2019-09-18_PERMIT FILE - C1981035 ‎(9)‎

• Permit No: C1981035
• IBM Index Class Name: PERMIT FILE
• Doc Date: 9/18/2019
• Doc Name: Hydrologic Designs
• Section_Exhibit Name: KI Appendix 11
• Media Type: D
• Archive: No

• sized using a normal depth, flowing full hydraulic analysis. The pipe roughness used in
the analysis is at the high end for standard corrugated metal and plastic pipe. A
backwater analysis and normal depth method were employed in sizing drainage
channels.
5.2 Yard Drainage Routed to Ponds
Reach 6 drains the west hillside drainage area. The channel is trapezoidal in shape
with a depth ranging from about 15 inches in the upper reach and over 20 inches in the
lower reach. The bottom width varies from 1 ft to 2 ft and the side slopes are generally
2:1. The channel invert slopes are approximately 0.0111 ftlft and 0.0600 ft/ft for the
upper and lower reaches respectively. The channel bottom is broken rock and dirt with a
moderate to heavy grass lining which appears to protect it from erosion. Normal depth
flow capacity is approximately 7 cfs for the upper reach and up to 60 cfs for the steep
lower reach. Critical flow will probably occur on these slopes resulting in a reduction of
the flow depth and a further increase in the channel's capacity.
A minimum design geometry for the ditch would include a trapezoidal or near
trapezoidal shape with a 1 ft bottom width, approximately 2:1 side slopes and a 1 ft.
depth. This would supply more than adequate capacity and freeboard for the design
flows. There are no signs of erosion in the existing ditch and since it has been in
operation for many years there is no need for riprap channel protection. At the bottom of
the hillslope the ditch, reach 6, is intercepted by a 24" corrugated metal pipe, reach 9,
• which is at a slope of 0.044 ft/ft. The normal depth flowing full capacity of this pipe is 21
cfs.
The upper portion of Reach 7 is an existing 36" reinforced concrete pipe, RCP,
which traverses the mine yard. It provides site drainage for portions of the mine yard. It
begins with a drain inlet located below the conveyor belt near the center of the yard and
extends to the north and terminates at an inlet across from the shower house. The lower
portion of reach 7 has two pieces. The first a 100 foot length of 24" CMP which is joined
to an 80 foot piece of black plastic corrugated pipe. It begins at the inlet where the RCP
end and it terminates in the large ditch that flows into the west sediment pond. The
flowing full capacity of the three segments of reach 7 are, upstream to downstream, 35
cfs, 27 cfs and 18 cfs. Reach 8 is a large open channel that drains reaches 6, 7, 9 and
11.
5.3 Drainage Structure Summary
A brief description of each structure is given:
Reach 1 - open channel with a minimum triangular design section two feet deep and
2:1 side slopes with a bed slope of 1 %.
~•
7
January 1998