Numerical modeling of rainfall thresholds for shallow landsliding in the Seattle, Washington, area

Reviews in Engineering Geology
By:  and 



The temporal forecasting of landslide hazard has typically relied on empirical relations between rainfall characteristics and landslide occurrence to identify conditions that may cause shallow landslides. Here, we describe an alternate, deterministic approach to define rainfall thresholds for landslide occurrence in the Seattle, Washington, area. This approach combines an infinite slope-stability model with a variably saturated flow model to determine the rainfall intensity and duration that leads to shallow failure of hillside colluvium. We examine the influence of variation in particle-size distribution on the unsaturated hydraulic properties of the colluvium by performing capillary-rise tests on glacial outwash sand and three experimental soils with increasing amounts of fine-grained material. Observations of pore-water response to rainfall collected as part of a program to monitor the near-surface hydrology of steep coastal bluffs along Puget Sound were used to test the numerical model results and in an inverse modeling procedure to determine the in situ hydraulic properties. Modeling results are given in terms of a destabilizing rainfall intensity and duration, and comparisons with empirical observations of landslide occurrence and triggering rainfall indicate that the modeling approach may be useful for forecasting landslide occurrence.

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Additional publication details

Publication type Article
Publication Subtype Journal Article
Title Numerical modeling of rainfall thresholds for shallow landsliding in the Seattle, Washington, area
Series title Reviews in Engineering Geology
DOI 10.1130/2008.4020(07)
Volume 20
Year Published 2008
Language English
Publisher Geological Society of America
Publisher location Boulder, CO
Contributing office(s) Geologic Hazards Science Center
Description 16 p.
First page 121
Last page 136
Country United States
State Washington
City Seattle
Online Only (Y/N) N
Additional Online Files (Y/N) N
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