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If the ditch is not stable, then WFC will use a larger ditch section and/or adequately line the ditch in <br />. order to comply with applicable regulations. <br />Drainage from haul roads within the areas disturbed by mining and reclamation activities (see Map <br />2.05.3-1) will be constructed to meet the requirements of 4.05.2 and such haul roads will at a <br />minimum be constructed and maintained to minimize erosion of the disturbed area. Erosion control <br />measures to be used singly or in combination include but are not limited to: <br />a. Stabilizing all exposed surface areas to promote a reduction in the rate and volume <br />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 overland <br />flow velocity, reduce runoff volume, or trap sediment; or <br />c. Such other measures to minimize erosion resultant siltation and disturbance to the <br />prevailing hydrological balance. <br />Culverts will be installed to avoid plugging or collapse and to avoid erosion at the inlets and outlets. <br />Riprap will be installed as necessary to reduce the exit velocity. The minimum width will be the <br />width of the natural downstream channel. The riprap will be sized in the field based on the "as- <br />built" slope of the culvert and final configuration of the exit channel slope area. The sizing shall be <br />based on the Federal Highway Administration's HEC No. 11 "Use of Riprap for Bank Protection" or <br />other standard methods. All pipes will have a minimum cover of 12 inches. Culverts and drainage <br />ditches will be maintained periodically to prevent accumulation of debris on the culverts inlets and <br />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 the <br />peak runoff from a 10-year, 24-hour precipitation event. <br />(Revised ~/zooa) 2.05.3(3) - 25 <br />