1987-12-01_PERMIT FILE - C1981017 ‎(111)‎

• Permit No: C1981017
• IBM Index Class Name: PERMIT FILE
• Doc Date: 12/1/1987
• Doc Name: Morrison Knudsen Haul Road Drainage Control Plan
• Section_Exhibit Name: Chapter II Attachment 2 to Appendix II-B-7
• Media Type: D
• Archive: No

L3) 0.385
H
Where L is the channel length in miles,
H is the elevation difference in feet, and
Tc is the time of concentration in hours.
it
�. The minimum time of concentration used in the studies was 15 minutes
i which was adopted as the minimum amount of time necessary for the
water to percolate through the shallow soil mantle and travel to the
point of concentration at each culvert.
Peak runoff rates in cubic feet per second (cfs) per square mile of
drainage area per inch of runoff were obtained from Figure S-1 in
Reference 4, using a Type II (Western Colorado) storm distribution
i
for each time of concentration. The design value of discharge for
each culvert was then computed as the product of runoff value, peak
t runoff rate per square mile and the tributary drainage area for each
culvert.
t .
Table 2 shows the computation of the peak discharges and culvert
capacities for the Road Systems Area drainage sub-basins.
For comparison, the peak discharges_from several of the Road Systems
Area drainage sub-basins were also computed using the method given in
1 ; 40