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<br />Bridges and culverts in the study areas were surveyed to obtain <br />elevation data and structural geometry. <br /> <br />Channel roughness factors (Manning's On") for the hydraulic analyses <br />were assigned on the basis of field inspection of flood plain areas. <br />Roughness values varied from 0.020 to 0.050 for the channels and <br />from 0.025 to 0.180 for overbank areas. <br /> <br />For study purposes herein, it has been assumed that limited clogging <br />of the river channels will occur and that all flood control structures, <br />bridges, and culverts would remain intact. <br /> <br />A rating curve developed by the COE upstream of State Highway 227 <br />was the source of starting water-surface elevations for the Arkansas <br />River and Fountain Creek. For Wild Borse-Dry Creek, University <br />Park Tributary, and the Bonforte Boulevard Area, starting water- <br />surface elevations were determined by the slope-area method. <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 />The Fountain Creek levee, which starts at approximately 8th Street, <br />causes a split flow situation as 100- and 500-year floodwaters <br />flow into the east overbank behind the levee. A split-flow analysis <br />was performed for Fountain Creek and the east overbank between the <br />Atchison, Topeka & Santa Fe Railway and 8th Street. The flow distri- <br />bution for the 100-year flood was based on channel capacities deter- <br />mined from the BEC-2 analyses and on overbank capacities determined <br />from rating curves that were also developed by the HEC-2 routine. <br />The 500-year flood overtops the levee along almost the entire length <br />of the structure. Consequently, 500-year flooding in the main <br />channel and in the east overbank was studied as a single flood <br />plain. <br /> <br />The 100- and 500-year flood flows leave the main Fountain Creek <br />flood plain in the vicinity of Santa Fe Avenue between 8th and <br />11th Streets. These flows move south through the downtown area of <br />the city as shallow flooding until they pond behind the Arkansas <br />River floodwall in the vicinity of Runyon Field. The diversion <br />option of the HEC-2 program (Reference 15) was used to determine <br />the 100-year discharge of 2,660 cfs for the west bank overflow, <br />assuming a 20 percent debris blockage at the 8th Street bridge. <br /> <br />Utilizing the COE HEC-l model (Reference 12) and BEC-2 results, in <br />conjunction with the previously developed hydrograph on Fountain <br />Creek, the shape of the diversion hydrograph through downtown <br />Pueblo was develOped. The storage effect of a wide, shallow, <br />flood plain area was investigated. The results of this <br />calculation confirmed insignificant attenuation effects. <br /> <br />19 <br />