2
I:\11\82323\0100\0122 TM\Feb14\11382323 TM PreFeasibilityHydrologyHydraulicsRevE 13FEB14.docx
the volume of sediment equal to one inch of runoff from the entire catchment area, or 3,630 ft3/acre of
sediment (Michigan DEQ 2012).
In addition to storage for environmental flows from the pit and Basin Pt-N, the Pit Pond is also sized to
accommodate pit dewatering flows of 500 gallons per minute (gpm). The pond water and sediment
capacity is estimated using an assumed retention time (2 days) and settling velocity parameters based on
particle size.
2.3 Channel and Culvert Hydraulics
Channel sizing calculations were performed with an open channel flow spreadsheet using Manning’s
equation. Riprap sizing was performed using U.S. Army Corps of Engineers methodology (USACE,
1994). Culvert crossings were modeled using HY8 culvert analysis software (FHWA 2011).
3.0 ASSUMPTIONS
Runoff from the top of the WRF travels down the 1-percent slope to the north and south
then cascades perpendicular to the slopes, and is collected in a perimeter channel at the
toe of the facility
Haul Road culvert crossings were located based on the proposed road alignments and
topography supplied by RER
All calculations assume the following facility conditions:
Full build out of the Pit and WRF
The WRF is in a closed condition with 50-percent of the area reclaimed
The Low Grade Ore (LGO) stockpile has been processed and either been sent to the
Upton facility or added to the footprint of the WRF
All runoff from the plant site is collected for discharge to a sedimentation pond
Time of concentration for both the Plant Site and the Mineable Pit are assumed to be 10
minutes
Channel lining criteria:
Design Flow
Velocity (ft/s)
Channel
Lining Material
<5
Grass
5 – 15
Riprap
>15
Concrete, Articulated Concrete Block
Curve Numbers Used in hydrology calculations (NRCS,1986, Web Soil Survey):
Description of
Soil & Land Cover
Woods-Grass Combination,
HSG B, Fair Cover
Newly Graded Areas, HSG B
SCS Curve Number
65
86
Applicable Site Areas
Undisturbed or Reclaimed
areas
Disturbed Areas, Pit, Unreclaimed
WRF, and Plant pad
