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<br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />, <br />I <br /> <br />( <br />~ <br /> <br />" <br />,:j <br />, <br /> <br />DRAFT FOR REVIEW <br /> <br />, <br /> <br />SITE PLAN LEVEL DRAINAGE REPORT <br />BOBTAIL STREET <br /> <br />INTRODUCTION <br /> <br />Bobtail Street is a new two-lane collector being constructed within the City of Black <br />Hawk (City) under the direction of the Public Works Department and is scheduled to be <br />completed in July, 1998. Bobtail Street is located upgradient and south of Main Street <br />and runs approximately parallel to Main Street. Bobtail Street connects Miners Mesa <br />Street to the east and Gregory Street to the west (Figure I). As of this writing, rough <br />grading is complete and some utilities have been installed within the right-of-way. <br /> <br />A preliminary drainage report was prepared for Bobtail Street by others in 1995 <br />(Reference I) using drainage design criteria no longer applicable in the City. The City <br />requested Love & Associates, Inc. to provide a drainage report based on the City's <br />updated drainage standards. <br /> <br />This report uses drainage requirements outlined within the City of Black Hawk Drainage <br />Checklist and the Urban Drainage and Flood Control District (UDFCD) Urban Stonn <br />Drainage Criteria Manual (USDCM). Base topographic mapping used for the study is <br />1994 aerial topographic mapping of the City of Black Hawk (Reference 2) in CAD <br />format. <br /> <br />HYDROLOGY - HISTORIC LAND USE <br /> <br />Drainage basins intersected by Bobtail Street drain generally to the north towards North <br />Clear Creek. These basins are mostly undeveloped upgradient of Bobtail Street. The <br />basins are steep and overlain by rock outcrops, forest, and meadows commonly found in <br />mountainous terrain. The native hydrologic characteristics of the basins have been <br />impacted by historic mining activities. Abandoned mines, including spoil piles and mine <br />portals, can affect drainage flow paths and soil characteristics. Extensive development <br />has occurred within the area downgradient of Bobtail Street between Bobtail Street and <br />North Clear Creek. This area does not have a unified plan for stonnwater control. <br /> <br />Historic drainage basins tributary to Bobtail Street are designated with the letter "B" and <br />are delineated on Map I. Basins Bl through B6 are tributary to Bobtail Street. <br />Individual drainage basins upgradient of Bobtail Street range in area between <br />approximately 3 to 70 acres. Two of the basins, Basins B I and B3, have defined <br />channels. The remaining basins, including basins B2, B4, B5, and B6, do not have <br />concentrated discharge points and have historically discharged at multiple locations or <br />sheet-flowed onto the properties downstream of the location of the Street. <br />