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<br />. <br /> <br />. <br /> <br />. <br /> <br />FLOODPLAIN REPORT - Tyra Tract D and Sawmill Gulch, Breckenridge, Colorado <br /> <br />the 100-year peak at 248 cfs, slightly more than double the 1979 value. Physical changes have <br />also taken place to Sawmill Gulch: there are clear signs of surface disturbance within the <br />floodplain limits on the south side of Four O'Clock Road. Finally, recent mapping data and <br />changes, a datum shift, and the revised hydrology render the 1979 floodplain mapping void. <br /> <br />Preliminary investigations associated with the development of the Tract D parcel indicated that <br />out-of-channel flooding will occur in Sawmill Gulch just upstream of Four O'Clock Road when <br />the revised hydrology is applied. As part of the planning process for the Tract D site, a detailed <br />floodplain assessment (culminating in this report) was initiated. Also underway is the FEMA <br />restudy of the lower reaches of Sawmill Gulch, the area between Four O'Clock Road and the <br />confluence with the Blue River. Lower Sawmill Gulch is being studied by FEC, who's submittal <br />is currently being reviewed by FEMA for its appropriateness in redefining the floodplain for the <br />lower gulch. <br /> <br />The portion of Sawmill Gulch upstream of Four O'Clock Road is the focus of this report. We <br />utilized revised hydrology, new topography mapping, and site-specific additional topographic <br />survey data to define the 100-year floodplain in the vicinity of the Tyra Tract D site. At the <br />request of the Town of Breckenridge and FEMA, the current study by Wright Water Engineers <br />(WWE) was extended further upstream on Sawmill Gulch to the Town of Breckenridge <br />boundary, some 4,800 feet southwest of the southern limit of Tyra Tract D. The "new" town <br />topographic mapping was used for this extension. <br /> <br />As will be discussed later in this report, WWE confirmed that out-of-channel flooding will occur <br />under current estimates of 100-year flood peak events for Sawmill Gulch. The channel capacity <br />of Sawmill Gulch is inadequate to carry the current estimate of 248 cfs for the 100-year flood. <br />This is caused both by limited channel capacity as well as the capacity of the culvert at Four <br />O'Clock Road. The resultant out-of-bank flooding generally follows Four O'Clock Road in an <br />easterly direction and does not rejoin Sawmill Gulch. This out-of-bank and split flow situation <br />comprises the existing condition, and the development proposal for the area continues this <br />existing condition in the future. Both FEMA and the Town of Breckenridge directed that this <br /> <br />971-055.010 <br /> <br />VVrightVVa~rEngmee~,m~ <br /> <br />Page 3 <br />