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The growing season is 136 days and lasts from mid-March through late October. Vegetation in the area consists of juniper and pinon forest cover with oak brush and sage dominating the drier slopes. Vegetation in the highest mountain areas is classified as alpine slope and meadow, with a cover of mixed alpine tundra grass, sedge, forbs, and alpine willow. Carbondale sits at approximately 6,000 feet and is bordered by high mesas ranging in elevation from 7,000 to 11,000 feet. 2.3 Principal Flood Problems Most of the annual precipitation in the Colorado River Basin occurs as snow resulting in a deep snowpack in the higher regions. Major floodflows on the Crystal River within the study area result from the rapid melting of the mountain snowpack during the period from late May through early July. Snowmelt floods are characterized by moderate peak flows, large volumes and long durations, and marked diurnal fluctuation in flow. Rainfall on melting snow accelerates the rate of snowmelt adding to floodflows. Large flows as the result of rainstorms have generated floods on tributaries to the Crystal River, but not on the main stem. A snowmelt flood that occurred in 1884 is generally considered to be the most severe known in Garfield County, with a 300-year recurrence interval. Other periods of high flow occurred in 1930, 1957, and 1971. More recently, in June 1983, snowmelt waters exceeded the riverbanks in many areas of the county. The flows for this flood were less than the 10-year flows used in this report. 2.4 Flood Protection Measures There are no flood control projects that afford protection to the study area. The flood control and related water resources development problems of the Upper Colorado River Basin have been under study by the COE for a number of years. At this time, however, no projects are proposed to protect the study area. 3.0 ENGINEERING METHODS FOr the flooding sources studied in detail in the community, standard hydrologic and hydraulic study methods were used to determine the flood hazard data required for this study. Flood events of a magnitude which are expected to be equaled or exceeded once on the average during any 10-, 50-, 100-, or 500-year period (recurrence interval) have been selected as having special significance for flood plain management and for flood insurance rates. These events, commonly termed the 10-, 50-, 100-, and 500-year floods, have a 10, 2, 1, and 0.2 percent chance, respectively, of being equaled or exceeded during any year. Although the recurrence 4