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<br />Meetings were held by the CWCB and COOT to discuss the feasibility of widening the existing <br />highway bridges. Because the northbound bridge is an existing wood structure it cannot be widened; <br />. therefore, total replacement would be necessary. <br /> <br />Two options were investigated to resolve 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 100-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 100-year peak discharge. <br />The culverts would be placed adjacent to and south of the existing bridge structure. <br /> <br />Plan Description <br /> <br />. <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 channel of Pawnee Creek 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 Atwood, to allow Pawnee Creek right overbank <br />flows to drain directly to the river. The second improvement area, designated as the "North <br />Improvement Area" is near the Riverside 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 of the two improvements areas are discussed separately below: <br /> <br />South Improvement Area: Based on discussions with the City, Logan County, CWCB, lIDd COOT, <br />and concerned citizens, it was believed essential that the project should take advantage of the existing <br />drainageway to the degree possible. Channel capacity near the HWY 6 bridges exceed 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 increased as well. COOT is planning to upgrade <br />the north bound bridge and work is schedule to begin in the next two years. 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 culverts. Since this work would be done only to <br />increase the hydraulic capacity of the bridge, this cost 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 downstream of the UPRR rlIDging in height from I <br />foot to 5.5 feet are planned. The north levee will extend east from about 300 feet downstream of the <br />railroad to the defined low flow channel of Pawnee Creek and then curve north lIDd follow the channel <br />to lID 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 lID existing residence and livestock pen. <br /> <br />. <br /> <br />III-22 <br />