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Broad-scale climatic influences on rainfall thresholds for debris flows; adapting thresholds for Northern California to Southern California

Raymond C. Wilson
Broad-scale climatic influences on rainfall thresholds for debris flows; adapting thresholds for Northern California to Southern California (in Storm-induced geologic hazards; case histories from the 1992-1993 winter in Southern California and Arizona, Robert A. Larson (editor) and James E. Slosson (editor))
Reviews in Engineering Geology (1997) 11: 71-80

Abstract

A Landslide Warning System (LWS) operated in the San Francisco Bay region until late 1995. The LWS issued public advisories when rainfall conditions reached or approached critical levels for triggering debris flows ("mudslides"). Interest in an LWS for southern California was revived by the destructive landslides triggered by the storms of January and February 1993 and by the debris-flow problems created by the extensive areas burned in large wildfires the following autumn. Although a number of elements for an LWS already exist in southern California, a critical element must still be developed: the "threshold," a defined set of values of rainfall intensity and duration that predicts debris-flow initiation within a specified region. Although reliable rainfall/debris-flow thresholds exist for the San Francisco Bay region, climatic dissimilarities between there and southern California produce differences in the thickness, character, and behavior of the hillslope materials that necessitate adjustment of the thresholds. Of particular importance are the amount and distribution of precipitation, which, along the California coast, are controlled by elevation, distance from the coastline, and storm frequency. Storm frequency, in turn, is strongly correlated with geographic latitude. Although storms are less frequent in southern California, with a consequent decrease in mean annual precipitation, average rainfall amounts for individual storms generally equal those of storms farther north. A procedure is developed for modifying existing rainfall/debris-flow thresholds to account for these changes in precipitation patterns. Then, a set of interim rainfall/debris-flow thresholds is derived for the greater Los Angeles region. As a demonstration, these interim thresholds are compared with data on rainfall and debris-flow occurrence during January and February 1993.


ISSN: 0080-2018
EISSN: 2169-799X
Coden: GAEGA4
Serial Title: Reviews in Engineering Geology
Serial Volume: 11
Title: Broad-scale climatic influences on rainfall thresholds for debris flows; adapting thresholds for Northern California to Southern California
Title: Storm-induced geologic hazards; case histories from the 1992-1993 winter in Southern California and Arizona
Author(s): Wilson, Raymond C.
Author(s): Larson, Robert A.editor
Author(s): Slosson, James E.editor
Affiliation: U. S. Geological Survey, Menlo Park, CA, United States
Affiliation: Los Angeles County Department of Public Works, Alhambra, CA, United States
Pages: 71-80
Published: 1997
Text Language: English
Publisher: Geological Society of America (GSA), Boulder, CO, United States
ISBN: 0-8137-4111-4
References: 24
Accession Number: 1998-019151
Categories: Engineering geology
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 1 table
Secondary Affiliation: Slosson and Associates, USA, United States
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute. Reference includes data supplied by the Geological Society of America, Boulder, CO, United States
Update Code: 199808
Program Name: USGSOPNon-USGS publications with USGS authors
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