HR: 16:15h
AN: H54A-02    [Abstracts]
TI: Partitioning of Water Discharge by Distributary Channels in the Prograding, Wax Lake Delta, Coastal Louisiana, USA
AU: * Buttles, J
EM: buttles@mail.utexas.edu
AF: Department of Geological Sciences, The University of Texas at Austin, Austin, TX 78712,
AU: Mohrig, D
EM: mohrig@mail.utexas.edu
AF: Department of Geological Sciences, The University of Texas at Austin, Austin, TX 78712,
AU: Nittrouer, J
EM: nittrouer@mail.utexas.edu
AF: Department of Geological Sciences, The University of Texas at Austin, Austin, TX 78712,
AU: McElroy, B
EM: bmcelroy@mail.utexas.edu
AF: Department of Geological Sciences, The University of Texas at Austin, Austin, TX 78712,
AU: Baitis, E
EM: elkebaitis@yahoo.com
AF: Department of Geological Sciences, The University of Texas at Austin, Austin, TX 78712,
AU: Allison, M
EM: mallison@mail.utexas.edu
AF: Institute for Geophysics, The University of Texas at Austin, Austin, TX 78758,
AU: Paola, C
EM: cpaola@umn.edu
AF: Department of Geology and Geophysics, University of Minnesota, Minneapolis, MN 55455,
AU: Parker, G
EM: parkerg@uiuc.edu
AF: Department of Civil and Environmental Engineering, University of Illinois, Urbana, IL 61801,
AU: Kim, W
EM: geowskim@uiuc.edu
AF: Department of Civil and Environmental Engineering, University of Illinois, Urbana, IL 61801,
AB: How water and sediment is routed through distributary networks on river deltas is incompletely known and a topic of much active research. We have undertaken a study to determine the controls on partitioning of water and sediment discharge in distributary channels of the Wax Lake Delta and to connect these transport processes to the land building associated with the growth of islands that separate distributary channels from each other. Here we present first results from the field project that defines how water from the upstream primary channel is partitioned between the first set of five distributary channels. Measurements of water discharge and channel bathymetry were collected using a 22-ft research vessel equipped with an acoustic Doppler velocity profiler, a swath bathymetry profiler and dual differential GPS antennas. Wax Lake Delta is situated at the downstream end of Wax Lake Outlet, a man-made channel that diverts water and sediment from the lower Atchafalaya River, roughly 20 km upstream from Morgan City, LA. The subaerial delta has been building out into Atchafalaya Bay since roughly 1973 with a delta-front advance rate of about 0.27 km/yr. Associated with this growth has been development of a distributary network of channels that continues to evolve as the delta progrades seaward. Measurements collected in May, 2007 define properties of the upstream channel and the first set of five distributary channels. Characteristic width, depth and water discharge for the upstream channel are 420 m, 21.2 m, and 2900 m³/s. Characteristic values for width, depth and water discharge for the five distributary channels are 1) 270 m, 6.7 m, and 310 m³/s, 2) 300 m, 6.5 m, and 350 m³/s, 3) 650 m, 6.8 m, and 820 m³/s, 4) 395 m, 6.5 m, and 560 m³/s, and 5) 440 m, 6.0 m, and 440 m³/s. These data highlight a number of interesting points regarding the initial set of bifurcations. First, the transition from one to five channels is associated with a two-thirds reduction in characteristic flow depth and one-third reduction in characteristic flow velocity. Measured discharge in the five channels sums to 86% of the upstream channel. Based on field observations we propose that the remaining 14% is associated with shallow flow onto and across the weakly emergent islands. There is very little difference in characteristic channel depth even though widths of the five channels vary by greater than a factor of two. There is also very little difference in the spatially average velocity for the five channels; velocities range between 0.17-0.22 m/s. All of these channel properties will be discussed in the context of sediment transport and sedimentation within this active delta.
DE: 1856 River channels (0483, 0744)
DE: 1861 Sedimentation (4863)
DE: 1862 Sediment transport (4558)
SC: Hydrology [H]
MN: 2007 Fall Meeting