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the bank and follow a direct alignment east to CR. 35. In the area of the oxbow, the <br /> Pawnee Creek channel contains the flows until they reach CR. 35 extended and at this <br /> point combines back with the main channel flows. <br /> CR. 33 to CR. 31 -- As in the lower reaches,the channel has limited capacity and cannot <br /> handle flows of even the 10-year magnitude. The 100-year floodplain is generally wide <br /> with shallow depths and has flows splitting off from the main channel. In the upstream <br /> area adjacent to CR. 31, the floodplain is very wide (approximately 4,600 feet). The <br /> existing channel and bridge crossing are undersized, and the road acts as a weir spreading <br /> out the flood waters. Along the south overbank, flows split in a southeasterly direction <br /> away from Pawnee Creek toward HWY 6 near the Town of Atwood. The highway and <br /> railroad redirect the flows northeast towards the Pawnee Creek main channel. A berm <br /> has been constructed approximately one mile south of the Pawnee Creek crossing. This <br /> berm blocks some of the flows and forces a portion of the water over the highway and <br /> railroad embankment. The remaining flows overtop the berm and continues north to the <br /> highway bridge where they combine with the flows along the main stem of Pawnee <br /> Creek. In the lower portion of this reach at CR. 33, the floodplain is confined by the <br /> channel banks south of the bridge crossing, as well as by a gravel driveway to the north <br /> and CR. 33 to the east. <br /> Upstream of CR. 31 -- No floodplain mapping is available upstream of CR. 31. <br /> However, hydraulic analysis was completed by the SCS for a distance of about 1,000 <br /> feet. Based on discussions with the City of Sterling and the Colorado Water <br /> Conservation Board, the floodplain is very wide in the upstream reaches. There is the <br /> potential for flooding of some local residences, as well as damage to agricultural <br /> farmland. No major flow splits have been determined in this area which would impact <br /> the City of Sterling. <br /> Hydrology <br /> A detailed hydrologic analysis was not completed for this study. Detailed hydrology <br /> used for this study was completed by the SCS and presented in their April 1992 Report. <br /> Flow data for various storm events generated for that report were used as a basis for <br /> development of existing floodplain information, as well as for the evaluation of proposed <br /> improvements. Final flows were reviewed and approved by the Colorado Water <br /> Conservation Board and the City of Sterling for use in this study. <br /> There are several areas where the flood flows exceed the capacity of the channel for the <br /> 10-year, 50-year, and 100-year events. Flows, which split from the main channel, are <br /> subtracted out and are accounted for under existing conditions; therefore, the discharges <br /> vary significantly from downstream to upstream. For Pawnee Creek Overflow in the City <br /> of Sterling, 100-year flows are estimated to be 5,000 cfs. <br /> As a result of the improvements proposed in this report, flood flows are partially <br /> contained in the areas adjacent to the channel in the north overbank. Therefore, these <br /> flows were considered a part of the main channel and were included in the analysis. For <br /> 29 <br />