HR: 09:45h
AN: H51H-08    [Abstracts]
TI: The cover effect in bedrock abrasion: Implications for fluvial dynamics and river morphology
AU: * Turowski, J M
EM: jmt43@esc.cam.ac.uk
AF: Department of Earth Sciences University of Cambridge, Downing Street, Cambridge, CB2 3EQ United Kingdom
AU: Lague, D
EM: dimitri.lague@univ-rennes1.fr
AF: Geosciences Rennes, UMR 6118 CNRS Campus de Beaulieu, Rennes Cedex, 35042 France
AU: Hovius, N
EM: nhovius@esc.cam.ac.uk
AF: Department of Earth Sciences University of Cambridge, Downing Street, Cambridge, CB2 3EQ United Kingdom
AB: The sediment load of a bedrock river plays an important role in the incision process, by providing tools for abrasion (the tools effect) and by covering and thereby protecting the bed (the cover effect). We derive a new formulation for the cover effect, where the fraction of exposed bed area falls exponentially with increasing sediment flux or decreasing transport capacity, and explore its consequences on the bedrock abrasion model by saltating bedload (Sklar and Dietrich, 2004, A mechanistic model for river incision into bedrock by saltating bed load, Water Resour. Res. 40). We present a mechanism that adjusts channel geometry (slope and width) to maximize erosion rates and derive a stream power type incision law where the erosion rate is linearly dependent on bed shear stress and an erosion threshold. The threshold for the onset of incision is equal to the threshold of motion for the particles. By optimizing the channel geometry to minimize the potential energy of the stream, and using an effective model for both discharge and grain size, we derive equations for the width and slope of a bedrock river and compare the predictions to sites in the South Fork Eel Creek, California, USA, and the LiWu River, Taiwan. Values agree within an order of magnitude. Acknowledging the limitations of the model, these comparisons suggest that the equations can be used to obtain order of magnitude estimates of channel erosion rates from knowledge of width, slope and rock properties.
UR: http://www.esc.cam.ac.uk/esp
DE: 1815 Erosion
DE: 1825 Geomorphology: fluvial (1625)
DE: 1856 River channels (0483, 0744)
SC: Hydrology [H]
MN: Fall Meeting 2005