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A prototype system for forecasting landslides in the Seattle, Washington, area

Reviews in Engineering Geology

By:
, , , and
DOI: 10.1130/2008.4020(06)

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Abstract

Empirical rainfall thresholds and related information form the basis of a prototype system for forecasting landslides in the Seattle area. The forecasts are tied to four alert levels, and a decision tree guides the use of thresholds to determine the appropriate level. From analysis of historical landslide data, we developed a formula for a cumulative rainfall threshold (CT), P3  =  88.9 − 0.67P15, defined by rainfall amounts in millimeters during consecutive 3 d (72 h) periods, P3, and the 15 d (360 h) period before P3P15. The variable CT captures more than 90% of historical events of three or more landslides in 1 d and 3 d periods recorded from 1978 to 2003. However, the low probability of landslide occurrence on a day when the CT is exceeded at one or more rain gauges (8.4%) justifies a low-level of alert for possible landslide occurrence, but it does trigger more vigilant monitoring of rainfall and soil wetness. Exceedance of a rainfall intensity-duration threshold I  =  82.73D−1.13, for intensity, I (mm/hr), and duration, D (hr), corresponds to a higher probability of landslide occurrence (30%) and forms the basis for issuing warnings of impending, widespread occurrence of landslides. Information about the area of exceedance and soil wetness can be used to increase the certainty of landslide forecasts (probabilities as great as 71%). Automated analysis of real-time rainfall and subsurface water data and digital quantitative precipitation forecasts are needed to fully implement a warning system based on the two thresholds.

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Additional Publication Details

Publication type:
Article
Publication Subtype:
Journal Article
Title:
A prototype system for forecasting landslides in the Seattle, Washington, area
Series title:
Reviews in Engineering Geology
DOI:
10.1130/2008.4020(06)
Volume
20
Year Published:
2008
Language:
English
Publisher:
Geological Society of America
Publisher location:
Boulder, CO
Contributing office(s):
Geologic Hazards Science Center
Description:
18 p.
First page:
103
Last page:
120
Country:
United States
State:
Washington
City:
Seattle
Online Only (Y/N):
N
Additional Online Files(Y/N):
N