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Peabody Sage Creek Mine — Drainage and Sediment Control Plan <br />4.0 DITCH AND CULVERT DESIGNS <br />4.1 Haul Road Ditches <br />Runoff from haul roads and access roads within the surface facilities area is generally routed to the <br />existing sediment ponds. Road -side ditches are designed to safely convey the peak flow from the <br />10 -year, 24 -hour storm event. Steeper slope sections of the road -side ditches may experience <br />erosive velocities during the design storm event. Routine maintenance of the road and ditches will <br />repair any erosion if and when it occurs. Armoring the ditches with large rock riprap is generally <br />not practical from an operational standpoint. Material from the roadbed is constantly being moved <br />into ditches from the movement of large haulage equipment. Consequently, the road -side ditches <br />need to be maintained continuously. Any rock placed in the road -side ditches would only last a <br />short time before it was covered with road material. <br />Existing ditches PM -9, PM -15, RA -D1, RE -D1 and the Northwest Diversion Ditch are historic <br />Seneca II Mine haul road ditches. They have been retained in the drainage control plan for both <br />operational and postmine phases. <br />Haul and access road ditch locations are shown on Map 2.05.3 M4. Designs for the existing Seneca <br />11 road ditches, as well as, the Peabody Sage Creek Mine operations ditches are presented in <br />Appendix 2.05.3 -E2.G, Operational Ditch and Culvert Designs. Minimum ditch configurations are <br />summarized in Table 2.05.3 -E2 -5, Operational Ditch Design Schedule. <br />• 4.2 Runoff Ditches and Postmine Channels <br />There are several existing diversion ditches constructed to convey runoff in the Pond 003 watershed. <br />The ditches were designed for mine- related activities at the Seneca H Mine (see Appendix 7 -6 of the <br />Seneca H Mine PAP). Channel designs were calculated using Fuller's Formula (Trans. ASCE, Vol. <br />77, pg. 564, 1914) or SEDCAD+ (Schwab, 1988). The diversion ditch locations are shown on Map <br />2.05.4 Ml, Postmining Topography. Design documentation is presented in Appendix 2.05.3 -E2.G, <br />Attachment 2.05.3- E2.G -1, North Facilities Area (Shop/Warehouse /Office) Diversion Ditch <br />Designs. Ditch configurations are summarized in Table 2.05.3 -E2 -6, North Facilities Area <br />Diversion Ditch Design Schedule. <br />The channel utility sub - routine contained within SEDCAD4 was used to design the runoff ditches <br />and postmine channels. The design methodology used in the channel sub - routine utility is based on <br />the limiting permissible velocity method. If the actual design velocity is less than the permissible <br />velocity, the channel is stable. <br />Four types of designs are used for the runoff ditches and postmine channels at the Peabody Sage <br />Creek Mine: <br />• earthen channels <br />• vegetated channels <br />• riprap channels <br />• vegetated channels with a turf reinforcement mat <br />2.05.3 -E2.11 <br />