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EXHIBIT 7, ITEM 20, PART E <br /> PERMANENT CHANNEL DESIGN <br /> There are two permanent primary channels and two permanent secondary channels associated <br /> with the South Taylor Pit. The primary and secondary channels are permanent channels that <br /> convey runoff from the areas near the watershed divide near the southernmost extension of the <br /> mining activity. The primary channels are associated with drainage from the face of the West <br /> Taylor permanent fill. Their purpose is to convey water to the north from the head of the Taylor <br /> Creek watershed towards the West Taylor Pond as shown on Map 41 A. The secondary channels <br /> drain reclaimed areas near the watershed divide to the Section 16 and 28 Ponds. <br /> All of these ditches are shown on Map 41A. Channel profiles for these channels are presented <br /> on Map 33B. <br /> Primary Channels <br /> The two primary channels are the following: <br /> • West Taylor, East Tributary Ditch <br /> • West Taylor, West Tributary Ditch <br /> By inspection, the area contributory to each ditch is less than one square mile, making the <br /> appropriate design storm the 10 year, 24 hour event as specified in Rule 4.05.3. However, <br /> portions of these ditches pass over permanent fills, so the design event required by Rule 4.09.2 <br /> becomes the 100 year, 24 hour event. For simplicity of design, the entire channel for each ditch <br /> is designed to this larger event. <br /> Exhibit 7, Item 14 describes the hydrologic design methodology used in all models. For <br /> channels protected by a riprap liner, selection of minimum rip rap size is done using the <br /> Simons/OSM method in SEDCAD. For channels to be protected by a vegetative liner, the <br /> permissible velocities are also determined using SEDCAD's routines. <br /> The upper segments of the permanent primary channels are flat enough that a vegetative liner <br /> will provide sufficient erosion protection, even for the 100 year flow. However, both ditches <br /> below the stock ponds require riprap lining to ensure long-term stability. <br /> The ditch configurations for the 100 year, 24 hour storm event for both tributaries are described <br /> on the tables below. <br /> East TributaryDitch <br /> Peak Average Channel Depth Erosion <br /> Station Flow Sloe % Type Side Slopes Feet Protection <br /> CFS <br /> Station 0+00 to 97.1 25.0 Trapezoidal 3H:1V 4.0 Riprap, <br /> 16+00 12' bottom D50 = 18" <br /> Station 16+00 to 100.5 3.4 Trapezoidal 3H:1 V 4.0 Vegetation <br /> 76+29 20' bottom <br /> Exh. 7-20E-1 Revision Date: 1/28/19 <br /> Revision No.: TR-131 <br />