Factors Determining Bed Forms of Alluvial Streams

Based on the analysis of laboratory and field data according to similarity methods, it is found that the following variables are important in determining the bed forms of sand bed streams: flow depth d and mean velocity, V, density, ρ, and viscosity, ν, of the water; median size of sediment d₅₀ and the acceleration of gravity, g. The data thus analyzed are presented in six graphs of d/d₅₀ against Froude number F for each of six ranges of R_g = d₅₀ (gd₅₀)¹/²/ν which accounts for the effects of sediment size and water viscosity or temperature. Flume data indicate that the size distribution of the bed sediment also affects bed form, but the extent of this effect could not be determined. The effect of grain shape and channel width could not be determined with the available data. A relation is developed between R_g and u⋆( gd₅₀)¹/² which predicts quite well the occurrence of ripple and dune beds in which ^⋆ = shear velocity.