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Airborne LiDAR
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… Acknowledgement 3| 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 FFEs for the study areas. Example: 5313 CHALET PLACE, VA Beach City Permit FFE – 6.9’ Google Earth Street View FFE – ~27’ 7| • This may improve over time 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: Flood Insurance Policy Data (control) Manasquan, NJ • Permit Data (control) Airborne LiDAR Laser Inclinometer Mobile LiDAR 11 | Virginia Beach, VA • • • • • • FFE Estimates Comparisons 12 | Airborne LiDAR-derived LAG vs Policy LAG - Manasquan Policy Lag/DEM Lag Scatter Plot 14.0 12.0 DEM - Lag (ft) 10.0 y = 0.8464x - 0.5913 R² = 0.76 8.0 6.0 4.0 Y = X Line Linear (Trend Line) 2.0 2 4 6 8 Policy - Lag (ft) 13 10 12 14 Manasquan FFE Comparison 30.00 Differences from Policy FFE ALTERNATE METHOD FFE 25.00 RMSE Airborne LiDAR-derived (HAG + Offset) = 2.86’ Laser Inclinometer = 0.42’ Mobile LiDAR = 3.96’ 20.00 15.00 10.00 5.00 Sample = 103 structures Airborne LiDAR offset = 1.86' 0.00 0.00 5.00 10.00 15.00 20.00 POLICY FFE POLICY LOW_FLOOR HAG + Offset Laser Inclinometer Moble LiDAR 25.00 VA Beach FFE Comparison Alternative Sources vs Permit Data 30 Differences from Policy FFE RMSE Airborne LiDAR-derived (HAG + Offset) = 2.26’ Laser Inclinometer = 2.89’ 25 ALTERNATE METHOD FFE 20 15 10 5 Sample = 128 structures Airborne LiDAR offset = 1.19' 0 0 5 10 15 20 PERMIT FFE CITY PERMIT FFE 15 | LASER INCLIN HAG + Offset 25 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 | Challenges with FFE Sources 17 | 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 PREMIUMS ESTIMATED USING AIRBORNE LIDAR DERIVED FFE (HAG + OFFSET) VS POLICY DATA FFE 40000 Number Compared = 85 % Difference in Total Premiums Across Sample= +4% RMSE = 12% 35000 Airborne LiDAR Derived FFE 30000 R² = 0.9786 25000 20000 15000 10000 5000 0 0 5000 10000 15000 20000 25000 30000 Policy FFE HAG + OFFSET 21 | POLICIES Linear (HAG + OFFSET) 35000 40000 Manasquan Insurance Analysis PREMIUMS ESTIMATED USING LASER INCLINOMETER FFE VS POLICY DATA FFE 40000 Number Compared = 94 % Difference in Total Premiums Across Sample = +0.5% RMSE = 12% LASER INCLINOMETER PREMIUMS 35000 30000 R² = 0.9792 25000 20000 15000 10000 5000 0 0 5000 10000 15000 20000 25000 30000 35000 POLICY PREMIUMS LASER INCLINOMETER 22 | POLICIES Linear (LASER INCLINOMETER) 40000 Manasquan Insurance Analysis PREMIUMS ESTIMATED USING MOBILE LIDAR FFE VS POLICY DATA FFE 40000 Number Compared = 94 % Difference in Premiums = +3% RMSE = 9% 35000 MOBILE LIDAR PREMIUM 30000 R² = 0.9873 25000 20000 15000 10000 5000 0 0 5000 10000 15000 20000 25000 30000 POLICY PREMIUM MOBILE LIDAR 23 | POLICIES Linear (MOBILE LIDAR) 35000 40000 Virginia Beach Insurance Analysis PREMIUMS ESTIMATED USING AIRBORNE LIDAR-DERIVED FFE (HAG+OFFSET) VS PERMIT DATA FFE 9000 Number Compared = 117 % Difference in Total Premiums = +10% RMSE = 42% 8000 HAG + OFFSET PREMIUM 7000 6000 5000 4000 3000 2000 1000 0 0 1000 2000 3000 4000 5000 PERMIT PREMIUM CITY PERMITS 24 | HAG + OFFSET 6000 7000 8000 9000 Virginia Beach Insurance Analysis PREMIUMS ESTIMATED USING LASER INCLINOMETER FFE VS PERMIT DATA FFE 10000 Number Compared = 117 % Difference in Total Premiums = +2% RMSE = 42% 9000 LASER INCLINOMETER FFE PREMIUM 8000 7000 6000 5000 4000 3000 2000 1000 0 0 1000 2000 3000 4000 5000 PERMIT FFE PREMIUM CITY PERMITS 25 | LASER 6000 7000 8000 9000 Insurance Analysis Results Summary Alternative FFE Source Manasquan, NJ Virginia Beach, VA (difference compared to Policy FFE data) (difference compared to permit FFE data) Airborne LiDARderived FFEs Total Premium +4% +10% RMSE 12% 42% Laser Inclinometer FFEs 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?
