S44. Modeling post-wildfire debris-flow inundation

Wildfire alters the hydrology of watersheds making them very susceptible to dangerous flash floods and debris flows. A tragic recent example struck on 9 January 2018 in Montecito, California following the Thomas fire (which at the time was the largest fire in California history). Intense rainfall on the recently burned slopes triggered a series of debris flows that carried boulders up to 6 m in diameter and travelled 3 km down alluvial fans, killing 23 people and damaging or destroying over 400 homes. 

The tragedy at Montecito underscores the need for accurate identification of post-wildfire debris-flow runout paths to inform emergency response and evacuation plans. Although past research has developed successful tools to rapidly assess the likelihood and potential volume of debris flow within a burn area, the complexity of debris-flow runout processes has precluded development of an operational tool to predict where the flows will end up.

Advances in computer processing power and the availability of high-resolution topography suggest that numerical modeling may be a viable route towards identifying likely zones of inundation. A variety of debris-flow runout models already exist; however, few have been applied or tested in post-wildfire settings. Moreover, there is no established protocol for calibrating model parameters, evaluating avulsion scenarios, or depicting uncertainty in estimates of runout paths.

We seek a Mendenhall Fellow to advance the understanding of debris-flow inundation after wildfire. Research is expected to result in a general and statistically robust protocol for creating probabilistic maps of post-wildfire debris-flow inundation. Research should also address the prediction challenges associated with modeling flows through the built environment.

This research opportunity can capitalize on a new data set documenting the inundation characteristics of the 2018 Montecito Debris-Flow Event (Kean et al., 2019), as well as data from the 2003 Old and Grand Prix Fires in southern California. The Montecito data includes high spatial resolution pre- and post-event topography and detailed field measurements describing the extent of inundation, flow depth, sediment thickness, and building damage along five debris-flow runout paths. The data set can be used to evaluate model skill in predicting deposit extent and thickness, as well as the peak flow depth that caused much of the destruction. The data can also be used to answer questions about model generality, such as: How well do model parameters calibrated for one drainage work on other drainages?  How should avulsion scenarios be treated in a model? How can pre-event field mapping be utilized to better constrain a model?

The postdoctoral fellow will have the opportunity to engage a research team of both USGS scientists and academic collaborators, with skill sets including numerical modeling, advanced geospatial analaysis, quantitative geomorphology and hydrology, and assessment of geologic hazards.  Additionally, the project will involve high levels of engagement with collaborators at the California Geological Survey, National Weather Service, and U.S. Forest Service.

Interested applicants are strongly encouraged to contact the Research Advisors early in the application process to discuss project ideas.

References

Kean, J.W., D.M. Staley, J.T. Lancaster, F.K. Rengers, B.J. Swanson, J.A. Coe, J.L. Hernandez, A.J. Sigman, K.E. Allstadt, D.N. Lindsay (2019), Inundation, flow dynamics, and damage in the 9 January 2018 Montecito debris-flow event, California, USA: Opportunities and challenges for post-wildfire risk assessment, Geosphere, doi: https://doi.org/10.1130/GES02048

Proposed Duty Station: Golden, Colorado

Areas of PhD: Earth Science (geology, hydrology, geography, geophysics), engineering, physics, applied mathematics (candidates holding a Ph.D. in other disciplines but with knowledge and skills relevant to the Research Opportunity may be considered).

Qualifications: Applicants must meet one of the following qualifications: Research Geologist, Research Hydrologist, Research Physical Scientist, Research Mathematician, Research Physicist, Research Civil Engineer, Research Engineer.

(This type of research is performed by those who have backgrounds for the occupations stated above.  However, other titles may be applicable depending on the applicant's background, education, and research proposal. The final classification of the position will be made by the Human Resources specialist.)

Human Resources Office Contact: Audrey Tsujita, 916-278-9395, atsujita@usgs.gov