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<br />- <br /> <br />.. <br /> <br />" <br />~ <br /> <br />- <br />~ <br />~. <br />\ <br />1 <br />~. <br /> <br />1 <br /> <br />I <br /> <br />! <br /> <br />Proposed Improvements: Based on discussions with the City, CWCB, and CDOT, A combination of <br />alternatives 1 and 2 was selected as the recommended approach to improving the crossings at HWY 6. <br />Sheet J of 4 presents the proposed improvement for Pawnee Creek. The proposed improvements for <br />Pa"'l1ee Creek include two levees downstream of the UPRR ranging in height from I foot to 5.5 feet. <br />These levees are shown on Map Sheet 1 and lA and are labeled Levee Number 1 North and Levee <br />Number 1 South. The north levee will extend east from about 300 feet downstream of the railroad to <br />the defined low flow channel of Pav,l1ee Creek and then curve north and follow the channel to an <br />existing dirt road just west of the limits of the ] DO-year floodplain of the South Platte River. This <br />levee will be approximately 1,400 feet in length. A 300 foot long floodwal1 will be required <br />immediately east of the railroad bridge on the north side of the channel where right-of-way is limited <br />by an existing residence and livestock pen. <br /> <br />The south levee will extend east from proposed channel improvements downstream of the UPRR for <br />about 1.500 feet to a dirt road just east of the limits of the 100-year floodplain of the South Platte <br />River. The south levee will prohibit low flows from draining along the:ir existing course around a <br />4,400 feet long oxbow formed by the existing channel; tht:refore, a new low flow channel must be <br />constructed to convey storm water between stations 16+00 and 72+00. This chaJmel will be <br />trapezoidal in shape utilizing a 30 foot bottom width and 3: 1 sideslopes. The depth of the low flow <br />channel will range from 2 feet at the point where it leaves the existing channel oxbow to about 9 feet <br />where it must daylight back into Pawnee Creek. <br /> <br />Channel improvements are also proposed from a point] 00 feet upstream of HWY 6 to approximately <br />200 feet downstream of the UPRR. The highway bridges will need to be improved to accommodate <br />the increase in discharges due to the confinement of the split flows by the proposed upstream levees. <br />As discussed earlier, the existing bridge for the northbound traffic is a wooden structure and CDOT <br />plans to replace this bridge in the next 3 to 5 years. For the southbound lanes, 4 cells of 20' x 8' RCB <br />would be installed just south of the existing bridge. The culverts could be pre-cast which would <br />minimize the time required to complete the installation, thus limiting the impacts to existing traffic. <br />Wing walls upstream and downstream. as well as riprap protection would be required. Conceptual <br />cross-sections of the channel and bridge improvements at HWY 6 and the UPRR are presented in <br />Figures 10 and 11. In order to construct the new box culverts south of the existing bridge. the existing <br />siphon along the Springdale Ditch which carries irrigation water under the railroad and highway may <br />need to be extended to the south. There is also an existing concrete ditch diversion structure located <br />just dov;nstream of the UPRR which will have to be removed. This structure is presently abandoned <br />and preliminary discussions with the owners indicated that they are agreeable to its removable. <br /> <br />" <br />~~ <br />