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<br />FLOODPLAIN REPORT - Tyra Tract D and Sawmill Gulch, Breckenridge, Colorado <br />(aHAFT>> <br /> <br />junction, These flows are anticipated to be on the order of less than 10 cfs, which have no <br />significant affect hydraulically on the design flow of 118 cfs. <br /> <br />At the culvert outlet, an energy dissipation structure is specified per a Bureau of Reclamation <br /> <br /> <br />design, This type of structure operates effectively with essentially no tailwater, which is <br /> <br /> <br />appropriate for this situation. Immediately below the outlet structure, the water will be forced to <br /> <br /> <br />spread out to approximate the pre-project conditions via a small (2 feet high or less) berm that <br /> <br />extends for 30 to 50 feet. Flow will pass over this grassed berm in a shallow flow condition and <br /> <br />be released in its historic flow path adjacent to Four O'Clock Road. <br /> <br />The flood wall elevation generally has a top-of-wall at or exceeding elevation 9,728. The only <br /> <br /> <br />exception is where this wall forms a cut-off between the building and Sawmill Gulch proper. <br /> <br />Due to environmental and aesthetic considerations, the wall height starts at elevation 9,726 <br /> <br />where it begins atop the right bank of Sawmill Gulch. The existing top-of-bank elevation is <br /> <br /> <br />slightly less than elevation 9,725. Thus, this minimal height wall is approximately 1.2 feet above <br /> <br /> <br />existing top-of~bank. Our predicted water surface at this location is elevation 9,724, some 0.6 <br /> <br /> <br />feet below the top-of-bank, From this point eastward, the existing ground topography drops <br /> <br />away, while the top-of-wall rises gradually to its ultimate elevation of 9,728. Thus, at a location <br /> <br /> <br />some 5 feet eastward of the top of the right bank, the height of wall has increased from ground <br /> <br /> <br />elevation of about 9,723 to the top-of-wall at about 9,726.5. <br /> <br />Lower Collection System <br /> <br />The lower collection system consists of an intake structure, a pipeline and an outlet structure, all <br /> <br />adjacent to Four O'Clock Road. The design capacity of this system is 50 cfs, the difference <br />between the culvert capacity of Four O'Clock Road, 130 cfs, and the predicted instream flow rate <br />of 180 cfs, which assumes out-of-channel flooding has occurred in the vicinity of the upper <br />collection system. The purpose of the lower collection system is to capture Sawmill Gulch <br />flooding and transport it so that it does not interfere with or endanger the proposed building or <br /> <br />971-055.010 <br /> <br />Wright Water Engineers, Inc_ <br /> <br />Page 16 <br />