Natural Roughness Effects in Rigid Open Channels

by A. G. Mirajgaoker,
K. L. N. Charlu,

Serial Information: Journal of the Hydraulics Division, 1963, Vol. 89, Issue 5, Pg. 29-44

Document Type: Journal Paper


The studies conducted to investigate the effects of large natural roughness in open channel flow are reported. There was an attempt to create conditions of boulder streams by fixing natural stones, from 2-1/2 in. to 3 in. in diameter, to the bed of a 3-ft wide rigid bed flume. Six different patterns of boulder placements were tried, and the roughness densities varied from 15 stones per sq yd to 114 stones per sq yd. It was observed that the Chezy's resistance function and the relative roughness parameter are related by a logarithmic formula and that the general resistance diagram, relating the resistance function and the Reynolds number, is also applicable for large natural roughness elements. A new roughness density parameter is introduced herein which was found to have a consistent relation with the resistance function, and which indicates the number of stones per unit area of the channel bed. Results have been compared with the previous investigators who have conducted experiments with idealized geometrical elements.

Subject Headings: Stones | Load and resistance factor design | Hydraulic roughness | Open channels | Open channel flow | Boulders | Parameters (statistics) | Flumes

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