PERMFILE104577

• Permit No: C1981026
• IBM Index Class Name: Permit File
• Doc Date: 12/11/2001
• Doc Name: GENERAL DESCRIPTION OF HYDROLOGY AND GEOLOGY
• Section_Exhibit Name: APPENDIX C - PART 3 OF 3
• Media Type: D
• Archive: No

Substituting the appropriate regression constants and coefficients
•
for the mountain region yields the following set of equasions:
0.815 1.592
Q = 0-12A P
10
0.795 1.110
Q = 9.91A P
50
for 10-year storm
for 50-year storm
0.787 0.932
Q = 1.88A P
10
where Q - flood discharge in CFS
for 100-year storm
A = drainage area in sq. mi.
P = mean annual precipitation in inches
•

•
In our analysis, a drainage basin size of 1.7 sq. miles is
utilized. In Lieu of using generalized state-wide precipitation
maps, more specific precipitation data collected by Wyoming
Fuel Co. for the Walden area was utilized. This data shows
an average annual precipitation for the mine site of 11 inches
per year. Incorporating these parameters into the above
equasions and solving for Qt yields discharges for the 10, 50
and 100 year precipitation events as follows:
Frequency of
Precipitation Events
10 yr. storm
50 yr. storm
100 yr. storm
Estimated P1arimum
Discharge
8.41 cfs
19.86
26.67
These numbers vary slightly (less than 1%) from those initially
presented in the permit. This slight variance results from the
graphical technique initially utilized to establish these
parameters.