Jeff Gangai, Dewberry 1/31/2012

FEMA Coastal Flood Study 1

FEMA Region II Coastal Flood

Hazard Project for New York

City and New Jersey

Jeff Gangai RAMPP

19 counties in NY and NJ

9 additional counties up the Hudson Valley

Scope of Effort

Jeff Gangai, Dewberry 1/31/2012

FEMA Coastal Flood Study 2

Topography Data Sources NJ

Atlantic & Ocean Co. USGS NED 1/3 arc second DEMs (10 m)

Lower Monmouth 2 FEMA compliant contours

All others LiDAR

NY

NYC DOITT 3 ft DEM

Westchester 2 FEMA compliant contours

Hudson Valley USGS NED 1/3 arc second DEM

Bathymetric Data Sources NOAA Hydrographic Surveys

National Geophysical Data Center Office of Coast Survey

NOAA Navigation Charts Frequently provides data in areas

where digital survey data is not available (fills gaps)

USACE SHOALS/CHARTS Hydrographic LiDAR

Limited coverage due to light penetration in the water column

USACE District Surveys (Retrieved from NAN and NAP) Limited to Federal navigation projects or project specific study areas

Jeff Gangai, Dewberry 1/31/2012

FEMA Coastal Flood Study 3

Seamless DEM

Storm Surge Study Approach

Recommend Regional application

Avoid discontinuities, maximize efficiency

Coupled 2-D hydrodynamic and wave model

ADCIRC

SWAN

Combined extratropical and tropical surge

JPM statistical method for tropical

GEV for extratropical

Jeff Gangai, Dewberry 1/31/2012

FEMA Coastal Flood Study 4

ADCIRC/SWAN Mesh

604,790 Nodes

1,188,640 Elements

Inland Spacing:

Smallest 80 m

Largest 500 m

ADCIRC/SWAN Mesh

Jeff Gangai, Dewberry 1/31/2012

FEMA Coastal Flood Study 5

Storm Selection

Validation Storms

1938 Hurricane (Long Island Express)

1944 Hurricane

1960 Hurricane Donna

1985 Hurricane Gloria

Extra-Tropical Storms

1984

1991

1992

Jeff Gangai, Dewberry 1/31/2012

FEMA Coastal Flood Study 6

Joint Probability Method (JPM)

Storm Parameters

Major Parameters Pressure deficit

Pressure radius

Holland B

Landfall location

Azimuth

Forward speed

Other Parameters Astronomical tide

Track variations

Wind/pressure field variations

Lack of model framework skill

Joint Probability Method (JPM-OS)

159 Model synthetic storms

on multiple tracks

Converts storm statistics

to surge height statistics

Jeff Gangai, Dewberry 1/31/2012

FEMA Coastal Flood Study 7

Winter Storms: Storm Analysis

19501125

19610413

19620306

19640112

19660123

19681112

19701217

19710208

19711125

19720219

19741202

19790125

19840329

19870123

19911031

19921211

19930314

19940303

19941224

19950204

19951115

19960108

19961020

19961206

19980128

19980205

20051025

20070416

20080512

20091113

Storm Dates (CYMD)

Residual water levels (tides

removed) scanned for peak

events above the 99th

percentile individually by

station

Time ranges with tropical

cyclone activity removed

Storms ranked individually by

station

30 storms identified in storm

ranking process

Top 5 storms at each station

represented in the storm list

Surge Return PeriodsDevelop 0.2%,1.0%,2.0% & 10.0% surge heights with wave set-up

Jeff Gangai, Dewberry 1/31/2012

FEMA Coastal Flood Study 8

15 15

Overland Wave Modeling TasksBEFORE STORM SURGE Data and Model Research

DEM Development

Transect Layout

Field Work

Obstruction Carding (landcover data setup)

Primary Frontal Dune (PFD) Delineation

AFTER STORM SURGE

Stillwater Surface Creation

Erosion Analysis

WHAFIS Simulations

Run-up Analysis

Delineate Coastal Floodplain

Develop FIRMs

Transect Layout

Jeff Gangai, Dewberry 1/31/2012

FEMA Coastal Flood Study 9

Storm surge stillwater elevation (SWEL)

Wave setup

Wave height above storm surge elevation

Wave runup above storm surge limits

FEMA Coastal Flood Hazards

Mapping

Jeff Gangai, Dewberry 1/31/2012

FEMA Coastal Flood Study 10

Mapping

Questions?