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<br />The current Flood Insurance Rate Map presents flooding information for <br />the geographic area of Adams County, excluding those communities which <br />fall within the more than one county as described in Section 1.1. <br />Previously separate Flood Insurance Rate Maps were prepared for each <br />identified floodprone incorporated community and the unincorporated <br />areas of the county. Historical data relating to the maps prepared for <br />each community are presented in Community Map History (Table 4). <br /> <br />7.0 OTHER STUDIES <br /> <br />This study includes information from the previously effective Flood <br />Insurance Studies/Flood Insurance Rate Maps for the unincorporated areas <br />of Adams County and incorporated communities into a countywide format. <br />This Flood Insurance Study supersedes all previous Flood Insurance <br />Studies/Flood Insurance Rate Maps covering the unincorporated areas of <br />Adams County and the incorporated areas of the Cities of Brighton, <br />Commerce City, Federal Heights, Northglenn, and Thornton (References 2, <br />5, 7, B, 9, and lO, respectively). The Cities of Arvada, Aurora, <br />Broomfield, and Westminster have individual separately published Flood <br />Insurance Studies (References 3, 4, 6, and ll, respectively), which are <br />not superseded by this countywide Flood Insurance Study. <br /> <br />Flood boundaries have been reconciled with previous studies on Big Dry <br />Creek (Reference 20), Little Dry Creek (Reference 30), Clear Creek <br />(Reference 12), and the South Platte River (References 18, 19, 21, and <br />40). <br /> <br />There are past published reports on flooding throughout Adams County <br />except on Box Elder Creek and Comanche Creek. The 1963 USACE Denver <br />Metropolitan Region Flood Plain Information (FPI) report, Volume I, <br />(Reference 21) was adopted by the Colorado Water Conservation Board <br />(CWCB) ~n 1967 as the official floodplain study for the South Platte <br />River. Following the 1965 flood and other more recent flood <br />experiences, as well as the construction of Chatfield Dam, the USACE <br />considers the 1963 FPI for the South Platte River to be outdated. In <br />September of 1977, the UDFCD published a Flood Hazard Area Delineation <br />of the South Platte River. This study has been revised to agree with <br />the UDFCD study, which is based on more detailed topographic mapping and <br />many more surveyed cross sections. The delineation shown of the South <br />Platte River is based on a lOO-year discharge assuming projected 1990 <br />basic conditions. Minor differences between the Adams County study and <br />the Flood Insurance Studies for the Cities of Brighton, Thornton, and <br />Commerce City can be attributed to the use of a projected 100-year <br />discharge in the county study, as opposed to present conditions analysis <br />in the city studies. <br /> <br />An FPI report (Reference 30) was prepared in 1968 by the USACE, Omaha <br />District, which included Little Dry Creek in Adams County. Minor <br />discrepancies occurred because the USACE assumed blockage at culverts <br />and bridges during flood stages, and the present study 15 based on <br />unobstructed flow. <br /> <br />67 <br />