Sand wavelets in laminar open-channel flows

The results of experimental investigations indicate that sand wavelets can be generated from plane-bed conditions in open-channel laminar flow, the lengths, shapes and patterns of generation for these wavelets being consistent with observations for alluvial flows. Wavelets are of a preferred wavelength which is relatively insensitive to the characteristics of the applied flow and primarily a function of the size of the sediment, these wavelengths lambda for alluvial and laminar open-channel flows over beds of quartz and lightweight sediments of size d = 0.2 mm to d = 1.6 mm being simply described by lambda = 175d(0.75), where lambda and d are expressed in millimetres. The laminar-flow sand-wavelet data present significant implications to contemporary understanding of bed-form mechanics, with both ripples and dunes being postulated to subsequently develop from these wavelets for alluvial flows. The data also raise significant questions as to whether the generation of ripples and dunes in alluvial flows can be attributed to an organised structure of turbulence within the flow.