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<br />2.4 Flood Protection Measures <br /> <br />Both structural <br />damage reduc t i on <br />effort to prevent <br /> <br />flood protection works and nonstructural flood <br />measures have been employed in Pueblo's cont inuing <br />or reduce recurring flood losses. <br /> <br />The U.S. Bureau of Reclamation constructed Pueblo Dam on the <br />Arkansas River at River Mile 1,293.7, approximately 6 miles upstream <br />from the City of Pueblo. The dam controls Arkansas River flows up <br />to 87,000 cfs, approximately an 800-year flood (Reference 9). <br /> <br />The county has also established zoning laws to regulate construction <br />in floodprone areas. <br /> <br />3.0 ENGINEERING METHODS <br /> <br />For the following 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 <br />floodplain management and for flood insurance rates. These events, <br />commonly termed the 10-, 50-, 100, SOO-year floods, have a 10-, 2-, 1-, <br />and 0.2-percent chance, respectively, of being equaled or exceeded during <br />any year. Although the recurrence interval represents the long-term <br />average period between floods of a specific magnitude, rare floods could <br />occur at short intervals or even within the same year. The risk of <br />experiencing a rare flood increases when periods greater than one year <br />are considered. For example, the risk of having a flood which equals or <br />exceeds the 100-year flood (l-percent chance of annual exceedence) in any <br />50-year period is approximately 40 percent (4 in 10), and, for any 90- <br />year period, the risk increases to approximately 60 percent (6 in 10). <br />The analyses reported herein reflect flooding potentials based on <br />conditions existing in the community at the time of completion of this <br />study. Maps and flood elevations will be amended periodically to reflect <br />future changes. <br /> <br />3.1 Hydrologic Analyses <br /> <br />Hydrologic analyses were carried out to establish the peak <br />discharge-frequency relationships for each flooding source studied <br />by detailed methods affecting the community. <br /> <br />For the St. Charles River, Fountain Creek, wild Horse-Dry Creek, and <br />Goodnight Arroyo, the 100-year floods were determined from analyses <br />of past floods that have occurred on the respective streams and <br />other streams in their general area. This flood information was <br />obtained from historical documents and newspaper files. <br /> <br />8 <br />