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<br />~,~~~)g~ <br /> <br />Creek. An unusual weather pattern within northeastern Colorado had been producing above <br />average rains and intense thunderstorms since June of this year. The weather pattern seemed to <br />be caused by a combination of the monsoonal moisture from the southwest, the position of the jet <br />stream, and other factors. The weather conditions which produced sev,ere storms and flooding in <br />1997 were not unlike the conditions that existed in 1965. <br /> <br />A rainfall bucket survey, which included areas within Logan County and eastern Weld County, <br />was performed by the flood documentation team, A map showing the collected rainfall amounts <br />is presented as Figure 2. <br /> <br />Hydrologic and Hydraulic Characteristics <br />In order to estimate peak discharges at various stream and overlfow locations, the flood <br />documentation team identified cross-section locations, flagged high water marks, and field <br />surveyed channel and overflow cross-sections for the Pawnee Creek flooded areas, A private <br />surveying company, which was under contract with the City of Sterling, surveyed several cross- <br />sections that were located and marked by the flood documentation team, Data from the field <br />surveys was transmitted to the CWCB and forwarded to the Omaha Corps for review and <br />analysis. <br /> <br />In general, this was a very significant flood event. Peak flow estimates on the Pawnee Creek <br />mainstem above Colorado Highway 14 ranged from 40,000 to ov,er 70,000 cfs (These are <br />preliminary estimates that need to be finalized). An eyewitness account from one landowner <br />(located along the left bank of the creek approximately 1,500 feet upstream of Highway 14) <br />pegged the 1997 high water mark at about 5 to 6 feet above the 1965 high water mark. Another <br />landowner downstream of Highway 14 estimated that the 1997 peak flow rate was at least 50% <br />higher than the 1965 peak flow rate. <br /> <br />The Pawnee Creek flows and the overflows into Sterling were estimated by field surveying high <br />water marks, ground slopes, water surfaces slopes, and floodplain cross-sections. The Pawnee <br />overflow into Sterling was based on' survey data taken perpendicular to Highway 6 and the <br />railroad embankment near the Riverside Cemetery. The flow estimates were made by using <br />indirect flow measurement techniques. The resulting discharge estimates are presented in the <br />table below: <br /> <br />Location <br />Pawnee overflow into Sterlin near Riverside Cemete <br />Pawnee overflow perpendicular to Highway 6 and <br />railroad at the Riverside Cemete . <br />Pawnee Creek uls of Hi hwa 14 (section I) <br />Pawnee Creek uls of Hi hwa 14 (section 2) <br /> <br /> <br />40,000 to 70,000 <br />40,000 to 70,000 <br /> <br />Pawnee Creek section 3) <br />Pawnee Creek (section 4) <br /> <br /> <br />data at this time <br />data at this time <br /> <br />4 <br />