Alluvial Flow Resistance—Engelund Sediment Waveform

In 1967 Engelund and Hansen proposed a sediment energy equation based in part on the characteristics of the sediment waveform. In this same monograph, based on the compilation of flume data they showed that the ratio of flow resistance to sediment waveform was a constant. This permitted a substitution of flow resistance for waveform—resulting in the widely used Engelund-Hansen sediment transport equation. The difficulty with the E-H equation is that flow resistance remains a function of waveform, which in most cases cannot be directly measured. In this paper, use of the E-H ratio (dimensionless shear stress to the 5/2 power divided by the dimensionless sediment transport rate) is evaluated further. It is shown that for bedforms in the dune range that the non-grain roughness component of alluvial roughness is a semi-logarithmic function of the E-H ratio. Beyond the dune range it is shown that non-grain roughness is a function of base dune roughness and a shape factor that is a linear function of Froude number. Utilization of the E-H ratio therefore provides for direct estimates of several important alluvial hydraulic properties including: flow resistance, sediment waveform characteristics, and sediment transport. The approach is valid for dune, transitional, and upper regime bedforms up to a Froude number of 0.8.