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| Titel |
Landslide-channel feedbacks amplify flood response and channel erosion |
| VerfasserIn |
Georgina Bennett, Jason Kean, Francis Rengers, Sandra Ryan, Sara Rathburn |
| Konferenz |
EGU General Assembly 2017
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 19 (2017) |
| Datensatznummer |
250149920
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| Publikation (Nr.) |
 EGU/EGU2017-14326.pdf |
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| Zusammenfassung |
| Flood stream power is amplified in mountainous catchments by channel confinement and
steep slopes, generating widespread channel erosion and causing significant challenges for
flood risk management. Approaches to predicting flood channel response include
identification of stream power thresholds. However, in a mountainous catchment in Colorado,
USA, we find that stream power, estimated from the pre-storm DEM, was not a good
predictor of channel flood response and that landslide-channel feedbacks better explain the
observed pattern of channel erosion.
The North St Vrain is a 250 km2 catchment in the Colorado Front Range. It was among
several catchments impacted by a 1000 yr prolonged rainfall event in September 2013, which
generated a 200 yr flood and >100 landslides in the catchment. We estimated peak discharge
and stream power using radar-based rainfall data, wherein the rainfall was converted to a
discharge based on the upstream drainage area and assuming no infiltration (a reasonable
assumption after 3 days of heavy rainfall). Measured high water marks in key reaches were
used to calculate a field-based estimate of peak discharge. These discharge estimates were
compared with spatial erosion estimates, calculated using the differenced pre- and post-flood
LiDAR DEMs.
We found that the onset of profound channel erosion was determined by the formation
and failure of an in-channel dam. The dam, composed of debris flow and tributary sediment
input, was sufficiently large (∼150,000 m3) to temporarily overwhelm channel transport
capacity even during flood. Our field-based estimate of peak discharge downstream of the
dam is more than 2 times greater than our rainfall-based estimate, which suggests a dam burst
event occurred. Further downstream we observe additional channel reaches in which
erosion was amplified by landslide and tributary sediment input, either through
the formation and failure of dams or potentially through sediment bulking alone.
These findings imply that when estimating flood risks along mountainous channels,
model accuracy might be improved if the effects of landsliding are also considered. |
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