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<br />Meetings were held by the CWCB and CDOT to discuss the feasibility of widening the existing <br />highway bridges. Because the nOl1thbound bridge is an existing wood structure it cannot be widened; <br />therefore, total replacement would be necessary. <br /> <br />Two options were investigated to rt:solve the problem of the undersized bridges at HWY 6. <br /> <br />Option 1 involves the removal and replacement of existing timber bridge along the northbound lanes. <br />The COOT currently has plans to replace the timber bridge within the next 3 to 5 years. For the <br />southbound lanes, the existing concrete bridge would be widened to convey the I DO-year peak <br />discharge. <br /> <br />Option 2 involves adding box culverts just south of the existing bridges in lieu of widening or <br />replacing them. Based on a cursory evaluation, it was determined that four 20' x 8' concrete box <br />culverts would be required in addition to the existing bridges to convey the I DO-year p,~ak discharge. <br />The culverts would be placed adjacent to and south of the ,~xisting bridge structure. <br /> <br />Plan Description <br /> <br />The selected plan consists of improvements at two separate locations. The first area, designated as the <br />"South Improvement Area" is the existing main chaImel of Pawnee Cr<~ek from the confluence of the <br />creek with the South Platte River, extending upstream of the HWY 6 bridge. This improvement area <br />also includes a proposed railroad bridge near Town of At\vood, to allow Pawnee Creek right overbank <br />flows to drain directly to the river. The second improvement ar'~a, designated as the "North <br />Improvement Area" is near the RivtTside Cemetery, where flood protection will prevent Pawnee Creek <br />left overbank flows from being trapped west of the HWY 6 and railroad embankments forcing flows <br />into the City of Sterling. Each ofth.~ two improvements an~as are discussed separately below: <br /> <br />South Improvement Area: Based on discussions with the City, Logar: County, CWCB, and CDOT, <br />and concerned citizens, it was believed essential that the project should take advantage: of the existing <br />drai,nageway to the degree possible, Channel capacity near the HWY 6 bridges excee:d the hydraulic <br />capacity of the bridge. Since the railroad bridge was recently rebuilt with a greater hydraulic capacity, <br />it was determined that the highway bridge should be incn:ased as well. CDOT is planning to upgrade <br />the north bound bridge and work is schedule to begin in the next two Yt:ars. Costs for construction of <br />the north bound bridge is not a project cost, since the wooden bridge is structurally and functionally <br />obsolete, and currently budgeted for replacement for those reasons. Improvements to the south bound <br />bridge will include installation of supplemental box <:ulverts. Since this work would be done only to <br />increase the hydraulic capacity of the bridge, this t;Ost is a portion of the proposed project. The <br />proposed improvements for Pawnee Creek include increasing the hydraulic capacity of the natural <br />channel downstream of the bridges. Two levees downstfl~am of the UJ>RR ranging in height from I <br />foot to 5.5 feet are planned. The north levee will extend '~ast from about 300 feet downstream of the <br />railroad to the defined low flow chaJUlel of Pawnee Creek and then curve north and follow the channel <br />to an existing dirt road just west of the limits of the 100-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 />III-22 <br />