Transcript Slide 1

Digital Flood Insurance
Studies
&
Their Development
and Use
Start with Gathering Digital Data

GIS Based Digital Data
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Base Maps
Aerial Topography
• LiDAR
• IFSAR


Digital Flood Insurance Rate Maps
Transition from Elevation Reference Marks
to National Geodetic Survey Monuments
 NAVD 88 Datum
 Map Service Center
GIS Data Layers — Digital Terrain
Modeling Formats
DTM
TIN
DEM
Contours
Components of a Flood Map
+
Base
=
Topography
+
Flood Data
Digital
FIRM
Base Data
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Digital Orthophotogrammetric Quarter Quads
(DOQQ) or community-supplied base
 Will allow precise map determinations
by all users
 Partner with USGS, States, and communities
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DOQQs Available for 56% of U.S.
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Additional 32% under production
Reduced cost for FEMA
Topography

Emerging technologies (LIDAR and IFSAR) allow
for cost-effective, accurate collection of digital
elevation data
 Partner with NASA, USGS, States, & communities
 LIDAR/IFSAR 20-50% of cost of collecting
topographic data
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GPS technology for field reconnaissance
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Bathymetry
Hydraulic structures
Merge to build Digital Elevation Models
LIDAR
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LIght Detection and
Ranging (LIDAR)
 Airborne Laser
System
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Fixed Wing
Helicopter
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Potential for High
Level accuracy (1 foot
range)
 Ongoing FEMA
related projects:
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Harris County, TX
 Louisiana
IFSAR
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Inter-Ferometric Synthetic Aperture Radar
(IFSAR)
 Airborne or spaceborne radar antennae
 Accuracy levels between 1.5m and 3m over
broad areas
 Cover larger areas at lesser cost (and accuracy)
than LIDAR
Global Positioning System
(GPS) Surveys
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Surveying with ground control
established through satellite signals
(xyz coordinates)
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Airborne
Vehicle
Handheld
Boat with underwater depth finder
Used for stream channel and structure
surveys to supplement LIDAR and IFSAR
Also useful for developing floodprone
building inventory for conducting risk
assessments
Vertical accuracy to 2cm
Very cost effective
FEMA Specifications
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LIDAR specification developed for FISs,
DEMs, and other NFIP products (this
technology is not yet mature)
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Performance-based calling for 30-cm
(approximately 1-foot) accuracy
Robust QA/QC requirements
Only LIDAR specification currently available
Aerial mapping and surveying specifications
being updated to include GPS, DOQQs, and
LIDAR and IFSAR DEMs
Current Issues with
LIDAR and IFSAR
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Many FEMA initiatives and partnerships underway
to evaluate
LIDAR specifications for DEMs and FISs
developed
Rapidly Developing Technologies
Data voids—water and vegetation
Non-standard and varying results and costs; fuse
with other technologies in near-term
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GPS, Photogrammetric, & Microwave radiometer
Flood Data
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Engineering analyses and digital mapping
of flood risk
 Use GIS-based hydrologic and hydraulic models
integrated with DEMs (Automated H&H)
 Contract with USACE, USGS, NRCS, local A/E
firms, States, and communities
Automated Hydrology and Hydraulics
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Use GIS and terrainbased models to
automate and link:
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Hydrologic modeling
Hydraulic modeling
Floodplain
delineation
Automates QA/QC
checking
Linking base maps, work maps, and
flood themes in GIS to a HEC-RAS
model
DFIRM
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Digital conversion of mapping inventory
 Approximately 92,000 panels need conversion
 Digital distribution (CD-ROM and Internet)
allows for automated applications:
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Risk assessment and map
determinations
Disaster response and
recovery
Repetitive loss applications
Planning and permitting
Supported by a fully integrated
relational and engineering database
DFIRM Database
Coastal
Remote Sensing
Land Use
Surveying
Base Maps
Hydrology
New DFIRM
Database
DEMs
DFIRMs
Applications Interface
Coastal
Models
Hydrologic
Models
Hydraulic
Models
Applications
Hydraulics
Automated
Floodplain
Delineations
DFIRM Database
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Open file formats for data exchange across
software applications
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Efficient archiving and retrieval allows for
rapid map updates and revisions
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Supports GIS and software applications
Elevation Reference Marks
Current
 Benefits:
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Elevation Reference Marks (ERMs) are located
throughout the study area.
Location, Descriptions and elevations are included
either on the FIRM panel or in the FIS Document.
 Drawbacks:
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ERMs do not have an horizontal location (x,y
coordinates)
Many ERMs damaged or destroyed
NGS (National Geodetic Survey)
Monuments – Map Modernization
 Benefits:
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NGS Monuments are available on-line.
NGS Monuments are maintained by the Federal
government.
X, Y, and Z coordinates are available for every
monument. These coordinates lend themselves to
GPS surveying.
 Drawbacks:
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A limited number of NGS Monuments will be
available for the County.
Conversion to NAVD 88
 The
majority of existing FIRM panels
vertical datums:
National Geodetic Vertical Datum
(NGVD) 29
 Local Datum
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 New
DFIRM Panel vertical datum will be
standardized to (North America Vertical
Datum) NAVD 88.
Layers of Digital Data
 Easily

updated
All data layers in Digital Flood Insurance Map
can be easily modernized when changes
occur
 Can
be overlaid with multiple datasets for
comparison and integration
 Creates
useful products for communities
References
 www.noaa.ngs.gov
 www.fema.gov/mit/tsd/dl_cgs.htm