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The sod erodbility factor (K) is a numeric representation of the ability of the soil to resist the <br />erosive energy of rainfall. The factor is dependent on particle size and distribution, structure, <br />void space and pore size, and organic matter content. For the study, 0.35 and 0.15 best <br />described the erodibFty of the natural ground and the coal mina waste (Civil Software Design, <br />7 992). <br />The control pretties factor (CPI accounts for the effects of erosion control measures. It is <br />defined as the ratb of sediment bss from an aros with a given cover and conservation practice <br />to that of a field leh in continuous fallow for one year. Since the coal mine waste will bs <br />mechanically manipulated, a practice factor of 1.2 was used. Assuming 60 percent of the <br />natural ground is covered by vegetation, a cortesponding practice factor of 0.09 was used for <br />the study. <br />The SEDCAD model predicted the sedimem loading to the pond. Ths SEDCAD results <br />indicated approximately 94.2 tons of coal mine waste aedsttent and 5.7 tons of natural ground <br />sediment. If the coal mine waste material is assumed to have a unk weight of 95 pounds per <br />cubic foot as determined by laboratory analyses (see Appendix A) and 120 pounds per cubic <br />n <br />•1 foot as an average value for the natural ground, the resulting volume is 2.099 cubic feet. <br />Computer output regarding this analysis is located in Append'a 8. <br />4.2.3 Estimated Sedknertt Pond Volumes <br />Based on the hydrologic analysis and the sediment loading analyses, the sediment pond must <br />be ebb to hold 2,099 cf + t 2,700 d ~ 14,799 d, or 0.34 sere feet. The design as shown <br />on Drawing 95255-03 will hold 18.000 cf, or 0.37 acre feet, up to the emergency spillway <br />elevation providing a factor of safety of 1.1. Figure 4.2 shows the sediment pond height- <br />volume curve and the calculated sediment and water volumes. <br />4.2.4 Sedltewtt Pond Wd <br />The sediment pond wall will bs a reinforced concrete stnxturs. Reinforced eonaete wee <br />chosen as the construction material because its ease of eonsuuetion and maintenance; cost <br />effectiveness; and ability to create an impenneabk boundary. The concrete was was designed <br />as a gravity retaining structuro, using its own weight to counteract forces applied by <br />accumulated water and sediment, and bacldill. A stability analysis was conducted to ensure <br />96266l1424.RPr Cul M'vw Wnt~ aank l)•tipn fa tM Suiborn CrMk Mow <br />OetoWr [9a0 WE9TEC, Inp. to <br />