Modeling rainfall conditions for shallow landsliding in Seattle, Washington

Reviews in Engineering Geology
By: , and 



We describe the results from an application of a distributed, transient infiltration–slope-stability model for an 18 km2 area of southwestern Seattle, Washington, USA. The model (TRIGRS) combines an infinite slope-stability calculation and an analytic, one-dimensional solution for pore-pressure diffusion in a soil layer of finite depth in response to time-varying rainfall. The transient solution for pore-pressure response can be superposed on any steady-state groundwater-flow field that is consistent with model assumptions. Applied over digital topography, the model computes a factor of safety for each grid cell at any time during a rainstorm. Input variables may vary from cell to cell, and the rainfall rate can vary in both space and time. For Seattle, topographic slope derived from an airborne laser swath mapping (ALSM)–based 3 m digital elevation model (DEM), maps of soil and water-table depths derived from geotechnical borings, and hourly rainfall intensities were used as model inputs. Material strength and hydraulic properties used in the model were determined from field and laboratory measurements, and a tension-saturated initial condition was assumed. Results are given in terms of a destabilizing intensity and duration of rainfall, and they were evaluated by comparing the locations of 212 historical landslides with the area mapped as potentially unstable. Because the equations of groundwater flow are explicitly solved with respect to time, the results from TRIGRS simulations can be portrayed quantitatively to assess the potential landslide hazard based on rainfall conditions.

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Additional publication details

Publication type Article
Publication Subtype Journal Article
Title Modeling rainfall conditions for shallow landsliding in Seattle, Washington
Series title Reviews in Engineering Geology
DOI 10.1130/2008.4020(08)
Volume 20
Year Published 2008
Language English
Publisher Geological Society of America
Contributing office(s) Geologic Hazards Science Center
Description 16 p.
First page 137
Last page 152
Country United States
State Washington
City Seattle
Online Only (Y/N) N
Additional Online Files (Y/N) N
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