Resistance to Flow in Alluvial Channels

A direct method of predicting flow resistance and uniform velocity in alluvial channels is developed. The method covers all known bed-form regimes and not only eliminates trial-and-error computations and use of rigid-boundary channel flow formulas but also avoids the difficulties associated with the use of the various existing alluvial channel flow computation techniques. The study shows that the Darcy-Weisbach friction factor can be expressed as a unique function of the ratio of the bed form and grain shear stress components for any anticipated discharge and flow geometry, the bed-form shear component being uniquely determinable from the flow and channel material characteristics. The results confirm that the friction factor is nonconstant but varies with the bed-form regime. The applicability of the method to laboratory flumes, field canals, and natural rivers is illustrated.