HR: 10:20h
AN: H41G-01 INVITED     [PDF]
TI: The Influence of the Grain Size Distribution of Sediments Supplied by Hillslopes on Rates of River Incision Into Bedrock and Steady-State Longitudinal Profile Form
AU: * Sklar, L S
EM: leonard@sfsu.edu
AF: Department of Geosciences, San Francisco State University, 1600 Holloway Avenue, San Francisco, CA 94132 United States
AU: Dietrich, W E
EM: bill@eps.berkeley.edu
AF: Department of Earth and Planetary Science, University of California, Berkeley, CA 94720 United States
AB: At the time-scale of landscape evolution, hillslope and channel erosion are strongly coupled through both the channel's role as baselevel for hillslope lowering and the hillslope's role in supplying sediments to the channel network. Here we use an experimentally-calibrated, process-specific model for fluvial incision into bedrock by saltating bedload to investigate the sensitivity of river longitudinal profile concavity and relief to the grain size distribution of sediments entering the fluvial system. We focus on the limited but illustrative case of topographic steady-state. Grain size strongly affects predicted incision rates, and thus steady-state profile form, by influencing the number and erosional efficiency of individual bedload impacts and the extent of bedrock exposure in the channel bed. The fraction of the total sediment load that moves as bedload depends on the initial grain size distribution as well as the rate of downstream particle comminution. Over a wide range of rock strength and uplift rates the model predicts that profile relief and concavity are most sensitive to bedload grain size and the downstream rate of change in coarse sediment grain size respectively. Rock strength and uplift rate have surprisingly modest influence on steady-state profile relief and concavity, in the absence of any modeled dependence of grain size on these variables. However, the grain size distribution of sediments produced by hillslope weathering and transport is likely to be influenced by bedrock lithology and rates of landscape denudation, and perhaps most importantly by climate. We use simple speculative relationships to quantify some of these linkages, and find that their effects on the grain size distribution produced by hillslopes may provide an essential yet indirect avenue for rock strength, rock uplift rate and climate to influence steady-state profile form.
DE: 1625 Geomorphology and weathering (1824, 1886)
DE: 1815 Erosion and sedimentation
DE: 1824 Geomorphology (1625)
DE: 1886 Weathering (1625)
SC: Hydrology [H]
MN: 2003 Fall Meeting