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<br /> <br />I <br /> <br />II <br />.. <br /> <br />. <br /> <br />. <br /> <br />I <br /> <br />. <br /> <br />. <br /> <br />. <br /> <br />I <br /> <br />I <br /> <br />I <br /> <br />I <br /> <br />I <br /> <br />J <br /> <br />CR 3" to CR. 33 -- The channel in this reach has limited capacity (less than the 10-year event). Once <br />the flows exceed the channel capacity, they follow along the relatively flat topography in a wide, <br />shallow floodplain. Along the north overbank in an area approximately 1,200 feet downstream of CR, <br />33, the flows split away from the main channel and are conveyed to the north towards the City of <br />Sterling contributing to the Pawnee Creek Overflow, These flows mainly inundate agricultural fields <br />with some potential for flooding individual strUcrures. Along the south overbank, the flood flows are <br />wide until the creek forms a large oxbow, At this location, the flood flows overtop the bank and follow <br />a direcr alignment easr to CR. 35, In the area of the oxbow, the Pawnee Creek channel contains the <br />flows unril they reach CR. 35 extended and ar this point combines back with the main channel flows, <br /> <br />CR "to CR. .,] -- As in the lower reaches, the channel has limited capacity and cannor handle flows <br />of even the ] O-year magnitude, The 100-year floodplain is generally wide with shallow depths and has <br />flows splining off from the main channel. In the upstream area adjacent to CR, 3], the floodplain is <br />very wide (approximately 4,600 feet), The existing channel and bridge crossing are undersized, and <br />the road acrs as a weir spreading our the flood warers, Along the south overbank, flows split in a <br />southeasrerly direction away from Pawnee Creek toward HWY 6 near the Town of Atwood, The <br />highway and railroad redirect the flows norJ1east towards the Pawnee Creek main channel. A berm <br />has been consrructed approximately one mile sourh of the Pawnee Creek crossing, This berm blocks <br />some of the flows and forces a portion of the water over the highway and railroad embankment. The <br />remaining flows overtop the berm and continues north to the highway bridge where they combine with <br />the flows along the main srem of Pav.-nee Creek, In the lower portion of this reach ar CR. 33, the <br />floodplain is confined by the channel banks sourh of the bridge crossing, as well as by a gravel <br />driveway to rhe north and CR. 33 to the east. <br /> <br />Upsrream of CR, ., 1 -- No floodplain mapping is available upstream of CR. 3 l. However, hydraulic <br />analysis was complered by the SCS for a distance of abour ] ,000 feer, Based on discussions with the <br />Ciry of Srerling and the Colorado Warer Conservation Board, the floodplain is very wide in the <br />upsrream reaches, There is the potential for flooding of some local residences, as well as damage to <br />agriculrural fannland, No major flow splirs have been derermined in rhis area which would impact the <br />Ciry of Sterling, <br /> <br />Hvdrologv <br /> <br />A derailed hydrologic analysis was nor complered for rhis study, Derailed hydrology was complered by <br />the SCS and presented in rheir April 1992 Report, FJow dara for various SlOrm events generated for <br />thar report were used as a basis for development of exisring floodplain informarion, as well as for the <br />evaluarion of proposed improvements. Final flows were reviewed and approved by the Colorado <br />Water Conservarion Board and rhe City of Sterling for use in rhis studv, A summary ofrhe discharges <br />~ - ~.. '-' <br />used for exisring conditions is presented in Table 6, <br /> <br />24 <br />