HR: 1340h
AN: U43B-1130    [Abstracts]
TI: Evidence for the Dynamical Origin of Ordered Channel Networks Driven by Subsurface Flow
AU: * Abrams, D M
EM: dmabrams@mit.edu
AF: Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences, 54-621 77 Massachusetts Avenue, Cambridge, MA 02139, United States
AU: Lobkovsky, A E
EM: leapfrog@mit.edu
AF: Georgetown University, Department of Physics, 527 Reiss Science 37th and O St NW, Washington DC, DC 20057, United States
AU: McElroy, B J
EM: bmcelroy@mail.utexas.edu
AF: The University of Texas at Austin, Jackson School of Geosciences, Department of Geological Sciences, 1 University Station C1100, Austin, TX 78712, United States
AU: Mohrig, D
EM: mohrig@mail.utexas.edu
AF: The University of Texas at Austin, Jackson School of Geosciences, Department of Geological Sciences, 1 University Station C1100, Austin, TX 78712, United States
AU: Petroff, A P
EM: petroffa@mit.edu
AF: Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences, 54-621 77 Massachusetts Avenue, Cambridge, MA 02139, United States
AU: Rothman, D H
EM: dhr@mit.edu
AF: Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences, 54-621 77 Massachusetts Avenue, Cambridge, MA 02139, United States
AU: Straub, K M
EM: kmstraub@mit.edu
AF: University of Minnesota, Department of Geology and Geophysics, St. Anthony Falls Laboratory, 2 Third AV SE, Minneapolis, MN 55414, United States
AB: Channel networks driven by subsurface flow exhibit a geometrically ordered structure distinguished in part by a characteristic spacing between channels. Here we ask whether such patterns are determined solely by local inhomogeneities, or if intrinsic growth dynamics likely plays a significant role. We study an especially ramified km-scale section of Little Sweetwater Creek located near Bristol, Florida. The creek is part of a larger network of channels incised in a bed of homogeneous sand, forming a particularly simple system. Erosion occurs primarily at channel heads due to outward seepage of subsurface water. Consequently, knowledge of spatial variation in the water table is sufficient to determine spatial variation in erosive driving. We performed a high-resolution three-dimensional ground-penetrating radar survey to determine the depth of the water table near the creek perimeter. Comparison of water table height with different features of the local environment shows that it does not closely follow either surface elevation or larger-scale topography; however, it does correlate well with the local distance to the nearest point on the channel. Moreover, the height of the water table rises roughly logarithmically with that distance. This correlation, along with a supporting theoretical model and numerical simulations, provides strong evidence in favor of an intrinsic dynamic mechanism for the formation and growth of this ordered network. Such a mechanism implies that regional geometric factors are more important than local inhomogeneities in determining this network structure.
DE: 1825 Geomorphology: fluvial (1625)
DE: 1835 Hydrogeophysics
DE: 1856 River channels (0483, 0744)
DE: 4460 Pattern formation
SC: Union [U]
MN: 2007 Fall Meeting