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OD~940 Chopter 3 . Affected EnviroN7lOtl and mass movement potential tend to be high (due to steep slopes, thin soils. and generally rapid runoff). Revegetation should be carried out during or prior to seasonal wet periods, due to the low water holding capacity of these thin, coarse soils. WATERSHED RESOURCES This section describes the existing watershed resources, hydrology, water quality, and water rights in the Aspen Highlands Ski Area. Readers are referred to the Watershed Resources Technical Report (USDA-FS 1996a) and Water Rights and Water Depletion Analysis (HRS 1996) for more detailed information. Aspen Highlands lies along a ridgeline that divides Maroon Creek and Castle Creek. There are a series of drainages on either side of the ridge, most of which are less than 100 acres in size. Rather than analyze each of these, the analysis area is generally described by two composite watersheds, each of which is a portion of a watershed that has no single discharge point (USDA-FS 1995a). These are the Maroon Creek composite watershed (MCW) and the Castle Creek composite watershed (CCW), reflecting the respective locations of outflow from the ski area. The two watersheds consist of a total of ten hydrographic areas (sub-watersheds). Only two of these areas within each composite watershed were analyzed because these receive runoff from a relatively significant portion of the CWTeIlt and potential future development areas. Each of these hydrographic areas represent drainage basins that collect and discharge surface flow through one outlet to Maroon or Castle creek. Figure 3.4 illusll'ates the locations of the composite watersheds and the constituent hydrographic areas. To limit the analysis to watershed effects of the ski area. the composite watershed boundaries follow topographic divides that describe areas that might be impacted by current and proposed ski area developments. Some private developments are also included within the composite watersheds because their location is within the' designated drainage area. Areas that do not receive runoff from current or proposed ski area development are ex.cluded from this analysis. BACKGROUND CUMATE The annual average precipitation in Aspen is 19.5 inches per year with relatively consistent monthly averages that range between 1.26 and 1.87 inches. The average annual snowfall is 145.5 inches per year, and accounts for almost two-thirds of the total precipitation received. Higher elevations receive increased snowfall (CSU 1996). The average maximum temperature ranges from 770 F at the base area to 680 F at the summit of Aspen Highlands, while the average minimum temperature ranges from 60 F at the base area to -1 0 F at the summit. Irvine (1993) generally describes four clirnate zones within Aspen Highlands including the lower montane, montane, subalpine, and alpine zones. In all four zones, the prevailing winds are from the east-southeast and precipilation gmerally occurs as summer thunderstorms in July and August and winter snowfall from November through April, except in the alpine area where snowfall may extend from September through June. Other characteristics of each area are sununarized in Table 3.3. RUNOFF AfIID SEDIMENTATION Aspen Highlands contributes runoff to Maroon Creek and Castle Creek, two tributaries to the Roaring Fork River. The U.S. Geological Survey measured Sll'eamflow between 1969 and 199 I at a gaging station in Maroon Creek located 7.2 miles southwest of Aspen and about 5 miles upstream of the northern boundary of the MCW, and at a gaging station in Castle Creek located 7 miles south of Aspen and about 6 miles upstream of the northern boundary of the CCW. Peak runoff usually occurs in June following snowmelt, while flow rates are usually Wasershed ResolU'ces Background 3-13