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I I I II I I I I I I I I I I I I I I I I The 1986 Big Ory Creek FHAD, however, calculated a water surface of 163.4 (MSL) (Greiner Engineering Sciences, Inc., Nov. 1986). The profile point plotted in the study is 165.4 feet, which is the energy grade line elevation. The current water surface does not agree with the previously published UOFCO FHAO at 1-25 for four reasons. First, the 1-25 bridge deck in the UOFCO study was modeled with an elevation of 163.0 feet, while a current field survey determined the elevation to be 163.4 feet (corrected to MSL datum). Second, 2.7-foot-high concrete (Jersey) barriers that cross the deck were not modeled in the UOFCO study. Third, the field survey showed a bridge open area of 641 square feet, compared to 634 square feet used in the UOFCO study. Finally, the orifice coefficient used in the UCFCD study is different from that used in this study. The orifice coefficient used in this study was calculated according to the method described in the HEC-2 Users Manual. A separate HEC-2 run was made using the orifice coefficient that was identical to the UOFCD study. The bridge open area was set at 634 square feet and the barriers were modeled in place. The calculated water surface was 166.6 feet (MSL). The difference between this water surface and the UOFCD FHAD is 3.2 feet, which is close to the difference in calculated water surfaces due to the bridge deck and barriers 0.1 feet). Therefore, not modeling the barrier results in a water surface that is significantly lower than for actual conditions. The other bridge parameters account for about a 0.7-foot difference. Since the UOFCO 100-year water surface calculated in this study is 3.9 feet higher than that used in previous studies, a water surface match occurred at Huron Street rather than at 1-25. Cross sections used between 1-25 and Huron Street were obtained from Greiner's (Nov. 1986) model and the sections were corrected to this project's datum. This study recommends using a 100-year water surface of 167.3 feet at 1-25, because it is based on an actual field survey with the barriers in place. Federal Emergency Management Agency The current Westminster FIS begins just upstream of 1-25. The elevation shown is 163.9 feet at a flow of 8,839 cfs for the 100-year event at Section 1010 +90, which is 545 feet upstream of 1-25. The 100-year elevation calculated for this study at 1-25 is 166.5 feet (165.6 MSL) at FEMA's 100-year flow of 8,839 cfs. The difference in water surfaces is again because the concrete (Jersey) barriers were not modeled for the FIS study. II1-11