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flows approximately 37 miles to the Town of Basalt. At the con- fluence of the Roaring FOrk and Fryingpan Rivers, 53 percent of the total drainage of the Fryingpan and Roaring Fork River basins has been collected (Reference 3). The Roaring Fork River is the major drainageway through Aspen and collects flow from tributary streams on both sides of the valley. The Fryingpan River originates in the Sawatch Mountain Range above the timberline and flows southwesterly to Basalt, where it empties into the Roaring Fork River on the western side of town. The Fry- ingpan River comprises approximately 19 percent of the total flow of the Roaring Fork River (Reference 3). Development in the flood plains of the Roaring Fork and Fryingpan Rivers is minimal. The soils in and around Basalt are variably textured, water-de- posited, sandy, and loamy, and with varying amounts of cobble and gravel occurring in the valley bottoms and benches. The mountains vary from colluvial to the north, basalt lava to the southwest, and sandstone and shale to the east and west. Average annual precipitation for Pitkin County is approximately 19.25 inches (Reference 4). On the average, 11.8 inches of this precipitation is snowfall and 7.5 inches is rainfall. Average temperatures range from approximately 200F during the winter to 600F to 700F during the summer. 2.3 Principal Flood Problems Flooding from streams in Pitkin County usually occurs during May through August, with the principal cause of flood-flows being snowmelt runoff. Summer rains do not cause major floods in this area. Thunderstorm activity creates major floods only on small tributary streams because of the storms. short duration. Major floods on the Roaring Fork and Fryingpan Rivers result from rapid melting of mountain snowpack during the period from late May through early July. These snowmelt floods are characterized by moderate peak flows, large volumes, long durations, and marked diurnal fluctuations in flow. Rainfall on melting snow may accelerate the rate of the snowmelt, thus augmenting floodflows. The largest discharge recorded on the Roaring "~rk River was in July 1957, with a peak of 19,000 cubic feet per second (cfs). A COE letter report (Reference 5) describes the 1957 flood as follows: Floods on the Roaring Fork result from snowmelt and occur pr incipally during the lIDnth of June. The flood of July 1, 1957 had an instantaneous peak discharge of 18,700 cfs at the Glenwood Springs gage. This flood was the maximum of 49 4