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<br />. <br /> <br />e <br /> <br />e <br /> <br /> <br />FLOODPLAIN REPORT - Tyra Tract 0 and Sawmill Gulch, Breckenridge, Colorado <br /> <br />over the sill, which has a capacity of about 50 cfs at elevation 9,716. The open grating will then <br />act as a potential orifice intake to the water flow, As is typical of urban designs, we assumed that <br />50 percent clogging of the grating may occur due to debris. Even with this assumption, there is <br />still capacity for inflow of over 100 cfs into the structure, more than the anticipated design flow. <br />Thus, both the sill and the grating provide for the design flow to enter this structure. <br /> <br />Once in the concrete box, flow is then controlled by the culvert pipe that will convey the water to <br />the east. This pipe is specified as a 30-inch diameter pipe; it is approximately 210 feet long, and <br />the average slope of the pipe is approximately 7 percent. At this steep slope, flow into and <br />through the pipe will typically be controlled by the inlet conditions at the concrete box. Using <br />standard culvert inlet flow nomographs, a 30-inch diameter pipe with an invert elevation of 9,710 <br />and a beveled intake will pass 55 cfs at a headwater elevation of 9,716. The plans call for the <br />culvert entrance to meet these criteria. This entrance configuration is the ultimate hydraulic <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 />the minimum slope is equal to 4 percent and "normal 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 />bubble-up structure. Under design flow conditions, a multiple Type R opening 15 feet long will <br />discharge 50 cfs of flow when the pressure is 2 feet higher than the center of the Type R opening. <br />(This assumes an orifice equation with a C coefficient of 0.6: Q = CA.j2gH.) The sill elevation <br />of the Type R outlet structure has been set at 9,699.75 feet. Therefore the required water surface <br />elevation to produce the design flow is 9,702 (sill center plus 2.25 feet). This elevation is <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 />971-055.010 <br /> <br />Wright Water Enginee~, Inc. <br /> <br />Page 18 <br />