TY - JOUR
T1 - Evolution of Debris-Flow Initiation Mechanisms and Sediment Sources During a Sequence of Postwildfire Rainstorms
AU - Tang, Hui
AU - McGuire, Luke A.
AU - Rengers, Francis K.
AU - Kean, Jason W.
AU - Staley, Dennis M.
AU - Smith, Joel B.
N1 - Funding Information:
We thank the Editor John Buffington, one anonymous reviewer, and Jen Pierce for helpful comments that improved the quality of the manuscript. This work was partially supported by the U.S. Geological Survey (USGS) Landslide Hazards Program. Any use of trade, product, or firm names in this paper is for descriptive purposes only and does not constitute endorsement by the U.S. Geological Survey. Code for the numerical model is stored in the Community Surface Dynamics Modeling System (CSDMS) model repository at https://csdms.colorado. edu/wiki/Model:SWEHR. Data used in this manuscript are stored in the USGS ScienceBase archive at https://doi.org/ 10.5066/P92HVD2T and https://doi. org/10.5066/P9F3YTBP.
Funding Information:
We thank the Editor John Buffington, one anonymous reviewer, and Jen Pierce for helpful comments that improved the quality of the manuscript. This work was partially supported by the U.S. Geological Survey (USGS) Landslide Hazards Program. Any use of trade, product, or firm names in this paper is for descriptive purposes only and does not constitute endorsement by the U.S. Geological Survey. Code for the numerical model is stored in the Community Surface Dynamics Modeling System (CSDMS) model repository at https://csdms.colorado.edu/wiki/Model:SWEHR. Data used in this manuscript are stored in the USGS ScienceBase archive at https://doi.org/10.5066/P92HVD2T and https://doi.org/10.5066/P9F3YTBP.
Publisher Copyright:
Published 2019. This article is a U.S. Government work and is in the public domain in the USA.
PY - 2019/6
Y1 - 2019/6
N2 - Wildfire alters vegetation cover and soil hydrologic properties, substantially increasing the likelihood of debris flows in steep watersheds. Our understanding of initiation mechanisms of postwildfire debris flows is limited, in part, by a lack of direct observations and measurements. In particular, there is a need to understand temporal variations in debris-flow likelihood following wildfire and how those variations relate to wildfire-induced hydrologic and geomorphic changes. In this study, we use a combination of in situ measurements, hydrologic monitoring equipment, and numerical modeling to assess the impact of wildfire-induced hydrologic and geomorphic changes on debris-flow initiation during seven postwildfire rainstorms. We predict the impact of hillslope erosion on debris-flow initiation by combining terrestrial laser scanning surveys of a hillslope burned during the 2016 Fish Fire with numerical modeling of sediment transport throughout a 0.12-km2 basin in southern California. We use measurements of sediment thickness within the channel to constrain numerical experiments and to assess the role of channel sediment supply on debris-flow initiation. Results demonstrate that debris flows initiated during rainstorms where hillslopes contributed minimally to the event sediment yield and suggest that large inputs of sediment from rill and gully networks are not essential for runoff-generated debris flows. Simulations suggest that both the gradual entrainment of sediment and the mass failure of channel bed sediment can increase sediment concentration to levels associated with debris flows. Finally, postwildfire debris-flow initiation appears closely linked to the same rainfall intensity-duration threshold despite temporal changes in the sediment source, initiation processes, and hydraulic roughness.
AB - Wildfire alters vegetation cover and soil hydrologic properties, substantially increasing the likelihood of debris flows in steep watersheds. Our understanding of initiation mechanisms of postwildfire debris flows is limited, in part, by a lack of direct observations and measurements. In particular, there is a need to understand temporal variations in debris-flow likelihood following wildfire and how those variations relate to wildfire-induced hydrologic and geomorphic changes. In this study, we use a combination of in situ measurements, hydrologic monitoring equipment, and numerical modeling to assess the impact of wildfire-induced hydrologic and geomorphic changes on debris-flow initiation during seven postwildfire rainstorms. We predict the impact of hillslope erosion on debris-flow initiation by combining terrestrial laser scanning surveys of a hillslope burned during the 2016 Fish Fire with numerical modeling of sediment transport throughout a 0.12-km2 basin in southern California. We use measurements of sediment thickness within the channel to constrain numerical experiments and to assess the role of channel sediment supply on debris-flow initiation. Results demonstrate that debris flows initiated during rainstorms where hillslopes contributed minimally to the event sediment yield and suggest that large inputs of sediment from rill and gully networks are not essential for runoff-generated debris flows. Simulations suggest that both the gradual entrainment of sediment and the mass failure of channel bed sediment can increase sediment concentration to levels associated with debris flows. Finally, postwildfire debris-flow initiation appears closely linked to the same rainfall intensity-duration threshold despite temporal changes in the sediment source, initiation processes, and hydraulic roughness.
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U2 - 10.1029/2018JF004837
DO - 10.1029/2018JF004837
M3 - Article
AN - SCOPUS:85068150660
SN - 2169-9003
VL - 124
SP - 1572
EP - 1595
JO - Journal of Geophysical Research: Earth Surface
JF - Journal of Geophysical Research: Earth Surface
IS - 6
ER -