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Mr. Jack Henris <br />December 1, 2016 <br />Page 2 <br />m:\min\tc1\_teller\m-1980-244 cc-v\tr-86 globehilldiv\m-80-244-tr86par2016-12-01.docx <br />likely when all the contributing area south of the diversion channel has been cleared and <br />grubbed, and the North Cresson/Globe Hill pit has not progressed to the point of <br />capturing any of the contributing area. Also, if CC&V elects to estimate the peak flow <br />using a more realistic infiltration assumption, the aforementioned conditions need to be <br />factored into the runoff estimate. <br />b. Please provide the Division with a watershed delineation map demonstrating the 74-acre <br />contributing area. <br />2) Diversion Channel / Hydraulic Design. The first paragraph under “Stormwater Design” on the <br />second page of the TR request indicates the channel is proposed to be five feet wide and two <br />feet deep, lined with clay, and armored with riprap. It is unclear as to whether the five feet is <br />the top or bottom width. The placement of riprap on top of fine clay where high flow velocity <br />is expected requires a filter layer between the clay and the riprap to prevent the clay from <br />migrating out of the base under high flow conditions. This might be a granular (e.g., Terzaghi <br />criteria) or a non-woven geotextile filter. No hydraulic analysis for the proposed channel <br />design was provided. No riprap size, sizing analysis, or gradation was provided. No details <br />were provided as to how the inlet will be designed to ensure capture of the upgradient Poverty <br />Gulch flows. No outlet energy dissipation size analyses, dimensions or details for transitioning <br />back to the natural channel were provided. Please provide the following: <br />a. Hydraulic analysis (e.g., Manning’s equation) for the channel using the appropriate peak <br />flow and justification for a selected roughness parameter; <br />b. Riprap sizing (e.g., D50 – the Division can provide some suggestions for appropriate <br />methods upon request); <br />c. Diversion outlet energy dissipation sizing analysis; <br />d. If a granular filter is proposed, please provide the appropriate analysis; <br />e. Engineering drawings showing the channel profile, plan view, typical cross-section <br />detail, inlet, and outlet details; <br />f. References to appropriate engineering specifications as approved in TR-78. If new or <br />additional specifications are required, please provide them for review and approval. <br />If you have any questions or need further information, please contact me at (303)866-3567 x8169. <br /> <br />Sincerely, <br /> <br /> <br />Timothy A. Cazier, P.E. <br />Environmental Protection Specialist <br /> <br />ec: Amy Eschberger, DRMS <br /> Elliott Russell, DRMS <br /> DRMS file <br /> Meg Burt, CC&V