2008-03-03_PERMIT FILE - C2006085A ‎(4)‎

• Permit No: C2006085A
• IBM Index Class Name: Permit File
• Doc Date: 3/3/2008
• Doc Name: Drainage and Sediment Control Plan
• Section_Exhibit Name: Exhibit V
• Media Type: D
• Archive: Yes

TABLE 2
Northfield Pro'ect Ditch Desi n Summa

Ditch
Flow
Slope Side

Slope Depth

of Flow
Velocity
Freeboard Total
De th
p
Stabilization
(cfs) (%) H:1 ft (fps) (ft) ft
North
Run-on 15.90 1.0 3.0 2.21 2.38 0.3 2,51 Grass Mix
Diversion

South
Run-on 22.14 1.0 3.0 2.38 2.73 0.3 2.68 Grass Mix
Diversion

North
Run-off 6.75 2.5 3.0 1.47 2.46 0.3 1.77 Grass Mix
Collection

South
Run-off 18.19 2.5 3.0 1.84 3.71 0.3 2.14 Grass Mix
Collection
The diversion and collection ditches on the north side of the facility are designed to safely pass the
peak flow from the 10-year, 24-hour storm event. However, the diversion and collection ditches on
the south side of the facility are upgradient and downgradient of the mine waste stockpile and have
been designed to safely convey the peak flow from the 100-year, 24-hour storm event. The South
Run-on Diversion Ditch is considered to be a permanent structure. Although the South Run-off
Collection Ditch gathers flow from facility areas that do not include the waste rock stockpile, the
entire ditch was sized to convey the 100-year, 24-hour storm event in order to simplify the
conceptual ditch design and to provide a conservative design for ditch stability. The ditch
dimensions were determined using the SEDCAD4 model for channel flow and sizing. Once final
design of site facilities and grading is completed, diversion and collection ditch locations and slopes
should be verified. It is anticipated that the ditches will be grass-lined; however, armoring may be
used depending on final flow velocities. For diversion ditches routing run-off from disturbed areas,
energy dissipaters shall be used at the ditch outlets to disperse flow and decrease flow velocities.
Energy dissipaters shall be sized and stabilized with vegetative cover or armoring (rip rap or gravel),
depending upon final flow velocities. Depending upon final site design and grading, diversion and
collection ditches may also include culverts to pass flow under haul roads or other facility structures.
Culverts should be designed to safely pass the peak flow from the 10-year, 24-hour storm event.
For the North Run-off Collection Ditch to be able to discharge into the sediment pond, it will need to
be constructed on the fill of the constructed facility bench area. If the ditch was constructed at the
toe of the bench area fill, the site topography would not allow the ditch to drain into the sediment
pond. Therefore, the ditch will collect all run-off from the disturbed facility area, except for the
initially disturbed area of the bench fill slope. Following construction of the facility bench area, the
slope will be revegetated for stability and sediment control and best management practices will be
used to control run-off. Following revegetation, the slope will not be disturbed by mining activities.
All ditches associated with haul roads located inside or outside the disturbed area shall also be
designed to contain the flow from the 10-year, 24-hour storm event and control erosive velocities.
Sedimentation control measures such as rip rap and straw bales shall be installed, as needed.
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