HYDRO30435

• Permit No: C1981041
• IBM Index Class Name: Hydrology
• Doc Date: 9/12/1997
• Doc Name: ROADSIDE PORTALS C-81-041 ROADSIDE FIELD DITCH DIMENSIONS USING SEDCAD
• From: DMG
• To: DAN MATHEWS
• Permit Index Doc Type: CORRESPONDENCE
• Media Type: D
• Archive: No

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STATE OF COLORADO
DIVISION OF MINERALS AND GEOLOGY
Depanmenl of Nalu rat Resources ~~~~
I l I J 7herman 51., Rnom 21 5
Denver, Colorado 8020]
Phone:13031 Rfib-3iG7
FAX IJOA R32-RIOfi
DEPARTMENT OF
NATURAL
RESOURCES
Roy Romer
Governor
DATE: September 12, 1997 lames 5. Euchhead
Evecmne Dvecmr
TO: ~ Dan Mathews m~chael B. Long
Division Director
FROM: Erica Crosby ~~
RE: Roadside Portals (C-81-041)
Roadside Field Ditch Dimensions using SEDCAD
Dan, l reviewed the refuse pile ditch measurements you took at Roadside Mine. I compazed the
designs to what is in the permit and used SEDCAD to verify if the ditches could handle the
designed flow. Attached aze the SEDCAD printouts. In summary;
CRDA #2 East Ditch J-J- designed for 100-yr/24-hr storm event 28.6 cfs
-Ditch measurements (DM) #1, #2, and #3 all contain rip-rap material D,a 12". Using
your dimensions, SEDCAD calculated a required Dso of 6". The ditches in place aze
adequate.
-DM #4 does not contain rip-rap. SEDCAD estimates that the ditch will not carry the
designed flow, and will be erosive without rip-rap. The operator should install the
required rip-rap in this portion of the ditch.
CRDA #2 West Ditch J-J- designed for 100-yr/24-hr storm event 27.6 cfs.
-DM #5 and #6 contain riprap material Dso l2". Using your dimensions, SEDCAD
calculated a required D,o of 6". The ditch in place is adequate.
CRDA #2 Upper Diversion designed for 100-yr/24-hr storm event 75 cfs.
-DM#7, #8, #9 and # ] 0 are not lined with rock. The bottom of the channel consists of
rocky soil. The channel will carry the designed flow, but will be erosive. The estimated
velocity of the design in the channel is over 6 fps. The average velocity exceeds the
permissible velocity established at 5 fps. The channel can be protected by erosion if it is
vegetated. The operator should vegetate the channel to protect it from erosion or use
some other form of channel lining.