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<br />Flood water surface elevations and floodplain boundaries are often revised by <br />road and bridge construction, floodplain development, flood control improvements, <br />or natural process. Prior to util ization of this report for planning or design <br />purposes, the user is advised to contact the Urban Drainage and Flood Control <br />District, the City of Boulder, and Boulder County to determine if the information <br />in this report has been amended. <br /> <br />Skunk Canyon Creek <br /> <br />BASIN DESCRIPTIONS <br /> <br />The Skunk Canyon Creek drainage basin originates in the Flatirons southwest <br />of Boulder and drains to the northeast a distance of about 2 mi les. The <br />undeveloped portion of the basin which exists in the mountains is steep, narrow <br />and rocky. As the drainage enters and crosses the Boulder City limits, the basin <br />becomes less steep in slope, and wider. Skunk Creek flows into Bear Canyon Creek <br />2000 feet south of the confluence of Bear Canyon Creek and Boulder Creek. <br /> <br />The major drainage basin and sub-basin boundaries along with their respective <br />drainage areas, are shown on Sheets 2 and 3 in the Appendix. A description of <br />each basin is presented below. <br /> <br />Bear Canyon Creek <br /> <br />Skunk Canyon Creek flows notheast from the Flatirons past Kohler Reservoir. <br />The stream channel is 10"to 12 feet high and very rocky. Stream banks rise <br />from the channel at 2:1 side slopes. Downstream, the creet flows through <br />Green Mountain Cemetery. The Creek banks within this reach are grass or <br />rip-rapped, and range in height from 2 to 5 feet. The width of the channel <br />ranges from 5 to 10 feet. As the creek leaves the cemetery, it crosses the <br />Anderson Extension Ditch. <br /> <br />Bear Canyon Creek drainage basin is the southernmost region of the study area. <br />Its overall length is about 5 miles. The source of the creek is near Koss1er <br />Lake. The drainage basin is rugged, steep and narrow as the creek drains Boulder <br />Mountain and its surrounding areas. As it leaves the Foothills, the creek flows <br />to the south of the National Center for Atmospheric Research. <br /> <br />Near Table Mesa Drive and Lehigh Street the basin enters residential and <br />commercially developed areas. As the stream crosses the southern line of the <br />City of Boulder, the basin remains highly developed. North of the Empson Ditch, <br />the basin is again undeveloped. The slope of the land is gradual, and the <br />vegetation is dense with native grasses and weeds. <br /> <br />Northeast of the ditch, the creek approaches developed residential and commercial <br />areas. The creek crosses Highway 36 at Baseline Road. Within the developed <br />areas of the basin the channel is natural with 4 foot banks at approximately a <br />2:1 side slope. The channel reflects the basin conditions as it approaches its <br />confluence with Bear Creek. Under a smaller gradient, the channel is wide and <br />sha 11 ow. <br /> <br />Bluebell Canyon Creek <br /> <br />The stream channel within the upstream reaches of the Bear Canyon Creek drainage <br />basin reflects the characteristics of the basin. The creek bed at Bear Mountain <br />Drive and Wildwood Road is very rocky with 10 to 12 foot banks, with 3:1 side <br />slopes. As the channel enters the developed reaches of the basin, it becomes <br />more defined. From Table Mesa Drive and Ithaca to Table Mesa Drive and Broadway, <br />there are several drop structures and culverts. The stream channel is grass1ined <br />approximately six feet wide with 2:1 side slopes. As the creek approaches its <br />confluence with Boulder Creek, the channel becomes wide and shallow. <br /> <br />Bluebell Canyon Creek also drains east from the Boulder Flatirons. The overall <br />length of the basin is about 1.8 miles. Approximately hal f of this distance is <br />within"B1uebel1 Canyon, which is undeveloped. In this portion of the basin, the <br />channel is steep, rocky and. well defined. The lower half of the basin is located <br />in fully developed residential areas. Again, the drainage channel is all but <br />obliterated by development. The channel enters this portion of the basin at 15th <br />Street. A small ditch carries trickle flows eastward along the backyard property <br />1 ines between r~ariposa and Columbine Avenues. The drainage flows directly into <br />the Anderson Extension Ditch at 20th Street. During a storm event, the creek <br /> <br />'2 <br />