Bedform Stability Fields for Smaller Density Ratio
Abstract
When the fluid flow moves on the granular materials, the bed geometry, i.e., bedforms, change corresponding the flow conditions. Bedforms are the important source of information. From geological point of view, the bedforms migrate to generate the variety of sedimentary structures which can be used to reconstruct the paleo-hydraulic conditions. From the engineering point of view, bedforms have to be considered when the sediment transport and/or the bed roughness are discussed. Although there have been done numerous flume experiments both in the geology and engineering, most of the diagrams of bedform stability fields have been made using the silica materials and water, whose density ratio is about 2.65. Here we performed flume experiments for smaller density ratio, 1.5. This is aimed at examining the effect of density ratio on the bedform stability fields. Different density ratio can occur in the natural environments, such as under the hyperconcentrated flow, or on the surfaces of other planets. We performed flume experiments using the fragments of melamine resin, whose specific gravity is 1.5, and we used five kinds of size distributions. Small recirculating-flumes, 4 m in length, 0.3 or 0.4 m in depth and 0.08 m in width, in Kyoto University and Osaka Institute of Technology are used. The flume floor was laid with the material, and unidirectional flow was operated. The flow discharge was increased gradually, and bedform formation was observed. Flow discharge, flow depth, water-surface slope, and water temperature were measured. Based on these data, non-dimensional parameters, such as Mobility parameter, Particle parameter, and Froude number, were calculated and compared with those of quartz grains (Van den Berg and Van Gelder, 1993). As a result, we got bedform stability fields for the density ratio 1.5. Comparing with that of quartz grains, the following features were found. (1) The kinds of bedforms observed in these experiments were the same with those of quartz grains, (2) In general, the upper-regime plane bed appear in the wider range of mobility and particle parameters, and Froude number.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2008
- Bibcode:
- 2008AGUFM.H53B1055Y
- Keywords:
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- 1824 Geomorphology: general (1625);
- 1825 Geomorphology: fluvial (1625);
- 1861 Sedimentation (4863);
- 1862 Sediment transport (4558);
- 1899 General or miscellaneous