bifurcation evolution; today roughly half of the side-channels take a greater proportion of the flow. After creation, bifurcate channels decreased in width by c. 15 %, with most of the reduction occurring in the first decade through bank accretion of scroll bars. Modern bifurcate channel depths and widths follow a hydraulic geometry scaling law (although they are wider and shallower than typical river channels), indicating a morphodynamically stable channel network. Most active bifurcations today are asymmetric; the average proportion of discharge through subordinate channels is 37 % with variation from 20 to 50 %. Local water surface slopes are flat approaching a bifurcation and steepen down the bifurcate arms, with the steeper slope in the shallower channel. All subordinate bifurcate channels possess morphologic ramps from the main channel with adverse bed slopes of 3-5 %. Although this suggests topographic steering of bedload is an important process in maintaining stability, it is not the only controlling process, because the subordinate ramp is shallower in c. 30 % of the cases.
DE: 1820 Floodplain dynamics
DE: 1825 Geomorphology: fluvial (1625)
DE: 1862 Sediment transport (4558)
SC: Hydrology [H]
MN: 2007 Fall Meeting