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,~ <br />III IIIIIIIIIIIII III <br />999 <br />STATE OF COLORADO <br />DIVISION OF MINERALS AND GEOLOGY <br />Department of Natural Resources <br />1313 Sherman 51.. Room 215 <br />Denver, CO 80203 <br />Phone: 13031 866-3567 <br />FAX: (303) 8328106 <br />DATE: September 9, 1993 <br />TO: Erica Crosby <br />Larry Routten <br />FROM: David Berry <br />RE: GEC/West Pit Channel Work <br />pF tOyp <br />~~ b <br />~~ / <br />0 <br />• ~ r8T6 ~' <br />Roy Romer <br />Governor <br />Michael B. Long <br />Division Director <br />I have reviewed the survey information given to me today, for the channel <br />transition areas located near the West Pit sediment pond. Specifically, I have <br />proposed a design for the anticipated channel junction which will result when the <br />native channel to the west of the West Pit is joined with the West Pit channel <br />above the currently existing pond. The same design applies to the transition area <br />located between the current pond location and the Magpie Diversion. <br />I have designed these sections for an estimated 100 year, 24 hour peak flow of <br />approximately 150 cubic feet per second (cfs1. This was derived using the STORM <br />program, with the following input numbers: <br />Precip = 3.8 inches <br />Avg. CN = 73 <br />Acreage = 443 (Rockvale Quad) <br />Length of basin = 12,530 ft. <br />Change in elevation= 1,500 ft. <br />This should be a conservative estimate of the peak flow. <br />Riprap is recommended at both transition areas, for total lengths of about 100 feet <br />at the top area, and about 175 feet at the Magpie transition area. <br />Channel and riprap calculations were estimated using the Oklahoma Technical <br />Press and SEDCAD programs. <br />