Recent Advances in Post-Fire Debris-Flow Hazard Assessment at the U.S. Geological Survey Dennis M. Staley, Jason W. Kean, Greg M. Smoczyk, Jacqueline A. Negri U.S. Geological Survey, Landslide Hazards Program, Golden CO USA

What Are Post-Fire Debris-Flows? Initiate from surface runoff and erosion processes. Progressive entrainment of sediment. Often exhibit evidence of both debris-flow and flood processes.

What Are Post-Fire Debris-Flows? Do not require a discrete source of material (e.g. landslide), with a significant percentage of material originating from shallow erosion. Impact constrained to gullies, stream channels and immediately adjacent areas. Probability of occurrence not empirically related to antecedent moisture conditions. Volume and velocity have been experimentally linked via flume studies to antecedent moisture conditions, but not yet empirically demonstrated.

What Are Post-Fire Debris-Flows? Measured debris-flows are generated within minutes after the start of intense rainfall. Average time lag between recorded debris-flows and 15-minute rainfall intensity is 0 minutes! First indication of flow is often a major surge. Challenges for debris-flow early-warning.

What Aren’t Post-Fire Debris-Flows? May 2014 West Salt Creek Landslide, Collbran CO Photo courtesy of Mesa County, CO

USGS Assessment Products - Past

BAER Teams, NWS, and other stakeholders use these maps for emergency planning and warning Feedback from stakeholders Need digital geo-spatial data for planning, not just a paper map. Need maps as soon as possible after burn severity available (days after fire) Want assessments for more than just a handful of fires every year Lesson Learned: Paper maps and reports were not all that useful!

USGS Assessment Products - Present Feedback: Need digital geo-spatial data for planning, not just a paper map. Interactive map Improvement: Interactive map (casual users) and geospatial data (advanced users) are available on website.

USGS Assessment Products - Present Interactive Map Zoom In / Out } Toggle Layers

USGS Assessment Products - Present Interactive Map

USGS Assessment Products - Present Interactive Map

USGS Assessment Products - Present Feedback: Need digital geo-spatial data for planning, not just a paper map. GIS files for download Improvement: Interactive map (casual users) and geospatial data (advanced users) are available on website.

USGS Assessment Products - Present Geospatial Data Basin-scale Predictions (Polygons) Segment-scale Predictions (Lines)

USGS Assessment Products - Present Feedback: Need maps as soon as possible after burn severity available (days after fire) Improvement: Leverage the methods, tools and approach developed by USGS Earthquake Hazards Program for online products (PAGER, ShakeMap, etc.) to rapidly disseminate online assessments Typical OFR Timescale Web-based Timescale (French Fire, CA)

USGS Assessment Products - Present Feedback: Need maps as soon as possible after burn severity available (days after fire) Improvement: Leverage the methods, tools and approach developed by USGS Earthquake Hazards Program for online products (PAGER, ShakeMap, etc.) to rapidly disseminate online assessments

USGS Assessment Products - Present Feedback: Increased Demand Number of hazards assessments conducted by year * 2007 Volume Maps Only # of assessments Move to the web 2015 More anticipated in 2015 as word spreads, 28 so far… 2014: More assessments done in more states than any other year These hazards assessments are now a standard operational product of the USGS Landslide Hazards Program Insufficient time/$ to respond to fires in these years *

USGS Assessment Products – Future (Near Term)

More Information: Google Us! post fire debris flow

Citations: Cannon, S.H., et al., Predicting the probability and volume of postwildfire debris flows in the intermountain western United States. Geological Society of America Bulletin 122, Gartner, J.E., et al., Empirical models for predicting volumes of sediment deposited by debris flows and sediment-laden floods in the transverse ranges of southern California. Engineering Geology 176, Kean, J. W., et al "In situ measurements of post-fire debris flows in southern California: Comparisons of the timing and magnitude of 24 debris-flow events with rainfall and soil moisture conditions." J. Geophys. Res. 116(F4): F Kean, J. W., et al "A low-cost method to measure the timing of post-fire flash floods and debris flows relative to rainfall." Water Resources Research 48(5): W Kean, J. W., et al "Runoff-generated debris flows: Observations and modeling of surge initiation, magnitude, and frequency." Journal of Geophysical Research: Earth Surface 118(4): 2013JF Staley, D.M., Kean, J.W., Cannon, S.H., Schmidt, K.M., Laber, J.L., Objective definition of rainfall intensity–duration thresholds for the initiation of post-fire debris flows in southern California. Landslides 10, Staley, D. M., et al "Characterizing the primary material sources and dominant erosional processes for post-fire debris-flow initiation in a headwater basin using multi-temporal terrestrial laser scanning data." Geomorphology 214(0): Contact Info: Phone: Phone: Website: More Information: URL, Citations, Contact Info