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Section 780.21 (b) Continued. <br />• used on all areas to be revegetated within the proposed permit <br />area. Across section and plan of the contour furrow is shown in <br />Figure 31, Typical Design of Contour Furrow. The advantages of <br />this system are many and provide closely spaced small depressions <br />within the topsoil layer that not only greatly reduce sheet flow <br />velocity and subsequent erosion, but also trap any transported <br />sediment within several yards of its original location. Additionally, <br />the furrows usually intercept and arrest the formation of small <br />rills and gullies. By the time that revegetation has developed to <br />a point that sediment transport is no longer a significant problem <br />and the contour furrows are no longer needed, the furrows will have <br />filled with topsoil, will blend in with the land surface and will <br />become inconspicuous. This contour furrowing system is the best <br />example of proximate sediment control, reduces the amount of down <br />gradient or off-site sediment control needed and provides specific <br />compliance with 30 CFR 816.45 (b)(3). A detailed discussion on <br />• seeding, planting, mulching and revegetation in general is set <br />forth under Sections 780.18 (b)(5) and 81b.111-816.114. Diversion <br />structures are planned at the locations shown on the Energy Mines <br />No. 1 and 2 Hydrology (Map 13) and on the Eckman Park Hydrology <br />(Map 14) and will serve to divert water from undisturbed areas away <br />from disturbed areas. Not only will this diversion system reduce <br />the amount of water flowing across disturbed areas and thus reduce <br />water velocity and sediment yield, but will also reduce the size or <br />number of sedimentation ponds required downstream. Temporary <br />diversion structures are designed and will be constructed and <br />maintained to handle the amount of runoff from the two-year, 24- <br />hour precipitation event and will be constructed using proper <br />roughness characteristics, maintenance of appropriate gradients, <br />revegetation, channel lining or detention basins, or a combination <br />of one or more of these measures, so that not only will they be <br />adequate for their intended purpose, but also so that they will, to <br />the extent possible, prevent additional contributions of suspended <br />• solids to stream flow and to runoff outside the permit area. <br />780-150 <br />