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I I I I I I I I , I I I I I . I I I I Topographic mapping, digitized cross sections, and survey data for stream crossings were provided by Reids Aerial Mapping, Additional data for bridge crossings was supplied by Boulder County and the COE, The mapping was prepared according to specifications of the Urban Drainage and Flood Control District. Ground control surveys for the topographic mapping were performed by Reids Aerial Mapping and Mil1er-Ernstsen and Associates. Topographic mapping was prepared with two-foot contour intervals at a scale of 1" = 100' (Reference 1). For inclusion in this report, the final mapping was reduced by 50-percent. Descriptions of the monument and benchmark locations and elevations used to develop the topography were obtained from Boulder County and are shown in Table 1. The hydrologic and preliminary hydraulic analyses were completed by the U.S. Army Corps of Engineers, Omaha District, Final hydraulic an~lyses and floodplain delineations were completed by Greenhorne and O'Mara, Inc. - BASIN DESCRIPTION - Genera 1 South Boulder Creek, which drains an area of 13Z square miles, is a right bank tributary of Boulder Creek (Figure 1). From its headwaters at the Continental Divide, South Boulder Creek flows in an easterly direction through relatively steep, narrow mountain canyons for nearly 22 miles whereupon it emerges onto the hi gh p1 a i ns at E1 dorado Spri ngs, Colorado. From E1 dorado Spri ngs, the creek flows northeasterly through a moderately wide valley over a distance of about 9.7 miles to its confluence with Boulder Creek. Gross Reservoir is a water storage facility located on South Boulder Creek approximately 3.5 miles upstream of E1dorado Springs. The reservoir was con- structed in 1955 and has a storage capac ity of 43,000 ac re- feet. The reservoi r is operated by the Denver Water Department and provides conservation storage for municipal use. A U.S. Geological Survey stream gaging station is situated approximately 6.7 miles downstream of the reservoir. The drainage area at the gaging station is about 109 square miles. TABLE 1 BENCHMARK/MONUMENT DESCRIPTIONS Monument No. Description Elevation 1 South Side of State Park Admission Gate Shack 5602.64 2 1/2 Mile East of State Park, South Side 5617.75 Road, Cap in Rock 50' East of Western Slope Gas Shed 3 On Southeasterly Corner Bridge Abutment/Headwall 5608,59 300~ West of W. Prado Dr. on South Side Road 4 Senda Rocosa @ E1dorado Springs Intersection 5530.39 South Side of E1dorado Springs Road Along Fence 5 SW Abutment/Headwa 11 Corner of Sta te Hi ghway 5452.02 Bridge E-15-A. West Side of #93 S.H. 93 6 Behind Guardrail North Side of Trailer Park 5484.52 Road on West Side of S,H. 93 7 South Side of South Boulder Road @ S. Boulder 5338.36 Creek in S.W. Wingwa11 of Bridge 8 On Denver/Boulder Turnpike @ S. Boulder Creek 5369,92 on SE Wingwa11 of Bridge 9 On South Boulder Road West of Cherryva1e North 5351.53 Side of Road. @ West End of (Fence Taper) 10 On South Boulder Road on Northeasterly Corner 5339.05 Abutment/Headwall N. Side of Road 500+ East of Manhatten Drive 11 On East Side of Cherryva1e (along fence line) 5283.24 0.2 Mile South of Baseline Road 12 On North Side Baseline Road @ Meadow Glen Dr. 5282.97 in Tip of Concrete Median Strip 13 S.E. Corner Baseline, Dimmit Dr. Cherryva1e 5272.92 Intersection in Front of Fence 14 East Side of Cherryva1e 0.1 Mile South of 5255.75 McSorley Lane Between Pole and Fence 15 NE Corner Area of NE Wingwall Bridge Crossing 5256.49 55th - 300' ~ North Pennsylvania 16 East Side of 55th North of Arapahoe and Just 5220.02 North of C&S Railroad Crossing On Dry Creek No. 2 Ditch 2