oa Civil Engineering = Siviele Ingenieurswese - Absolute roughness of concrete-lined channels

Volume 24, Issue 4
  • ISSN : 1021-2000



Observations on absolute roughness and Manning n values were done in concrete-lined canals at four major schemes (Gamtoos, Hartebeespoort, Lower Orange River and Vaalharts) of the Department of Water Affairs, Forestry and Environmental Conservation. Manning n values which are still being used extensively by the Directorate of Water Affairs for open channel flow calculations were first obtained by means of flow measurement and then determined independently by linear roughness measurements of the canal surfaces during off-periods. The correlation between these two methods was found to be very satisfactory, 92 per cent of the observations yielding similar results. During the investigations a number of important advantages of the method using roughness measurements to determine friction coefficients such as Manning n values were observed on site.

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