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I ,. . 2. The 8th Street Bridge was modeled as a special bridge with a calculated 800 cfs weir flow over the road. This resulted from not coding the east bank of the bridge in the model and forcing all flow over the bridge deck. 3. The HEC-2 calculated trapazoided area was 12,639 square feet compared to the USACOE inputted 5,837 square feet bridge area. . . 4. The USACOE calibrated the special bridge routine coeffi- cients to match the historic 1965 flood elevations in the vicinity of the structure. No documentation was provided to support the coefficients and the use of the calibrated model for the larger 100-year flood event. For the diversion into the downtown area, it was observed that the USACOE utilized the results from the HEC-2 model on Fountain Creek and an overflow section at Sante Fe Avenue to calculate 5000 cfs crit ical depth overflow for the 100-year flood event. Utilizing the 5000 cfs value, the USACOE constructed a HEC-2 model of the downtown area to calculate 100-year flood elevations and depths. The source of the USACOE cross sections is un- known. Use of the HEC-2 model ,for the downtown area was a justi- fiable procedure since data was scarce, however was not represen- tative of the very disected nature of the street flows and street ponding areas. Through Runyan Field the USACOE routed the diver- ted hydrograph (source unknown) through the area and back to the Arkansas River. . . Examples of the questionable Fountain Creek HEC-2 coding are in- cluded in the appendix of this report. . RESTUDY ENGINEERING . Utilizing the approved 100-year flood discharge of 64,000 cfs on Fountain Creek upstream of 8th Street MSM/SP Group recoded the Fountain Creek HEC-2 developed by the U.S. Army Corps of Engi- neers from roughly section 1050 (G in 1977 USACOE Report) to sec- tion 1150 (section J) to include recent field surveyed cross sec- tions by the City of Pueblo. In addition, to assure a match with the previous USACOE flood profiles, four sections downs tream of Eighth Street the upstream face of 4th Street and 3 sections up- stream to section 1180 were added to the model. Comparison of the recent survey sections to the previous USACOE cross sections confirmed within reasonable error limits the same datum. . . At the 8th Street Bridge, a new coding, using the USACOE geo- metrics and the city surveyed top of road was added to the HEC-Z model as a normal bridge routine. It was felt that a substantial flow would be diverted around the structure beyond the 50-year flood event and the overflow did not act as a weir. Although the normal bridge routine will not account for pressure flow or pier losses it was felt that pressure flow was not critical since only -2- .