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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 />1 <br />I <br />I <br />I <br />I <br />:I <br />I <br />I <br />I <br /> <br />BOBTAIL STREET HYDROLOGY AND HYDRAULICS <br /> <br />Drainage Control Alternatives <br /> <br />Construction of drainage conveyance facilities for Bobtail Street are constrained by <br />available right-of-way, existing and soon to be installed utilities in the street, steep street <br />slopes, and existing development downgradient of the street. Many of the drainage <br />design solutions discussed in this section will require the acquisition of additional right- <br />of-way or drainage easements. <br /> <br />A variety of alternatives for drainage and sediment control along Bobtail Street were <br />evaluated in this study. These alternatives and the constraints of each alternative are <br />summarized below. <br /> <br />1. Widen the street or modify its cross section to convey additional storrnwater. <br />Constraints include acquiring additional right-of-way and construction timetable. <br />2. Install stonn sewers and culverts in the Street. Constraints include acquiring <br />additional right-of-way, utilities installed or soon to be installed in the Street, and <br />existing development downgradient of the street which limits the location of <br />storrnwater discharge points. <br />3. Install storrn sewers along top of highwall to capture storrnwater flows before they <br />enter the Street. Constraints include acquiring additional right-of-way, highwall <br />stability, maintenance access, and identifying release points for storrnwater discharge. <br />4. Install slotted drains to capture nuisance flows. <br />5. Provide stonnwater detention basins upstream of the Street. Constraints include <br />acquiring additional right-of-way, steep slopes which limit detention volumes, lack of <br />drainage master plans, and maintenance access. <br />6. Maintain historic sheet flows. Constraints include modifications of historic flow <br />paths and discharge points by proposed. grading and street construction and <br />uncontrolled stonnwater flowing over the highwall affecting highwall stability, and <br />potential for damage claims by downstream properties caused by changes to historic <br />discharge patterns. <br />7. Install debris capture basins upstream of the Street. Constraints include acquiring <br />additional right-of-way and maintenance access. <br />8. Move or redesign the street. Constraints include existing grading, acquiring <br />additional right-of-way, and construction timetable. <br /> <br />Methodology <br /> <br />Based on the most recent profile of Bobtail Street, the historic drainage basins shown on <br />Map I were subdivided into design basins which are shown on Map 2. The design basin <br />delineation incorporates such items as storrnwater conveyance by Bobtail Street, <br />proposed or future construction of stonnwater conveyance facilities, and proposed or <br />probable development activities based on drainage reports submitted to the City. <br /> <br />9 <br />