PERMFILE139435

• Permit No: C1981019
• IBM Index Class Name: Permit File
• Doc Date: 6/14/1985
• From: MLRD
• To: COLOWYO COAL CO
• Section_Exhibit Name: Gulch A sed pond
• Media Type: D
• Archive: No

-18-
•
Mr. Richard Atkinson
May 14, 1981
Page Four
Using the disturbed area pzrcent~~pes cs listed in the preceding tabulation
weighted CS values were computed v:ith the results being:
Streeter Gulch, CS = O.G92 x 8.6?5 + 0.013 x 91.4°5 = 0.020
Gulch A, CS = 0.092 x 15.455 + 0.013 x84.6°5 = 0.025
The Adequacy Review also questioned the C factor asking ho•f~ mony diversions
were used in its camputation. In cur calculations we had used a P fector, the .
.. equivalent of the C factcr; of 1.0. This is the maximum value to ae used for this
factor and core_pona's to no diversions in the formula CR = 1 /(n+1)--.
Using the revised sediment delivery rctios and the weichted C factcr the 3-year
sediment yields have been recomputed v+ith the results es follov+s: S
Sedimentation Ponds
u
Seci„gent yield - 3 years
. ... previeusly_compu.ted (ace-feet).
Se.i.-.,ent yield - 3 years
as revised (ace-feet)
Tcyla Gulch Streeter Gulch Work
1"ributarv Gulch A Area
.0.92
1.38
1.x07 0.`? .0.52
1.66 1.17 0.62
Provided sediment
volume (aQe-feet) 1.78(1) 1 .85
(1) \Vith principal spillway elevation revised from 6938.0 to
6939.Oo No other changes needed.
(2) With principal spillway elevation revised from 6614,0 to
6615.0. No other changes needed.
1.26(2) 12.73
4. Sediment Clean-out: The Adequacy Re~rt requires that ponds have a sediment
mar.er installed at the 60;5 sediment storage volume (60'0 of the 3 year sediment
yield) elevation. 1'Je concur with this requirement and the 60',5 elevations are
as follo•++s:
Elevations
Sedimentation Pond Invert 60°5 Vo 100'-;5 Vo .
Toylor Gulch Tributary
Streeter Gulch
Gulch A
• Work Areo
Loadout Area
6935.0 6937.3 6938.4
6581.7 6583.2 6583.8
6611.0 6613.8 6614.8
7149.5 7149.7 7149.8
6381.0 6383.9 6384.7
Laodcut
Area
0.32
0.74
1.04