Ripple Concentration and Friction Factor

by Fred F. M. Chang, (M.ASCE), Assoc. Prof.; Dept. of Civ. Engrg., South Dakota State Univ., Brookings, SD,

Serial Information: Journal of the Hydraulics Division, 1970, Vol. 96, Issue 2, Pg. 417-430

Document Type: Journal Paper


Flow over ripples in alluvial channels is essentially the same as the flow over rigid roughness elements, the main difference lying only in the shapes of the ripples and roughness elements. The total friction factor is the summation of grain-roughness friction factor and form-roughness friction factor. Nikuradse's formula for grain-roughness friction factor is found to be satisfactory in determining the value of grain-roughness friction factor for the flow in alluvial channels. The form-roughness friction factor is proportional to the exposure parameter and inversely proportional to mean relative height of the ripples. And, it is also proportional to the coefficient of expansion loss, which is found to be a function of the mean relative height of the ripples.

Subject Headings: Channel flow | Alluvial channels | Grain (material) | Friction | Hydraulic roughness | Professional societies | Parameters (statistics)

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