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III IIIIIIIIIIIIIIII <br />999 <br /> STATE OF COLORADO <br />DIVISION OF MINERALS AND GEOLOGY <br />Depanmenl of Natural Resources <br />1317 Sherman SI., Room 215 <br /> <br />Denver, Colorado 80203 ~~~~ <br />Phone. (303) 866-3567 <br />FAY. (303) 832-8106 <br /> DEPARTMENT OF <br /> ~$ <br />DATE: July 20, 1994 j~$QLJjt <br />TO: Erica Crosby R <br />oo R n <br />mer <br /> C <br />o <br /> <br />FROM: Susan Burgmaier lames S. Lochhead <br />Executive Director <br />Michael B. Long <br />RE: Hawk's Nest Reclamation Project Drvaion Dveaor <br />Drainage Control Structures <br />Per your request, I have designed the ditches for drainage control at the Hawk's Nest Loadout <br />and East Mine areas. Based on maps, photographs, and your description of the site, I <br />recommend the following ditch designs. These spectftcations are the minimum required to safely <br />convey a 100-year, 24-hour precipitation event. You can round the numbers up for a general <br />sizing requirement. <br />~~ For the ditch at the outlet of the Highway Culvert #2, East Mine: <br />~ A trapezoidal channel, bottom width of 3', top width of 10'. The ditch should be lined <br />~(;~~ with a blanket equal to the I_ANDLOK TRM 1060 mat, as we discussed with Tom Kelly <br />~~ at Bowman Construction. Please see attached specifications for that product. This design <br />is based on a ditch slope of 20%. <br />+3.. For the ditch along the railroad tracks of the Loadout, draining to the 24" culvert: <br />-t <br />IA~'tri~ngulaz channel, 1.82' depth, 7.27' top width. No lining required. This is based on <br />~~ a ditch slope of .1%. <br />s ~. ,For the ditch along the railroad tracks of the Loadout, draining to the 12" culvert: <br />,~h~~$~ A triangutar channel, 1.21' depth, 4.83' top width. No lining required. This is based on <br />~y~Q a .1% slope. <br />,.y For the ditch from the outlet of the 12" culvert, draining to the North Fork: <br />~~i~ A triangulaz channel, .89' depth, 3.56' top width. No lining required. This is based on <br />Gt~f a 1% ditch slope. <br />For the ditch from the outlet of the 24" culvert, draining to the North Fork through the <br />d a- reclaimed sedimentation pond: <br />~ih A triangular channel, 1.24' depth, 3.79' top width. The ditch should be lined with a <br />,~' blanket equal to the BonTerra C2 mat. Please see attached for product specifications. <br />This is based on a channel slope of 2%. As we discussed, for extra ProteMlon, it would <br />~~ ,q~j probably be a good idea to try to run the end of the ditch through the existing pond <br />~7••t1Y spillway rip rap. <br />If you have questions or if I can be of further assistance, let me know. <br />SLB\OTt041B.WP <br />S, <br />