Bedform existence diagrams for open channel flow: light weight plastic versus quartz
Abstract
Fluvial bedforms such as ripples, dunes and antidunes provide partial indicators of the flows that created them. Bedforms seen in outcrops are thus useful for the reconstruction of paleoflow conditions. Fluvial sediments most commonly have specific gravities near the standard value for quartz, i.e. 2.65. All bedforms commonly observed in the field can also be reproduced in the laboratory. Most such experiments, however, involve a substantial reduction in macroscopic scale such as depth. One way to account for reduced laboratory scale is the use of a grain size that is correspondingly finer than the target field case. Another commonly method is the use of lightweight sediments such as plastic, coal or walnut shells. The reduced grain density renders the particles more mobile than quartz particles with the same grain size, and thus in principle allows a wider range of applicability to field-scale conditions. The question remains, however, as to whether or not bedforms in lightweight material fall into the same existence regimes as those observed for quartz. Here this issue is explored using non-dimensional plots involving three parameters: dimensionless grain size, Shields mobility number and Froude number. The analysis presented here indicates that the regimes for ripples, dunes and lower-regime plane bed are generally similar for both sediment densities. This suggests the utility of applying results obtained using lightweight sediment to paleoflow interpretation. The upper regime plane bed observed for lightweight sediments, however, is noticeably biased toward lower Froude numbers than that observed for quartz.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2011
- Bibcode:
- 2011AGUFMEP23A0726Y
- Keywords:
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- 1847 HYDROLOGY / Modeling