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<br /> <br />. <br /> <br />. <br /> <br />I <br /> <br />I <br /> <br />I <br /> <br />tf <br />, <br /> <br />LI <br /> <br /><" ' <br />Li <br /> <br />t <br /> <br />I <br /> <br />l <br /> <br />1 <br /> <br />t <br /> <br />IV. PAWNEE CREEK/P A WNEE CREEK OVERFLOW <br /> <br />Existing- Flooding Conditions <br /> <br />This study includes the reach along Pawnee Creek from its confluence with the South Platte River 100- <br />vear 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 />farmlands, county roads, and houses. Also of concern is the Pa",nee Creek Overflow where flood <br />water overtops the channel to the north and eventually inundates portions of the City of Sterling. In <br />addition to the Pawnee Creek Overflow, there are areas adjacent to and upstream of CR. 31 where <br />flows overtop the channel to the south and eventually flow into the Town of Atwood. Improvements <br />for confining split flow areas to the south were not evaluated for this study. <br /> <br />Historically, Pawnee Creek has proven to be the most significant flooding source for the City of <br />Sterling. Flooding in the City of Sterling from Pawnee Creek has occurred mainly as a result of <br />insufficient channel capacity, roadway crossing structures, and the bridges at HWY 6 and the UPRR. <br />A floodplain analysis was completed by the Soil Conservation Service (SCS) in April of 1992 which <br />determined the 1 DO-year floodplain for existing basin and channel conditions. A floodplain map was <br />prepared which delineated the 1 DO-year floodplain for Pawnee Creek through this study reach. Based <br />on the SCS Report, a description of the existing flood potential is presented bdow: <br /> <br />South Platte River to UPRRJHWY 6 -- Flooding in this reach is limited by the capacity of the existing <br />bridge structures. However, the flooding can be severe and inundate much of the highway and railroad <br />as shomt on the photo in Figure 7. This event occurred in ! 935 and a similar rainstorm occurred again <br />in 1965. As shown on Sheet I of 4, located in the map pocket in the back of this report, flows split <br />dO\\l1stream of the UPRR bridge causing a very wide (approximately 4.500 feet), shallow floodplain <br />to the confluence with the South Platte River. Two residences are potentially flooded in this reach: <br />One residence is located in the I DO-year floodplain and is on the north bank of Pawnee Creek adjacent <br />to the railroad; and the other residence is located further downstream on a higher plateau which could <br />be impacted by potential shallow flooding. <br /> <br />.!1ERRJHWY 6 to CR. 35 -- Flooding in this reach is basically caused by: (1) Insufficient capacity of <br />the bridges at HWY 6 and the UPRR; (2) insufficient channel capacity on Pawnee Creek: and (3) <br />storrnwater draining from the Town of Atwood, which is a result of flow splits from the upper reaches <br />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 fatmlands, inundating the <br />Riverside Cemetery, and 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 City of Sterling to make <br />flood improvements along Pawnee Creek. <br /> <br />22 <br />