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Utilizing Property-Level Datasets to Interpret Coastal Flood Risk
Betsy Hayden and Curtis Smith
April 1st, 2015
Overview
– Background
– Approach
– Example
– Limitations
– Applications & Next Steps
April 20, 2015Utilizing Property-Level Datasets to Interpret Coastal Flood Risk Page 2
Overview
– In a nutshell:• GIS tools to compute the risk to
coastal flooding at individual structures
• Highlights vulnerable structures in a tangible way
April 20, 2015 Page 3Utilizing Property-Level Datasets to Interpret Coastal Flood Risk
Background
– Toolset initially developed for internal QC of flood mapping
– Thought experiment to explore new applicationsApril 20, 2015 Page 4Utilizing Property-Level Datasets to
Interpret Coastal Flood Risk
Background
– Many sources for information on flooding and sea level rise• FEMA Flood Maps• USACE SLR Calculator• NOAA SLR Viewer• Climate Central’s Surging Seas
Platform
April 20, 2015 Page 5Utilizing Property-Level Datasets to Interpret Coastal Flood Risk
Background
– Few maps combine probabilistic flooding with sea level rise estimates
April 20, 2015 Page 6Utilizing Property-Level Datasets to Interpret Coastal Flood Risk
Background
April 20, 2015 Page 7Utilizing Property-Level Datasets to Interpret Coastal Flood Risk
– Four components to coastal storms
Background
April 20, 2015 Page 8Utilizing Property-Level Datasets to Interpret Coastal Flood Risk
– Superimpose SLR onto storm surge (bathtub method)
– When water depth increases, wave heights can also increase
Background
April 20, 2015 Page 9Utilizing Property-Level Datasets to Interpret Coastal Flood Risk
Approach
April 20, 2015 Page 10
– Data requirements:• Flood elevation• Spatial representation of
properties• Topographic dataset• SLR Estimate
– Public availability
Utilizing Property-Level Datasets to Interpret Coastal Flood Risk
Approach
April 20, 2015 Page 11
– Extract topographic information at individual properties
– Determine the lowest grade at property
Utilizing Property-Level Datasets to Interpret Coastal Flood Risk
Approach
April 20, 2015 Page 12
– Extract flood information at individual properties
– Add SLR prediction
– Estimate added wave contribution
Utilizing Property-Level Datasets to Interpret Coastal Flood Risk
– Conservative estimate of wave height contribution based on water depth• Wave contribution = up to 55% of water depth
Approach
April 20, 2015 Page 13
wave height = 0.55 x water depth
water depth
Depth-limited
wave
Estimated sea level rise
Stillwater
Utilizing Property-Level Datasets to Interpret Coastal Flood Risk
Approach
– Options for representing waves in SLR predictions:1. Exclude wave contribution2. Uniform increase in wave height3. Depth limited analysis based on new stillwater4. Proportional increase in wave height
April 20, 2015 Page 14Utilizing Property-Level Datasets to Interpret Coastal Flood Risk
Example
– Estimated Relative Sea Level Change (NOAA High) for 2065 = 3.29 feet
April 20, 2015 Page 15Utilizing Property-Level Datasets to Interpret Coastal Flood Risk
Example – Option 1
BFE2065= BFE2015+ SLRsurge
= BFE2015 + 3.29 feet
Bathtub approach
April 20, 2015 Page 16Utilizing Property-Level Datasets to Interpret Coastal Flood Risk
Example – Option 2
April 20, 2015 Page 17Utilizing Property-Level Datasets to Interpret Coastal Flood Risk
BFE2065= BFE2015 + SLRsurge + SLRwave
= BFE2015 + 3.29 feet + 1.8 feet
Double bathtub approach
Example – Option 3
April 20, 2015 Page 18Utilizing Property-Level Datasets to Interpret Coastal Flood Risk
BFE2065= (surge2015 + SLRsurge) + (surge2015 + SLRsurge – ground) × 0.55
Example – Option 4
April 20, 2015 Page 19Utilizing Property-Level Datasets to Interpret Coastal Flood Risk
BFE2065= (surge2015 + SLRsurge) + proportional wave contribution
Example - Comparison
April 20, 2015 Page 20Utilizing Property-Level Datasets to Interpret Coastal Flood Risk
Example - Comparison
April 20, 2015 Page 21Utilizing Property-Level Datasets to Interpret Coastal Flood Risk
Differences highlighted by concentrating on one area
Each option shows different BFE
Example - Comparison
April 20, 2015 Page 22Utilizing Property-Level Datasets to Interpret Coastal Flood Risk
Differences highlighted by concentrating on one area
Sheltered area, depth limited BFE not expected
Example – Bigger Picture
– Analyzing affect of SLR on storm waves just one application• Structures flooded by MHHW + SLR• 0.2% coastal flooding at critical facilities• 1% flood depth
– Cross-reference with census information, social vulnerability
April 20, 2015 Page 23Utilizing Property-Level Datasets to Interpret Coastal Flood Risk
Limitations
– Approach doesn’t capture:• Non-linear effects• Wave runup• Wave setup
– Dependent on quality of spatial data
– Public usage
April 20, 2015 Page 24Utilizing Property-Level Datasets to Interpret Coastal Flood Risk
Applications
– Community resilience planning
– Benefit-cost analysis incorporating SLR
– Land development
April 20, 2015 Page 25Utilizing Property-Level Datasets to Interpret Coastal Flood Risk
Next Steps
– Compare estimates to wave modeling• Evaluate performance in developed vs. undeveloped areas• Evaluate performance in sheltered vs. open coast
– Brainstorm how to adapt for future development
April 20, 2015 Page 26Utilizing Property-Level Datasets to Interpret Coastal Flood Risk
