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| Titel |
Field measurements of pressure fluctuations on an instrumented wall: implications for channel-bed erosion |
| VerfasserIn |
B. W. McArdell, B. Fritschi |
| Konferenz |
EGU General Assembly 2012
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 14 (2012) |
| Datensatznummer |
250066247
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| Zusammenfassung |
| Debris flows typically increase their volume and flow depth through entrainment of sediment.
This produces hazardous flows which are also capable of eroding bedrock and changing the
morphology of steep torrent channels. Few observations of entrainment are available to shed
light on the mechanisms occurring in the field. Herein we describe pressure observations
from a vertical array of six force plates, each 0.3 m x 0.3 m in size, installed in a 14
m long wall, oriented parallel to the mean flow direction, at the Illgraben debris
flow observation station, Switzerland. The force plates, sampled at 2 kHz, allow
determination of the mean and fluctuating component of the pressure at the lateral
edge of a debris flow. The median pressure measurements are consistent with data
from a large (8 m2) force plate located near the wall. The fluctuating component of
the pressure is typically an order of magnitude larger than the mean pressure at
the front of the flow, and probably corresponds to the impact of large boulders
(and possibly force chains produced by several boulders) with the force plates as
they flow past the sensors. The fluctuating component of the pressure is largest at
the head of the debris flow were the flow is not yet fully saturated with the liquid
phase of the flow. After the passage of the front of the flow, the pressure fluctuations
decrease in amplitude and are of similar magnitude to the median pressure value.
Previously published measurements of debris flow erosion at the Illgraben torrent
channel (Berger et al., 2011, J. Geophys. Res. Earth Surface) show that sediment
erosion takes place at the front of the flow, coinciding with our observations of large
pressure fluctuations at the front of the flow. We propose that the pressure fluctuations
generated within the debris flow drive both sediment entrainment and bedrock erosion. |
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