HR: 0800h
AN: H41D-0762    [Abstracts]
TI: Structural Controls on Channel Geometry and Dynamics in the Peikang River, Central Taiwan
AU: * Yanites, B J
EM: brian.yanites@colorado.edu
AF: Department of Geological Sciences, University of Colorado, Campus Box 399, Boulder, CO 80309, United States
AU: Tucker, G E
EM: gtucker@cires.colorado.edu
AF: CIRES & Department of Geological Sciences, University of Colorado, Campus Box 399, Boulder, CO 80309, United States
AU: Mueller, K
EM: Karl.Mueller@colorado.edu
AF: Department of Geological Sciences, University of Colorado, Campus Box 399, Boulder, CO 80309, United States
AU: Wilcox, T
EM: tarka.wilcox@colorado.edu
AF: Department of Geological Sciences, University of Colorado, Campus Box 399, Boulder, CO 80309, United States
AU: Chen, Y
EM: ygchen@ntu.edu.tw
AF: Department of Geosciences, National Taiwan University, No. 1, Sec. 4 th, Roosevelt Rd, Taipei, 106, Taiwan
AB: The Western Foothills of central Taiwan contain numerous rivers flowing nearly orthogonal to a series of west- verging thrust sheets. This relationship offers an exceptional opportunity to document channel dynamics across active faults. The study focuses on a ~45 km stretch of the Wu River and its principal tributary, the Peikang River. Geomorphic data, including channel width, slope, bed cover, and grain size, are derived from a combination of field mapping and DEM analysis, and are used to estimate unit stream power along the channel. Correlation and dating of strath terraces provide estimates of late Quaternary incision rates. Incision rates, terrace deformation, and estimated stream power all correlate with mapped structures. Estimated incision rates are fairly high but spatially variable (0.35-4 mm/yr). Normalizing channel width by contributing drainage area exhibits a strong correlation between channel width and mapped structures, revealing channel width as the first-order control on variations in stream power. Regions where thrust faults have been mapped show significant narrowing in contrast to anomalously wide reaches where synclines have been proposed. Analysis of the longitudinal profile and normalized steepness indices does not show a strong correlation between gradient and incision rate suggesting that channel bed elevation is readily adjusted to seismic events through incision and/or changes in alluvial cover. We combine this interpretation with field observations of stream response to recent seismic events along the Cho Shui River to formulate a working hypothesis explaining the long term narrowing of streams over active thrust faults. This work underscores the necessity to understand the processes and rates of channel widening for interpreting tectonics from channel geometry.
DE: 1815 Erosion
DE: 1825 Geomorphology: fluvial (1625)
DE: 1856 River channels (0483, 0744)
DE: 8175 Tectonics and landscape evolution
SC: Hydrology [H]
MN: 2007 Fall Meeting