N.C. Floodplain Mapping Program

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1 N.C. Floodplain Mapping Program Current Status and Update April 23, 2018

2 NCFMP Program Objectives Purpose: Develop, Maintain, and Disseminate current, accurate, digital flood hazard data for all of NC, to include: Update Flood hazard data, models and displays (approximately 40,000 miles / Review every 3 ½ years); Calculate the financial loss at the structure level; Calculate anticipated flood insurance rates / ranges; and, Provided real-time and forecasted inundation, impact and alerting (FIMAN). Flood hazard data and studies (BFEs and Impact): support: Determination of Required Flood Insurance Purchase; Calculation of Insurance Rating; and, County and municipal floodplain management. Since its inception, NCFMP has: Acquired more accurate data (i.e. LiDAR-derived topography, building footprints, first floor elevations); Transitioned to database-derived, digital display of flood data, models and maps; Studied approximately 32,000 stream / coastal miles and replaced all unnumbered A Zones with AE Zones (that have BFEs) Calculating impact / financial loss to properties from different flood elevations; and, Integrated data with FIMAN.

3 Modeling FIMAN Observed / Current Flood Impacts Structure Specific Impact Data Building Footprints Parcel Data Forecasted Flood Impacts Hotspots by Impact Count First Floor Elevations Hotspots by Financial Loss Repeater Gage Sensors Total Count and Cost Reporting

4 FEMA Coastal Flood Hazards BFE on FIRM based on 4 components: Storm surge Wave setup Overland waves Wave runup Surge

5 Need for Upgrade - Effective / Legacy Surge Model Limitations Surge modeling performed in 1981 Last FEMA Surge software update in 1988 Code is not being maintained or updated Surge model did not include wave setup Model resolution of 1-mile (1 point per nautical mile to represent land features and movement of water) Model did not extend far enough inland to reflect coastal influence from coastal surge (e.g. Jacksonville) Wind and pressure field data is low resolution (very few points to represent wind and pressure fields in model) Topography and bathymetry are low / coarse resolution The legacy model can not simulate water piling up in inlets from wind driven surge More comprehensive, higher resolution data Advances in coastal surge modeling methods and functions Significant Surge Events since 1980 (Emily, Fran, Isabel, Ophelia) Changes in FEMA Coastal Mapping Guidelines (LIMWA and 2% Runup)

6 Coastal Flood Study Resulting Changes Overall the coastal flood studies resulted in the following impacts to regulatory flood zones, buildings and National Flood Insurance Program insurance policies in the State of North Carolina: o A seaward shift of the mapped regulatory PFD, and thus a subsequent reduction in the width of VE zones based on more detailed and updated topographic information o On average, regulatory base flood elevations (BFEs) are lower for the majority of coastal counties

7 Factors Resulting in BFE Changes New Coastal Surge Study; first update since early 1980 s Substantially more detailed terrain (NC LiDAR vs. USGS Quads) and bathymetric data Higher-resolution storm surge model grid/mesh and increased inland extents 21 more actual strong NC Hurricanes in the model More detailed wind fields; significant advancements in wind field modeling and measurements Topographic constrictions factored in modeling; missing in the effective model Wave set up in model; missing in the effective model for many counties More overland wave transects and reverse transects Refinement of primary frontal dune Enhanced wave runup modeling and new guidelines Added coastal/riverine combined probability

8 BFE Changes Building Impacts in Effective SFHA Net reduction in the regulatory BFE for structures in the effective coastal regulatory flood boundary (for the total of 94,332 buildings in the SFHA): o 58,154 (a lower BFE for 62% of total buildings) - average 2.0-ft lower o 23,682 (a higher BFE for 25% of total buildings) - average 1.5-ft higher o 12,496 (13% of total buildings) no change in BFE

9 BFE Changes - Flood Zones A net reduction in the number of buildings and NFIP policies in the regulatory coastal AE and VE flood zones including: o 14,882 buildings and 10,179 NFIP policies removed from the VE zone Statewide o 17,005 buildings and 8,681 NFIP policies removed from the AE zone Statewide

10 Changes relative to effective study: Decrease Blue Increase Yellow/Red No Change - Grey

11 NCFMP Current Mapping Status

12 What type of storm is creating the 1-percent flood in my area? Winds are most important component of storm surge (Approximately 95% of surge elevation) Wind probabilities derived from historical storm record between 1940 and 2007 Approximate 1-Percent Annual Chance Flood Hurricane Saffir-Simpson Winds

13 Why have I never encountered flooding at the proposed levels? P Time (years) P flood % % % % % % % % % % Percent chance of seeing one 1-pct annual chance flood over certain time period 37 percent chance you will not have one 1-pct annual chance event in 100-years Need a very long period of record to accurately derive 1-percent annual chance flood potential from measured water levels

14 Areas For Further Improvement Coastal Gages Bathymetry Terrain (New LIDAR) Risk Analysis Continued Improvement to ADIRC Model

15 Current and Proposed Coastal Tidal Gages Current NOAA Tidal Gages (7) Proposed Tidal Gages (13) 2014 NCFMP Tidal Gages (7)

16 Accessing our Data:

17 FLOOD RISK INFORMATION SYSTEM FRIS.NC.GOV/FRIS FRIS How to Access the Data

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19 FRIS DFIRM Map Symbology

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22 FRIS FIRM Map Symbology - Coastal

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24 FRIS Benchmark Layer

25 FRIS LOMR View Now Default

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28 FRIS Engineering Models

29 FRIS Data Downloads

30 FRIS Financial Vulnerability/Risk

31 FRIS Reduce My Risk

32 FRIS Preliminary DFIRM

33 Base Year Elevations

34 Changes Since Last FIRM

35 Buildings in and out Preliminary vs Effective

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40 FRIS Flood Insurance Estimator

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