Evaluation of Using Alternative First Floor Elevation Sources for Flood Risk Mitigation Jerry W. Sparks, P.E., CFM Michael K. Buckley, P.E. ASFPM Conference June 23, 2016
A Look Back Crowds panic as floods hit ASFPM 2015
3 Acknowledgement
Question What would be the impact on flood risk mitigation activities of using alternatives to Elevation Certificate surveys for First Floor Elevations?
Use Cases Examined 1. Flood Insurance Policy Premium Rating 2. Risk Assessment 3. Mitigation Evaluation (BCA for Building Elevation Projects)
Alternative FFE Data Sources Evaluated Policy /Permit data (assume surveyed) Registered Land Surveyor/License Professional Engineer $150-$1000+/building Airborne LiDAR Intersect DEM and Building Footprint to determine LAG and HAG Assume/estimate offset from HAG to first floor $0.15-$0.35/building Mobile LiDAR Truck-based LiDAR measured FFE and LAG (visible from street) $20-$40/building Laser Inclinometer GPS-derived FFE $18-$40/structure
Google Earth FFE Estimates Google Earth Street View grossly overestimates or underestimates FFEsfor the study areas. Example: 5313 CHALET PLACE, VA Beach City Permit FFE 6.9 Google Earth Street View FFE ~27 This may improve over time 7
Case Study Areas 1. Manasquan, NJ 2. Virginia Beach, VA 8
Study Area Manasquan, NJ 352 structures Assessed value: $300K to $1.6MM Project Objective: BW12 impact on a study area 9
Study Area Virginia Beach, VA 117 structures City Permit FFE and LAG Data Airborne LiDAR LASER Inclinometer 10
Overview of Datasets Used To Derive FFE Estimates for this Evaluation FFEs derived from: Manasquan, NJ Virginia Beach, VA Flood InsurancePolicy Data (control) Permit Data (control) Airborne LiDAR Laser Inclinometer Mobile LiDAR 11
12 FFE Estimates Comparisons
Airborne LiDAR-derived LAG vs Policy LAG - Manasquan 14.0 Policy Lag/DEM Lag Scatter Plot 12.0 DEM -Lag (ft) 10.0 8.0 y = 0.8464x -0.5913 R² = 0.76 6.0 4.0 2.0 2 4 6 8 10 12 14 Policy -Lag (ft) Y = X Line Linear (Trend Line) 13
Manasquan FFE Comparison 30.00 ALTERNATE METHOD FFE 25.00 20.00 15.00 10.00 Differences from Policy FFE RMSE Airborne LiDAR-derived (HAG + Offset) = 2.86 Laser Inclinometer = 0.42 Mobile LiDAR = 3.96 5.00 Sample = 103 structures Airborne LiDAR offset = 1.86' 0.00 0.00 5.00 10.00 15.00 20.00 25.00 POLICY FFE POLICY LOW_FLOOR HAG + Offset Laser Inclinometer Moble LiDAR
VA Beach FFE Comparison 30 Alternative Sources vs Permit Data 25 Differences from Policy FFE RMSE Airborne LiDAR-derived (HAG + Offset) = 2.26 Laser Inclinometer = 2.89 ALTERNATE METHOD FFE 20 15 10 5 Sample = 128 structures Airborne LiDAR offset = 1.19' 0 0 5 10 15 20 25 PERMIT FFE CITY PERMIT FFE LASER INCLIN HAG + Offset 15
Challenges with FFE Sources Elements of Uncertainty: Policies: who entered them? Do they resemble elevation certificates? Elevation Certificates: what s the accuracy? Mobile LiDAR: you are limited to a view from the street Laser Inclinometer: you are limited to field judgment 16
17 Challenges with FFE Sources
Flood Insurance Premium Estimates Comparison 18
Primary Inputs For Calculating NFIP Insurance Premiums Flood Zone Base Flood Elevation (BFE) Building Type Date of Construction Occupancy/Use First (Lowest) Floor Elevation (FFE) Amount of Coverage/Deductible
Uncertainties in the Rating Process Depth damage relationship Cross subsidies Rounding of FFE Calculation of the BFE 20
Manasquan Insurance Analysis 40000 PREMIUMS ESTIMATED USING AIRBORNE LIDAR DERIVED FFE (HAG + OFFSET) VS POLICY DATA FFE 35000 30000 Number Compared = 85 % Difference in Total Premiums Across Sample= +4% RMSE = 12% R² = 0.9786 Airborne LiDAR Derived FFE 25000 20000 15000 10000 5000 0 0 5000 10000 15000 20000 25000 30000 35000 40000 Policy FFE HAG + OFFSET POLICIES Linear (HAG + OFFSET) 21
Manasquan Insurance Analysis LASER INCLINOMETER PREMIUMS 40000 35000 30000 25000 20000 15000 10000 PREMIUMS ESTIMATED USING LASER INCLINOMETER FFE VS POLICY DATA FFE Number Compared = 94 % Difference in Total Premiums Across Sample = +0.5% RMSE = 12% R² = 0.9792 5000 0 0 5000 10000 15000 20000 25000 30000 35000 40000 POLICY PREMIUMS LASER INCLINOMETER POLICIES Linear (LASER INCLINOMETER) 22
Manasquan Insurance Analysis 40000 35000 PREMIUMS ESTIMATED USING MOBILE LIDAR FFE VS POLICY DATA FFE Number Compared = 94 % Difference in Premiums = +3% RMSE = 9% 30000 R² = 0.9873 MOBILE LIDARPREMIUM 25000 20000 15000 10000 5000 0 0 5000 10000 15000 20000 25000 30000 35000 40000 POLICY PREMIUM MOBILE LIDAR POLICIES Linear (MOBILE LIDAR) 23
Virginia Beach Insurance Analysis PREMIUMS ESTIMATED USING AIRBORNE LIDAR-DERIVED FFE (HAG+OFFSET) VS PERMIT DATA FFE 9000 8000 7000 Number Compared = 117 % Difference in Total Premiums = +10% RMSE = 42% HAG + OFFSET PREMIUM 6000 5000 4000 3000 2000 1000 0 0 1000 2000 3000 4000 5000 6000 7000 8000 9000 PERMIT PREMIUM CITY PERMITS HAG + OFFSET 24
Virginia Beach Insurance Analysis PREMIUMS ESTIMATED USING LASER INCLINOMETER FFE VS PERMIT DATA FFE 10000 9000 8000 Number Compared = 117 % Difference in Total Premiums = +2% RMSE = 42% LASER INCLINOMETER FFE PREMIUM 7000 6000 5000 4000 3000 2000 1000 0 0 1000 2000 3000 4000 5000 6000 7000 8000 9000 PERMIT FFE PREMIUM CITY PERMITS LASER 25
Insurance Analysis Results Summary AlternativeFFE Source Airborne LiDARderived FFEs Laser Inclinometer FFEs Manasquan,NJ (difference compared to Policy FFE data) VirginiaBeach, VA (difference compared to permit FFE data) Total Premium +4% +10% RMSE 12% 42% Total Premium +0.5% +2% RMSE 12% 42% Mobile LiDAR FFEs Total Premium +3% - RMSE 9% - 26
Conclusions & Recommendations Utilization of alternate FFE sources result in slightly to moderately higher total premiums across sample than from EC surveys SJ1 Risk Analysis and BCA tests were inconclusive but seemed to result in much higher sensitivity to FFE differences Recommend further investigation: Evaluate larger sample area(s), including inland/riverine areas More extensive, rigorous testing of Risk Assessment and BCA 27
Slide 27 SJ1 Reword Sparks, Jerry, 6/22/2016
Questions?