Friction Factor of Armored River Beds

Abstract

Friction factors of armored river beds at the discharge that forms the armor coat are investigated. The analysis shows that the friction factor is rather independent of grain‐size distribution of the material forming the bed and the maximum grain size of this material. The major controlling parameter is the slope of the energy grade line. These unexpected results are explained by the coupling of the friction factor with the incipient motion problem and the rearrangement of the grains of the coarsest fraction in the armor coat. The difference between rounded and angular material is discussed. Field data collected in irrigation canals support the results obtained from laboratory experiments.