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<br />On the Little Thompson River, approximate flood boundaries were delineated using aerial <br />photographs at a scale of 1: 12,000 (Reference 27). Approximate flood boundaries for the <br />Cache La Poudre River were delineated from two USACE Flood Plain Information reports <br />(References 6 and 28). <br /> <br />Floodplain boundaries for the Cache La Poudre River were delineated using topographic <br />maps at a scale of 1: 1 ,200, with a contour interval of 2 feet (Reference 42). <br /> <br />The flood boundaries for the 1-, and 0.2-percent annual chance floods, for the revised area <br />of Cache La Poudre River, were delineated using the flood elevations determined at each <br />cross section. The flood boundaries were plotted on 1" = 200'-scale orthophoto maps <br />(Reference 58). There were several low-lying areas protected from flooding from the main <br />channel by gravel banks with minimum freeboard. Because of the potential hazard if these <br />banks fail, these areas are shown as subject to shallow flooding. <br /> <br />For the revised area of the Cache La Poudre River from Wood Street to Watson Lake the <br />1- and 0.2-percent annual chance floodplain boundaries were delineated using the flood <br />elevations determined at each cross section. Between cross sections, the boundaries were <br />interpolated using topographic maps prepared for Larimer County with a contour interval <br />of 2 feet. <br /> <br />For each section of Boxelder Creek and Cooper Slough studied by detailed methods, the 1- <br />percent annual chance floodplain boundary were delineated using the flood elevations at <br />each cross section. Between cross sections, the boundaries were interpolated using <br />topographic maps at a scale of 1: 100, with a contour interval of 2 feet (Reference 75). <br /> <br />Boundaries of the 1-, and 0.2-percent annual chance floods for Boxelder Creek in the <br />vicinity of the Town of Wellington were delineated using the flood elevations determined <br />at each cross section; between cross sections, the boundaries were interpolated using <br />topographic maps at a scale of 1 : 1,200, with contour intervals of 2 feet (Reference 30). <br /> <br />Boundaries of the I-percent annual chance flood for Spring Creek were interpolated using <br />topographic maps ranging in scale from 1" = 50' to 1" = 100', with contour intervals 1 and <br />2 foot (Reference 71). <br /> <br />The 1- and O.2-percent annual chance floodplain boundaries are shown on the FIRM. On <br />this map, the I-percent annual chance floodplain boundary corresponds to the boundary of <br />the areas of special flood hazards (Zones A and AE); and the O.2-percent annual chance <br />floodplain boundary corresponds to the boundary of areas of moderate flood hazards. In <br />cases where the 1- and O.2-percent annual chance floodplain boundaries are close together, <br />only the I-percent annual chance floodplain boundary has been shown. Small areas within <br />the floodplain boundaries may lie above the flood elevations but cannot be shown due to <br />limitations of the map scale and/or lack of detailed topographic data. <br /> <br />For the streams studied by approximate methods, only the I-percent annual chance <br />floodplain boundary is shown on the FIRM. <br /> <br />41 <br />