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<br />Peak discharges along Cherry Creek were 1,000 cfs upstream from <br />Franktown, 39,900 cfs near Melvin, and 58,000 cfs at Cherry Creek <br />Dam. An estimated peak flow of 14,000 cfs discharged from Piney <br />Creek, a right-bank tributary of Cherry Creek. During the evening <br />and night of June 16, the Cherry Creek Reservoir impounded a flood <br />that had a volume of 116,000 acre-feet. Three of the 18 small dams <br />constructed by the SCS in the upper Cherry Creek basin between <br />Franktown and Parker were filled. Two of these were subsequently <br />overtopped and sustained erosion damage. The remaining 15 struc- <br />tures were outside of the area of high-intensity rainfall and re- <br />ceived only moderate runoff. The heavy runoff caused major flood- <br />ing along the main stem of Cherry Creek from the vicinity of <br />Franktown to the Cherry Creek Reservoir. Approximately 2,720 <br />acres were flooded. Most of the bridges across Cherry Creek Were <br />either damaged or destroyed. One life was lost during the flood <br />on Cherry Creek. Flood damages totaled $1,306,000. <br /> <br />scenes of the 1965 flood are shown in Figures 2 through 6. <br /> <br />2.4 Flood Protection Measures <br /> <br />The possibility of flood damage in the upper Cherry Creek area has <br />been reduced somewhat by the construction of 32 floodwater- <br />retarding structures. The SCS completed construction of these <br />structures in 1965 as part of an overall plan. The plan is <br />presented in two watershed work plans (References 6 and 7). These <br />structures were designed for a rural agricultural community with <br />design floods having a 25-year recurrence interval. <br /> <br />Chatfield Dam, completed in 1976, provides flood protection, <br />recreation, and water supply facilities for the City of Denver and <br />its environs. The dam is located downstream of the mouth of Plum <br />Creek. The effects of the dam have been taken into consideration <br />in this FIS. <br /> <br />3.0 ENGINEERING METHODS <br /> <br />For the flooding sources studied by detailed methods in the community, <br />standard hydrologic and hydraulic study methods were used to determine <br />the flood hazard data required for this study. Flood events of a <br />magnitude which are expected to be equaled or exceeded once on the <br />average during any 10-. 50-, 100-, or SOO-year period (recurrence <br />interval) have been selected as having special significance for flood <br />plain management and for flood insurance rates. These events. commonly <br />termed the 10-, 50-, 100-, and SOO-year floods, have a 10, 2, 1, and 0.2 <br />percent chance, respectivel~. of being equaled or exceeded during any <br />year. Although the recurrence interval represents the long-term average <br />period between floods of a specific magnitude. rare floods could occur <br />at short intervals or even within the same year. The risk of experienc- <br />ing a rare flood increases when periods greater than 1 year are consid- <br />ered. For example, the risk of having a flood which equals or exceeds <br /> <br />12 <br />