FEMA Region III Storm Surge Project

Construction of The Digital Elevation Model

The Foundation of a Storm Surge Model

FEMA Region III Coastal Storm Surge ProjectWorkshop November 1 2011

Michael F. Forte, Lisa Stillwell, Jason F. Miller, Jeffrey L. Hanson

FEMA Region III Domain

6 StatesPennsylvaniaDelawareMarylandVirginiaNorth CarolinaNew Jersey

Chesapeake and DelawareBays, Numerous Rivers &Atlantic Seaboard

Data Gathering

Over 125 data sets evaluated (~2 TB)

Data types:• TIFF• CSV• ASCII GRID• Raster• FLT• LAS• Shapefile• SID• and more…

Projections:• NJ, DE, MD, VA State Plane• UTM

Datums:• NAD27• NAD83• Tidal (MSL, MLLW, etc.)

USACE District offices of Philadelphia, Baltimore, and Norfolk played critical role in obtaining the most accurate up-to-date datasets for Region

Data Sources

• US Army Corps of Engineers• USGS• NOAA / NGDC• NC Division of Emergency Management Flood

Plain Mapping Program (NCDEM – FMP)• Individual States

Topographic LiDAR Coverage

24 LiDAR Data sets

National Elevation Dataset (NED) covered remaining areas

Bathymetric Data Coverage

SHOWEX Bathymetric Data Set“SHOaling Waves Experiment”

Conversion

Geographic Coordinates Decimal Degrees (NAD83)Elevation/depth relative to North American Vertical Datum 1988 (NAVD88) meters

Horizontal Conversion

Conversion

•Vertical Datum Conversion

•V – Datum (NOAA)

•Unit Conversion

•Mean Lower Low water MLLW

•North American Vertical Datum of 1988 NAVD 88 m

FEMA Region 3 Divided Into 20 Tiles For Efficient Data ManagementCertain Tiles Contain Up To 6 Gigabytes Of Data.

Regional Organization

Weighted Moving Average Algorithm

Search weight – average value of 3-5 used

Grid Cell Size - 0.00011degrees ~10m cell size

Iterative process obtaining best result given data density and Quality

IVS 3-D Fledermaus Interpolation Parameters

Ex. Search Weight

10m ResolutionInterpolation

Result after interpolationObvious errors literally “jump out”

QA/QC

USACE Districts DEM Review

USACE Districts DEM Review

Cross section from tile 8 reveals anomaly Coordinates are defined for peak and Investigated using Google earth.

8NS5 – Google earth search revealed some square areas that may contain higher elevations (possible mining activities).

USACE Districts DEM Review

ARCADIS DEM Review

Tile 3 DEM Reveals Barrier Island not present in Aerial Photograph

Bridge Removal

Tile 3 Bridge serves as impediment to water flow

Tile 3 Delaware River Bridge Impediment

Fledermaus conversion to “PFM” and bridge is manually removed

Bridge Removal

Tile 3 Re-interpolated with bridge removed

Bridge Removal

Lidar Datasets Need Clipping Around land/water interface

Profile displays jump of 2.5m

Land Water Interface

Most Complete up to date seamless DEM available for Mid-Atlantic Region

Comprised of 120 Datasets (~2TB)

Serves a variety of purposes from modeling to sea level rise studies

High Quality DEM for Mid-Atlantic

Documents DEM data, procedures, and USACE District Review

Published as U.S. Army Corps of Engineers ERDC-CHL Technical Report

Available at: dodreports.com/pdf/ada539477.pdf

Documentation /Submittal 1.1