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On a Reasonable, Functional Form for Bed-Load Formulas

Author(s): Shinji Egashira; Robin Biswas; Daisuke Harada; Kuniaki Miyamoto

Linked Author(s): Shinji Egashira

Keywords: Bed-load formula; Sediment transport; Flume tests; Flow width ratio

Abstract: Present study insists that longitudinal bed profiles obtained from flume tests support the bed-load formula proposed by Egashira et al. (1997). The flume tests are conducted to test reasonability of functional forms for bed-load formulas, using open channels which have different flow widths in the upstream and downstream reaches. We reviewed studies on river bed variations which take place in river channels with different flow widths. In addition, we derived regime equations describing the relations among the ratio of the upstream and downstream bed slopes, the flow width ratio, shear stress ratio etc., using the equations of continuity for water flow and sediment transportation, resistance law for quasi-uniform flow and bed-load formulas which have different, functional forms of bed shear stress. Our experiences suggest that the bed slope is steeper in the channel reach with wide cross sections in comparison to the bed slope forming in the narrow reach, because the sediment transport capacity is larger in narrow channel reach. Such characteristics of bed slopes are obtained from flume tests, and are predicted by a new regime relation. However, the regime relation which is derived from widely accepted bed-load formulas don’t provide the bed slope ratios obtained from the present flume tests as well as from the new method. The results of the present study suggest that the bed-load formula, which is different from the widely accepted equations, may have reasonable structure with respect to its functional form.

DOI: https://doi.org/10.3850/IAHR-39WC2521711920221438

Year: 2022

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