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<br />FLOODPLAIN REPORT - Tyra Tract D and Sawmiff Gulch, Breckenridge, Colorado <br />(."AFT>> <br /> <br />particularly when overbank flows occur. There were nine cross-sections utilized over <br />approximately 450 feet of Sawmill Gulch, beginning at the upstream face of the culvert under <br />Four O'Clock Road. The floodplain represents significant overbank flooding which escapes the <br />main channel of Sawmill Gulch. As discussed in the following section, Split Flow Assessment, <br />substantial quantities of the 100-year flow were calculated to exceed the capacity of the channel, <br />resulting in flooding over the right bank of the channel. At the upstream limit of the Tract D <br />parcel, the channel flow is 248 cfs. Overbank flooding begins to occur at Cross-Section No. 58 <br />and continues up to Cross-Section No. 55. Between Cross-Sections No. 58 and No. 57, WWE <br />estimated that 36 cfs would leave the main channel of Sawmill Gulch, resulting in a main <br />channel flow of 212 cfs. This 212 cfs is contained in the Sawmill Gulch channel between <br />stations No. 56 and No. 57, Additional out-of-bank flooding then occurs between stations No. 56 <br />and No. 55, releasing an additional 32 cfs from the main channel flow. This leaves 180 cfs as the <br />main channel flow from Cross-Section No. 55 downstream until Four O'Clock Road is reached. <br />At Four O'Clock Road, ponding occurs due to the restriction of the existing Four O'Clock Road <br />culvert. An amount of 130 cfs passes through the culvert and continues on into Sawmill Gulch, <br />while 50 cfs is forced over the right bank of the channel. This flow then follows Four O'Clock <br />Road and soon joins with the overbank flooding that occurs from the upstream areas between <br />Cross-Sections No, 55 and No. 56, and Cross Sections No. 57 to No. 58. <br /> <br />The flood releases from the main channel of Sawmill Gulch from Cross Sections No. 57 to No. <br />58 and Cross-Sections No. 55 and No. 56 combine together and flow through a historic <br />secondary channel roughly parallel to Sawmill Gulch. The combined flow is 68 cfs, which <br />results in shallow flooding through the secondary channel. This continues in a northerly to <br />northeasterly direction until it meets the area adjacent to Four O'Clock Road. At this location, <br />the overbank flow of 68 cfs joins the 50 cfs that is forced out of the Sawmill Gulch channel by <br />the Four O'Clock Road culvert, resulting in 118 cfs of flow that parallels Four O'Clock Road, <br />Discussions with the Town of Breckenridge indicate that they are developing plans for a storm <br />sewer system to capture this potential 100-year overflow, and convey it in a storm sewer system <br />parallel to Four O'Clock Road until reaching the Blue River. <br /> <br />971-055.010 <br /> <br />Wright Water Engineers, Inc, <br /> <br />Page 8 <br />