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• An additional consideration is the use of large boulders which are available <br />on-site from previous highwall development. These can be placed at the base of <br />the steepest section (Segment 3) along the western bank to direct flow toward <br />the lower channel segment and the Highway 160 culvert. A single boulder <br />placed mid-channel will also assist in dissipating energy at the base of the <br />steep channel segment. <br />The channel and flow dimensions included in the appendix define the riprap <br />requirements for both the temporary Ditch No. 1 and the permanent Coal Gulch <br />channel. Thickness requirements for granular bedding (Table 1) and gradation <br />of riprap to be used (Table 2) are provided in the appendix. Atypical cross <br />section showing locations of granular bedding, riprap and channel geometry <br />based on sideslopes of 2H:1V are shown on Figure 6. The riprap to be located <br /> in Ditch No. 1 segments will be saved during backfilling and grading and <br /> utilized in reclamation of the permanent channel. <br />The design presented essentially precluded any requirements for future channel <br />maintenance. Peerless will monitor the structure during the active mining <br />operation and evaluate the need for any additional armoring or stabilization <br />to ensure compliance with all applicable regulations. <br />Revised 9/12/86 <br /> <br />12 <br />