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Exh. 7-20B-2 Revision Date: 10/23/23 <br /> Revision No.: TR-161 <br />Permanent Post Mine Channels <br /> <br />The West Taylor watershed is comprised of two primary post-mining channels and six tributaries <br />channels. Both of the primary channels convey the post mining surface water flows to the West <br />Taylor Pond, while the six tributaries channels route water to both primary post mining channels. <br />The locations of both the primary and tributary channels are presented on Map 12 and Figure <br />Exh. 7-20B-2. The channel profiles are presented on Map 33B. <br /> <br />The assumed hydrologic condition for all three channels is the post mine condition when the <br />entire West Taylor watershed is reclaimed and reporting to the West Taylor Pond. <br /> <br />West and East Fork Taylor Ditch <br /> <br />The area contributory to each permanent primary channel is less than one square mile, making <br />the appropriate storm event the 10-year, 24-hour event as specified in Rule 4.05.3. However, <br />portions of these channels pass over permanent fills, so the correct storm event required by Rule <br />4.09.2 becomes the 100-year, 24-hour event. For simplicity, both primary channels are modeled <br />to this larger event. <br /> <br />The upper segments of the primary channels are flat enough that a vegetative liner will provide <br />sufficient erosion protection, even for the 100-year flow. However, both channels below the <br />lower stock ponds require riprap lining to ensure long-term stability. <br /> <br />A SEDCADTM model has been included below which evaluates the peak flow and total runoff <br />volume for each of the channel segments for the 100-year, 24-hour storm event. The channel <br />configurations for the 100-year, 24-hour storm event for both primary channels are described on <br />the tables below. <br /> <br />East Fork Taylor Ditch <br />Station Peak Flow <br />(CFS) <br />Average <br />Slope (%) <br />Channel <br />Type <br />Side <br />Slopes <br />Minimum <br />Depth <br />(Feet) <br />Erosion <br />Protection <br />Station 0+00 to <br />EFSP-1 25.00 25 Trapezoidal <br />12’ bottom 3H:1V 4.0 Riprap, <br />D50 = 9” <br />EFSP-1 to <br />EFSP-2 54.25 2.1 Trapezoidal <br />12’ bottom 3H:1V 4.0 Vegetation <br />EFSP-2 to <br />Station 116+97 26.15 5.4 Trapezoidal <br />12’ bottom 3H:1V 4.0 Vegetation <br />