2013-01-29_PERMIT FILE - C1981022A (3)

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Sctziar - 2.05.4 as illustrated by the Facilities Postmining Topography (Map 2.05-M6), and Premining and Postmining • Goss-Sections, (Map 2.05-M7); placement of riprap materials, as required; replacement of available soil material on the upper channel slopes; and revegetation of both channel and sideslope areas. The reconstructed Elk Geek channel has been designed to safely pass the peak flows resulting from a 100-year, 24-hour storm event. The designed channel has 3H:1V sideslopes, a 10-to12-foot bottom width, and overall gradients consistent with both the original channel and the existing culvert. During reconstruction of the channel, minor variations in gradient will be incorporated to promote riffle and pool development and enhance conditions for aquatic habitat. Channel design calculations for the reconstructed Ellt Geek channel are included in Exhibit 2.05-E3, Drainage and Sediment Control Plan. Suitable 12-inch Dso riprap material will be placed and bedded in the reconstructed channel to m;nimi~e channel erosion. Riprap placement will extend 1 foot above the design peak flow level on the channel sideslopes to m,mmi~v the potential for erosion from normal variations in flow levels. Riprap will be obtained from one or both existing permitted borrow sources along Elk Geek and downstream on the North Fork of the Gunnison River if these materials are suitable or from anoff- site source. Large boulders resulting from slope stabilization activities during the construction phase will be randomly placed along the margins of the reconstructed scream channel to create favorable microhabitat conditions. Requirements for design and construction of permanent diversions under applicable provisions of Rules 4.05.4(4)(a), (b), (c), and (d) are addressed by these reclamation plarts; design discussions and calculations previously referenced in Appendix B; the Postmining Topography Map (Map 2.05-M6), Elk Geek Profiles (Map 2.05-M7 Series), and D-Seam Portal Area Goss-Sections (Map 2.05-M7 Series); and the 2/ 15/00 submittal to the U.S. Army Corps of Engineers tided, "Amendment to COE Perrnit No. 199975232 for Elk Geek Culver Extension" (relevant portions of which have been previously provided to the Division). Specifically, average gradient is maintained and a • geomorphically stable channel and floodplain configuration are provided as documented by the Elk Geek Profiles (Map 2.05-M7 Series) and the geomorphology analysis included in the U.S. Army Corps of Engineers submittal Because Elk Geek is a relatively immature stream, no significant meander pattern exists, as confirmed by site examinations. The design postntining stream alignment, however, retains approximatelythe same overall channel length, gradient, and general configuration as the original. The design postmining channel should be in dynamic equihbrium with the rest of the Ells Creek drainage, although OMI u proposing the rue of designed riprap to prevent or minimi~r down-cutting and deviation of the reestablished channel as a long-term stability consideration. Annual seasonal high flows (spring runoff), normal low intermittent flows through the remainder of the yt'az, and a relatively steep stream gradient result in a sandy stream substrate and limited water availability, which are not conducive to establishment or maintenance of effective aquatic habitat. Habitat restoration/establishment measures will include placement of larger boulders along the stream tnatgins to create favorable micro6abitat conditionu and implementation of the riparian revegetation plan to establish a viable riparian community in immediate proximity to the stream channel. While intended primarily as a stabilization measure, placement of riprap in the reestablished stream segment may provide improved conditions for establishment and maintenance of macro- invertebrates since these species generallyprefer a rockyto a sandysubstrate. Because no well-defined floodplain exists, the only defined hydraulic channel is the very narrow existing Elk Geek channel. Seasonal high !lows vary from yeaz to yt az and appeaz to overtop the existing flow channel and flow out over adjacent area. Because seasonal flows are variable, this extended flow cannot be readily defined or delineated nor can normal high water mazk The design postmining reestablished channel combines a defined floodplain and channel to effectively contain all anticipated normal and peak flows while providing some flexibility within the riprapped channel • cross-section For natural stream movements. The designed channel provides a significant margin of safery for full flow containment with more flow carrying capaaty than the undisturbed upstream and downstream channel. Please refer to the D-Seam Portal Area Goss-Section (Map 2.05-M7 Series) PR04 2.05-63 Revised August 2000