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12-18-85 <br />Stipulation No. 10 Response <br />. Following mining at the Coal Gulch Mine, the Coal Gulch drainage will be <br />re-established in its approximate original position as shown on the <br />Postmining Topography Map (Map 14). The existing Coal Gulch Diversion <br />will be backfilled as shown on the Postmining Topography Map (Map 14) to <br />blend with the existing adjacent undisturbed land. The backfill slopes <br />will be less than or equal to 3H:1V to minimize erosion and to ensure <br />overall slope stability. <br />Large riprap material from the existing Coal Gulch diversion channel <br />will be used to provide velocity control measures in the permanent <br />channel. As shown on the Postmining Topography Map (Map 14) and the <br />Coal Gulch Permanent Channel Profile Map (Map 16), permanent channel <br />gradient established during backfilling and grading is very similar to <br />estimated pre-disturbance gradient from the existing Coal Gulch upstream <br />from the mine to the State Highway 160 crossing downstream of the mine. <br />Therefore the re-established channel with armouring will pass the <br />• 100-year, 24-hour peak flow at conditions similar to the original Coal <br />Gulch channel. <br />The area has been previously disturbed by mining operations in the early <br />1900's so the location and configuration of the original channel is not <br />precisely known. Peerless Resources, Inc. plans to re-establish the <br />channel in the best suited location given backfilling and grading <br />constraints. <br />The channel design shown in the Drainage and Sediment Control Plan <br />Appendix, Appendix 1, for Ditch No. 1 shows the appropriate calculations <br />of peak flow and riprap requirements for the permanent channel. Two (2) <br />segments have been evaluated for velocity of flow and subsequent riprap <br />requirements. From these calculations, the existing riprap located in <br />Ditch No. 1 is applicable to the permanent channel. Therefore, this <br />material will be saved during backfilling and grading and utilized in <br />• reclamation of the permanent channel. <br />-4- <br />