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I:\11\82323\0100\0122 TM\Feb14\11382323 TM PreFeasibilityHydrologyHydraulicsRevE 13FEB14.docx
5.1 Proposed Stormwater Management Arrangement
A berm around the upgradient side of the Mineable Pit highwall (PIT DIV N. and PIT DIV S.) prevents
surface water flows from running into the Mineable Reserve pit during the design storm event and diverts
the stormwater north and east into the existing drainages. Perimeter channels (as assumed) carry
stormwater flows along the north and west side of the WRF to a proposed sediment trapping pond on the
north side of the WRF (Pond 1 on Figure 1). Perimeter channel (as assumed) carry stormwater flows
along the north and east side of the WRF to a proposed sediment trapping pond on the northeast corner
of the WRF (Pond 2 on Figure 1). Perimeter channels (as assumed) carry stormwater flows along the
south side of the WRF to a proposed sediment trapping pond on the southeast corner of the WRF (Pond
3 on Figure 1). Parallel diversion channels along the south and west sides of the WRF will divert the
undisturbed upper reaches of Beaver Creek along the toe of the WRF and terminate into an upper
tributary of Beaver Creek. Perimeter channels along the north and south sides of the Plant Site Pad
(labeled PD-N and PD-S, respectively) convey flow to a sediment trapping pond on the east side of the
Plant Site Pad. The following table provides a summary of the proposed diversion channels:
Reach ID
100-yr/6-hr
Peak Flow
(cfs)
Length
(ft)
Slope
(ft/ft)
Side Slope
(_H:1V)
Bottom
Width
(ft)
Depth
(ft)
Freeboard
(ft)
Left Right
WRF 1
299.8
4110
0.030 3.0
3.0
20
2.5
1.0
WRF 2a
417.1
2400
0.030 3.0
3.0
20
3.0
1.2
WRF 2b
417.1
3580
0.030 3.0
3.0
20
3.0
1.2
WRF 3
556.8
7400
0.030 3.0
3.0
20
3.5
1.4
WRF DIV W
36.6
2505
0.080 3.0
3.0
10
2.0
1.5
PIT DIV S
48.5
2745
0.091 3.0
20.0
0
2.0
1.2
PIT DIV N1
65.1
3375
0.108 3.0
20.0
0
2.0
1.2
PIT DIV N2
101.2
1180
0.055 3.0
20.0
0
2.5
1.4
BC DIV U
280.7
2025
0.010 3.0
3.0
15
3.5
1.3
BC DIV L
370.7
1310
0.010 3.0
3.0
15
3.5
1.0
PD-N
157.5
1660
0.030 3.0
3.0
10
2.5
1.1
PD-S
70.4
410
0.073 3.0
3.0
10
2.0
1.3
5.2 Preliminary Sedimentation Pond Sizing
The required volumes for each of the sediment trapping ponds are presented in the table below. The
volumes are representative of storage to accommodate runoff from the 10-year 24-hour event and
sediment storage. The Pit Pond also includes storage for water and sediment as a result of 500 gpm pit
dewatering (calculations presented in Appendix C). The ponds and any associated embankments will be
protected by outlet works and overflow spillways to be provided as part of detailed designs. The overflow
spillways will likely be designed to flow over the face of the embankment in a controlled manner in a
