Laserfiche WebLink
safely convey the peak runoff from a 10 -year, 24-hour precipitation event while maintaining a <br />minimum of one half foot of freeboard to the top of the road embankment (see Map 2.05.3(3)-3 <br />for typical details of drainage structures). <br />Drainage ditches will be placed at the toe of all cut slopes formed by the construction of haul <br />roads. Water will be intercepted before reaching a large fill and drained safely away in <br />accordance with the requirements of 4.03.1. Water from a fill will be released below the fill <br />through conduits or in adequately lined channels and will not be discharged onto the fill. <br />When drainage ditches discharge onto open terrain, a number of measures will be taken to <br />protect the terrain from erosion. When the drainage discharges onto a disturbed area, the area <br />will be revegetated to control runoff. In an area where revegetation would not be sufficient to <br />control erosion, the area will be rip -rapped. Temporary measures to reduce erosion will be <br />employed while the area is undergoing revegetation such as straw dikes, containment ditches, <br />etc. WFC typically constructs ditches on the inside of roadway cuts and safety berms for <br />drainage. As most road cuts are into resistant bedrock -type material, ditches normally do not <br />require lining. Culverts will be designed and installed to minimize the runoff volume conveyed <br />in each ditch. Culverts and ditches will typically be designed using SEDCAD or other generally <br />accepted software to predict the peak runoff and Manning's equation to determine the peak <br />velocity and flow depth. <br />If the ditch is not stable, then WFC will use a larger ditch section and/or adequately line the ditch <br />in order to comply with applicable regulations. <br />Drainage from haul roads within the areas disturbed by mining and reclamation activities (see <br />Map 2.05.3(3)-3) will be constructed to meet the requirements of 4.05.2 and such haul roads will <br />at a minimum be constructed and maintained to minimize erosion of the disturbed area. Erosion <br />control 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 of <br />runoff, <br />b. Using straw dikes, riprap, check dams, berms, geotextile materials, mulches, vegetation <br />sediment filters, contour furrows or other measures that reduce overland flow velocity, <br />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 <br />outlets. Riprap will be installed as necessary to reduce the exit velocity. The minimum width will <br />be the width of the natural downstream channel. The riprap will be sized in the field based on the <br />"as -built" slope of the culvert and final configuration of the exit channel slope area. The sizing <br />shall be based on the Federal Highway Administration's HEC No. 11 "Use of Riprap for Bank <br />Protection" or other standard methods. All pipes will have a minimum cover of 12 inches. <br />Section 2.05.3(3) Page 7 December 2014 (TR -08) <br />