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The draincge arec effected by Colowyo's coal mining operations was delinecte•~ and <br />divided into sub-basins "A" through "O" as indicated on Figure I. Hydraulic oarameier; <br />for the sub-basins were determined using procedures outlined in the USDA Soii ConserJation <br />Service National Engineering Handbook, Section 4 -Hydrology, Chapter 15 end the USBR <br />Design of Smcl! Dams, Chapter III. <br />B. Minimum Sedimentation Por,d Storage Volume <br />Totcl runcff'rom the desic•~ storm tributary to the sedimentation pond was cclculated <br />in accordance with data set `girth in Tabie S-3, SCS Procedures For Determining Peak Flows <br />in Colorado. The volume required to detain the 10-year, 24-hour precipitation evens For <br />the soeci~~ad r,ven ~-'cur.-cur perio Is ..2'_' 7_ic-rc:2t ;see r.l'Jpl'I~dix, p. 1). <br />Using the Universal Soil Loss Equation, the total accumulated sediment volume from <br />the drainage area to the sedimentation pond for athree-year period was estimated to be <br />0.52 acre-feet (see Appendix, p. 2-3). The minimum sedimentation pond storage vciume <br />required to provide adequate storage for both accumulated sediment and runoff from the <br />design storm is 4.74 acre-feet. <br />C. Inflcw Hydrograph <br />A .. - -c ..= e:,.-:tina the inf,- .~: .,.__ .~_.. ~ ... .. _ "= "~ <br />_ '. ..'.v tC 1:2n ~t°~r; per <br />24-hour design storm was determined using the Tabular Method of Determining Peak Discharge <br />discussed ~.^. Chcot_~ SCS Procedures for Determining Peak Flows in Colorado (see <br />._.,, - - <br />24-hour precipitation event is 4i .0 cfs. <br />D. DrainaSe Ditch and Structure Desi <br />Design capacities of drainage ditches and other structures were calculated using the <br />Tabular Method of Determining Peak Discharge noted above (see Appendix, p. 7-16). <br />Locations and design capacities of all ditches and other structures are shown on Figure I. <br />The design velocities in some portions of the drainage ditch system exceed 5.0 feet <br />per second. In those reaches, the use or' riprep or other suitable protective channel lining <br />material will be necessary, or one or more drops not to exceed three Feet may be used and <br />the ditch slope decreased so that velocities will not exceed 5.0 feet per second. <br />Z <br />