Constraining parameter uncertainty in modeling debris-flow initiation during the September 2013 Colorado Front Range storm

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The occurrence of debris flows during the September 2013 northern Colorado floods took the emergency management community by surprise. The September 2013 debris flows in the Colorado Front Range initiated from shallow landslides in colluvium. Most occurred on south- and east-facing slopes on the walls of steep canyons in crystalline rocks and on sedimentary hogbacks. Previous studies showed that most debris flows occurred in areas of high storm-total rainfall and that strength added by tree roots accounts for the low number of landslides in densely forested areas. Given the lack of rainfall thresholds for debris flow occurrence in northern Colorado, we want to parameterize a numerical model to assess potential for debris flows in advance of heavy rainfall. Natural Resources Conservation Service (NRCS) soil mapping of the area, supplemented by laboratory testing and field measurements, indicates that soil textures and hydraulic properties of landslide source materials vary considerably over the study area. As a step toward modeling storm response, available soil and geologic mapping have been interpreted to define zones of relatively homogeneous properties. A new, simplified modeling approach for evaluating model input parameters in the context of slope and depth of observed debris flow source areas and recorded debris-flow inducing rainfall helps narrow the range of possible parameters to those most likely to produce model results consistent with observed debris flow initiation. Initial results have narrowed the strength parameters to about one third of possible combinations of cohesion and internal friction angle and narrowed hydraulic conductivity to a range spanning slightly more than one order of magnitude.

Study Area

Publication type Conference Paper
Title Constraining parameter uncertainty in modeling debris-flow initiation during the September 2013 Colorado Front Range storm
Year Published 2019
Language English
Publisher Association of Environmental and Engineering Geologists and Mountain Scholar (Colorado School of Mines)
Contributing office(s) Geologic Hazards Science Center
Description 8 p.
Larger Work Type Book
Larger Work Subtype Conference publication
Larger Work Title Debris-flow hazards mitigation: Mechanics, monitoring, modeling, and assessment; proceedings of the Seventh International Conference on Debris-Flow Hazards Mitigation, Golden, Colorado, USA, June 10-13, 2019
First page 249
Last page 256
Conference Title Seventh International Conference on Debris-Flow Hazards Mitigation
Conference Location Golden, CO
Conference Date June 10-13, 2019
Country United States
State Colorado
Other Geospatial Colorado Front Range
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