Map Changes and Technical Resources

Bridge and/or Culvert Floodplain Requirements

Letters of Map Revisions

A Letter of Map Revision (LOMR) is a letter from FEMA officially revising the Flood Insurance Rate Map (FIRM) or Flood Insurance Study (FIS) to show changes to floodplains, floodways, or flood elevations.

LOMRs are often completed when there is a proposed project that changes the circumstances in a watershed or stream. A CLOMR is used to show that a proposed project would be eligible for a LOMR (or physical map revision) once the project is constructed.

Examples of projects that may require a LOMR:

  • Projects that affect or change watershed hydrology - such as a dam, diversion channel, or detention basin
  • Projects that affect or change stream hydraulics - such as channelization, new bridges or culverts, or levees
  • Projects that change topographic conditions in the floodway - such as grading or filling
  • Projects that change the floodway boundary such as stream realignment

LOMRs may be completed if there are errors in the effective FIRM or FIS or if there is better available data that can be incorporated into the FIRM or FIS, but they are not required.

Changes in watershed hydrology require an additional review by the Interagency Hydrology Review Committee (IAHRC) in addition to the LOMR or CLOMR review by FEMA and the MnDNR. If a proposed project will change watershed hydrology for a FEMA modeled and mapped stream, contact the DNR for guidance on submitting information to the IAHRC.


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