Pelletier, J.D., and S. DeLong, Oscillations in arid alluvial channels, Geology, in press.

Abstract: Arid alluvial channels on piedmonts and valley floors often exhibit an alternating pattern of narrow, deeply-incised reaches and wide, shallow reaches with a characteristic spacing. Here we introduce a two-dimensional numerical model that reproduces this behavior based on the coupling between the channel longitudinal profile and cross section. In this model, small variations in channel width are amplified as wider-than-average channel reaches become zones of distributary flow that store sediment, aggrade, and widen in a positive feedback. In contrast, narrower-than-average reaches focus stream power, incise, and narrow in a positive feedback. This instability is balanced by the diffusive nature of longitudinal-profile evolution. Following an initial phase of instability growth in the model, a steady state is reached in which solitary waves propagate in the upstream direction. The model predicts a specific quantitative relationship between oscillation wavelength and channel depth, width, and slope that is verified by channel geometries from southern Arizona.

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