Alluvial rivers often exhibit self-similar gravel size distributions and abrupt gravel-sand
transitions. Experiments suggest that these sorting patterns are established rapidly, but how—and how
fast—this convergence occurs in the field is unknown. We examine the establishment of downstream
sorting patterns in a kilometer-scale alluvial fan. The sharp transition from canyon to unconfined,
channelized fan provides a well-defined boundary condition. The channel changes from deep and
entrenched at the fan apex to shallow and depositional over a short distance, exhibiting nonequilibrium
behavior. The resulting gravel-fining profile is not self-similar; the particle size distribution narrows until
approximate equal mobility is achieved. Downfan, the gravel-sand transition appears to exhibit a self-similar
form; field and laboratory data collapse when downstream distance is normalized by the location of the
transition. Results suggest a generalized sorting profile for alluvial fans as a consequence of the threshold
of motion and nonequilibrium channels.
Litwin Miller K., Reitz M.D., and Jerolmack D.J. (2014): Generalized sorting profile for alluvial fans. Geophysical Research Letters.
This Paper/Book acknowledges NSF CZO grant support.