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JD -6 Mine Drainage Design — Revised Third Adequacy Review <br />Page 2 <br />April 2, 2014 <br />5. Page 7, section 2.3.4: <br />a. Please provide criteria for the referenced evaluation... The provided response is <br />inadequate. The response cites the Urban Drainage and Flood Control Manual <br />stating that stable conditions are met if the velocity is 7 ft /s or the Froude No. is <br />0.8. This is incorrect. The referenced manual requires the velocity < 7 ft/s and <br />Froude No. < 0.8. Please also note that the Urban Drainage Manual criteria cited <br />are for grass -lined channels. The Urban Drainage does not address channel <br />design for earth -lined channels. The summary of results on pages 36 -37, in Table <br />20 show all but two channel segments with Fr > 0.8 and most greater than 1.0. <br />The DRMS requires channel protection for channel velocities that exceed five feet <br />per second under design flow conditions. Alternatively, if the Operator wishes to <br />pursue the "cobble and boulder substrate" material as stable, then analyses based <br />on incipient motion, tractive force, and critical shear stress should be provided <br />along with appropriate laboratory test showing channel substrate gradation. There <br />are several published methods that can be used to evaluate this approach. The <br />DRMS would require at least three of these methods demonstrate stable channels <br />(for each reach with a different 100 -year peak design flow and/or channel slope) <br />and that a consistent channel geometry is, or will be present. Please provide the <br />requisite designs and analyses. <br />b. Please clarify ... "channel protection "... The provided response is inadequate. <br />Based on the DRMS Comment 5a above and the results shown in Table 20 of the <br />DDP (pp. 36 -37), only section LDS -E -P3 has a Froude No. less than 0.8. Please <br />re- evaluate the Table 20 channel sections based on Comment 5a and respond to <br />the original comment related to "if revetment is to be placed in existing channels, <br />how will the reduction in conveyance capacity be addressed ?" <br />c. The fourth bullet states... The response is adequate. <br />d. There is no reference to design drawings... The response is adequate. <br />e. The last paragraph discusses using "gravel mulch "... The response is adequate. <br />6. Page 11, Figure 1. The response is adequate. <br />7. Page 13, Figure 2. The response is adequate. <br />8. Page 16, Table 10. No response required <br />9. Page 16, Section 4.5.1. The response is adequate. <br />10. Page 24, Section 5.2 and Channel Geometry Tables... <br />a. Please confirm channels have a minimum design /constructed depth... The <br />provided response is inadequate. The original comment to provide a summary of <br />minimum constructed channel depths does not appear to have been met. A review <br />of the revised Tables 12 and 13 shows a significant variation in channel <br />conveyance (i.e., area with 0.5 ft of freeboard) for those sections surveyed. <br />Comparing MDS conveyance data shows a factor of —4 between MDS -P1 and <br />MDS -P3, and comparing LDS -N -PS with LDS -N -P6 shows a factor of 8 in <br />conveyance with 0.5 feet of freeboard. In addition, the local longitudinal slope <br />varies from 3.56% to 13.76% in the MDS and 4.07% to 12.76% in the LDS -N. <br />Given this large variability in the hydraulic parameters, the DRMS believes the <br />m \min \tc1 \_uranium \m -77 -310 jd -6\m -77- 310_ 3rdstrmwtrcmnts _mem02apr14crtdhdr.docx <br />