21. Deterministic Rainfall Thresholds for Landslide Hazard Forecasting

Shallow landslides and debris flows triggered by severe rainstorms occur frequently with widespread destructiveness in mountainous areas throughout the United States. Landslides in Southern California, Ohio, and Pennsylvania triggered by winter season rainfall in 2005 and those in North Carolina triggered by the remnants of Hurricane Ivan in September 2004 are the most recent examples of these destructive and deadly occurrences. Forecasting landslide hazard requires an understanding of where and when such landslides occur, as well as the extent of a specific storm-induced event. Typically, forecasting shallow landsliding has relied on empirical correlations between landslide occurrence and storm rainfall to define a threshold condition above which shallow landsliding can be expected (e.g. Keefer and others, 1987). Because of spatial variations in climate, topography, and geology, empirically based rainfall thresholds are regionally specific and their application for forecasts or warnings requires historical documentation of landslide occurrence and corresponding rainfall information. For most areas of the United States where shallow landslides and debris flows pose a hazard, with a few exceptions (e.g. San Francisco Bay region, Seattle), these data are limited or unavailable. In order to forecast rainfall-induced landslide events throughout the U.S., there is a pressing need for new quantitative, transferable, and physics-based methods to define triggering rainfall conditions. Recent work by USGS scientists provides a foundation for developing such thresholds deterministically (Iverson, 2000; Savage and others, 2003). Preliminary results from an application of this approach in southwestern Seattle, Washington, show promising comparison with empirical thresholds.

The focus of research under this opportunity is to develop and test new, physics-based methods for deterministically defining rainfall thresholds to forecast shallow landslide and debris-flow occurrence over broad regions. This research will likely involve:

1. Applying remote sensing data and technologies (e.g. LiDAR, InSAR) to develop new methods for mapping material and moisture properties of the shallow subsurface over wide areas.
2. Collecting critical data on soil response to severe rainfall using field, experimental, and monitoring data.
3. Using coupled hydrologic and mechanical models to simulate rainfall effects on shallow instability over a variety of field conditions.
4. Developing and testing systems for near-real-time data analysis and display of changing slope stability with prolonged rainfall.

Allied project work planned for Oregon and Southern California provides an opportunity for close collaboration with USGS scientists in developing a state-of-the-art hazard forecasting system. A unique facility that may be utilized is the USGS/Colorado School of Mines experimental soil mechanics laboratory.

REFERENCES

Iverson, R.M., 2000, Landslide triggering by rain infiltration: Water Resources Research, v. 36, no. 7, p. 1897-1910. http://vulcan.wr.usgs.gov/Projects/MassMovement/Publications/WRR_July2000/framework.html

Keefer, D.K., Wilson, R.C., Mark, R.K., Brabb, E.E., III, W.M.B., Ellen, S.D., Harp, E.L., Wieczorek, G.F., Alger, C.S., and Zatkin, R.S., 1987, Real-time landslide warning during heavy rainfall: Science, v. 238, no. 13 November, p. 921-925.

Savage, W.Z, Godt, J.W., and Baum, R.L., 2003, A model for spatially and temporally distributed shallow landslide initiation by rainfall infiltration, in Rickenmann, D. and Chen, C.L., (eds.), Debris-flow hazards mitigation: Mechanics, prediction, and assessment: Rotterdam, Millpress, p. 179-187.

Proposed Duty Station: Golden, CO

Areas of Ph.D.: Earth sciences and some combination of experience and training in geomorphology, soil physics, subsurface hydrology, remote sensing, climatology, soil mechanics, and spatial statistics

Qualifications: Applicants must meet one of the following qualifications: Research Geologist, Research Hydrologist

(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 Personnel specialist.)

Research Advisor(s): Jonathan Godt, (303) 273-8626, jgodt@usgs.gov; Rex Baum, (303) 273-8610, baum@usgs.gov; Mark Reid, (650)-329-4891, mreid@usgs.gov; Jim Verdin, (605) 594-6018, verdin@usgs.gov

Personnel Office contact: Kathleen Scheich, (303) 236-9581, kscheich@usgs.gov

Summary of Opportunities