Flow Resistance of Dunes in Alluvial Streams

Citation

Hwang, Li-San (1965) Flow Resistance of Dunes in Alluvial Streams. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/HRDZ-N222. https://resolver.caltech.edu/CaltechETD:etd-05092003-173224

Abstract

NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document. Studies were made of the hydrodynamic resistance of channels with beds covered with dunes generated by flows over granular sediments of the kind normally found in alluvial rivers. The principal objectives of the studies were to determine the pertinent geometric properties of a dune bed by means of which one can express the dune resistance and to establish a quantitative relation between resistance and these geometric quantities. The main results reported here were obtained through experiments in laboratory flumes. A series of 23 experiments with flows over dune-covered beds of fine sand were performed in tilting flumes 130 ft. and 40 ft. in length respectively. In addition, two dune beds generated by different flows were stabilized chemically without disturbing their surface configurations and texture. By doing this, it was possible to explore velocity and pressure distributions in the flow fields and to determine the effect of Reynolds number on the friction factor of the dune beds. It was found that the hydrodynamic roughness of a dune field can be described by the average dune height and the exposure parameter which is the fraction of the total bed area occupied by the horizontal projection of the steep lee slopes of the dunes. It was also found from the results of flume experiments that the bed friction factor due to dunes is a function of the modified relative roughness, [...] , where r[?] is the bed hydraulic radius, e is the exposure parameter defined above and [...] is the average dune height. A function for dune resistance in straight uniform channels, that is, Equation (6-1) was established from experimental results obtained in the flume. Friction factors for typical alluvial rivers cannot be calculated from Equation (6-1) above because some important features of streams, such as meandering, which contribute to resistance are not reproduced in flumes.

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