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<br />flooding that occurred in 1957, which also caused damage to homes, <br />waterlines, and sewerlines. Another 2 inches of rain fell the next <br />day, accompanied by hail. Farmers reported a 100 percent loss of <br />their crops from the rain and hail. Emergency assistance was provided <br />by the Red Cross. <br /> <br />In 1965, heavy rains and hail again destroyed many crops and homes, <br />sending flows of water and mud into basements and living rooms. <br />Housing damages were reported to be in the thousands of dollars <br />(Reference 5). <br /> <br />2.4 Flood Protection Measures <br /> <br />A levee has been constructed on the south and southeast edge of <br />Frederick to divert waters from the major drainages to a drainage <br />channel along the Union Pacific Railroad on the west side of town. <br />The flood protection facilities have sufficient capacity to protect <br />the town during floods having a recurrence interval of less than 10 <br />years. For larger floods, the levee is overtopped. Field inspection <br />of the levee, which has a maximum height of 5 feet, indicated poor <br />placement and compaction of embankment materials. Overtopping of <br />the levee will likely cause erosion and failure of a portion of the <br />embankment, resulting in flooding in the town. <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 50Q-year period (recurrence interval) have been <br />selected as having special significance for flood plain management and <br />for flood insurance premium rates. These events, commonly termed the <br />10-, 50-, 100-, and SOO-year floods, have a 10, 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 lOa-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 90-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 eleva- <br />tions will be amended periodically to reflect future changes. <br /> <br />4 <br />