FEMA Region III Coastal Hazard Analyses and DFIRMs Update

Jeff Gangai – DewberryRobin Danforth – FEMA Region III

Introduction

State of Effective Coastal StudiesWhy a coastal restudy is needed? Elements of a Coastal Flood Insurance StudyOngoing FEMA Region III Storm Surge

Modeling EffortOverland Wave Analysis ComponentsPreliminary coastal tasks to be performed for

coastal counties.

State of Effective Coastal StudyTopographic data used for modeling and mapping date

back to the Mid-1970’s and mid-1980’s from USGS mapsSWELs go back to a 1978 VIMS study for the Chesapeake

Bay and Tidal Gage Analysis on the Atlantic Coast.Coastal studies date back to late 1970’s and early 1980’sWave height determined with NAS method. Erosion analysis not performedWave setup not accounted forLimited WHAFIS nad/or wave runup modeling performed

Why a coastal restudy is needed? New Guidelines need to be implemented

Atlantic Ocean and Gulf of Mexico Guidelines Update (2007)

Sheltered Water Report (2008) PM 50 Limit of Moderate Wave Action (LiMWA) (2008)

To update base data such as topographic dataset and aerial imagery to high resolution products and seamless Digital Elevation Model (DEM)

To utilize newer coastal hazard modeling methodologies developed during the FEMA Mississippi Coastal Restudy

To take advantage of higher performance numerical modeling

To take advantage of improvement in GIS technologies to allow for more accurate and detailed FIRMs

Hurricane Isabel Sept 18, 2003

Recorded Surge Levels:

7.5 ft/2.2 m Chesapeake Bay Bridge-Tunnel

8.3 ft/2.5 m at Gloucester Point

Hurricane Isabel, Chesapeake Bay

FEMA Region III Study Area• Four states plus District of

Columbia• Five metropolitan areas• Complex coastal geomorphology• Delaware River/Bay system

- Tidal up to Trenton, NJ - 782 square mile bay - Strategic shipping and military port

• Chesapeake bay - Third largest estuary in world - 11,000 miles of tidal shoreline - Major shipping, seafood and military ports

Elements of a Coastal Flood Insurance Study BFE on a FIRM includes 4 components:

1. Storm surge stillwater elevation (SWEL)2. Wave setup3. Wave height above total stillwater elevation4. Wave runup above storm surge elevationAll applied to an eroded beach profile

The above components are computed through:1. Terrain processing and profile erosion2. Storm surge study for SWELs determination3. Coastal Hazard Analyses

Floodplain boundaries, flood hazard zones and LiMWA are then mapped on FIRMs

FEMA Project Officer

Robin Danforth DHS Region III

Project Support

J. Gangai (Dewberry)E. Drei-Horgan (Dewberry)

B. Batten (Dewberry)

USACE Storm Surge Program Manager

J. Hanson (USACE-FRF)J. Roughton (USACE-FRF)D. Nelson (USACE-CRREL)

Advisory Board

R. Luettich (UNC-CH)B. Ebersole (USACE-CHL)

J. Smith (USACE-CHL)K. White (USACE-CRREL)

K. Galluppi (RENCI)M. Powell (DE)R. Wise (NAP)

Bathy / Topo

J. Miller (NAP)C. Rourke (NAP)

M. Hudgins (NAO)P. Moye (NAO)

M. Schuster (NAB)J. Scott (NAB)

M. Forte (USACE-FRF)M. Blanchard (RENCI)

L. Stillwell (RENCI)

Storm Specification

P. Vickery (ARA) V. Cardone (Oceanweather)

A. Cox (Oceanweather)

Modeling System

B. Blanton (RENCI)P. Vickery (ARA)

V. Cardone (Oceanweather)A. Cox (Oceanweather)R. Luettich (UNC-CH)

H. Friebel (NAP)E. Devaliere (UNC)C. Fulcher (UNC)

J. Atkinson (ARCADIS)H. Roberts (ARCADIS)

GIS Database

K. Gamiel (RENCI)B. Blanton (RENCI)

M. Forte (USACE-FRF)J. Yuan (ECSU)

FEMA RIII Storm Surge ProjectOrganizational Chart

US Army Engineer Research and Development CenterUS Army Engineer Research and Development Center

Approach

Return Period Analysis- JPM-OS Hurricanes- EST Extratropicals

Flood Levels 10-, 50-, 100-, & 500-year

0

2

4

6

8

1 10 100 1000

Surg

e (m

)

Return Period (years)

5663jpm

stochastic

0

2

4

6

8

1 10 100 1000

Surg

e (m

)

Return Period (years)

5667jpm

stochastic

0

2

4

6

8

1 10 100 1000

Surg

e (m

)

Return Period (years)

6251jpm

stochastic

0

2

4

6

8

1 10 100 1000

Surg

e (m

)

Return Period (years)

6492jpm

stochastic

0

2

4

6

8

1 10 100 1000

Surg

e (m

)

Return Period (years)

5663jpm

stochastic

0

2

4

6

8

1 10 100 1000

Surg

e (m

)

Return Period (years)

5667jpm

stochastic

0

2

4

6

8

1 10 100 1000Su

rge (

m)

Return Period (years)

6251jpm

stochastic

0

2

4

6

8

1 10 100 1000

Surg

e (m

)

Return Period (years)

6492jpm

stochastic

0

2

4

6

8

1 10 100 1000

Surg

e (m

)

Return Period (years)

5663jpm

stochastic

0

2

4

6

8

1 10 100 1000

Surg

e (m

)

Return Period (years)

5667jpm

stochastic

0

2

4

6

8

1 10 100 1000Su

rge (

m)

Return Period (years)

6251jpm

stochastic

0

2

4

6

8

1 10 100 1000

Surg

e (m

)

Return Period (years)

6492jpm

stochastic

High-Resolution Bathy / Topo

Mesh

Storm Surge Modeling

Winds

Waves Water Levels

Storm Forcing- Extratropical Wind Fields

- Hurricane Tracks

Extra-TropicalStorm Forcing• Selection based on water levels at 7 stations

• Total of 31 historical storms 1975-2009

• Kinematic reanalysis of all wind fields

• Empirical Simulation Technique (EST) used for return period calculations

• To include sampling at 5 tidal stages

Return PeriodAnalysis

Nor’Ida November 2009

Delaware

6-ft Surge

Sewells Point, VA

Norfolk, VA

• Remnant of Hurricane Ida

• Added to extratropical data set

Tropical Storm Forcing

Modeled TracksVA/DE/NJ

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0 20 40 60 80 100

CDF

Central Pressure Difference (mbar)

MP 2300

SimulatedHistorical

Central PressureDifference

0

0.2

0.4

0.6

0.8

1

-180 -135 -90 -45 0 45 90 135 180

CDF

Heading

MP 2300

Historic

Simulated

Heading

• Record of 20 hurricanes in 60 years insufficient for 100- and 500-yr computations

• Synthetic storm set used to develop landfall frequencies and hurricane parameters

• Joint Probability Method for return period analysis

• Demonstrated validity with comparisons to historic data

Development of a Topo/Bathy Digital Elevation Model (DEM)10 m DEMDEM covers:

NJDEMDVA Portions of PADelaware BayChesapeake

Bay and main tributaries

Atlantic Ocean

High Resolution Bathymetry and Topography

• Data assimilation through USACE districts

• Use Lidar for topography where available

• Region divided into 20 tiles

• Consistent bathy/topo surface with 10-m horizontal resolution

Region III DEM10-m

Resolution

Geographic Tiles

ADCIRC GridGrid allows to capture

complex coastal morphologies and provide high resolution of shoreline features, embayment and estuaries

Expected grid resolution 50 m at shore/high developed areas, 1-2 km offshore

ADCIRC will be coupled with the 2D wave model SWAN

The coupling of the two models will allow to compute starting wave conditions and wave setup for the overland wave analyses

Storm Surge Modeling SystemWind and Pressure Fields

TC96 PBL Hurricane ModelOWI Extratropical Reconstructions

Water Levels

ADCIRC Coastal Circulation and Storm Surge Model

Waves/ Radiation Stress

WaveWatch III Basin Scale WavesSWAN Coastal Waves Radiation Stress

WW3

Coupling

SWAN

Storm Surge Project Status Accomplishments:

Bathy/Topo Inventory Draft DEM Establish JPM Approach Winter Storm Selection and Windfield Develop. Prototype Modeling System Validation Tools – Interactive Model Evaluation and Diagnostics

System

Ongoing: DEM Review ADCIRC Mesh Development Models Calibration and Validation Synthetic Storms Development

Future Tasks: Production Frequency Analysis

Coastal Hazard Analyses ComponentsTransect layoutField Reconnaissance (land use, obstructions, shoreline

conditions, structures)Starting wave conditions (wave height and period) from 2D

wave modeling eliminating the need for limited fetch analysis

Wave setup from 2D wave modelingPrimary Frontal Dune (PFD)Dune erosion: 540 sqft ruleWHAFIS modeling for overland wave height computation2% Wave RunupAll above analyses will be performed with the Coastal

GeoFIRM tool

Transect Placement

Shoreline in High and Low Population Density Areas

Field Reconnaissance

Overland Wave Hazard Modeling

WHAFIS 4.0Profile

elevation1% SWELsStarting

wave conditions

Wave Setup Obstruction

cards (OF, IF, BU, VE, MG)

Wave RunupFEMA G&S 2007 requires the

use of the 2% runup vs. the mean runup computed prior to 2007

Mild-sloping beaches, bluffs and cliffs

Coastal Structures: Will structure survive the 1%

event? Is structure certified? Modeling of integral structure

vs. fail structure to determine higher hazard

Runup on structures limited to 3 ft on top of the structure’s crest w/overtopping possible AO Zone

Methods: Runup 2.0, TAW, ACES, SPM

Added Detail with GIS

Mapping

Limit of Moderate Wave Action (LiMWA)

FEMA Procedure Memorandum No. 50, 2008At present not a regulatory requirementNo Federal Insurance requirements tied to

LiMWACRS benefit for communities requiring VE

Zone construction standards in areas defined by LiMWA or areas subject to waves greater then 1.5 ft.

• Potential of additional 650 points

Limit of Moderate Wave Action (LiMWA)

Defined by the area subject to wave action with waves greater than 1.5 ft in height

LiMWA – mapped example

Project Schedule

Spring 2010

Summer 2010

Fall 2010

Spring 2011

Summer 2011

Complete DEM

Surge Model validation Initiate Surge production

Complete Surge production and return period analysisGIS site fully populated

Complete Overland Wave Analysis

Complete Hazard Mapping

Hurricane Isabel September 2003

Web/GIS Interface

• Public outreach site under construction

• GIS interface to results for stakeholders

• Google-earth displays of storm tracks, model output fields and return periods

Maximum Wave Heights

Inundation Levels

Storm Selection

Questions?