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2.4 Flood Protection Measures <br />The Montezuma County and the Colorado State Highway Department crews <br />constructed rock and dirt embankments near bridges throughout the county. <br />The U.5. Army Corps of Engineers (COE) completed bank protection work along <br />the Mancos River banks at the sewage lagoans near the Town of Mancos <br />December 1973. <br />In 1985 the U.S. Bureau of Recl~nation completed construction of the Dolores <br />landfill and protective dike. This project, which was built in conjunction with the <br />Bureau's construction of the McPhee Dam, involved construction of 2,100 feet of <br />levee and landfill between the State Route 145 embankment and the Fourth Street <br />Bridge, along the right bank of the Dolores River. In addition, the project <br />included the rehabilitation of two segments of existing levee along the right bank <br />of ~1ie Dolores River upstream of the Fourth Street Bridge. These levees were <br />constructed to prevent flooding resulting from the maximum pool elevation of the <br />McPhee Reservoir. The levees upstream of Fourth Street do not have sufficient <br />freeboard to be recognized as providing protection from 100-year overbank <br />flooding. In addition, these levees are not federal certified levees and they do not <br />meet the FEMA's National Flood Insurance Program (NFIP) regulations (LJ.S. <br />Army Corps of Engineers, Sacramento District, August 2005). <br />3.0 ENGINEERING METHODS <br />For the flooding sources studied by d~tailed methods in the community, standard <br />hydrologic and hydraulic study methods were used to deternune the flood hazard data <br />required for this Flood Insurance Study. Flood events of a magnitude which are expected <br />to be equaled or exceeded once on the average during any 10-, 50-, 100-, or 500-year <br />period (recurrence interval) have been selected as having special significance for <br />floodplain management and for flood insurance rates. These events, commonly termed <br />the 10-, 50-, 100-, or 500-year floods, have a 10-, 2-, 1-, and 0.2-percent chance, <br />respectively, of being equaled or exceeded during any year. Although the recturence <br />interval represents the long term avera~e period between floods of a specific magnitude, <br />rare floods could occur at short intervals or event within the same year. T'he risk of <br />experiencing a rare flood increases when periods greater than one year are considered. <br />For example, the risk of having a flood which equals or exceeds the 100-year flood (1 <br />percent chance of annual exceedence) in any 50-year period is approximately 40 percent <br />(4 in 10), and for any 90-year period, the risk increases to approximately 60 percent (6 in <br />10). The analyses reported herein reflect flooding potentials based on conditions existing <br />in the community at the time of completion of this Flood Insurance Study. Maps and <br />flood elevations will be amended periodically to reflect future changes. <br />9 <br />