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<br />The Unnamed Tributary to Gypsum Creek flows intermittently from <br />the hills just west of Gypsum, across a field and~into Gypsum <br />Creek. The narrow, deep channel is well defined in the mountains <br />and in the area just upstream from Gypsum Creek. However, it is <br />undefined through the field. The surrounding vegetation is mostly <br />sagebrush and native grasses. <br /> <br />The primary underlying soils at Gypsum are the Haploborolls- <br />Halargrids-Argoborolls Association. These soils are cool, shallow <br />to moderately deep, and well drained to somewhat poorly drained <br />(Reference 3). <br /> <br />2.3 Principal Flood Problems <br /> <br />Flooding along the Eagle River and Gypsum Creek, in Gypsum, usually <br />occurs from May through September. Floodwaters can OCcur from <br />either snowmelt, intense rainstorms and cloudbursts, or rainstorms <br />augmented by snowmelt. <br /> <br />Past floods in Gypsum, on both the Eagle River and Gypsum Creek, <br />occurred in August and September 1963 and in June 1965. Both of <br />these floods caused minor damage (Reference 4}. There are no <br />recorded discharges available for these floods. <br /> <br />2.4 Flood Protection Measures <br /> <br />There are no major flood protection measures in the Town of Gypsum <br />or along Gypsum Creek. A wall has been constructed near the <br />Denver and Rio Grande Western Railroad that affords a small amount <br />of flood protection to the area. <br /> <br />3.0 ~N-"IN&ERING 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 (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 SOQ-year floods, have ala, 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 <br />period between floods of a specific magnitude, rare floods could occur <br />at short intervals or even within the same year. The risk of experiencing <br />a rare flood increases when periods greater than 1 year are considered. <br />For example, the risk of having a flood which equals or exceeds the <br />lOa-year flood (1 percent chance of annual occurrence) in any 50-year <br />period is approximately 40 percent (4 in 10), and, for any 90-year <br /> <br />4 <br />