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Response to DRMS Adequacy Review(2)—Cotter-9 Mine Reclamation Plan Amendment <br /> regarding velocity and the high ranges (most rough)for calculations regarding <br /> capacity. Doing this maximizes the potential need for armoring with respect to <br /> velocity and maximizes the potential need for channel oversizing with respect to <br /> capacity. Using this conservative approach, it is our professional opinion that the <br /> values originally used for Manning's "n" are well within reason and do not require <br /> recalculation. The ranges we selected were all within the maximum and minimum <br /> values shown on the Table. To reiterate our original response: our selection of <br /> Manning's "N" coefficients involves looking at a variety and range of possible <br /> values found in several reliable and respected resources such as: tables from the <br /> SCS TR-55 Manual (Urban hydrology for Small Watersheds),the National <br /> Engineering Handbook(Section 4, Hydrology), V.T. Chow(Open Channel <br /> Hydraulics), and the Mesa County Stormwater Management Manual which includes <br /> tables from many of these sources. Copies of the tables referred to here were <br /> included with the original response. The values used in the calculations are <br /> determined by comparisons of similar materials from a variety of sources and, <br /> based on experience, selecting those from the tables which most closely match <br /> the particular surfaces being evaluated. A range of values was used, as <br /> suggested, to evaluate channels for capacity and freeboard using the roughest <br /> numbers and to evaluate them for velocity and armoring requirements using the <br /> smoothest numbers. For onsite channels, existing or proposed, these values <br /> typically ranged from n=0.035 to n=0.045. For offsite channels with existing trees, <br /> brush, and large rocky material, the values ranged from 0.045 to 0.060. <br /> b. Please design...ditches with appropriate freeboard/channel design depths...The <br /> August 1, 2013 response is partially adequate. Please review the revised <br /> Attachment for additional channel segments identified by the DBMS that are <br /> not included in the analyses provided, and submit analyses for these segments. <br /> All engineered channels were designed with appropriate freeboard. The channel <br /> geometries and flow depths are shown on the details included in the drawings <br /> (Attachment 4)and on the calculation worksheets included in Attachment 2. <br /> c. Please review Attachment A...The August 1, 2013 response is partially adequate. <br /> Please review the revised Attachment for additional channel segments <br /> identified by the DRMS that are no included in the analyses provided and submit <br /> analyses for these segments. <br /> The additional channel segments identified in the review"Attachment A" have <br /> been added for analysis. Results of these analyses are included on the <br /> worksheets included in Attachment 2 of this response. <br /> 2 <br />