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<br />Cross section data for the Town of Frederick were obtained from <br />topographic mapping produced as part of a 1975 drainage study for <br />Weld County (Reference 9). Bridges were measured to obtain structural <br />geometry. <br /> <br />A summary of cross section locations and elevations for the Town <br />of Frederick as shown in Table 2. <br /> <br />Table 2. <br /> <br />Summary of Cross Section Locations and Elevations <br /> <br />Base Flood ~i1ater <br />Surface Elevation <br />(Regulatory) <br /> <br />Cross Section <br /> <br />. 1 <br />Cross Section Locatlon <br /> <br />A <br />B <br />C <br />D <br />E <br />F <br />G <br /> <br />5555 <br />5660 <br />6190 <br />6750 <br />7280 <br />8215 <br />8290 <br /> <br />4970.3 <br />4970.4 <br />4970.6 <br />4973.3 <br />4978.4 <br />4984.3 <br />4987.0 <br /> <br />1 <br />Feet Above County Road Along Profile Base Line <br /> <br />locatior_s of selected cross sections used in the hydraul~c analyses <br />are shown on the Flood Profiles. <br /> <br />Roughness coefficients (Manning's "nl:) were estimated by field <br />inspection. The roughness coefficients for the Tri-Area Drainageway <br />and overbank areas generally ranged between 0.045 and 0.060. In <br />some overbank areas, llnll values up to o~ 090 were appropriate. <br /> <br />The water-surface profiles for the 10-, 50-, 100-, and 50Q-year <br />floods were computed using the u.s. Army Corps of Engineers' HEC-2 <br />Computer Model (Reference 10). Starting water-surface elevations <br />were taken from water surface profiles developed for the Weld County, <br />Colorado, Flood Insurance Study (Reference 11). <br /> <br />Divided flow occurs in Frederick. For this reason, a divided flow <br />profile base line is shown on the map. <br /> <br />Flood profiles were drawn showing computed water-surface elevations <br />to an accuracy of 0.5 foot for floods of the selected recurrence <br />intervals (Exhibit 1). <br /> <br />All elevations are referenced to the National Geodetic Vertical <br />Datum of 1929 (NGVD). Elevation reference marks used in the study <br />are shown on the maps. <br /> <br />6 <br />