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i <br />i ? <br />Chief Drainage Channel Reclamation Work Plan <br />Little Deadwood Gulch <br />Work Plan <br />Channel Design <br />Chief channel design calculations are summarized in Attachment T-4 Table SWMP-A <br />with supporting calculations. In summary the channel design criteria using pre-mine channel <br />slope was greater than 16 percent for the 100 year 24 hour storm of 87 cubic feet per second. <br />A trapezoid channel configuration has been selected because the channel foundation <br />consists of historical run of mine rock. The channel configuration (see figure 2) is designed on <br />the following hydraulic input parameters: <br />• Mannings coefficient - 0.040 <br />• Channel slope of 0.05 feet per foot <br />• Channel flow depth of approximately 2 feet <br />• Side slopes of 3 H: 1 V <br />• Bottom Width of 2 feet <br />Utilizing these design criteria the channel has the capacity to convey a peak flow of <br />approximately 210 cfs with an estimated flow velocity of 9.6 feet per second Using the rating <br />curve, the design channel will carry the 100 year storm peak flow with a freeboard exceeding 0.4 <br />feet. The channel top width will be approximately 16 feet. <br />Site Preparation <br />Remove trees, stumps, roots, steel and historical mine rock-stockpile material from <br />the designated construction area. <br />Construction <br />• Install silt fences wattles parallel to the access road to the drainage channel (Figure 2) <br />(See Installation Guidelines-Appendix A) <br />• Install wattles in strategic areas to control runoff and sediment-include the bales <br />perpendicular to drainage channel in two separate locations up and down gradient of <br />the disturbed area. (See Installation Guidelines) <br />• Install survey grade stakes per the engineering design; <br />• Density: drv specific gravity of 2.5 or greater: <br />• Durability: riprap shall be hard and durable; <br />• Gradation will provide interlocking strength: <br /> <br />• Segregate mine rock for future use to create check dams and or for the use as stream <br />channel riprap. Rocks used for riprap will be sized as D50=6 inches. For future use, <br />salvage 25 cubic yards (rip rap size) for stream restoration activities; <br />• Conduct the following site grading activities: <br />1. Prepare temporary storage area to contain rock removed from Little Deadwood <br />Gulch at bottom of access road to the constructed May Day man way; <br />2. Using a backhoe remove material from Little Deadwood Gulch; <br />4 <br />Revised 6.6.2011 <br />