Flow Resistance in Large Test Channel

Abstract

Experiments in a large test channel defined friction factors for equilibrium flows up to 150 cfs over a sand bed. Although the friction factors were generally higher than those predicted by either of the three most cited published procedures, they were consistent with published data from smaller flumes with similar sand as the bed material. The Froude number seemed to unify the data into a single average trend. Correlations between the friction factor for flat bed flows and the Reynolds number and relative sand‐grain roughness were also shown to embody a strong Froude number dependency with only minor Reynolds number effect. Division of the total friction factors into components associated with the channel walls, sand grain resistance, and bed form resistance did not improve correlations with the Froude number. The apparent absence of Reynolds number effect in correlation of the friction factor with Froude number may not be general for finer sediments and an extended range of Reynolds numbers. A transformation of the Alam/Kennedy friction diagram for bed forms suggests a decrease in friction factor for finer sands or larger Reynolds numbers or both.