Variable discharge controls on channel width and sinuosity in mixed bedrock-alluvial river channels: a combined field, remote-sensing, and modeling study

HR: 15:25h
AN: H43H-08 [Abstracts]
TI: Variable discharge controls on channel width and sinuosity in mixed bedrock-alluvial river channels: a combined field, remote-sensing, and modeling study
AU: * Stark, C P
EM: cstark@ldeo.columbia.edu
AF: Lamont-Doherty Earth Observatory, Columbia University, 61 Route 9W, Palisades, NY 10964, United States
AU: Barbour, J R
EM: jbarbour@ldeo.columbia.edu
AF: Lamont-Doherty Earth Observatory, Columbia University, 61 Route 9W, Palisades, NY 10964, United States
AU: Chen, H
EM: hchen@ntu.edu.tw
AF: Department of Earth Sciences, National Taiwan University, No. 1, Sec. 4, Roosevelt Road, Taipei, 10617, Taiwan
AU: Lin, C
EM: chingwee@mail.ncku.edu.tw
AF: Disaster Prevention Research Center, National Cheng-Kung University, 3F, 500, Sec.3, An-Ming Rd, Tainan, 709, Taiwan
AU: Horng, M
EM: mjhorng@wra.gov.tw
AF: Water Resources Agency, Ministry of Economic Affairs, Hsin-Yi Road, Taipei, 10651, Taiwan
AU: Ko, C
EM: chinpin@dprc.ncku.edu.tw
AF: Disaster Prevention Research Center, National Cheng-Kung University, 3F, 500, Sec.3, An-Ming Rd, Tainan, 709, Taiwan
AU: Yi, T
EM: c44851275@dprc.ncku.edu.tw
AF: Disaster Prevention Research Center, National Cheng-Kung University, 3F, 500, Sec.3, An-Ming Rd, Tainan, 709, Taiwan
AU: Tsai, T
EM: victor@dprc.ncku.edu.tw
AF: Disaster Prevention Research Center, National Cheng-Kung University, 3F, 500, Sec.3, An-Ming Rd, Tainan, 709, Taiwan
AU: Chang, W
EM: conifer@dprc.ncku.edu.tw
AF: Disaster Prevention Research Center, National Cheng-Kung University, 3F, 500, Sec.3, An-Ming Rd, Tainan, 709, Taiwan
AU: Lee, S
EM: morris@dprc.ncku.edu.tw
AF: Disaster Prevention Research Center, National Cheng-Kung University, 3F, 500, Sec.3, An-Ming Rd, Tainan, 709, Taiwan
AU: Huang, C
EM: chunghuang@ntu.edu.tw
AF: Department of Earth Sciences, National Taiwan University, No. 1, Sec. 4, Roosevelt Road, Taipei, 10617, Taiwan
AU: Huang, C
EM: chunghuang@ntu.edu.tw
AF: Water Resources Agency, Ministry of Economic Affairs, Hsin-Yi Road, Taipei, 10651, Taiwan
AU: He, G
EM: hargong.tw@yahoo.com.tw
AF: Disaster Prevention Research Center, National Cheng-Kung University, 3F, 500, Sec.3, An-Ming Rd, Tainan, 709, Taiwan
AU: Lee, W
EM: n8695110@mail.ncku.edu.tw
AF: Disaster Prevention Research Center, National Cheng-Kung University, 3F, 500, Sec.3, An-Ming Rd, Tainan, 709, Taiwan
AU: Hovius, N
EM: nhovius@esc.cam.ac.uk
AF: Department of Earth Sciences, University of Cambridge, Downing Street, Cambridge, CB2 3EQ, United Kingdom
AU: Turowski, J
EM: jens.turowski@wsl.ch
AF: Department of Earth Sciences, University of Cambridge, Downing Street, Cambridge, CB2 3EQ, United Kingdom
AU: Fukahata, Y
EM: fukahata@eps.s.u-tokyo.ac.jp
AF: Dept of Earth and Planetary Science, Sci. Bldg. No.1-712, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo, 113-0033, Japan
AB: Rates of erosion in mountain river channels are the integrated effect of broad distributions of discharge rather than the result of a single, bankfull discharge. So, we can expect discharge variability, and the shape of the discharge PDF, to have a first-order effect on the morphodynamics of mixed bedrock-alluvial channels. Here we report the results of field surveys of Japanese and Taiwanese mountain rivers and analysis of corresponding gauging data, time-series satellite imagery, and SRTM topography. We show that: (1) bedrock channel width scales with both discharge mean and discharge variance; (2) wall sediment (by hillslope debris) and not just bed buffering must be considered; (3) relative discharge variability exerts on stronger effect on lateral channel mobility (meandering) than on typical channel width. To help explain such behavior we introduce a basic, dynamic model of bedrock channel geometry that employs a trapezoidal geometry, sediment buffering on both the channel bed (using queueing theory) and along the walls, semi-empirical channel hydraulics, and a schematic discharge PDF that maps (surprising well) the broad range of observed flood frequencies into a two-valued discrete distribution reflecting high-stage and extreme-stage flows. We solve for the model dynamics and derive a host of predicted relationships between discharge statistics and mixed bedrock-alluvial channel geometry at equilibrium and beyond. The model reproduces many of our empirical observations, in particular that bedrock channel meandering should accelerate with greater discharge variability. The model also suggests that increased bed sediment throughput drives channel widening, while increased fluxes of hillslope debris and transient storage along channel margins drives narrowing. We conclude there is a strong morphodynamic link between the shape of a mixed bedrock-alluvial channel and both the shape of its discharge distribution and its fluxes of hillslope and bed sediment. Our results point particularly to the need for more study of discharge variability and hillslope sediment buffering on erosion distributions in bedrock rivers.
UR: http://geomorph.ldeo.columbia.edu/grg
DE: 1625 Geomorphology and weathering (0790, 1824, 1825, 1826, 1886)
DE: 1804 Catchment
DE: 1825 Geomorphology: fluvial (1625)
DE: 1826 Geomorphology: hillslope (1625)
DE: 1862 Sediment transport (4558)
SC: Hydrology [H]
MN: 2007 Fall Meeting