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D.6.5.6 Diversion Ditches <br />• Diversion ditches will be constructed to divert <br />undisturbed area runoff around the south and east sides of the <br />tailings disposal area. The catchment area on the north side <br />of the tailings disposal area is small and runoff will not be <br />diverted but will be captured in the tailings disposal area. <br />The catchment area on the south side is approximately <br />equal to 0.97 square miles or about 621 acres. Flows from this <br />area are currently routed through one of four ephemeral <br />drainages as delineated on Figure D.6-1. Elevations within the <br />catchment area vary from approximately 8,600 ft at the tailings <br />facility to about 9,582 ft at the southerly limit of the <br />watershed boundary. The watershed slopes in a northerly <br />direction towards the facility at an average gradient of <br />approximately 8.5 percent. <br />• Catchment Areas A, B, and C will be intercepted along <br />the southern perimeter of the tailings disposal area and <br />diverted to the west. Storm flow from these areas will be <br />routed through a diversion ditch along the south side of the <br />tailings disposal area. A corrugated metal pipe will serve as <br />a drop structure to convey flows to the valley bottom to rejoin <br />the existing drainage downstream of the tailings Aisposal area <br />and collection pond. <br />Catchment Area D will be intercepted along the eastern <br />perimeter of the tailings disposal area and diverted to the <br />north over the saddle through a diversion ditch. <br />The diversion ditches have been designed to carry the <br />peak discharge from the 100-yr 24-hr storm. All storm <br />discharges were determined with the computer program WASHED. <br />. All analyses were performed using a SCS Type II rainfall <br />~-4D <br />