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The flood elevation differences, FHFs, flood insurance zones, and base flood elevations for each flooding source studied in detail in the county are summarized in Table 7. 5.4 Flood Insurance Rate Map Description The Flood Insurance Rate Map for Montrose County is, for insurance purposes, the principal product of the Flood Insurance Study. This map contains the official delineation of flood insurance zones and base flood elevations. Base flood elevation lines show the loca- tions of the expected whole-foot water-surface elevation of the base (lOa-year) flood. The base flood elevations and zone numbers are used by insurance agents, in conjunction with structure eleva- tions and characteristics, to assign actuarial insurance rates to structures and contents insured under the NFIP. 6.0 OTHER STUDIES A Flood-Prone Area Map for the San Miguel River, including Naturita, was prepared by the USGS in 1974 (Reference 18). The 100-year flood boundaries were estimated from regional stage-frequency relations. The Flood-Prone Area Map was based on approximate methods. This study used llIOre detailed methods in determining flood plain boundaries. A hydrology report for the upper San Miguel River was completed in May 1977, as a Technical Addendum for the San Miguel County Flood Insurance study (Reference 19). The hydrologic data compiled for the San Miguel County report were used in the determination of floodflows for this study and are in agreement with this study. A Flood Hazard Boundary Map (Reference 17) was prepared and revised for Montrose County in August 1977. The 100-year flood plains were delineated using approximate methods. Flood-Prone Area Quadrangle Maps prepared by the USGS (Reference 20) for the Uncompahgre River are available for the Town of Olathe. This study uses more detailed methods of analysis and, therefore, supersedes the Flood-Prone Area Quadrangle Maps. A Flood Hazard Information report prepared by the U.S. Army Corps of Engineers covering the Uncompahgre River in Montrose County was completed in February 1980 (Reference 21). The U.S. Army Corps of Engineers work was revised by the study contractor to reflect changes in Manning-Is "n" value, bridge codings, and flood plain delineation. The Uncompahgre River was revised from station 679.8 to 1,033.2 in and around Olathe, and from station 1,244.5 to 1,698.5 in and around Montrose. The Colorado Water Conservation Board has concurred with these revisions. Flood Insurance Studies for the City of Montrose, the Towns of Olathe and Naturita, and adjacent areas of Delta County have been prepared 36