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JD -7 Mine — Drainage Design Plan 36 <br />the valley floor. The steeper slopes of the western OPWRD are eroded to bedrock in places, similar to <br />natural channels on the Monogram Mesa escarpment (Figure 13). The NRCS has identified the soil types <br />in the vicinity of the OPWRD as rock outcrop (Figure 5). Erosion - resistant coarse material also occurs at <br />the toe of the waste rock pile as larger material (cobbles and boulders) commonly rolls to the toe during <br />waste -rock emplacement by end - dumping, which protects the waste rock pile from erosion by the OPWRD. <br />Improvements to the OPWRD are shown in Plate 3 and are planned in conjunction with the expanded Pit <br />Pool storage structure (Section 4.5.1). The OPWRD channel will be improved with a 5 -ft bottom width <br />and 3:1 side slopes, where practical, along its length. (Rock outcrop may prevent the construction of 3:1 <br />side slopes in some areas.) The first reach (VTR-Divl) will be constructed with a uniform slope of 1.5% <br />from the Pit Pool spillway to the 5746.5 -ft elevation point located 401 ft downstream from the spillway. <br />Due to an existing average slope of 7.2 %, the second reach (WR -Div2) will be constructed using multiple <br />drop structures to eliminate scour effects. With these drop structures in place, a continuous slope of <br />approximately 1.7% will be maintained in the channel. The geometry and hydraulic parameters of the two <br />reaches modeled for the OPWRD are shown in Table 13. <br />Figure 17. Photographs of OPWRD Diversion and Tributary Reach NECh1 <br />(Taken from Open Pit Waste Rock Pile, facing south toward sub -basin N -E and <br />contributing reach NEChl) <br />4.4.4 Stormwater Collection Ditches for the Underground -Waste -Rock Pile <br />Drainage ditches have been constructed to collect and route water from the perimeter of the underground - <br />waste -rock pile to the south catchment (Catchment 001 B -A South) and north catchment (Catchment 00113- <br />A North). The north collection ditch is 316 feet long with an average slope of 0.0538 and routes <br />stormwater to Catchment 00113-A North. The east collection ditch is 125 feet long with an average slope <br />4149A.140207 Whetstone Associates <br />