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• ~G <br />STAT~OF COl ~~~ ~~~~~~~~~~~~~~~~ <br />MINED LAND RECLAMATION DIVISION <br />Department of Natural Resources <br />1313 Sherman St.. Room 215 <br />Denver, CO 60203 <br />303 866-3567 <br />FA X: 303 632-8106 <br />July 24, 1991 <br />Mr. Bill Agnew <br />Trapper Mining, Inc. <br />P,O. Box 187 <br />Craig, CO 81626 <br />Re: Technical Revision 55 -Johnson Pond Spillways - C-81-010 <br />Dear Mr.. Agnew: <br />OF Cp~ <br />~~~-- A7 <br />„~~ <br />., ; i~'Ir o t <br />Roy Romer, <br />Governor <br />Fretl R. Banta, <br />Division Director <br />We have reviewed the submittal dated July 10, 1991, which presents spillway <br />designs for the Johnson Ponds 9D and IOB. It appears that the proposed <br />Johnson Pond 9D spillway system is undersized. Revised plans must be <br />submitted. The proposed Johnson Pond lOB spillway plans are adequate. <br />Our analysis was based upon the previously approved discharge values for the <br />Johnson Ponds. Specifically, the 10 year, 24 hour, and 25 year, 24 hour peak <br />discharge values for Johnson Pond 9D are 103 cubic feet per second (c.f.s.), <br />and 259 c.f.s, respectively. We applied Mannings equation and assumed an n <br />value of 0.015 (concrete) for the spillway channel. The proposed Johnson 9D <br />primary spillway will only pass about 40 c.f.s., and the combined spillway <br />will pass the entire 25 year, 24 hour peak flow,. but with only 0.3 feet of <br />freeboard. <br />Please submit a revised spillway design <br />retain the previously approved spillway <br />necessary 1.0 foot freeboard above the <br />for Johnson Pond 9D. Be sure to <br />elevations, and incorporate the <br />25 year, 24 hour peak floor. <br />Please call with any questions. <br />Si nce~ly~'~ <br />~~ <br />~ ~/ ~ <br />avid A. Berry <br />Senior Reclamation Specialist <br />DAB/lac <br />CC: Kent Gorham <br />7203E <br />