Longitudinal Dispersion for Flow over Rough Beds

by Nabil D.Abd El-Hadi, Grad. Student; Dept. of Civ. Engrg., Univ. of New Brunswick, Fredericton, N.B., Canada,
Kersi S. Davar, Prof.; Dept. of Civ. Engrg., Univ. of New Brunswick, Fredericton, N.B., Canada,


Serial Information: Journal of the Hydraulics Division, 1976, Vol. 102, Issue 4, Pg. 483-498


Document Type: Journal Paper

Abstract:

The longitudinal dispersion coefficient, DL, is evaluated on the basis of a one-dimensional analysis as affected by large bed roughness in a laboratory flume. The experimental results have shown that the dimensionless dispersion coefficient, DL/Yu*, in which Y is the water depth and u* is the bed shear velocity, is a function of the relative roughness height, Y/h, and the relative roughness spacing, X/Y. It is also found that DL/Yu* reaches a maximum value at a roughness density h/X = 0.111. The commonly used equation for estimating the longitudinal dispersion coefficient (DL = C Yu*) is also examined. It is found that this straight line relation between DL and Yu* is no longer valid for values of Yu* greater than 0.1 sq ft per sec (0.009 m²/s).



Subject Headings: Hydraulic roughness | Dimensional analysis | River and stream beds | Laboratory tests | Flumes | Shear stress | Fluid velocity | Spacing

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