2014-02-07_REVISION - M1979094HR ‎(5)‎

• Permit No: M1979094HR
• IBM Index Class Name: REVISION
• Doc Date: 2/7/2014
• Doc Name: Revised DDP
• From: Whetstone Associates
• To: DRMS
• Type & Sequence: AM1
• Email Name: TC1
• Email Name: DMC
• Media Type: D
• Archive: No

JD -7 Mine — Drainage Design Plan 34
4.4.1 Pit Diversion Ditch — West
The Pit Diversion Ditch West (PDW) diverts stormwater from upslope around the existing JD -7 Open Pit
and routes it westward into a natural channel in the adjacent sub -basin N -E. The PDW was constructed in
1980 and has been improved and maintained in subsequent decades. The PDW has achieved a relatively
stable channel configuration over time, and is 1,144 ft in length with an average bed slope of 0.0213. The
excavated channel has a broad floor (10 to 20+ ft) and top widths range from 23 ft (measured) to over 35
feet (visual estimate). The channel currently has shallow sloping sides with an average slope of 4.6:1 based
on field- measured profiles4 (Figure 15, Figure 16). On average, the existing channel has a 2.2 -ft bottom
width and 4.6:1 ft side slopes. The channel is normally dry, and flows only in response to precipitation
events.
The PDW will be improved/maintained to achieve a prismatic channel geometry as shown in Figure 15 and
Plate 3. The channel will be reconstructed with an 8 -ft bottom width and 3:1 side slopes. The PDW will
have a uniform slope of 2.1% along its 1144 -ft length. Stability analysis for the improved structure is
provided in Section 5.4.1.
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Distance (ft)
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Distance (ft)
Figure 15. Channel Profiles Measured and Improved in Pit Diversion West
4 Channel side slopes were measured at 5.3:1 and 4.3:1 for the left bank and right bank of Profile PDW -1, and at 5.6:1 and 3.1:1 for
the left bank and right bank of Profile PDW -2.
4149A.140207 Whetstone Associates