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J .' Proposed Improvements: Based on discussions 'With the City, CWCB, and CDOT, A combination of alternatives 1 and 2 was selected as the recommended approach to improving the crossings at H\VY 6, Sheet I of 4 presents the proposed improvement for Pawnee Creek, Tne proposed improvements for Pa'Wnee Creek include two levees downstream of the lJ1'RR ranging in height from I foot to 5,5 feeL Tnese levees are shown on Map Sheet 1 and lA and are labeled Levee Nwnber 1 l-.ior..h and Levee Nwnber 1 South, The north levee will extenc east from about 300 fee: downstream of the railroad to the defmed low flow channel of Pawnee C:eek and then curve north and follow the channd to an existing dir: road just west of the limits of the 100-year fle,odplain of the South Platte River, This levee will be approximately 1,400 feet in length, A 300 foot long floodwall "ill be required immediately east of the railroad bridge on the north side of the channel where right,of,way is limited by an existing residence and livestock pen. .. "" The south levee will extend east from proposed channel irnprove:7lents downstream of the UPRR for about 1,500 feet to a dirt road just east of the limits of the 100,year floodplain of the South Plane River. The south levee will prohibit low flows from draining along their existing course around a 4.400 feet long oxbow formed bv the existing channel; therefore, a new low flow char~el must be , -- . - constructed to convey storm water between stations 16.,..00 and 72e-OO, 'This channel wil] be trapezoidal in shape utilizing a 30 foot bonom width and 3: I sideslopes, The depth of the low flow channel will range from 2 feet at the point where it leaves the existing channel oxbow to about 9 feet where it must daylight back into Pawnee Creek, Channel improvements are also proposed from a point 100 :eet upstream Df H\VY 6 to approximately 200 iee: do'Wnstream of the UPRR, Tne highway bridges will need to be improved to accommodate the increase in discharges due to the confinement of the split flows by the proposed upstream levees, As discussed earlier. the existing bridge for the northbound traffic is a wooden structure and CDOT plans to replace this bridge in the next 3 to 5 years, For the southbound lanes, 4 cells of 20' x 8' RCB would be installed JUSt south of the existing bridge, The culverts could be pre,cast which would minimize [he time required to complete the installation, thus limiting the impacts to existing traffic, Wing walls upstream and downstream, as well as :iprap protection would be ~equired, Conceptual cross,sections of the channel and bridge improvements at HVv'Y 6 and the CPRR are presented m Figures 10 and j 1, In order to construct the new box culverts south of the existing bridge, the existmg siphon along the Springdaie Ditch which carries irrigation water under the railroad and highway may need to be extended to the south. There is also an existing concrete ditch diversion structure located just dov.nstream of the DPRR which wi]) have to be removed, Tnis strucnlIe is prese;]tl)' abandoned and preliminarv discussions with the o'Wners indicated that they are agreeable to its removable, ~.J