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<br />2.4 Flood Protection Measures <br /> <br />There are no flood control structures on the Cache La Poudre River <br />in the study area, although there are two irrigation dams on the <br />North Fork of the Cache La Poudre River. The effects of the two <br />dams are considered negligible in the study area. <br /> <br />The Spring Creek Drainage Basin does not have any flood control <br />structures below Horsetooth Reservoir. The City of Fort Collins is <br />presently studying the Spring Creek area and analyzing the possibility <br />of improving existing bridges, culverts, and the channel in order to <br />reduce floodflow obstructions. The city is also contemplating <br />reducing potential flood damage through land use restrictions within <br />the flood plain areas. <br /> <br />Dry Creek has several lakes and storage reservoirs which reduce the <br />contributing drainage area by approximately 13 percent, although <br />they are not really flood control structures. Douglas Lake, located <br />outside Fort Collins corporate limits is also an irrigation reservoir. <br />and reduces flood peak discharges significantly. <br /> <br />The City of Fort Collins is provided some protecticn from floods <br />through flood warning and forecasting by the National Oceanic and <br />Atmospheric Administration, National Weather Service. <br /> <br />3.0 ENGINEERING METHODS <br /> <br />For the flooding sources studied in detail in the community, standard <br />hydrologic and hydraulic study methods were used to determine the flood <br />hazard data required for this study. Flood events of a magnitude which <br />are expected to be equalled or exceeded once on the average during any <br />10-, 50-, 100-, or 500-year period (recu~ce interval) have been <br />selected as having special significance for flood plain managa~ent and <br />for flood insurance premium rates. These events, commonly termed the <br />10-, 50-, 100-, and SOO-year floods, have a la, 2, 1, and 0.2 percent <br />chance, respectively, of being equalled or exceeded during any year. <br />Although the recurrence interval represents the long term average period <br />between floods of a specific magnitude, rare floods could occur at short <br />intervals or even within the same year. The risk of experiencing a rare <br />flood increases when periods greater than 1 year are considered. For <br />example, the risk of having a flood which equals or exceeds the 100-year <br />flood (1 percent chance of annual occurrence) in any 50-year period is <br />approximately 40 percent (4 in 10), and, for any gO-year period, the risk <br />increases to approximately 60 percent (6 in 10). The analyses reported <br />here reflect flooding potentials based on conditions existing in the <br />community at the time of completion of this study. Maps and flood elevations <br />will be amended periodically to reflect future changes. <br /> <br />5 <br />