Grimes, Iowa

FEMA Preliminary Flood Mapping Appeal

  • Client City of Grimes
  • Type Stormwater
  • Services Assessment, Evaluation, Planning
  • Project Manager Steve P. Soupir, P.E., CFM

Challenge

The city of Grimes is one of the fastest growing communities in the state of Iowa. The Federal Emergency Management Agency (FEMA) issued new National Flood Insurance Program (NFIP) preliminary flood insurance rate maps.  The preliminary mapping provided more detailed analysis of the floodplain in and around the city of Grimes and replaced the outdated flood maps completed in the 1980s. Unfortunately, the mapping affected several new property owners and the city needed to verify the accuracy of the information used by FEMA to develop the new maps. After review, it was determined that several areas in the mapping appeared to be using information that was outdated, thereby incorrectly affecting various property owners.

Solution

FOX Engineering reviewed the hydrologic and hydraulic information provided by FEMA and verified several areas of the mapping that appeared to be either scientifically or technically incorrect. FOX completed a revised hydraulic analysis of the areas of concern and updated the mapping based on current information. Computer software was used to revise the 100-year and 500-year floodplain delineation of the Special Flood Hazard Area (SFHA) boundaries; this information was then provided to FEMA as an appeal to the preliminary mapping.

Outcome

The appeal of the preliminary mapping provided to FEMA allowed the city to revise the mapping information to more accurately reflect floodplain conditions within the city of Grimes. This appeal lowered the impact of the proposed mapping in some areas and lessened requirements for flood insurance for many property owners in the community, a welcome result for Grimes citizens.