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convey the water to the sedimentation pond. Exhibit 3.5-22, Sheet 1, shows <br />• conceptualized locations for culverts on the regraded Moffat Area. The <br />regraded surface is used to assist in visualizing where appropriate locations <br />will occur. The actual placement of culverts will be determined by mine <br />personnel based on the actual field conditions. <br />Final culvert locations will be synonymous with the restored drainage <br />basin channels. Prior to installing a given culvert the watershed area <br />serviced by the culvert will be calculated and design parameters determined to <br />size the culvert for the design flow. If discharge from the culverts is <br />determined to be sufficient, in terms of volume and velocity, to cause <br />significant erosion, the construction of designed channels to carry the runoff <br />downslope or other erosion control and energy dissipation methods will be <br />implemented, where appropriate. Design details of these structures, where <br />used are provided in Appendix 3.5-E and locations are shown on Exhibit 3.SD-1. <br />3.5.3.2 Design Criteria for Peak Flow Determination <br /> Runoff from drainage areas to the culverts along the upper haulroad in <br /> the Moffat Area which will serve as a postmining access road will be designed <br />• using the computer modeled SEDIMOTT II, developed by the University of <br /> Kentucky. The model simulates the storm routing of a 10-year, 24-hour storm <br /> event from the drainage area to the culvert. In order to simulate the storm <br />event the drainage area of the culverts will be divided into subwatersheds <br />according to the mining and reclamation sequence. Input parameters for each <br />subwatershed including area, hydraulic length and slope of the subwatershed, <br />hydraulic length and slope from the subwatershed to the culvert and curve <br />number will be determined. Of these parameters only the curve number is not <br />measured directly from a map. The curve numbers are dependent upon the soil <br />type, and the vegetation type and quantity found within the subwatershed. The <br />majority of the soils in the Moffat Area are hydrologic classification "B" and <br />"C". In order to simply calculations and since topsoil will combine several <br />soil types, all replaced topsoil will be assigned a hydrologic classification <br />"C". The designs and associated with the culverts to be placed along the <br />upper haulroad/access road will be kept on file at the Mine office for review. <br />For areas other than the Moffat Area, runoff from drainage areas to the <br />• 3.5-4 September 10,1993 <br />