Flood - Glossary of terms

Flood Glossary of Terms

Have you received a letter notifying you that Washington County is preparing a Conditional Letter of Map Revision (CLOMR) to the Federal Emergency Management Agency (FEMA)?

Visit Flood Information and/or Flood Resources for more information about this project.

The definitions below will help define terms commonly used by FEMA in communications with the public.

  • Base Flood Elevation (BFE): The elevation a flood is anticipated to reach during the base flood. The base flood is also called the 1-percent annual chance flood or 100-year flood.
  • Conditional Letter of Map Revision (CLOMR): A letter from FEMA stating that a proposed project would affect the hydrologic or hydraulic characteristics of a flooding source and that may modified an existing regulatory floodplain.
  • Letter of Map Revision (LOMR): A letter from FEMA stating a parcel or proposed structure that will be elevated by fill will not be flooded by the base flood.
  • Flood Insurance Rate Map (FIRM): Depicts the Special Flood Hazard Area (SFHA) which has been determined to be subject to a 1% (100-year) or greater chance of flooding in any given year. The FIRM is used to determine flood insurance rates and to help the community with floodplain management.
  • Floodway: The portion of the floodplain that includes the channel of a river (or other watercourse) and the adjacent area that must be reserved to discharge the 1% annual chance (base) flood without increasing the water-surface elevation by more than a designated height. 
  • Special Flood Hazard Area (SFHA): An area having special flood hazards as shown on a Flood Insurance Rate Map (FIRM). In Washington County's FIRMs, these areas are Zone A and Zone AE. SFHAs are where the National Flood Insurance Program's (NFIP's) floodplain management regulations are enforced and where flood insurance is mandatory. SFHAs are commonly referred to as the 100-year floodplain or the 1% annual chance flood area.