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<br />I. DRAINAGE FACILITY CAPACITY ANALYSIS <br /> <br />A. INTRODUCTION <br />The purpose of this report is to analyze the path and the magnitude of the runoff of different <br />frequency stonn events through the City of Aspen and the capabilities of the existing drainage <br />facilities to convey this flow to the Roaring Fork River, This report is presented as the initial <br />portion of the Stonn Runoff Master Plan Study that WRC Engineering is currently preparing for <br />the City of Aspen, This report will discuss the existing conditions with in the City and identify <br />areas of concern in respect to stonn runoff conveyance, Future documents will present alternatives <br />to alleviate possible drainage problems and other aspects of the Master Plan Study, <br /> <br />B, STUDY AREA <br />The City of Aspen is located in Township 10 South, Range 85 West of the 6"' Principal Meridian, <br />in Pitkin County, The City lies at the base of the north side of Aspen Mountain adjacent to the <br />Roaring Fork River, Runofffrom the north side of the mountain flows through the City on its way <br />to the Roaring Fork River, The River then empties into the Colorado River, <br />The selected study area is bounded on the north by the Roaring Fork River, on the west by the <br />drainage boundary of Castle Creek, and on the east .and south by the drainage basins on Aspen <br />Mountain tributary to the City, The 2.5 square mile study area for this project includes the Spar, <br />Pioneer, Vallejo, and Copper Gulches to the south, The study area also includes that portion of the <br />City of Aspen that is bounded by the Roaring Fork River to the north and Castle Creek to the west, <br />Surface runoff from the study area generally travels to the north and outfalls into the Roaring Fork <br />River, <br /> <br />WRC used stonn sewer infonnation, field data, and topographic mapping to subdivide the study <br />area into 25 sub-basins. The largest sub-watershed size is 248 acres (Spar Gulch) and the smallest <br />is 9.5 acres (Sub-basin 10 which flows directly into the Roaring Fork River), The sub-basin <br />delineations are presented in Figures I through 4, <br /> <br />The mountain sub-basins that drain into the City are divided into Pioneer Gulch, Lower Spar <br />Gulch, Upper Spar Gulch, Vallejo Gulch, and Copper Gulch (designated by WRC as Sub-basins <br />21, 14,23, 16, and 22, respectively), <br />