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.; <br />iiiiiiiiiiiiiiiiiii <br />COAL <br />COMPANY <br />August 20, 1993 <br />Ms. Janet Binns <br />Reclamation Specialist <br />Colorado Division of Minerals and Geology <br />215 Centennial Building <br />1313 Sherman Street <br />Denver, Colorado 80203 <br />RE: Permit C-81-019 <br />Colowyo Coal Company <br />Postmininq Topography <br />Additional Info., W. <br />Designs <br />Dear Janet: <br />5731 State Highway 13 <br />Meeker, Colorado 81641 <br />(303) 824-4451 <br />f'I=GElVEC <br />auc 2 s 1693 <br />Die,.g,c~~ c~~ F~~,neri; n uec..,9Y <br />Changes, T.R. 22 <br />Tributary to Streeter Channel <br />The purpose of this letter is to address item #2 of the <br />Division's August 4, 1993 letter requesting additional information <br />with respect to T.R. 22. <br />The Division has concerns regarding the channel designs <br />for the "West Tributary to Streeter" channel. Juan Garcia <br />completed a review of the drainage area in question based upon a 10 <br />year/24 hour storm event. The attached SEDCAD design titled "west <br />Tributary to Streeter Permanent Channel Watershed l0 Yr. Hydrology" <br />summarizes his findings. J. Garcia found that for this scenario <br />utilizing an interim reclamation C.N. of 61, the peak discharge <br />would be .48 cfs. For such a small discharge, a rock-lined ditch <br />would not be necessary due to a limited estimated velocity of 2.94 <br />fps. Additionally, as it is our intention to build a rock-lined <br />ditch anyway, the resultant ditch design resulting from this <br />scenario was too small (3.5 ft. top-width, .37 depth) for Colowyo <br />to consider building. <br />In order to obtain a ditch design more appropriate for <br />Colowyo to construct given our equipment and rock materials <br />available, J. Garcia ran a scenario using the 100 year/24 hour <br />storm event in a rock-lined channel. The attached SEDCAD design <br />titled "West Tributary to Streeter Permanent Channel Watershed 100 <br />Yr. Hydrology" summarizes his findings. Based upon a predicted <br />discharge of 13.18 cfs. from such an event, the program does <br />provide a more appropriate channel design for a ditch utilizing a <br />top width of 10.59 feet and depth of .65 feet. Colowyo will <br />utilize this configuration as the general design for the ditch. <br />