Grain size, sediment transport and alluvial channel pattern

The Shields parameter, a dimensionless bed shear stress which can be expressed as a ratio of the slope, depth and characteristic properties of bed material in an alluvial channel, has been observed in natural rivers to take on modal values for the regimes of bedload, mixed-load and suspension transport [Dade, W.B., Friend, P.F., 1998. Grain size, sediment-transport regime and channel slope in alluvial rivers. J. Geology, 106: 661–675.]. Such conditions correspond to channel geometries associated with conserved sediment flux and thus to a state of approximate equilibrium in which the channels are neither aggrading nor degrading to a significant degree. These findings are extended here to accommodate the effects of channel width in the context of a comprehensive data set on stable, perennial rivers. The new analysis reconciles existing empirical and theoretical approaches to predict alluvial channel geometry.