Evaluation of Using Alternative First Floor Elevation Sources for Flood Risk Mitigation

Transcription

1 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

2 A Look Back Crowds panic as floods hit ASFPM 2015

3 3 Acknowledgement

4 Question What would be the impact on flood risk mitigation activities of using alternatives to Elevation Certificate surveys for First Floor Elevations?

5 Use Cases Examined 1. Flood Insurance Policy Premium Rating 2. Risk Assessment 3. Mitigation Evaluation (BCA for Building Elevation Projects)

6 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

7 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

8 Case Study Areas 1. Manasquan, NJ 2. Virginia Beach, VA 8

9 Study Area Manasquan, NJ 352 structures Assessed value: $300K to $1.6MM Project Objective: BW12 impact on a study area 9

10 Study Area Virginia Beach, VA 117 structures City Permit FFE and LAG Data Airborne LiDAR LASER Inclinometer 10

11 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 12 FFE Estimates Comparisons

13 Airborne LiDAR-derived LAG vs Policy LAG - Manasquan 14.0 Policy Lag/DEM Lag Scatter Plot 12.0 DEM -Lag (ft) y = x R² = Policy -Lag (ft) Y = X Line Linear (Trend Line) 13

14 Manasquan FFE Comparison ALTERNATE METHOD FFE Differences from Policy FFE RMSE Airborne LiDAR-derived (HAG + Offset) = 2.86 Laser Inclinometer = 0.42 Mobile LiDAR = Sample = 103 structures Airborne LiDAR offset = 1.86' POLICY FFE POLICY LOW_FLOOR HAG + Offset Laser Inclinometer Moble LiDAR

15 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 Sample = 128 structures Airborne LiDAR offset = 1.19' PERMIT FFE CITY PERMIT FFE LASER INCLIN HAG + Offset 15

16 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 17 Challenges with FFE Sources

18 Flood Insurance Premium Estimates Comparison 18

19 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

20 Uncertainties in the Rating Process Depth damage relationship Cross subsidies Rounding of FFE Calculation of the BFE 20

21 Manasquan Insurance Analysis PREMIUMS ESTIMATED USING AIRBORNE LIDAR DERIVED FFE (HAG + OFFSET) VS POLICY DATA FFE Number Compared = 85 % Difference in Total Premiums Across Sample= +4% RMSE = 12% R² = Airborne LiDAR Derived FFE Policy FFE HAG + OFFSET POLICIES Linear (HAG + OFFSET) 21

22 Manasquan Insurance Analysis LASER INCLINOMETER PREMIUMS PREMIUMS ESTIMATED USING LASER INCLINOMETER FFE VS POLICY DATA FFE Number Compared = 94 % Difference in Total Premiums Across Sample = +0.5% RMSE = 12% R² = POLICY PREMIUMS LASER INCLINOMETER POLICIES Linear (LASER INCLINOMETER) 22

23 Manasquan Insurance Analysis PREMIUMS ESTIMATED USING MOBILE LIDAR FFE VS POLICY DATA FFE Number Compared = 94 % Difference in Premiums = +3% RMSE = 9% R² = MOBILE LIDARPREMIUM POLICY PREMIUM MOBILE LIDAR POLICIES Linear (MOBILE LIDAR) 23

24 Virginia Beach Insurance Analysis PREMIUMS ESTIMATED USING AIRBORNE LIDAR-DERIVED FFE (HAG+OFFSET) VS PERMIT DATA FFE Number Compared = 117 % Difference in Total Premiums = +10% RMSE = 42% HAG + OFFSET PREMIUM PERMIT PREMIUM CITY PERMITS HAG + OFFSET 24

25 Virginia Beach Insurance Analysis PREMIUMS ESTIMATED USING LASER INCLINOMETER FFE VS PERMIT DATA FFE Number Compared = 117 % Difference in Total Premiums = +2% RMSE = 42% LASER INCLINOMETER FFE PREMIUM PERMIT FFE PREMIUM CITY PERMITS LASER 25

26 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

27 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

28 Slide 27 SJ1 Reword Sparks, Jerry, 6/22/2016

29 Questions?