INSPEC40802

• Permit No: M1977215
• IBM Index Class Name: Inspection
• Doc Date: 3/15/1994
• Doc Name: BULLDOG MINE HYDROLOGIC EVALUATION
• From: CANONIE ENVIRONMENTAL
• To: ENVIRONMENTAL AFFAIRS
• Media Type: D
• Archive: No

Mr. Luke Russell

March 15, 1994
channel stability evaluation described in my September 21, 1993 letter, the toe of the
waste dump itself should not be directly impacted from this runoff, given the average
rock size. However, portions of the Windy Gulch channel may require some upgrading
to minimize headcutting and potential undercutting of the dump to safely convey the
theoretical runoff from this 100-year, 24-hour event. Table 1 describes the upgrading
and riprap size requirements. Table 2 shows the riprap gradation required. This riprap
material should be available within the mine area without disturbing additional land or
developing a new quarry.
Table 1
~Jllindy Gulch Design Criteria

Design Flow
(cfs)

Channel
Slope (ft/ft)

Side Slope
H:V
Existing
Bottom
Width (ft)
Required
Bottom
Width Ift) Required
Maximum
Stone Size
(inches)
140 0.10 1:1 4 12 12
1:1 30 30 7
1:2 18 18 9
0.25 1:2 18 28 12
Table 2
Rpprap Gradation Requirements
Rock Size (inches) Maximum Stone Stone Weight Weight range of
Uleight (Ib) range (Ib) 75 percent of
stones (Ib)
12 125 25-125 50-125
9 100 20-100 30-100
For comparison purposes, I computed the theoretical 100-year, 24-hour runoff using
a CN of 75, as suggested by Mr. Sorenson. The resulting runoff is approximately 360
cfs. The resulting theoretical velocities in Windy Gulch indicate that up to 30 inch
angular rock riprap would be required to stabilize the channel in its narrowest locations
at the base of the waste rock dump. Table 3 shows riprap size required for a runoff
of 360 cfs.
BZ:W:\94-012\LETTERS\BULLDOG2.LTR (March 15, 19931 CanonleErivironmental