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• Design of Permanent Drainage Channels ~~ntinr:rirr~p <br />n <br />C`~ `` Gp0 REC~S'~i~~ <br />~` • C <br />National King Coal Mine ~~ ~• gip- <br />Hesperus, Colorado ~ ~~~~~ F~:o <br />~~!/` G 5 ~ <br />May 29, 1995 ~90~; t/,~1~~~~~4e, <br />Don R. May, P.E. _.... .''''~~~~~~7~piiMN~~`````, <br />Sco e <br />The permanent East and West Drainage Channels will consist only of open <br />channel. The existing pipe sections will be removed and replaced with ditches. The <br />design of these reaches are presented below and shown on the final reclamation <br />contour map. <br />West Channel <br />The permanent West Channel must carry a 100yr-24hr peak discharge of <br />8.2 cfs. This is the sum of flow produced by the West Basin and the yard. The <br />• yard flow must be included because the channel bisects the yard thus intercepting <br />yard flow. See the final reclamation contour map for ditch placement. <br />The West Channel consists of three parts; two steep sections near the <br />canyon mouth and a relatively flat section extending across the yard. The <br />hydraulics for each section is summarized below. Because of the high velocities <br />these reaches must be protected with arip-rap/filter blanket combination or an <br />equivalent system. The design parameters for the rip-rap are also shown below. <br />Note that the velocity and slope for reach 2 are so large that the D60 rock size is <br />30 inches. It may not be practical to construct such a small channel with such <br />large rock. An equally valid alternative would be to construct a channel out of <br />Gabions (rock filled wire basketsl, concrete or soil cement for this reach. A stilling <br />pool with a width of 6 feet and length of 10 feet should be constructed at the <br />bottom of reach 2. The pool should be filled with 9" to 20" rock to prevent <br />scouring. <br />West Channel: <br />shape -trapezoidal <br />side slopes = 2.5 horz : 1 vert <br />bottom width = 2 feet <br />freeboard depth = lfoot <br />total depth = 2 feet <br />required discharge = 8.2 cfs <br />• <br />Jame 1995 <br />