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III IIIIIIIIIIIIIIII <br />999 <br />STATE OF COLORADO <br />DIV1510N OF MINERALS AND GEOLOGY <br />Deparlmenl of Natural Resources <br />1373 Sherman 51., Room ?IS <br />Denver, Colorado 80203 <br />Phone: 13031 R6fi-3567 <br />FAX: 1301) A3? R106 <br />DATE: <br />TO: <br />FROM: <br />RE: <br />September 12, 1997 <br />Dan Mathews '~ <br />Erica Crosby ~~ <br />Roadside Portals (C-81-041) <br />Roadside Field Ditch Dimensions using SEDCAD <br />R <br />6 <br />DEPARTMENT OI <br />NATURAL- <br />RESOURCE~r <br />Roy Romer <br />Governor <br />lames S Lochhead <br />Pecw rve Director <br />Michael B Long <br />Drvi•ion Duector <br />Dan, l reviewed the refuse pile ditch measurements you took at Roadside Mine. I compared the <br />designs to what is in the permit and used SEDCAD to verify if the ditches could handle the <br />designed flow. Attached are the SEDCAD printouts. In summary; <br />CRDA #2 East Ditch J-J-designed for 100-yr/24-hr storm event 28.6 cfs <br />-Ditch measurements (DM) # 1, #2, and #3 all contain rip-rap material DSO 12". Using <br />your dimensions, SEDCAD calculated a required DSO of 6". The ditches in place are <br />adequate. <br />? N~e~ { <br />„r <br />-DM #4 does not contain rip-rap. SEDCAD estimates that the ditch ill not carry he ~ w ~~ 1~ ~ <br />designed flow, and will be erosive without rip-rap. The operator should insta e <br />required rip-rap in this portion of the ditch. 1~ AS ~~~t r <br />CRDA #2 West Ditch J-J- designed for 100-yr/24-hr storm event 27.6 cfs. '^~ <br />6;c n~~,K,,~~~. <br />wow ~! K1 <br />-DM #5 and #6 contain riprap material DSO 12". lJsing your dimensions, SEDCAD <br />calculated a required DSO of 6". The ditch in place is adequate <br />~ oin~(, not e<(e~ti4{p <br />CRDA #2 UQper Diversion designed for 100-yr/24-hr storm event 75 cfs. S ° ` ©'`f"'t <br />-DM#7, #8, #9 and #10 are not lined with rock. The bottom of the channel consists of <br />rocky soil. The channel will carry the designed flow,~but will be erosive. The estimated <br />velocity of the design in the channel is over 6 fps. The average velocity exceeds the <br />perntissible velocity established at 5 fps. The channel can be protected by erosion if it is <br />vegetated. The operator should vegetate the channel to protect it from erosion or use <br />some other form of channel lining. / <br />~ dM !~ 8 ^ia'Ziw/ <br />see e„:~t~., f <br />