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U.S. Department of the InteriorU.S. Geological Survey
Climate Change Based Prediction of Coastal Cliff Landslides Near San Francisco, California
Brian D. CollinsUnited States Geological SurveyWestern Earth Surface Processes Team, Menlo Park, California
Climate Change, Natural Resources and Coastal Management WorkshopConcurrent Session C – Nearshore and Open Ocean
Introduction
Coastal bluffs/sea-cliffsSusceptible to a number of forcing agentsWaves, rainfall
Climate change effectsSea level riseChanges in wave climateVariability of storms and precipitation
This researchProcess-based investigation of failure mechanismsEmpirical prediction of triggering event thresholds
Pacifica, California
Coastal Cliff Landslides
December 22, 2002 January 30, 2003
Area of Failure ~10m
Goals and Methods
Predict coastal cliff failures through development of intensity-duration thresholds
Collection of temporally and spatially high-resolution landslide dataset
Correlation with landslide process-based indicators
Develop ability to forecast – predictions from expected weather (short-term) and climate (long-term)
Planning for expected coastal response
Study Area(San Francisco, California)
Pacific Ocean
Study area ~1.5 km
SAF
San Francisco
Bluff N1 Bluff S1(N) Bluff S1(S) Bluff S3
Bluff N4 Bluff N3 Bluff N2
Bluff S2
Copyright © 2002-2007 Kenneth Adelman, California Coastal Records Project, www.californiacoastline.org
South
North
Stairs
Stairs
USA
Qw
Qs
Failure Mechanisms of Weakly Lithified Sandstones
Wave action and vertical toe formation
Failure surfaces and slope profile
prior to failure
Stronger layer
1.5 m (typical crest failure)
Weakly cemented sand
~65°
~24 m
Slope surface after failure (~40°)
Weaker layer
Loose dune sand
Impermeable layers with seepage
Seepageinduced
failure of upper
materials
Moderately cemented
sand
~24 mFailure surfaces(~0.5 m)
Angle of repose slope
Strongly Cemented (UCS 100-400 kPa) Weakly Cemented (UCS 5-30 kPa)
Collins, B.D. and Sitar, N., 2008, Processes of coastal bluff erosion in weakly lithified sands, Pacifica, California, USA, Geomorphology 97, pg.483-501.
Data Collection – 2001-2006
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Copyright © 2002-2007 Kenneth Adelman, California Coastal Records Project, www.californiacoastline.org
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BDC5
Slide 7
BDC5 BCollins, 5/16/2007
Intensity - Duration Relationships
Wave Action: Mean Daily Total Water Level (MD-TWL)Average of the hourly wave run-up elevation
Measured local tide gauge height Off-shore wave buoy data
TWL = η + R2%, where R2% = 0.5Hs-0.22 (Ruggiero et al, 2001)
Cumulative sum of TWL difference from season average (duration index)
Precipitation: 48-hour Rainfall48 hours gives indication of passing stormsCannot take into account full delay of seepageCumulative sum of precipitation (duration index)
Correlation with Wave Action
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failurenon-failure
y=1.3 + 2.3e-0.045x
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The average water elevation on the beach from waves and tides.
The cumulative sum of the difference in MD-TWL to the average of the MD-TWL for the entire season.
Area of Expected Failures
Correlation with Precipitation
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failure non-failure
Area of Expected Failures
Prediction of Future Response from Global Warming (Expected Sea Level Rise)
Prediction of failure events for a 5-year period in 100 years based only on sea level trend.
Sea level # points # days of % Global Trend* exceeding predicted increase emissions(m/100yr) threshold failure of failure scenario*
0 434 54 0 emissions decline0.2 506 61 17 present rate0.4 594 71 37 A2 average0.6 675 81 56 A2 maximum0.72 719 86 65 A1fi maximum
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*Source: California Climate Change Center, derived from IPCC results.
Prediction of Future Response from Global Warming (Potential Changes in Wave Action)
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Implications
Pacifica, California – a site specific model
But… weakest end member in California… a proxy for effects of climate change (canary in the coal mine)
Important to continually monitor sites like this.
Also important to establish new monitoring sites in other locations (more canaries)
Conclusions
Observations give new level of understanding to processes and insight to making predictions
Empirical correlations show promise for defining conditions for failureNewly developed wave-action thresholds.
Ability to forecast landslide events from expected climate change is a new prospect for science and public awareness.
Future direction I – incorporate effect of extreme sea-level events (predictions of increased North Pacific storm activity)
Future direction II – extend methodology to other areas of the west coast
Thank you.
Analysis and prediction of coastal bluff erosionPacifica, San Mateo County, California
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Bluff N1 (Oct 2002-May 2003)
Oct 2002 - May 2003
Prediction Analysis for
Qw Bluffs