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| Titel |
Rapid assessment of debris flow erosion and deposition dynamics by means of terrestrial laser scanning at Illgraben, Switzerland |
| VerfasserIn |
P. Schuerch, A. L. Densmore, N. J. Rosser, B. McArdell |
| Konferenz |
EGU General Assembly 2009
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 11 (2009) |
| Datensatznummer |
250023890
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| Zusammenfassung |
| Debris flows are a primary geologic hazard in mountainous areas worldwide but we have
a poor understanding of how flows interact with their channels as they progress
downstream. This interaction is important because it affects the hazard of a single
flow and makes subsequent flows harder to predict and control. We quantify the
patterns of, and controls on, erosion and deposition in debris flows by comparing
high-resolution topographic change with flow properties (discharge, composition,
density). An understanding of how debris flows erode and deposit is crucial for
hazard mitigation. Such interactions affect flow volume and thus maximum runout
distance. Changes to the channel cross-section also influence the behaviour of future
flows.
The Illgraben fan has experienced 36 debris flows since June 2000, generally in response to
summer (May–October) convective storms. The local geology and high relief allow for a very
high sediment yield of 150’000 m3/yr.
A debris flow channel may be dominated by erosion, translation (no net volume change) or
deposition. We show that at the Illgraben areas of erosion and deposition have a complex
distribution along the channel, and that this distribution changes between events. These
observations suggest that local channel geometry and slope play a major role. We present
high resolution (0.2 m grid) change maps from successive sets of terrestrial laser scanning
data along a 300 m study reach. We use change maps to derive lag rates of single debris flow
events by projecting the volume change onto a flow axis down the channel Thalweg. We
relate lag rate and pattern of deposition and erosion to the flow properties of these events
including hydrograph, bulk density, volume, front velocity and composition. We test these
results for correlation with measures of channel geometry including hydraulic radius, bed
slope, and flow cross-section. |
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