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<br />i <br />t <br />. <br />t <br />. <br />. <br />j <br />. <br />f <br />, <br />- <br />t <br />t <br />t <br />~ <br /> <br /> <br />t <br />* <br /> <br />PA~~EE CREEK OVERFLOW <br />B d di ' , ALT. NO. 1 <br />Proposed Improvements: ase on SCUSSIODS WIth the City, eWCB, 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 1 of 4 presents the proposed improvem~nt for Pawnee Creek, Tne proposed improvements for <br />Pawnee Cr~ek include two levees downstream cifthe UPRR ranging in height from 1 foot to 5.5 feet. <br />These levees are shown on Map Sheet 1 and IA and are labeled Levee Number 1 Nort'l and Levee <br />Number I South. The north levee will extend east from abom 300 feet downstream of the railroad to <br />the defined low flow channel of Pawnee Creek and then curve nor-ill and follow' the channel to an <br />existing dirt road just west of the limits of the lOa-year floodplain of the South Platte River, This <br />levee will be approximately 1,400 feet in length, A 300 foot long floodwall 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 Plane <br />River. The south levee will prohibit low flows from draining along their existing course around a <br />4.400 feet long oxbow fonned by the existing channel; therefore, a new low flow channel must be <br />constrUcted to convey storm water between stations 16TOO and 72+00. This chalmel will be <br />trapezoidal in shape utilizing a 30 foot bottozn width and 3: I 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 100 feet upstream of HWY 6 to approximately <br />200 feet downstream of the UPRR. The high't'ay bridges will need to be improved to acco=odate <br />the increase in discharges due to the confinement of the split flows by the proposed upstream levees. <br />As discl.lssed earlier, the existing bridge for the borthbound 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 of20' x g' RCB <br />would be installed just south of the existing bridge. The culverts could be pre-cast which would <br />mL"Jimize 1:.'1e time required to complete the installation, thus limiting the impacts to existing traffic. <br />Wing wall. 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 SpriIlgdale 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 downstream of the UPRR which will have to be removed. This structure is presently abandoned <br />and preliminary discussions with the OWDers indicated that they are agreeable to its removable, <br /> <br />33 <br />