Dissipative analogies between a schematic macro-roughness arrangement and step-pool morphology

摘要

We investigate flow resistance developed by macro-roughness represented by pebbles positioned on a granular layer according to a regularly spaced stripe pattern on steep bed slopes. Flume experiments under various geometrical and hydraulic conditions are carried out and interpreted by means of a theoretical model. Results show that flow resistance reaches a maximum and is due mainly to form drag when the spacing between macro-roughness stripes is about 10 times the average macro-roughness height. A statistical analysis based on various field observations of step-pool geometry underlines that this spacing appears to be one of the most frequent occurring in step-pool bed morphology sequences. Comparison between the present results and flow resistance evaluated for step-pools reproduced in the laboratory and observed in the field suggests that step-pool streams are characterized by a bed geometry able to develop the maximum flow resistance. Finally, a criterion is obtained to estimate flow resistance developed by natural step-pool streams when a formative flow discharge occurs based on geometric quantities only. Copyright (C) 2007 John Wiley & Sons, Ltd.