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<br />Deta il ed infonnati on on fl oods before the turn of the century is vpry <br />limited. Infonnation on past flooding is based on newspaper accounts <br />and interviews with longtime residents of the area. Largp floods <br />occurred at Canon City in 1909, 1921, 1933. 1941. 1957, 1965 amI <br />1974. Peak discharges for these historic flood events were all less <br />than the 10-year flood peak discharge, as predicted by the hydrologic <br />analysis used for this flood insurance study. These floods have <br />caused maj or damage, di srupti ng hi ghway and ra i 1 road tra Hic and <br />communication services, drowned livestock. destroyed agricultural <br />lands, roads, bridges. and buildings. Several lives have been lost <br />and numerous others injured. <br /> <br />The flood of August 1921. which registered the highest flood flows <br />ever at Canon City caused the most damage downstream of Canon <br />City. The river reached a discharge of 19.000 cubic feet per second <br />(cfs) (Reference 2), flooding many streets and also washing out many <br />bridges. The railroad through the Royal Gorge and Canon City has <br />been washed out or damaged in the floods of 1909, 1933, 1941, 1947, <br />and 1965. In all of the mentioned floods many bridges were lost and <br />large amounts of acreage were inundated as in the flood of 1957 when <br />150 to 200 ac res of 1 and between Canon City and Florence were under <br />wa ter . <br /> <br />2.4 Flood Protection Measures <br /> <br />Along the lower reaches of Forked Gulch, SOO feet above the confl u- <br />ence with Arkansas River. the city has constructed a concrete <br />1 ined channel to stabil ize the banks to prevent further destruction <br />of the Griffin Avenue bridge. The city has also adopted an ordinance <br />regulating development in the flood plain (Reference 3). <br /> <br />3.0 ENGINEERING METHODS <br /> <br />The flood plains in Canon City were estimated using standard hydrologic <br />and hydrau1 ic study methods to detennine the flood hazard data required <br />for this study. Flood events of the magnitude which are expected to be <br />equalled or exceeded once on the average during any 10-, 50-, 100-, and <br />500-year period (recurrence interval) have been se1 ected as having special <br />significance for flood plain management and for flood insurance premium <br />rate. These events, commonly tenned the 10-,50-,100-, and 500-year <br />floods, have ala, 2, I, and 0.2 percent chance, respectively, of being <br />equalled or exceeded during anyone year. Although the recurrence inter- <br />val represents the long tenn average period between floods of a specific <br />magnitude, rare fl oods coul d occur at short interval s or even withi n the <br />same year. The risk of experiencing a rare flood increases when periods <br />greater than 1 year are considered. For example, the risk of having a <br />flood which equal s or exceeds the laO-year flood (1 percent chance of <br />annual occurrence) in any 50-year period is approximately 40 percent (4 in <br />10), and, for any 90-year period, the risk increases to approximately 60 <br />percent (6 in 10). The analyses reported here reflect flooding potentials <br />based on conditions existing in the county at the time of completion of <br />this study. Maps and flood elevations will be amended periOdically to <br />reflect future changes. <br /> <br />6 <br />