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Peabody typically constructs ditches on the inside of roadway cuts for drainage. A <br /> typical V-ditch section would be a minimum of two feet deep with side slopes 2:1 or <br /> flatter. As most road cuts are into resistant bedrock-type material, ditches normally do <br /> not require lining. Culverts will be designed and installed to minimize the runoff volume <br /> conveyed in each ditch. Culverts and ditches will typically be designed using SEDIMOT II <br /> to predict the peak runoff and Manning's equation to determine the peak velocity and flow <br /> depth (see Attachments I and J). <br /> If the ditch is not stable, then Peabody will use a larger ditch section and/or adequately <br /> line the ditch in order to comply with applicable regulations. <br /> Drainage from access roads within the areas disturbed by mining and reclamation activities <br /> (see Exhibits 12-2 and 12-3) will be constructed to meet the requirements of 4.05.2 and <br /> such access roads will at a minimum be constructed and maintained to minimize erosion of <br /> the disturbed area. Erosion control measures to be used singly or in combination include <br /> but are not limited to: <br /> a. Stabilizing all exposed surface areas to promote a reduction in the rate and <br /> volume of runoff; <br /> b. Using straw dikes, riprap, check dams, berms, geotextile materials, mulches, <br /> vegetation sediment filters, contour furrows or other measures that reduce <br /> overland flow velocity, reduce runoff volume, or trap sediment; or <br /> C. Such other measures to minimize erosion resultant siltation and disturbance to <br /> the prevailing hydrological balance. <br /> Surfacing. See Exhibit 13-20 for typical detail. <br /> Culverts. Each access road will be designed, constructed, and maintained to have adequate <br /> drainage using ditches and culverts to safely convey the peak runoff from a 10-year, <br /> 24-hour precipitation event to sediment ponds before being released from the permitted <br /> area (see Exhibit 13-20 for typical details of drainage structures). <br /> Culverts will be installed to avoid plugging or collapse and to avoid erosion at the <br /> inlets and outlets. Riprap will be installed as necessary to reduce the exit velocity. <br /> The minimum width will be the width of the natural downstream channel. The riprap will be <br /> sized in the field by Peabody's project engineer based on the "as-built" slope of the <br /> culvert and final configuration of the exit channel slope area. The sizing shall be based <br /> 13-27 Revised 04/11/88 <br />