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<br />53 <br />are generally wide and short and will have short circuiting problems. In order <br />to minimize short circuiting, the Environmental Protection Agency recommends <br />that the ratio of average length of floe path to effective width of the reservoir <br />be greater than two. The effective width is calculated by dividing the surface <br />area by the length. Table 14 gives the length, surface area, effective width, <br />and length to effective width ratio for existing and proposed sediment ponds. <br />The surface areas were estimated using the 1" ~ 200' scale, five-foot contour <br />interval mapping. Photographs taken during site visits were also used to help <br />estimate dimensions of existing structures. The resulting L/4/e ratios are <br />considered only estimates and these values should be verified in the field. <br />Only Sediment Pond "e" has an estimated L/lie ratio less than two. This <br />[. sediment pond will require baffling to provide adeavate flow length and detention <br />time. The flow length for proposed sediment Pond "E" is based on placement of <br />(' the outflow device at the opposite end of the dam embankment to the entrance of <br />minor diversion channel E1 (Hydrology Map 2, Appendix A). This locates the out- <br />. let device and emergenry spillway on the east end of the embankment. <br />6.3.6 Sediment Pond Maintenance <br />The sediment pond will collect water and sediment. As sediment collects, <br />the water storage wlume will be reduced. To account for this, the impoundments <br />have included a three-year sediment volume. If the original water design volumes <br />are to be maintained, the sediment accumulation will need to be removed approxi- <br />mately every three years. If maintenance is not desired, a larger initial volume <br />of sediment pond will be required for proposed sediment ponds. Generally, <br />the existing ponds have larger storage volumes than recommended and the period <br />between sediment removal can be longer. Through periodic observation, the need <br />for sediment removal should be determined. <br />6.4 Diversion Channel Evaluation and Design <br />Diversion channels within the G.E.C. permit boundary are used for two <br />purposes. The first is io intercept runoff from disturbed and/or reclaimed areas <br />and divert it to sediment ponds. Second is diversion of runoff from undisturbed <br />drainages around or through the mine permit boundary. The diversions used to <br />. divert runoff to sediment ponds aenerally drain small areas and are considered <br />minor diversions. The diversions used to divert undisturbed drainage around <br />or through the mine., drain large areas and are considered major diversions. <br />