HR: 0830h
AN: NG31A-0599    [PDF]
TI: Dynamic Bedrock Fluvial Channel Networks: Analytic Model and Field Evidence
AU: * Oskin, M
AF: Department of Geological Sciences, University of North Carolina, Chapel Hill, NC 27599-3315 United States
AB: Fundamental processes in landscape evolution are the establishment and elaboration of stream channel networks. Network geometry, and in particular efficient concentration of discharge to incise channels, controls the first-order distribution of mountain range relief. This study explores the mechanisms that organize a pre-existing channel network into a series of regularly-spaced drainages that dissect a linear mountain range. The elevation of the channel network is approximated analytically using a stream power law. Channel elevations are minimized to produce an optimal channel network simulating competition between adjacent incising stream channels. Solving for the minimum range crest elevation predicts the position of the principle tributary junction point - where two tributaries join to form the main stream channel. For reasonable values of channel concavity of 0.4 to 0.7, the junction point resides at 3/4 to 5/6 the catchment length as defined by the distance from the outlet to the divide. Solving for the ridge line elevation between catchments predicts a catchment length / width ratio between 1.8 and 2.1, also consistent with published numerical models and studies of natural landscapes. Field investigations of the tectonically active Kyrgyz Range of the western Tien Shan reveal evidence for natural processes that optimize stream networks. Comparisons of youthful, intermediate, and mature catchments define a pattern of tributary junction points that migrate upstream to maximize concentration of discharge. Differential incision of adjacent tributary catchments leads to upstream drainage capture and formation of under-fit parallel paleo-valleys. The extent of evidence for dynamic bedrock fluvial channel networks in the Kyrgyz Range suggests that these networks undergo significant reorganization over several million years before reaching an optimal topology. Complete understanding of the time scale of drainage network evolution and response to changing tectonic boundary conditions will thus require calibration of processes that contribute to lateral bedrock channel migration and capture. Processes observed to be occurring in the Kyrgyz Range include differential channel incision rates, deep-seated landslides, and the effects of debris loading from tributaries
DE: 1815 Erosion and sedimentation
DE: 1824 Geomorphology (1625)
DE: 1848 Networks
DE: 1860 Runoff and streamflow
SC: Nonlinear Geophysics [NG]
MN: 2003 Fall Meeting