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 Project Photo 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 studies DFIRMs TWL data pointsPWA_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 Toe Offshore Baseline Qs Air Photo from 2005

Results - Dunes Majority of Norcal “accreting” Accreting to Erosion reversal in sign seen between 2050 and 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 Risk At 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 SLR 5.Conduct local vulnerability assessment of future erosion and flooding hazards 6.MHW will move don’t be next to it…

BFE compared to MOP Similar, but large scatter

For More Information David Revell Report p?pubNum=PWAOPC GIS Data - Results Photos by R. Battalio