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• Best level of protection for Sterling <br /> • No upstream impacts are possible due to the project <br /> • Intercepts Pawnee Overflow flows and excess Sterling No. 1 Ditch flows <br /> • No human intervention required for protection <br /> In general, the project can be broken into three projects. The HWY 6 Bridge and the <br /> railroad bridge can each be built independent of the rest of the project. The bridges will <br /> need to be built first so any drainage that the channel collects can be drained into the <br /> South Platte. The channel east of the railroad could be started while the bridges are being <br /> built. The channel can also be built separately after the bridges are finished. The <br /> proposed channel would be excavated under the bridges and would not interfere with <br /> train or highway traffic. <br /> Note: Alternative 5 was originally selected after a review of the projects and preparation <br /> of a decision matrix. Alternative 4 is one component of Alternative 5. After further <br /> review of project function and overall project costs, Alternative 4 was found to meet the <br /> requirements of providing flood protection to Sterling. Alternative 4 can also remove all <br /> of the Pawnee Creek Overflow floodplain areas from the City of Sterling floodplain <br /> maps. Based on this information and that Alternative 4 is more cost effective for the City, <br /> Alternative 4 became the selected alternative. -if <br /> IX. DETAILED DESCRIPTION OF SELECTED ALTERNATIVE <br /> Project Location <br /> The selected alternative is focused around intercepting the Pawnee Creek Overflow that <br /> flows from Pawnee Creek north towards Sterling. The Pawnee Creek Overflow is the <br /> floodwater that breaks away from the Pawnee Creek channel at both HWY 6 and near <br /> County Road 31 and converges near the southern limits of Sterling. These floodwaters <br /> travel through farm fields and over county roads as they move north. <br /> The project is primarily an interceptor channel that collects water as it crosses over <br /> County Road 22.5. The channel carries the water to the South Platte River under both <br /> HWY 6 and the railroad. As a part of the project, a bridge will be constructed at both the <br /> highway and railroad that is designed to pass the 100-year flow. The channel is located <br /> parallel to and immediately north of County Road 22.5. The western limits of the <br /> channel will be determined after locating the area of County Road 22.5 that is <br /> overtopped. The approximate western limit of the channel is 6000 feet west of HWY 6. <br /> The channel size has been optimized to carry the 5000 cfs 100-year design flowrates. In <br /> most cases, the width varies to accommodate the channel depth. Transitions have been <br /> sized using a 4:1 expansion ratio. The eastern project limit is at the confluence with the <br /> South Platte River. <br /> Also included in this project is a siphon structure to carry the 200 cfs Sterling No. 1 Ditch <br /> flows under the proposed channel, a spill way to pass excess water into the channel from <br /> the ditch, the relocation of three wells, the extension / connection of county roads <br /> -coy A..4'k l�- — S"► cl twig-, <br /> If e. <br /> v. w.-4'11'0 1.. �pv ,M K(4' <br /> 27 0 - C; , c...„ I�. l 5.���L+, V {' <br /> Q„� -crY� z RII-��u��{-' — J�,1",)2 Zoo 2- <br />