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If the ditch is not stable, then WFC will use a larger ditch section and /or adequately line the <br />ditch in order to comply with applicable regulations. <br />Drainage from haul roads within the areas disturbed by mining and reclamation activities <br />(see Map 2.05.3(3) -1 ) will be constructed to meet the requirements of 4.05.2 and such haul <br />roads will at a minimum be constructed and maintained to minimize erosion of the disturbed <br />area. Erosion control measures to be used singly or in combination include but are not <br />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 <br />to the prevailing hydrological balance. <br />Culverts will be installed to avoid plugging or collapse and to avoid erosion at the inlets and <br />outlets. Riprap will be installed as necessary to reduce the exit velocity. The minimum <br />width will be the width of the natural downstream channel. The riprap will be sized in the field <br />based on the "as- built' slope of the culvert and final configuration of the exit channel slope <br />area. The sizing shall be based on the Federal Highway Administration's HEC No. 11 "Use <br />of Riprap for Bank Protection" or other standard methods. All pipes will have a minimum <br />cover of 12 inches. Culverts and drainage ditches will be maintained periodically to prevent <br />accumulation of debris on the culverts inlets and outlets. <br />The following is an outline of the general design procedures used in the design of culverts: <br />1. Identify the need for a structure from topographic maps, and a visit to the site; <br />2. Determine the size and hydrology of the watershed in question; <br />3. Perform SEDCAD, or other acceptable software, computer run to determine <br />the peak runoff from a 10 -year, 24 -hour precipitation event. <br />Revised June 2010 (PR06) 2.05.3(3) -24 <br />