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<br />A cloudburst over Williams and Waldo Canyons in May 1947, caused <br />flooding on Williams Canyon and Fountain Creek. Many small bridges <br />were washed out, and the debris created' dams that eventually broke <br />and caused further damage (Refer,nce 3). <br /> <br />A correlation between the elevations of previous floods and the <br />elevations of possible future floods as presented in this study is <br />difficult to determine because of changes in the stream channels as <br />a result of high 'flows and subsequent development. At Fountain, <br />Colorado, approximately 25 miles, downstream from Manitou Springs, a <br />40-foot-10ng bridge. spanning Fountain Creek was washed out in a <br />flood in 1902 and was replaced by one 70 feet long. Succeeding <br />floods have widened the channel ievenmore, so that the bridge span <br />now exceeds 200 feet. Due to ehe changing channel capacities, an <br />estimate of the recurrence int~rva1s of past floods would not be <br />valid (Reference 5). Photograpqs of potential flooding at Manitou <br />Springs are shown in Figures 2 and 3. <br /> <br />. <br /> <br />2.4 Flood Protection Measures <br /> <br />The flood-carrying capacity of. the streams has been increased <br />through channe1izat~on in many areas. For this to be an effective <br />flood protection measure, the entire stream length in flood-prone <br />areas must be channelized to the extent necessary to carry <br />low-frequency flows. Because this 'is not the case in Manitou <br />Springs, the channeHzation that exist,s. is not sufficient to <br />'protect ,the city from floods of the selected; recurrence intervals <br />in all areas. <br /> <br />The city has enacted ordinances that are directed at the reduction <br />of flood hazard. These ordinances' specify' that drainage be <br />designed to reduce exposure to' flood hazard and not to subject <br />other property to flood hazard' and that new construction be <br />reasonably safe from flooding. The city also requires that new and <br />replacement water-supply and san~tary sewage systems be designed to <br />minimize or ,eliminate infiltration of floodwaters. <br /> <br />There are no s.tructura1 means of flood protection, such as dams or <br />levees, in the city. <br /> <br />1.0 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 500-ye'ar periOd (recurrence <br />interval) have been selected as having special significance for <br />floodp1:ain management, and fo'r floQd insurance rates. These events, <br />cQmmQn1y termed the 10-., ,.50-, 100-, alld 500"'year flQQds, have a 10, 2, 1 <br />and 0.2 percent chance, respective+y, Qf .being equaled Qr exceeded <br />during any year. A1thQugh the recurrence interval represents the <br />long-term, averal!:e period between floods of a specific magnitude, rare <br /> <br />. <br /> <br />. <br /> <br />6 <br />