Author(s): H. Arisz; K. S. Davar; T. C. C. Tang
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Keywords: No Keywords
Abstract: With the onset of winter, a natural stream which normally has an open channel regime, gradually develops partial ice-cover and finally complete cover. Information about hydraulic resistance characteristics during the transient partially ice-covered regime is nearly non-existent; also, it is difficult and dangerous to make field measurements under these conditions. However, such information is important for river management and design of projects. Hence, the variation of hydraulic resistance for such conditions has been investigated in a laboratory channel with an artificial cover. The channel resistance characteristics were studied by varying percentage coverage (0-100%), flow depths (127-254 mm) and average velocity (0.2-1.2 m/s). The investigations indicated that the Manning’s coefficient of the bed zone changes with percentage cover, contrary to the commonly made assumption that it remains the same as for open water conditions. The maximum value obtained for N (the composite channel resistance coefficient) was 0.036 between 45-55% cover for fixed covers with vertical wall openings. For floating covers a value of 0.031 was obtained between 35-45% cover for vertical wall openings; increased to 0.050 between 20 - 30% cover for inclined wall openings. These results were based on a bed roughness for which N was in the range of 0.021 to 0.023; values of N outside this range may be expected to yield values of N different from those given above. Although, these studies cannot be considered model simulations, they should approximate the hydraulic resistance of a uniform ice cover with a relatively smooth under surface and varying degrees of openings in the cover.
Year: 1988