Letters of Map Revision

Three separate projects were completed by our firm to prepare Federal Emergency Management Agency Letters of Map Revision (LOMRs) in Bentonville, AR., and portions of unincorporated areas in Benton County. These LOMRs were initiated by the city to update approximate Zone A special flood hazard areas to areas of detailed Zone AE with published base flood elevations and floodways.


The work included the following:

  • Field survey activities, including GPS ground control and hydraulic structure and valley cross section surveys;
  • Review of the existing hydrologic analyses included in the Benton County Flood Insurance Study (FIS) to determine if the existing hydrologic data were still valid and production of newly updated hydrologic analysis for annual-chance rainfall events;
  • Extraction of geometric data from the ground survey, GIS, and topographic data;
  • Hydraulic analyses using HEC-RAS to compute the water surface profile for the 10%-, 2%-, 1%-, and 0.2%-annual-chance flood events;
  • Use of the HEC-RAS hydraulic model to compute the floodway and performing quality assurance/ quality control using FEMA’s CHECKRAS software;
  • Flood hazard mapping in Digital Flood Insurance Rate Map format along the project area, tying in downstream to the FIS;
  • Preparation of water surface elevation profiles;
  • Preparation of the necessary documentation for the LOMR application to FEMA.