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`` I V <br /> �. <br /> Harry Ranney <br /> Mine Land Reclamation Division 4AR 0 2 799t- <br /> Department of Natural Resources Mined <br /> 1313 Sherman St., Room 215 j Land <br /> Denver CO 80203 <br /> February 25, 1992 <br /> RE: Amendment to Technical Revision 04 - Mine Drainage - C-81-035, Riprap Design for <br /> Eastside Drainage, National King Coal Mine. <br /> Dear Mr. Ranney, <br /> I have evaluated the hydraulics of the Eastside Channel and concur that erosion could be a <br /> problem. Based on our discussion I have prepared a riprap design for reach 1, as designated <br /> on figure 1 of the TR dated September 1991. The sizing of riprap was completed using two <br /> methods. The first is a stability analysis technique proposed by Simons and Sunturk (see <br /> attached worksheet), the second is a procedure used by the Colorado Department of <br /> Highways and outlined in "Roadway Design Manual" 1990. The results are as follows. <br /> Simons and Sunturk: bed d50 = 12 inches <br /> bank d50 = 18 inches <br /> Colo. Dept of Highways: bed dso = 10 inches <br /> bank dso = 14 inches <br /> As you can see the CDH technique results in a slightly lower d50 that the Simons and <br /> Sunturk method. Based on these results I recommend a bed d50 = 12 inches and a bank dso <br /> = 14-18 inches. These sizes are based on a side slope of 2:1 which is a recommended <br /> minimum for scouring channels. The gradation for the riprap mixture should be as indicated <br /> below. <br /> size (in) dio dzo d3o d40 dso deo d70 dso d90 dioo <br /> d50=12, 14' S 7 9 11 14 16 19 21 25 26 <br /> d5o=18" 7 9 12 14 18 21 24 1 27 1 32 36 <br />