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Coal Canyon Permanent Diversion _ <br />Engineer's Certification <br />As part of the design for CRDA -2, Coal Canyon was permanently realigned to provide <br />a more uniform, controlled flow between CRDA 1 and 2 and to provide room for the <br />construction of sediment pond 10. The rock check dams constructed in the channel <br />caused significant deposition and necessitated frequent maintenance. In order to <br />assure the channel is in equilibrium with the flow regime, the rock check dams were <br />removed and the excess sediment was harvested and used as refuse cover soil. <br />During the first quarter of 2002, the channel was graded to an approximate uniform <br />grade, to the cross section presented on Exhibit 53, between the dip section concrete <br />structure at the upper end and the two 81" by 59" culverts at the lower end. <br />Cross section F-F on Exhibit 53 shows a trapezoidal channel, with a 40 foot wide <br />bottom, 2H:iV side slopes, 5.5-feet deep including freeboard. The rip-rap shown on <br />this section was placed from the dip section concrete approximately 300 feet <br />downstream to protect the embankment of sediment pond 6. The uniform grade of the <br />channel is approximately 2.5%. The flow generated by the 100-year event is 1458 or <br />965 cfs, ref. appendix 13-2 pages MISC-11 & 17. The channel depth referenced above <br />is no longer valid because the grade of the channel was increased to 2.5%. <br />The channel was constructed as designed except there is a short section where the <br />channel bottom is only about 35-feet wide. The Operator was not able to develop the <br />total width because of a rock ledge located downstream of sediment pond 6. The flow <br />depth does not vary significantly where the channel changes from 40 feet wide to 35- <br />feet wide. The flow depth is 2.2 feet and 2.4 feet for the 40 foot and 35 foot wide <br />sections respectively, a difference of only 0.2 feet (1458 cfs). See attached SEDCAD <br />calculation sheet. Based on this minor difference inflow depth, I do not be{ieve this <br />short narrow section of channel will have a noticeable impact on the channel's flow <br />characteristics. <br />I James E. Stover have inspected the reconstructed channel. To the best of my <br />knowledge and belief, the reconstructed channel meets all applicable performance <br />standards and des~n criteria presented in Snowcap Coal Company's Mining and <br />Reclamation Pe~j{9i1;~`p41. <br />L~ cL <br />to <br />19230 <br />Engineer <br />r ~a~ ~ ~~ <br />