Author(s): Elsayed Ismail; K. S. Davar
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Keywords: No Keywords
Abstract: Rivers and streams in cold regions are normally covered with ice during long winter seasons. Design information relating to resistance to channel flows under such conditions is essential for effective river regulation for hydropower, navigation, flood control, etc. However, field information is scarce due to difficulties, uncertainties, and dangers associated with such measurements. Hence, a laboratory study based on laws of hydraulic similitude, was undertaken to investigate the problem. This paper presents the results of a laboratory investigation to evaluate the resistance to flow in a relatively wide-covered channel with the top cover artificially roughened by relatively large strip roughnesses of different heights and varying spacing, simulating the effects of rough ice cover on rivers. Measurements showed that depending on the pattern of roughness on the top boundary, energy dissipation for the whole conduit with a very rough top boundary could be as high as ten times that for the same channel without any additional roughness. Analysis of results shows that resistance to flow with such large roughness may be due to two components: first, skin friction on the normal relatively smooth boundaries, and second, very large form drag at the roughness elements at the top boundary. The results showed that generally over 90% of the total energy dissipation could be allocated to form drag due to the additional large roughnesses. Results also showed that the traditional constants A and B in the conventional logarithmic velocity distribution law has to be replaced by two functions to account for the variation of turbulence structure between the roughness elements.
Year: 1978