Author(s): Nabil D. Elhadi; Kersi S. Davar

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Abstract: This paper presents the results of laboratory studies of longitudinal dispersion in open and covered rectangular flume channels; smooth to very rough covers were investigated. The relative roughness height h/y was varied from 0.1 to 0.4; the roughness density H/X varied from 0.025 to 0.25; here H = roughness height, Y = depth of water, and X = spacing between the roughness strips. The velocity varied from 0.7 to 2.0 ft. /sec. (0.21 to 0.61 m/sec). The results showed that the longitudinal dispersion coefficient DL used in the one-dimensional dispersion equation did not vary significantly in the vertical nor lateral directions for the experimental conditions; it was deduced that an average value of DL could be considered representative for the entire cross-section for a wide rectangular channel. It was also found that the introduction of a smooth cover resulted in a reduction of approximately 45% in compared to that for similar depths and velocities for open channel conditions. The addition of relatively large roughness at the top boundary led to increases in DL up to 34% compared to open water conditions.

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Year: 1981