2012-05-11_PERMIT FILE - C1981033 ‎(4)‎

• Permit No: C1981033
• IBM Index Class Name: Permit File
• Doc Date: 5/11/2012
• Section_Exhibit Name: EXHIBIT 11 DRAINAGE AND SEDIMENT CONTROL PLAN
• Media Type: D
• Archive: No

EXHIBIT 11
• DRAINAGE AND SEDIMENTATION CONTROL PLAN
STORM EVENTS
10 YEAR 24 HOUR EVENT 2.0 INCHES
25 YEAR 24 HOUR EVENT 2.4 INCHES
100 YEAR 24 HOUR EVENT 2.8 INCHES
The run-off calculations presented below are calculated based
on the manual - Procedures for Determining Peak Flows in
Colorado - published by the Soil Conservation Service March
1984.
The drainage areas are shown on Drawing EXH 11 - 1.
The area south of Areas 1, 2, 3 & 7 is covered with dense oak
brush. It is estimated that the oak brush has a vegetative
cover of over 75$. This estimate is based on visual
observations and a study of a similar area made for Somerset
Mining Company by Resource Development Corp. dated 4/26/90.
Oak brush with a 75$ vegetative cover has a curve number
of 46. There is no run-off from the 10 year or 25 year
events from an area with a curve number of 46 therefore, the
area south of Areas 1, 2, 3 & 7 has no effect on the following
run-off calculations.
The southern boundaries of areas 1, 2, 3 & 7 were established
by viewing an aerial photo to determine where the dense
• vegetation line exists.
CURVE NUMBERS
The vegetation of the drainage area varies from bare
gravel roads, to coal stockpiles, to a stand of aspen,
to a revegetated grassland area. It is estimated that 1/2
of the area is bare ground which would have a curve
number of 87 with a hydrologic soil group C. The
other 1/2 of the area has vegetation that is estimated
to have 40$ cover which yields a curve number of 77.
The weighted average curve number for the area is 82.
FLOW CAPACITY CALCULATIONS
The flow capacity of the culverts is taken from a nomograph
contained in the Handbook of Steel Drainage & Highway
Construction Products.
The flow capacities of the earth and concrete ditches are
calculated using Mannings Equation.
•
11-1 Rev. 02-15-94