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, 10 Pre"ipitation varIes wIdely throughout the Iloaring Fork Basin above Basalt. DntheCor1tinental Divide, near Independence Pass, the average annualprec.1pitation Is 26.3 Inches with 17.5;nchesoccurringduring the winter months (November-April). NellrBasalt, the ,,'(erag.. annual pre. clpltation is approximately 16.5 Inches with 7.3 inches occurring during the winter "",nths (Reference 6). Data on precipitation from the National Oceanic and AtmospherIc AdministratIon indicate that in the Aspen area, the 100-year 2~-hour storm would produce 2.6 Incoes of precipitation. Study Reach Description This floodplain study encompasses about 5.7 mile, of the Roaring Fork River beginning at the Garfield County LIne and extending upstream to the Pitkin County Line. In additIon, this report covers the Fryingpan River from Its confluence with the Roaring Fork upstream for about 1.0 ml1e. The Roaring Fork River in the study area has an average range of about 90 to 120 feet wide as it flows through an alluvial valley,with a grade of approximately 0.007 feet per foot. The stream channel Is braided, having a bed composed mostly of gravel, cobbles, and small round boulders ranging In the 6 to 15-inch diameter size. There are many riffles and rapidswithmany,hallowpoolsalong its course. Several irrigation ditches divert from the Roaring Fork along this reach. There are no across-the-river diversion structures. In most areas, the river banks arc low wi th steep slopes (often over ~5 degrees), being c","posed most Iy of sand. gravel, and cobbles, with little or no vegetation below the mean annual hlghwatermark. The steep slopes and ]ackofvegetationreduce the resistance of the banks to scour. Temperature and precipitation varies greatly from location-to-location and season-to-season within the drainage basin and are Important variables ;n flooding conditions. Above normal spring temperatures can cause early and heavy flows on the Roaring Fork River. The Aspen weather station is the only official weather statIon In the study basin. Records from the Aspen weather station Indicate that the mnth of July has the highest nor. mal total precipitation for the year at 2.06 Inches. The rnontll of March follows closely with 1.98 Inches of total precIpitation. The fIrst month with" nor",al ,pring temperature above the freezing point 15 A.prll with """,an....,nthly temperature of 38.6 degrees Fahrenheit. Thefryingpan in the study reachhes an average width of about 60 to 80 feet, and maintains a grade of approximately 0.015 feet per foot. The ri~er b"nks are steep and wel T-deftned dlong the re..ch, dnd the bed Is cov",cdwithan armor ldverof largc cobbles and boulders. Todateonly limited development has occurred in the floodplain areaS. Most structure, have been bui It adjdcent to or in shallow flood prone aredS. ThefollowingpictyresshowtheRoarlngForkandf"ryingpanstreamch..rac. t~ri,t ics dt s~v~ral points.