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debris flow big wheel FAQ

1. Q: What does the wheel do?
A: The wheel allows us to study the particle dynamics, boundary forces, and bedrock erosion caused by natural debris flow material in a controlled laboratory environment.

2. Q: What is the motivation for this research?
A: We are interested in the stresses exerted by debris flows on bedrock channels and the related channel erosion rates because field evidence suggests that debris flow erosion may be the dominant geomorphic agent incising steep channels. We want to understand the mechanisms and rates of bedrock incision by debris flows so that the results can be incorporated into landscape evolution models.
3. Q: Why is the wheel so big?
A. The wheel is 4 meters diameter because that is the largest size that would fit in our building. We donít want to scale down the grain sizes in our flows because small particles (clay and silt size) behave differently from sand and gravel when subjected to water.

4. Q: What can the wheel measure? How fast can it go?
A. A laser profiler measures the longitudinal profile of the flow, up to 20 scans per second. A load plate measures the force exerted on a 225 cm2 area of the bed. A camera-laser system measures the topography of erodible bedrock samples embedded in the flume. The maximum tangential speed is 3 m/s.

5. Q: How much material goes in the flume at once?
A. In a typical experiment, the flow consists of about 2000 lbs of material.

6. Q: Who built the wheel?
A. The wheel was designed and built by Engineering Laboratory Design, in Lake City, Minnesota. The laser profiler and load plate were designed and installed by Jim Mullin and Chris Ellis of St. Anthony Fall's Laboratory, University of Minnesota (National Center for Earth Surface Dynamics). Many other flume parts were designed and built by Stuart Foster at the Richmond Field Station.

7. Q: What's the effect of the drum-geometry?
A: The advantage to the drum shape is that we can run a continuous granular
flow until the bedrock samples erode. But the continuously concave shape of the drum is different from any natural channel. Sediment cannot be deposited in
our flume. A centrifugal force may be significant at higher drum speeds, so we
usually keep the drum velocity below a threshold value.

8. Q: What have you learned from the wheel?
A: So far we've measured the forces exerted on the bed from water-saturated gravel and muddy flows, and those same flows with large (20 cm diameter) boulders. The boulders exert large localized stresses on the bed. The bed roughness is very important in controlling the amount of sliding and type of wear on the erodible bedrock sample.

9. Q: Can you run in it and/or go for rides?
A: I don't know who would do such a thing.

last modified 06 december 2007