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III IIIIIIIIIIIII III <br />STATE OF COLORP~9UU <br />DIVISION OF MINERALS AND GEOLOGY <br />Dcpunmem ni Natural Resources <br />l i l t Sherman SL. Rrnlm 215 +tl` <br /> <br />Denver. (-ulorado NOZO.} I <br />~ <br />Y <br />Phone: (111}( Nhh-}Sh7 III <br />Fi\%: l 311}1 N}LNI Ilh <br /> DEPARTMENT OF <br /> NATURAL <br /> RESOURCES <br /> Ruy Romer <br /> Governor <br />December 30, 1997 lames s. wrnhead <br /> Execmive Direanr <br /> <br />Mr. Larry Reschke Michael N. long <br />i <br />i <br /> v <br />sion Duector <br />D <br />Powderhorn Coal Company <br />P.O. Box 1430 <br />Palisade, CO 8 (526 <br />RE: Roadside Portals (Permit No. C-81-041) <br />Technical Revision No. 24 <br />Dear Mr. Reschke: <br />The Division has reviewed the revised ditch designs which were received from Powderhotn on <br />December 19, 1997. Please note that our records indicate this is TR-24. It was submitted as <br />TR-23. TR-23 was the revision dealing with change of ownership which was withdrawn. I am <br />forwarding our remaining technical adequacy comments to you since Dan Mathews is out of the <br />office this week. If responses prepared before January 5, 1998, I would suggest they be sent to <br />me at the Denver office in order to expedite review of the revision. Dan will be back in the <br />Grand Junction office next week. <br />We agree that the ditch segments with vegetative lining which you pointed out were due <br />to cheat grass are more appropriately described by another stability class in the SedCad <br />model. The model indicates that those ditch segments will adequately handle design flow <br />events. <br />2. In the previous channel designs a curve number of 89 was used representing a "D" soil <br />group and soil type of Persayo-Badland-Chipeta. (n the most recent submittal a curve <br />number of 83 was used. Please inform the Division as to why a different curve number <br />was used in the runoff calculation for the permanent diversion ditch above CRDA-2, or <br />revise the model using a curve number factor of 89. <br />3. Powderhom designed the same channel using a 5.5 fps maximum velocity, which is based <br />on material classified as graded silts to cobbles when colloidal. According to the text <br />titled, Design Hydrolow and Sedimentology for Small Catchments, by C.T. Hann, B.J. <br />Barfield, and J.C. Hayes, a limiting velocity for this material is 4.0 fps for clear water and <br />5.5 fps for sediment laden water. <br />