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North Carolina Emergency Management
Coastal Flood Hazard MappingCurrent Status and Update
April 4, 2017
North Carolina Emergency Management
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 additional 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.
NCFMP Program Objectives
North Carolina Emergency Management
All coastal flood studies and mapping were performed in accordance with FEMA standard coastal guidelines and specifications for flood hazard mapping partners for the Atlantic Basin and sealed by Licensed Professional Engineers and Land Surveyors in the State of North Carolina.
Apply the latest state-of-the-art models capable of providing better resolution of coastal hydrodynamic processes, based on the latest FEMA methodologies and standards developed following Hurricane Katrina.
Current effective / legacy coastal storm surge along the North Carolina coastline was determined by a FEMA study developed in 1981 (using JPM; the same as the updated modeling methodology).
Study and mapping was applied to the existing shoreline characteristics, and wave and storm weather data available at the time of study, and in accordance with current Code of Federal Regulations (CFRs); updated mapping and flood hazards did not consider or analyze anticipated future sea levels or climate change.
We Evaluate and update flood studies where appropriate every 3 1/2-years, subject to need and funding
Coastal Flood Study Updates Summary
North Carolina Emergency Management
The surge model is one of many components used for developing the digital flood insurance rate maps (DFIRMs) for coastal areas. Other integral components:
o Field transect survey and reconnaissanceo Evaluation of the regulatory primary frontal dune (PFD)o Storm included erosion processeso Wave hazard modeling o Coastal flood hazard mapping
All modeling and mapping for the updated studies are reviewed for compliance with standard engineering practices and FEMA specifications and standards by Licensed Professional Engineers (PE) in the State of North Carolina, including:
o NCFMP o FEMA o Independent quality assurance/quality control (QA/QC) contractor PE’s
Coastal Flood Study Updates Summary
North Carolina Emergency Management
BFE on FIRM based on 4 components: Storm surge Wave setup Overland waves Wave runup
FEMA Coastal Flood Hazards
Surge
North Carolina Emergency Management
Coastal Modeling and Mapping
Storm Surge Modeling
Overland Wave Hazard
ModelingMapping
North Carolina Emergency Management
Storm Surge Modeling
Storm Surge Modeling
Overland Wave Hazard
ModelingMapping
North Carolina Emergency Management
Storm Surge Modeling Process
Collect Topo/Bathy
Create Seamless DEM & Mesh
Surge Model Tidal Calibration
Select Validation Storms
Surge Suite Validation
Select Hurricanes for Water Levels
Runs
Compute Surge Suite Water
Levels
Return Period Analysis (Water levels statistics)
Stillwater/Wave Setup Surface
North Carolina Emergency Management
NC Surge Study Approach
Entire coastline restudiedo Avoid discontinuities, maximize
efficiency
Integrated 2-D hydro-dynamic and wave model
o Surge – ADCIRCo Tidally and wind driven
circulationo Hurricane surge and flooding
o Nearshore Waves - SWAN
Combined extratropical and tropical surge
o Joint Probability Method - statistical method for tropical
o Empirical Simulation Technique (EST) – statistical method for extratropical storm
North Carolina Emergency Management
NC Surge Modeling TeamNCFMP
John Dorman, DirectorKen Ashe, Assistant Director
Tom Cadwallader, Lead Engineer/PMTom Langan, Engineer
DEWBERYChris Mack – Team Leader
Mike Hanson – Assistant Team Leader
TECHNICAL ADVISORSDon Resio – USACOE, ERDC
Jessie Feyen – NOAAEnrique Reyes – ECUDave Divokey – WSC
Spencer Rogers – NC Sea Grant
RENAISSANCE COMPUTING CENTER (RENCI) TEAMKen Galuppi – Team Leader
CONSULTANTAndrew Cox - OCEANWEATHER
FEMA – REGION IV
L. Algeo, EngineerTucker Mahoney, Coastal Eng.
Christina Lindemer, Coastal Eng.
VA INTERFACE – REGION III
David Gunn – VA DCR
SC INTERFACE – REGION IV
Lisa Jones – SC DNR
COMPUTER SERVICESSallie WrightBrian BlantonLisa StillwellKevin Gamiel
DATABASE/DEM DEVELOPMENT
Scott MadryHong Yi
Helena Mitasonova -NCSU
PROGRAM MANAGEMENT
Tara AimsTim McCormick
QUALITY ASSURANCE/
QUALITY CONTROLJeff Gangai
Elena Drei-Horgan
TECHNICAL SUPPORT
Kevin SloverJeff Sample
MODELINGRick Leuttich - UNC
Crystal FulcherCraig Mattock
CONSULTANTSPeter Vickery – ARA John McCormick – CRT
Jeff Hanson – USACOE, Duck
QA/QC
North Carolina Emergency Management
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)
North Carolina Emergency Management
Need for Upgrade - Effective / Legacy Surge Model Limitations
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)
New FEMA Coastal Mapping Guidelines (LIMWA and 2% Runup)
North Carolina Emergency Management
Coastal Flood Study – Resulting Changes
Overall, the coastal flood studies result in the following impacts to regulatory flood zones, buildings and National Flood Insurance Program insurance policies in 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
North Carolina Emergency Management
Changes relative to effective study:Decrease – BlueIncrease – Yellow/RedNo Change - Grey
North Carolina Emergency Management
BFE Changes – Building Impacts in Effective SFHA
Net change 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
North Carolina Emergency Management
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
North Carolina Emergency Management
NC Coastal Flood Mapping Timeline
North Carolina Emergency Management
NCFMP: 6 Years of Coastal Outreach Coastal Regional Updates Meetings (April 2011): Three regional coastal meeting held prior to
preliminary issuance to provide background and details on coastal modeling methods and draft storm surge modeling results, and training on coastal construction/development standards. (All 20 Coastal Counties)
Flood Risk Review Meeting (Dec. 2015): six months prior to Preliminary issuance, share draftflood hazard risk data with local officials and staff, for the purpose of building awareness of the upcoming changes in flood risk, as well as provide communities extra time to develop their outreach strategies for areas showing an increased flood risk. (June 2016 Preliminary Issuance – 6 Counties)
Development Stakeholders Meetings (May/June 2016): prior to Preliminary Issuance, meet with local development community stakeholders (home builders, developers, bankers, insurance agents, etc.) to inform them of changing flood risk. (Carteret, Craven and Onslow)
Pre-release Officials Meetings (May/June 2016): prior to Preliminary Issuance, meet with community officials and staff (elected officials, floodplain administrators, development review staff) to inform them of changing flood risk, and explain the post-preliminary and appeals process. (Carteret, Craven, Onslow and New Hanover)
Preliminary DFIRM Public Officials Meetings (Sept. 2016): present the preliminary flood map and flood study to CEOs, floodplain administrators, and other officials for their review, discuss the results of the study/mapping project, and solicit community officials’ feedback on the information provided. (This is the only FEMA-required meeting – 18 Counties Completed)
Public Open House Meetings (Oct. 2016): provide an opportunity for citizens to learn about the Preliminary flood map and flood study, FEMA’s expanded appeals process, floodplain management regulations and flood insurance, as well as ask questions and provide comments. (18 Counties Completed)
North Carolina Emergency Management
NCFMP Current Mapping Status
Appeal period has ended
Appeal period has not started
Preliminary Fall 2017
North Carolina Emergency Management
NCFMP Current Coastal Adjustments Sensitivity Analysis
NCFMP is updating new riverine flood studies based on recently published new empirical regression equations from the United States Geological Survey for urban areas in the City of Jacksonville.
NCFMP is performing sensitivity analyses of the tropical storm surge model to mesh resolution and more recent LiDAR-derived topographic data for the City of Jacksonville, Morehead City (Newport River area), and Surf City.
The NCFMP has been actively sharing data, coordinating and meeting with Carteret County’s consultant to assist in their review and possible revisions to the preliminary DFIRM maps.
North Carolina Emergency Management
Key Points of Discussion
North Carolina Emergency Management
Factors Resulting in BFE ChangesNew 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
North Carolina Emergency Management
Surge Model GRID/MESH Resolution
ADCIRC MESH(Yellow) - 150-800-ft
FEMA SURGE GRID (1980)(Blue) – 6,067 x 6,067-ft
North Carolina Emergency Management
Surge Model GRID/MESH Extents
ADCIRC MESH(Yellow) – 45-ft Elevation
FEMA SURGE GRID (1980)(Blue)
Effective Coastal Flood Extents (Blue Area)
North Carolina Emergency Management
21 Additional Hurricanes 1980-2006 (Start of new surge study)
• Updates the JPM Storm Parameters and Probabilities (Central pressure, forward speed and heading, wind speed and direction, and radius of maximum winds)
• JPM Storms• Effective – 300• New Studies -
675
North Carolina Emergency Management
Topographic Constrictions
Highest surge water levels in inlets as water builds from winds and wave setup.FEMA Surge 1 NM Gridcould not simulate this process
North Carolina Emergency Management
Wave Setup
ADCIRC/SWAN Wave Setup (0.1-3.8 ft,Avg 0.4 ft) (Yellow)
Effective – Empirical wave setup computed (0.6-2.6 ft)
Setup for Open Coast Only• Pender - Topsail Beach
and Surf City• Onslow and Carteret
North Carolina Emergency Management
Overland Wave Analyses: Statewide
No Effective Overland Wave Analyses(Yellow)
Restudy Transects(Red Lines)
Effective – 783 Transects
New Studies – 2,739 Transects9 New Counties (New FEMA Sheltered Water Guidelines and Specifications)
North Carolina Emergency Management
Reverse Transects: Statewide
County With Effective Reverse Transects(Yellow)
Restudy Reverse Transects(Red Lines)
Transects
Effective - 67New Studies – 192 (4 Counties)
North Carolina Emergency Management
Primary Frontal Dune Refinement
Effective VE Zone(Yellow)
Restudy PFD and VE Zone Extent(Black/White Line)
North Carolina Emergency Management
Wave Runup
Runup Transects (Yellow)
Runup Based VE Zone (Red)
Effective – No BFEs based on Runup
North Carolina Emergency Management
Coastal/Riverine Combined Probability
Effective Combined Probability (Yellow)9 Counties
North Carolina Emergency Management
All survey data used for the study has been sealed by NC Licensed Professional Land Surveyors and meets all FEMA vertical and horizontal accuracy requirements
Overland Wave Model Transect Survey Data Sources Dune transects surveys field collected 2009-2011
Primary frontal dune and overland wave transects near shoreline NC LIDAR 2001-2005 (Vertical accuracy +/- 0.7-ft)
Is the survey data used for the flood study accurate?
Mapped PFD Limit
Field Survey Points
Overland Wave Model Transect
North Carolina Emergency Management
What type of storm is creating the 1-percent flood in my area?
Approximate 1-Percent Annual Chance Flood Hurricane Saffir-Simpson Winds
Winds are most important component of storm surge (Approximately 95% of surge elevation)
Wind probabilities derived from historical storm record between 1940 and 2007
North Carolina Emergency Management
What type of storm is creating the 1-percent flood in my area?
ACIRC run closest to 1% at Morehead City (Cat 3 – Strength Similar to Max from Fran) 2 other tracks produced similar surge elevations for Morehead City area
North Carolina Emergency Management
Why have I never encountered flooding at the proposed levels?
PTime (years) Pflood
0.99 1 1%0.99 10 10%0.99 30 26%0.99 50 39%0.99 100 63%0.99 150 78%0.99 200 87%0.99 300 95%0.99 460 99%0.99 530 100%
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
North Carolina Emergency Management
Why ADCIRC for Surge? There were only three FEMA-authorized
2-D models available for Storm Surge in 2006 – ADCIRC, MIKE-11 and FEMA Surge (Last update 1988)
ADCIRC Advantageso Existing Mesh/Grid – entire Atlantic
seaboard and Gulf of Mexicoo Ability to have variable resolution
flexible mesh (FEMA Surge is a GRID)o Able to combine/integrate with 2-D
offshore and nearshore wave and wind field models
o Local NC experts on modelo No software fees
North Carolina Emergency Management
Why ADCIRC for Surge?o Methodology and application of
ADCIRC are well-established in the coastal engineering community and in the published literature.
o ADCIRC has been used and validated extensively for storm surge and flooding predictions and forensic and academic studies
o ADCIRC has been used in all coastal FEMA NFIP studies conducted in the last decade from Texas to New York and the Great Lakes.
ADCIRC was recommended as the model to use by the FEMA, the NCFMP, various academic advisors and NCFMP coastal storm surge professional engineering firms.
North Carolina Emergency Management
How Accurate is ADCIRC?
High Water Mark (Blue triangle)
ADCIRC/SWAN Water Level (Red circle)
Hurricane Fran Track – Cat 3 115 mph(Black line)
North Carolina Emergency Management
Hurricane Matthew Existing NCFMP, USGS, NOAA and USGS Rapid Deployment Gages
North Carolina Emergency Management
Hurricane Matthew ADCIRC Comparison to NOAA Beaufort Gage
North Carolina Emergency Management
Hurricane Matthew ADCIRC Comparison to Swansboro USGS Rapid Deployment Gage
North Carolina Emergency Management
Hurricane Matthew ADCIRC Comparison to New River USGS Rapid Deployment Gage
North Carolina Emergency Management
NOAA Tidal Gages (7 Gages)
Methodology used for all new coastal flood studies for the Atlantic Basin
Statistical historical storms are required for FEMA coastal flood frequency analyses where:
o Insufficient period of record and gage coverage to analyze flood frequency water based on gages alone NC – only 7 active NOAA coastal 3,250 miles of open and inland
coastline at risk from coastal flooding
Only 3 gages have adequate period of record to compute flood frequencies (30-years) Could over or
underestimate risk depending on hurricane activity during period
Larger statistical errors at greater recurrence intervals
Why use historically derived statistical hurricanes?
North Carolina Emergency Management
NOAA Historical Hurricane Tracks Since 1851
Flood frequencies analyses based solely on gages and high water marks are lacking:
o Only relevant for a small geographic area
o Does not capture spatial variability of water levels during hurricanes
Historical statistical storms developed to capture risk for the entire coastline are based on historical tracks and data
Relying on historical water levels alone would significantly underestimate risk of NC coastal flooding
Risk is based on meteorological data, not gages alone, since hurricanes tracks are random
Tropical Model Hurricane Tracks
Why use historically derived statistical hurricanes?
North Carolina Emergency Management
Wind Weather Stations
Wind Model is validated at 29 weather locations all over the state (ASOS, mesonet, buoy)
Why use historically derived statistical hurricanes?
North Carolina Emergency Management
Coastal Gages Bathymetry Terrain (New LIDAR)
Risk Analysis Continued Improvement to
ADIRC Model
Areas For Further Improvement
North Carolina Emergency Management
Current Coastal Tidal Gages
2014 NCFMP Tidal Gages (7)
Current NOAA Tidal Gages (7)
North Carolina Emergency Management
Current and Proposed Coastal Tidal Gages
2014 NCFMP Tidal Gages (7)
Current NOAA Tidal Gages (7)
Proposed Tidal Gages (13)
North Carolina Emergency Management
Questions?