Sediment Sorting in Alluvial Channels: ABSTRACT

The formation of primary sedimentary structures in and along an alluvial channel occurs as a result of interactions between gravity, the physical characteristics of the sediment and fluid as well as the hydraulic environment. However, the actual process by which recognizable structures develop arises from sorting of the sediment with respect to size, shape, or density, both along the bed and within the stream. The settling rates of the particles, turbulent diffusion, gravitational sliding, and the shear stress in the vicinity of the bed, all contribute to the sorting processes. Certain aspects of the various sorting processes may be predicted by analytical means, whereas others may be determined only by laboratory experiments. Using an alluvial channel together with the n rmal sequence of bed regimes as a point of departure, a discussion of the underlying principles of the various aspects of sorting in alluvial channels along with some related laboratory experiments is presented in this paper. From the laboratory experiments, quantitative information pertaining to the spectrum of bed forms, including subaqueous dunes and ripples which develop in an alluvial channel, is presented, and the data are compared with existing empirical and analytical relationships. Under favorable conditions of preservation, limited estimates of the hydraulic environment may be made by measuring the physical characteristics of cross-stratified units and related bed forms. End_of_Article - Last_Page 519------------