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<br />Explanation of Flood Types <br /> <br />Predicting how floodwaters will flow and <br />how they will affect people's lives is a <br />difficult task requiring careful planning and <br />response. Hydrologists estimate the <br />probability or recurrence interval of future <br />floods by studying the past behavior of a <br />stream and/or surrounding streams. Floods <br />are often categorized according to their <br />return interval (e.g. 1O-50-100-year flood). <br />Each flood interval is related to a percent <br />chance that a flood may actually occur <br />within a given year. A recurrence interval is <br />the average frequency with which storms <br />occur. So the I DO-year flood is not <br />something that will occur at equal I DO-year <br />intervals. It can occur in two consecutive <br />years, or not at all in over 100 years. <br /> <br />There isa 1.0% chance that the 100- <br />year flood will occur in any given <br />year, If it occurred in 1994, there is <br />stilla 1.0% chance that it would occur <br />again in 1995. Instead of calling it the <br />1.fJ% flood, we call it the 100 year <br />flood, to demonstrate the magnitude of <br />the flood more effectively. <br /> <br />I. <br /> <br />Colorado state law requires that the I DO-year <br />flood plain be used for land use regulation, <br />as the flood plain concept provides a <br />national standard for the National Flood <br />Insurance Program. It is critical for flood <br />plain residents to remember that floods <br />greater than the I DO-year flood event may <br />occur at any time and may also exceed <br /> <br />Pueblo Flood H IlZIUd Miti"ation Pltm <br /> <br />proj ected estimates designated by the 100- <br />year flood plain boundary. It is important to <br />realize that it is difficult to plan in a cost- <br />effective manner for a sizable flood; <br />however, risk can be minimized using a <br />combined effort of structural and non- <br />structural mitigation. <br /> <br />Fountain Creek reached a peak <br />flow of approximately 11,000 cubic <br />feet per second (cfs) during the <br />June 3, 1994 storm. This peak can <br />be equated roughly to a flood with <br />a 5 Yellr recurrence interval. A <br />flood on Fountain Creek with a 50 <br />year recurrence interval would <br />reach about 45,000 efs. Likewise, a <br />100 Yellr interval would reach about <br />64,000 cfs. <br /> <br />Other historical peak flows in the <br />Pueblo arell: <br /> <br />-SL Charles, 1901- 56,000 cfs <br />-Arkansas, 1921- 100,000 cfs <br />-Huerfano, 1923- 19,400 cfs <br />-Fountain, 1965- 47,000 cfs <br />-Chico Creek, 1965- 50,900 cfs <br /> <br />Note: Recurrence intervals vary for <br />different strellms. Each stream must <br />have its own study to determine <br />flood recurrence intervals. <br /> <br />7 <br />