REV105597

• Permit No: C1981019
• IBM Index Class Name: Revision
• Doc Date: 2/20/1992
• Doc Name: COLOWYO COAL MINE PN C-81-019 MR-19 HYDROLOGIC REVIEW
• From: MLRD
• To: STEVE WATHEM
• Type & Sequence: MR19
• Media Type: D
• Archive: No

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999
MINED LAND RECLAMATION DIVISION
Department of Natural Resources
7373 Sherman St., Room 2t5
Denver, GO 80203
303 8663567
Fax: [phone]
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Roy Ramer.
Governor
Fretl R. Banta.
Divrsion D~ractor
DATE: February 20, 1992
T0: Steve Wathen
FROM: Joe Dudash D
RE: Colowyo Coal M~ne, Permit No. C-81-019, MR-19, Hydrologic Review
This review examined the question of erosive velocities at Colowyo, in
response to your telephone conversation with Juan Garcia on February 18,
1992. Juan questioned the need for riprap downstream of the MR-19 culverts at
the Gossard Loadout, even though the velocity was calcuiated to be
4.94 ft/sec. The Division would normally require riprap in a loam soil if the
velocity was above 3.5 ft./sec.
In Exhibit 7, part 6, of Volume 3, I found several examples of the
not requiring riprap in
velocities were between
in that area came from
to Map 6, soils for the
examples similar to the
riprap.
portions of the Streeter Fill Ditches even
4 and 5 ft./sec. According to Carl Mount,
the area immediately south of Streeter Fill
south area, these topsoils were also loam.
Gossard Loadout situation and where we did
Division
though the
the topsoil
According
These are
not require
Cathy Begej suggested that if those no-riprapped portions of the Streeter
Gulch Ditch are showing any downcutting, this would be evidence that what was
allowed before may not be working for the type of rainfall that has occurred.
Of course the opposite can also be true. I can only suggest that you find
someone who has seen those ditches and can remember any signs of erosion. Or
else see it for yourself.
As to the assertion in Colowyo's permit revision that the soil can withstand
water velocities up to 6.0 ft./sec without erosion, I believe they have to
submit proof. Since there is a drought going on in that area, I do not
believe recent in-the-field experience qualifies as evidence.
/ern
cc: Larry Routten
STATE OF COLORADO
1513E