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<br />FLOODPLAIN REPORT - Tyra Tract D and Sawmill Gulch, Breckenridge, Colorado <br />(...FT) <br /> <br />culvert entrance to meet these criteria. This entrance configuration is the ultimate hydraulic <br /> <br />control for this system, which therefore provides for the design flow of 50 cfs, <br /> <br />The barrel of the 30-inch diameter pipe will pass 50 cfs of flow at a depth of 1.4 feet or less when <br /> <br />the minimum slope is equal to 4 percent and "nonnal depth" is assumed. Thus, the pipe has the <br />capacity to pass the desired flows. <br /> <br />The outlet structure is intended to be a reverse flow Type R inlet, sometimes referred to as a <br /> <br />bubble-up structure. Under design flow conditions, a multiple Type R opening 15 feet long will <br /> <br />discharge 50 cfs of flow when the pressure is 2 feet higher than the center of the Type R opening <br /> <br /> <br />(this assumes a orifice equation with a C coefficient of 0.6: Q = CA,j2gH. The sill elevation of <br /> <br /> <br />the Type R outlet structure has been set at 9,699.75 feet. Therefore the required water surface <br /> <br /> <br />elevation to produce the design flow is 9,702 (sill center plus 2.25 feet). This elevation is <br /> <br />comfortably below the intake system elevations, and thus the outlet hydraulics do not force a <br />backwater condition that would control the amount of flow through the lower collection system, <br /> <br />Finally, it should be noted that the Town of Breckenridge ultimately intends to connect a <br />continuing stonn sewer system to the eastern end of the Type R structure to provide an <br />underground stonn sewer system that conveys water eastward along Four O'Clock Road towards <br />the Blue River. Specific design criteria have not yet been defined. For now, however, the water <br />will discharge to the shoulder area of Four O'Clock Road as would occur in the pre-project <br /> <br />conditions. <br /> <br />SUMMARY <br /> <br />This report provides detailed technical infonnation regarding the floodplain extents for Sawmill <br /> <br /> <br />Gulch between Four O'Clock Road and the Town of Breckenridge limits. The gulch is currently <br /> <br /> <br />a FEMA-designated floodplain for a short portion of the reach upstream of Four O'Clock Road. <br /> <br />971-055.010 <br /> <br />Wright Water Engineers, Inc, <br /> <br />Page 18 <br />