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. . one barrel of the structure was overtopped and pier losses were not as critical as the correct calculation of the diverted flow. As requested by FEMA roughly 20% debris blockage was added to the bridge coding. . To check the valadity of the normal bridge routine, historic flood limits for the 1965 flood event were reviewed to determine the elevation discharge relationship upstream of 8th Street. This was accomplished by calculating the 1965 flood elevations utilizing the flooded area map and critical spot elevations supplied by the city (see Appendix). Based on the June 1965 flood and spot elevations supplied by the city, the high water elevations were estimated as 4684.7 and 4687.5 at sections 1120 and 1140 respectively for the U.S.G.S. estimated discharge of 47,000 cfs. . . The updated HEC-2 model was run for a discharge of 47,000 cfs and yielded energy grade line elevations of 4684.7 and 4687.3 at sec- tions 1120 and 1140 respectively. In the overbank areas where the velocity head approaches zero, it is anticipated that the energy grade line elevation would match the historic flood eleva- tion. This calculation confirms the normal bridge routine coding for the historic event. . At higher flows, it is anticipated that large diversion flows will occur on the east overbank area. This diversion area is not a weir and will not be treated as one by the normal bridge cod- ing. . Using the calibrated HEC-2 model and the debris blocka~e factor, Fountain Creek was studied for a range of flows from 18,500 cfs to 99,000 cfs and the HEC-2 diversion routine was used to cali- brate the diversion flow for the 100-year event. The rating curve inserted into HEC-2 identifying the diversion critical sec- tion was constructed from detailed survey conducted by the City. The critical section consisted of rectangular weirs outlining the street flow areas with the buildings blocked out of the calcula- tions. The results of this investigation adjusted for 20% debris blockage confirmed 2660 cfs was diverted. Utilizing the HEC-l model and HEC-2 results in conjunction with the previously developed USACOE hydrograph on Fountain Creek, MSM developed the shape of the diversion hydrograph through downtown Pueblo and investigated the storage effects of a wide shallow floodplain area. The results of this calculation confirmed in- significant attenuation effects. Utilizing the peak 100-year diversion flow of 2660 cfs an analy- sis was undertaken to track the flow street-by-street from the point of diversion to its outlet. For this analysis, Mannings Equation was used with average street slopes obtained from the detailed survey. The Mannings "n" value used in the calculations was chosen as 0.025 which is a composite value for a highly urban area where the street flow paths are open. The sections used in . . . -3- .