Flow Resistance from Cylindrical Roughness

by Soronadi Nnaji, Grad. Student; Dept. of Hydr. and Water Resour., Univ. of Arizona,
I-pai Wu, (M.ASCE), Assoc. Prof.; Agr. Engrg. Dept., Univ. of Hawaii, Honolulu, HI,

Serial Information: Journal of the Irrigation and Drainage Division, 1973, Vol. 99, Issue 1, Pg. 15-26

Document Type: Journal Paper


The root mean square, σ, of the heights of wires simulating crop stems is found to be a good measure for quantifying roughness of a cylindrical type. An expression is derived for σ in terms of the geometric characteristics of the elements. The Prandtl-von Karman ... Universal velocity distribution equation for turbulent flow over a rough surface was adopted in the form presented by Sayre and Albertson. A relationship between the resistance parameter, X, in this latter equation and the derived σ was obtained and substantiated with data obtained from experiments performed by Wessels and Strelkoff and Fenzl. The relationship is of a power-type function and holds good for values of the resistance parameter greater than 0.0015 ft (0.0005 m). The composite resistance of the soil and vegetative roughness in the field was investigated. The percentage relative contribution of the soil to the total resistance follows an asymptotic decay curve with increasing flow depth.

Subject Headings: Flow resistance | Load and resistance factor design | Hydraulic roughness | Velocity distribution | Turbulent flow | Parameters (statistics) | Field tests | Crops

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