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<br />estimated at about $250,000; one person was killed, and many were <br />badly injured. The flood that occurred in 1969 was not as <br />destructive as the flood of 1914 and was confined to the western <br />part of town. Again, mud and debris flows were the principal <br />factors. (Frequencies of major floods are not available.) <br /> <br />Past records indicate that most of the severe floods in this region <br />were caused by cloudbursts, especially for small drainage basin.. <br />A flood resulting from a cloudburst rises so quickly that it hag a <br />peak duration of only a few minutes, followed by a rapid <br />sub_sidence. <br /> <br />2.4 Flood Protection Measures <br /> <br />No specific flood protection structures have been constructed in <br />the designated study areas. Some flood protection measures are <br />provided, however, by San Miguel County Subdivision Regulations. <br />Article VII (Special Regulations) of the Subdivision Regulations <br />provides for the protection and control of marsh and lowland. and <br />the floodplain within 100-year flood limits. Article IX <br />(Improvement Standards) of the Subdivision Regulations provides <br />control for new developments that should provide drainage and flood <br />control facilities for 100-year frequency storm events and provide <br />protection for structures within the 100-year floodplain. <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 500-year period (recurrence <br />interval) have been selected as having special significance for <br />floodplain management and for flood insurance rates. These events, <br />cORlnonly termed the 10-, 50-, 100-, and 500-year floods, have a 10-, <br />2-, 1-, and 0.2- percent chance, re.pectively, of being equaled or <br />exceeded during any year. Although the recurrence interval represents <br />the long-term average period between floods of a specific magni tude. <br />rare floods could occur at .hort intervals or even within the same <br />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 equals or exceeds the lOO-year flood (l percent chance of <br />annual exceedence) in any 50-year period is approximately 40 percent (4 <br />in 10), and for any 90-year period, the risk increases to approximately <br />60 percent (6 in 10). The analyses reported herein reflect flooding <br />potentials based on conditions existing in the community at the time of <br />completion of this study. Maps and flood elevations will be amended <br />periodically to reflect future changes. <br /> <br />7 <br />