Digital Flood Insurance Studies

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Digital Flood Insurance Studies Their
Development and Use
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Start with Gathering Digital Data

• GIS Based Digital Data
• 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

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GIS Data Layers Digital Terrain Modeling Formats
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Components of a Flood Map
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Base Data

• Digital Orthophotogrammetric Quarter Quads (DOQQ)
  or community-supplied base
• Will allow precise map determinationsby all
  users
• Partner with USGS, States, and communities
• DOQQs Available for 56 of U.S.
• Additional 32 under production
• Reduced cost for FEMA

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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
• GPS technology for field reconnaissance
• Bathymetry
• Hydraulic structures
• Merge to build Digital Elevation Models

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LIDAR

• LIght Detection and Ranging (LIDAR)
• Airborne Laser System
• Fixed Wing
• Helicopter
• Potential for High Level accuracy (1 foot range)
• Ongoing FEMA related projects
• Harris County, TX
• Louisiana

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IFSAR

• 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

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Global Positioning System(GPS) Surveys

• Surveying with ground control established through
  satellite signals
• (xyz coordinates)
• 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

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FEMA Specifications

• LIDAR specification developed for FISs, DEMs, and
  other NFIP products (this technology is not yet
  mature)
• 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

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Current Issues withLIDAR and IFSAR

• Many FEMA initiatives and partnerships underway
  to evaluate
• LIDAR specifications for DEMs and FISs developed
• Rapidly Developing Technologies
• Data voidswater and vegetation
• Non-standard and varying results and costs fuse
  with other technologies in near-term
• GPS, Photogrammetric, Microwave radiometer

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Flood Data

• Engineering analyses and digital mappingof flood
  risk
• Use GIS-based hydrologic and hydraulic models
  integrated with DEMs (Automated HH)
• Contract with USACE, USGS, NRCS, local A/E firms,
  States, and communities

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Automated Hydrology and Hydraulics

• Use GIS and terrain-based models to automate and
  link
• Hydrologic modeling
• Hydraulic modeling
• Floodplain delineation
• Automates QA/QC checking

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DFIRM

• Digital conversion of mapping inventory
• Approximately 92,000 panels need conversion
• Digital distribution (CD-ROM and Internet) allows
  for automated applications
• Risk assessment and mapdeterminations
• Disaster response andrecovery
• Repetitive loss applications
• Planning and permitting
• Supported by a fully integratedrelational and
  engineering database

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DFIRM Database
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DFIRM Database

• Open file formats for data exchange across
  software applications
• Efficient archiving and retrieval allows for
  rapid map updates and revisions
• Supports GIS and software applications

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Elevation Reference Marks Current

• Benefits
• 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
• ERMs do not have an horizontal location (x,y
  coordinates)
• Many ERMs damaged or destroyed

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NGS (National Geodetic Survey) Monuments Map
Modernization

• Benefits
• 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
• A limited number of NGS Monuments will be
  available for the County.

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Conversion to NAVD 88

• The majority of existing FIRM panels vertical
  datums
• National Geodetic Vertical Datum (NGVD) 29
• Local Datum
• New DFIRM Panel vertical datum will be
  standardized to (North America Vertical Datum)
  NAVD 88.

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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

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References

• www.noaa.ngs.gov
• www.fema.gov/mit/tsd/dl_cgs.htm