HR: 0800h
AN: H51C-1134    [Abstracts]
TI: Location and Lateral Migration of Drainage Divides
AU: * Mudd, S M
EM: simon.m.mudd@vanderbilt.edu
AF: Department of Civil and Environmental Engineering, Vanderbilt University, VU Station B 351831 2301 Vanderbilt Place, Nashville, TN 37235 United States
AU: Furbish, D J
EM: david.j.furbish@vanderbilt.edu
AF: Department of Earth and Environmental Sciences, Vanderbilt University, VU Station B 357805 2301 Vanderbilt Place, Nashville, TN 37235-1805 United States
AB: We investigate the mechanisms driving the lateral migration of drainage divides on hillslopes experiencing dispersive-like soil creep due to changes in downcutting rates in the channels bordering these hillslopes. If two channels are downcutting at the same rate and are at the same elevation the hillslopes will be symmetric about the divide. This symmetry may be broken by a vertical offset in the elevation of the channels or by unequal rates of channel incision. The rate and distance of divide offset will depend on the dominant sediment transport mechanism on the hillslope. For hillslopes undergoing sediment transport that is linearly proportional to the slope, the divide offset distance is one quarter of the ratio of the vertical offset of the channels to the relief of the symmetric hillslope. If channels are downcutting at different rates, the speed of the divide migration will only depend on the ratio of the two downcutting rates and the density ratio, which is the ratio of the dry bulk density of the bedrock to the dry bulk density of the soil. The density ratio plays a fundamental role in determining the transient response of the divide if the bounding channels are lowering at the same time-averaged downcutting rate but whose instantaneous incision rates vary. Lower density ratios lead to faster transient responses of the divide to changes in channel downcutting rates. Other parameters that affect the transient response of the divide are the magnitude of transient differences in downcutting between the two channels, the time averaged incision rate, and a ratio of the relaxation time of the hillslope to the particle residence time on the hillslope. The soil depth profile reacts to transient changes in downcutting at a different rate than surface topography. Hillslopes experiencing transient channel downcutting may have surface topography that is symmetric about the divide but will at the same time have a soil depth profile that is asymmetric. The implications for long term adjustments of drainage basin morphology are considered.
DE: 1815 Erosion and sedimentation
DE: 1824 Geomorphology (1625)
SC: Hydrology [H]
MN: 2004 AGU Fall Meeting