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An Initial Assessment of the Impacts of
Sea Level Rise to the California Coast
Dr. David Revell and Bob Battalio, P.E.Matt Heberger, P.E., Dr. Peter Gleick, Heather Cooley, Justin Vandever
and Brian Spear
California Coastal Records ProjectPhoto by D. Revell – 2/23/08
Outline• Coastal Hazards and
Vulnerability– Estimate future flood and
erosion hazards– Methods– Results
Photo by D. Revell
Photo by D. Hubbard
General Approach - Vulnerability
• Adopt CA climate scenarios (1.4 and 1.0 m by 2100).• Develop maps of flood and erosion hazards for CA coast.• Identify populations and infrastructure at risk.
Hazard Maps
Naval Postgraduate School
NOT FOR PLANNING PURPOSES
Risk - Mapping Flood Hazards
100-yr Still-Water Elevation (MSL)
100-yr Flood Elevation
Wave height
New 100-yr Flood Elevation with Sea Level Rise
•Review all existing FEMA Flood Insurance Studies
•Extract Coastal Base Flood Elevations into GIS
•Add Sea level rise scenarios to BFE elevations
•Map inundation using terrain datasets
Cliff
Dune
Risk - Mapping Erosion Hazards
Analyses Scale
Geology and Erosion Rates
K - Cretaceous Marine -2.8 m/yr
Kjf - Franciscan complex -1.8 m/yr
Total Water Levels
Total Water Level, TWL = “measured” Tides, (T) + Wave Runup, (R)
T = Sea level rise scenarios (Cayan et al), 100 years at 3 hour tides coupled waves and storm effects (ENSO, surge) for 2 scenarios 2 locations – SF, Crescent City
R = Wave run-up - Deepwater waves (Cayan et al) for three sites – Pt. Conception, San Francisco, Crescent City– CDIP models to transform waves at 140 nearshore locations at 10m – Calculated wave run-up (Stockdon et al 2006).
Generated excedance curves for each subdivided geologic unit (500m) using individual slopes and toe elevations
Total Water Levels
• Combined SLR and Wave Run-up • Generate excedance curves for each block using
individual slopes and toe elevations
CA Coastal Counties
Existing BFE Info
FIS and Ott studiesDFIRMsTWL data points PWA_BFE Estimates
PWA Backshore Classification
4095 segments
Dune Erosion Model
• 3 components –– Changes in TWL from SLR combined with shoreface slope– Historic shoreline trends (USGS)– Impact of a “100 year storm event”
Dune Hazard Zones
1998 ToeO
ffshor
e Bas
eline Q
s
Air Photo from 2005
Results - Dunes
•Majority of Norcal “accreting”
•Accreting to Erosion reversal in sign seen between 2050 and 2100
•300 km or 185 miles
Revell et al in review
Cliff Erosion Model
• Acceleration of historic erosion rates (Rh)• Prorated based on % increase in TWL exceeding
the elevation of the toe of the beach/cliff junction• Include geologic unit standard deviation x planning
horizon to account for alongshore variability
Cliff Hazards
Air Photo from 2005
Results - Cliffs
California Coastal Records Project
•Geology exerts strong influence
• Wave exposure and toe elevation important
•1,140 km or 710 miles
Revell et al in review
Infrastructure at RiskAt Risk by 1.4m SLR• Roads: 3,500 miles*• Highways: 400 miles*• Railroads: 300 miles*• Schools: 139• Hospitals: 55• Police/Fire Stations: 34• Power Plants: 30• Wastewater Plants: 28
• * Did not include So.Cal erosion
Conclusions• Downscalable model for evaluating coastal hazards resulting from SLR
• GIS hazard zones of two scenarios at 3 planning horizons – erosion
• Initial Flood elevations for the CA coast – 2 methods
Next steps• Focused Regional Studies• Integrate erosion and flooding• Adaptation planning with robust
cost/benefit analysis• Validation with storm impacts and
hindcast data sets
Photo by D. Revell – 2/23/08
Policy and Management Recommendations - General
1. Integrate future sea level rise and accelerating erosion into coastal policies –LCP, LUP revisions.
2. Limit scales of development in areas at risk from SLR – setbacks, size of development, uses
3. Preserve adjacent uplands to keep options open. 4. Maintain historic ecological linkages between oceans,
beaches, dunes, and wetlands – MLPA, RSM.5. Cost-benefit analyses should explicitly evaluate the
social, recreational and environmental tradeoffs of adaptation strategies.
6. Use sediment wisely, it is a valuable resource
Policy and Management Recommendations - Specific
1. Direct staff to investigate standard methods to incorporate sea level rise into permit decision making
2. Adopt policies to implement avoidance of future erosion hazards- e.g. managed retreat, rolling easements
3. Have future seawalls bonded to have upfront costs for removal, maintenance at end of structure life/ nuisance.
4. Review flood insurance programs in light of SLR5. Conduct local vulnerability assessment of future erosion
and flooding hazards6. MHW will move don’t be next to it…
BFE compared to MOP
Similar, but large scatter
For More Information David Revell
Reporthttp://www.energy.ca.gov/publications/displayOneReport.php?pubNum=PWAOPC-1000-2009-013
GIS Data - Resultshttp://www.pacinst.org/reports/sea_level_rise/index.htm
Photos by R. Battalio
