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5.4 Flood Insurance Rate Map Description The Flood Insurance Rate Map for Mesa County is, for insurance purposes, the principal result of the Flood Insurance Study. This map contains the official delineation of flood insurance zones and base flood elevation lines. Base flood elevation lines show the locations of the expected whole-foot water-surface elevations of the base (lOO-year) flood. This map is developed in accordance with the latest flood insurance map preparation guidelines published by the Federal Insurance Administration. ~, 6.0 OTHER STUDIES In 1973, the U.S. Army Corps of Engineers, Sacramento District, published a Flood Plain Information report on the Colorado and Gunnison Rivers in the Grand Junction area (Reference 5). The report contained information on flood stage elevations.. water-surface elevations, and flooded area limits for the intermediate regional and Standard Project floods. An intermediate regional flood has a frequency of occurrence of once in 100 years. The Standard Project Flood used in the Flood Plain Information report was of less magnitude than the 500-year flood and was, therefore, not directly comparable. The lOO-year floodflows in both reports were found to be identical, but: flooded areas and flood profiles for the Colorado and Gunnison Rivers in the Flood Insurance Study varied from those in the Flood Plain Information report due to the use of more accurate topography than was available during preparation of the Flood Plain Informa- tion report. Flood profiles and flooded area delineations for the two rivers in this study are, therefore, more precise and supersede those in the Flood Plain Information report. A -t,' Flood Hazard Information studies of the Palisade, Fruita, and Grand Junc- tion areas (References 2, 3, and 4, respectively) were made in 1976. The streamways covered by those reports are also included in this study. Floodflows for the lO-, 50-, 100-, and 500-year floods and the flood profiles and flooded area delineations in the Flood Hazard Information reports were reviewed in detail, found to be accurate, and adopted for the present Flood Insurance St:udy. The Federal Insurance Administration has prepared a Flood Hazard Boundary Map for portions of the unincorporated areas of Mesa County (Reference 14) which is compatible with delineations presented herein. This study is authoritative for the purposes of the Flood Insurance Program; data presented herein either supersede or are compatible with all previous determinations. .. " 27 ,"""",