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Flood Modernization
   Flood Map Modernization   

The Mapping Process

1. Scoping

  • Incorporate Base Map Data
    • Aerial Photography
    • Roads & Railrods (Centerlines and names)
    • Stream & Lakes (Centerlines and names)
    • Municipal Boundaries
    • Elevation (Data)
  • Data Standards and Data Sharing Agreements

    • Data must meet FEMA accuracy standards-vendor data certification and metadata should be provided

    • Elevation data is used for floodplain delineation but does not appear on the maps

    • If your data is proprietary, options exist that allow the best available data to be used

    • The table below lists default data used to make DFIRMs:
  • Base Map Data Needed Default Sources
    Possible Sources
    USGS 2005 digital orthophotos--- 1"=500'
    USGS 7.5 minute quadrangle maps (10' contours)
    Roads & Railroads
    2000 TIGER files
    Streams & Lakes
    Municipal boundaries
    Department of Revenue, 2005
    Airport and Parks
    USGS quadrangles
  • Incorporate Flood Study Data
  • Flood Insurance Rate Map (FIRM)
  • Flood Insurance Study (FIS)
  • Letters of Map Change (LOMC)
    • All LOMRs are incorporated for the source of flooding
    • LOMAs and LOMR-Fs are revalidated unless a new study is incorporated for the source of flooding
    • A Summary of Map Actions (SOMA) describes the action taken for each LOMC and is distributed with the preliminary maps
2. Mapping
  • Convert FIRM
    • Register (align) existing FIRM to the photographic base map (or fit the paper map to the base map)
    • Digitize flood data (floodplain boundaries, cross sections, BEFs, etc.)
    • Convert the elevation reference to NAVD 1988 vertical datum
    • Incorporate LOMCs

  • Correct and Update
    • Validate cross section locations using FIS profile data
    • Align floodplains with stream locations on base map, cleaning up areas where the paper map obviously does not match the base map
    • Correct and update street names
    • Correct stream or lake names
    • Update railroads, airports, and parks
  • Studied Streams (Zone AE)

    • For studied streams in the effective FIS, re-delieneate floodplain boundaries using the best available topographic data (10' or less contour intervals)
    • Re-project the published base flood elevations from the profile onto the topography
    • If the topographic data is newer, the floodplain boundaries will likely change, but base flood elevations will not
    • Incorporate changes that may affect BFEs such as removed bridges, new bridges, channelization, open channels replaced by storm sewers
    • If changes have occurred that invalidate the model used for Zone AE, BFE computation, the floodplain zone may revert to Zone A until a new floodplain may revert to Zone A until a new study is completed
3. Post-Processing
  • Preliminary Maps
    • The county will receive a complete set of printed preliminary map panels and preliminary FIS
    • Communities will receive the preliminary FIS and their respective preliminary map panels
    • Preliminary map panels and FIS will be posted on the web in PDF format at www.illinoisfloodmaps.org
    • Any BFE changes will be sent to community CEOs and published local newspapers and the Federal Register

  • Flood Risk Information Open House
    • Preliminary maps and FIS are presented to the public
    • Inform public of their flood risk to promote good risk management decisions
    • Provide public access to a variety of experts
    • The Open House begins the 30-day Comment Period. Communities have 30 days from the date of the Open House to submit comments to the IDNR

  • 90-day Appeals Period
    • Only occurs in counties where there are Base Flood Elevations (BFE) changes. Communities have 90 days to submit appeal and protests to IDNR
      • Appeals --- technical disagreements; must be based on scientific and technical data
      • Protests --- non-technical errors, oversights, or cosmetic changes

  • FEMA resolves all appeals and protests
  • Effective Maps
    • FEMA issues a Letter of Final Determination (LFD) to community CEOs and publishes final BFEs in the Federal Register
    • Final FIS Report and Maps are printed and distributed to map repositories
    • FIRM/FIS becomes effective on the date set in the LFD
    • NFIP communities must enact required ordinances and send a certified copy of the ordinance to IDNR before the effective date. Communities have a six (6) month period to adopt the new FIS and maps. Failure to adopt the new FIS and maps within this timeframe will result in suspension from the National Flood Insurance Program (NFIP).

Flood Map Modernization

 Advantages of Digital Maps
 Project Status
 Model Ordinance
 Program Material
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