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<br />3. DETAILED DESCRIPTION OF SELECTED ALTERNATIVE <br /> <br />. PrQieet Location <br /> <br />This study includes the reach along Pawnee Creek from its confluence with the South Platte River 100- <br />year floodplain upstream to CR. 29, a distance of about 7.5 miles. Areas of concern include locations <br />where potential floodwaters exceed the existing Pawnee Creek channel capacity and damaged <br />farmlllDds, CRs, and houses. Also of concern is the Pawnee Creek Overflow where flood water <br />overtops the channel to the north and eventually inundates portions of the City of Sterling. In addition <br />to the Pawnee Creek Overflow, there are areas adjacent to and upstream of CR. 31 where flows overtop <br />the channel to the south and eventually flow into the Town of Town of Atwood. Improvements for <br />confining split flow areas to the south were not evaluated for this study. <br /> <br />Existing Flooding Conditions <br /> <br />. <br /> <br />Historically, Pawnee Creek has proven to be the most signifiCllDt flooding source for the City of <br />Sterling and for Logan County. Flooding in the City of Sterling from Pawnee Creek has occurred <br />mainly as a result of insufficient channel capacity, roadway structures, and the bridges at HWY 6 and <br />the UPRR. A floodplain analysis of the Pawnee Creek overflow area in unincorporated Logan County <br />was completed by the Soil Conservation Service (SCS) in April of 1992 which determined the 100- <br />year floodplain for existing basin and channel conditions. This report supplemented the previous <br />LeaflResource Consultants report of 1983, which was completed for the portion of the Pawnee <br />overflow in the City of Sterling. A floodplain map was prepared which delineated the 100-year <br />floodplain for Pawnee Creek through this study reach. Based on the SCS Report, a description of the <br />existing flood potential is presented below: <br /> <br />South Platte River to HWY 6/UPRR -- Flooding in this reach is limited by the capacity of the existing <br />bridge structures. However, the flooding can be severe lIDd inundate much of the highway and railroad <br />as shown on the photo in Figure 7. As shown on the floodplain mapping, located in the map pocket in <br />the back of this report, flows split downstream of the UPRR bridge causing a very wide <br />(approximately 4,500 feet), shallow floodplain to the confluence with the South Platte River. Two <br />residences are potentially flooded in this reach: One residence is located in the 100-year floodplain <br />and is on the north bank of Pawnee Creek adjacent to the railroad; and the other residence is locatcd <br />further downstream on a higher plateau which could be impacted by potential shallow flooding. <br />Additional flooding occurs to the Sterling No. 1 Ditch, and adjacent agricultural lands. <br /> <br />IJPRRJHWY 6 to CR 35 -- Flooding in this reach is basically caused by: (I) Insufficient capacity of <br />the bridges at HWY 6 and the UPRR; (2) insufficient channel capacity on Pawnee Creek; and (3) <br />floodwater draining into the Town of Town of Atwood, which is a result of flow splits from the upper <br />reaches of the basin. The greatest impact of flooding occurs along HWY 6 to the north. Flood flows <br />exceeding the capacity of the bridges travel along HWY 6 damaging farmlands, inundating the <br />Riverside Cemetery, lIDd eventually spreading out to the northwest into the City of Sterling. This area <br />is referred to as the Pawnee Creek Overflow, and is the driving force for the Community to make flood <br />improvements for the Pawnee Creek flood events. <br /> <br />. <br /> <br />III-I 8 <br />