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<br />FLOODPLAIN REPORT - Tyra Tract D and Sawmill Gulch, Breckenridge, Colorado <br />(D.tAFT) <br /> <br />capacity was sufficient to carry 180 cfs downstream of Cross-Section No. 55 until reaching Four <br /> <br />O'Clock Road. Thus, in general, no additional overbank flooding occurs through this reach. <br /> <br />However, the flow restriction of the Four O'Clock Road culvert (an existing 5.5-foot wide x 4.5- <br />foot high corrugated metal pipe, 63 feet long at a slope of about 4.8 percent) allows only 130 cfs <br />to pass underneath Four O'Clock Road. Thus, ponding occurs immediately adjacent to Four <br />O'Clock Road. Flows in excess of 130 cfs will flow over the right bank and follow the right <br />shoulder of Four O'Clock Road to the east. Under our calculated scenario (Attachment A), this <br />means that 50 cfs, out of the channel flow of 180 cfs, will flood over the right bank of Sawmill <br />Gulch at Four O'Clock Road. This flow will continue eastward for approximately 80 to 100 feet <br />where it will be joined by the flows that overtop the right bank further upstream. These <br />combined flood overflows comprise the split flow of Sawmill Gulch, and they total 118 cfs. <br /> <br />We did not continue beyond the eastern limit of the Tract D property. The Town of <br />Breckemidge Engineering Department (Eric Guth and Tom Daugherty) and the FEMA <br />representative (John Liou) concurred with our mapping limits. <br /> <br />The overflow flooding from Cross-Sections No, 58 to No. 55 in Sawmill Gulch flow eastward <br /> <br /> <br />for a short distance before turning northward and following a natural swalelhistoric flow path <br /> <br /> <br />through the central portion of Tyra Tract D. This is in the area where the proposed building will <br /> <br />be built. The area currently has no defined channel and the flooding condition is essentially <br /> <br />shallow, widespread flow through an area currently vegetated with willows, <br /> <br />The conclusion of the split flow analysis is that significant flow leaves the main channel of <br />Sawmill Gulch. Thus, the peak flow rate of Sawmill Gulch reduces in the downstream direction <br />as a result of the overbank outflows. This is reflected in Table I, showing Sawmill Gulch peak <br />flow rates "stepped downward" from 248 cfs at the upstream limit of Tyra Tract D to 180 cfs, at <br />approximately the central portion of Tract D, to 130 cfs at the Four O'Clock Road culvert. The <br />split flow amounts flow to the east out of the channel and then turn north until reaching Four <br />O'Clock Road where they are redirected to the east. <br /> <br />971-055,010 <br /> <br />Wnght Water Engineers. Inc. <br /> <br />Page 10 <br />