2004-07-01_REVISION - M1987064 - Laserfiche WebLink

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of the river (figure 3). Lcvccs were conshvcted between [hc river and the cast bank to prevent the river from meandering into the gravel mining area. In- channcl grave] mining at the Dalton Pit will cease by November 30, 2004 (U.S. Army Corps of Engineers, letter to Sandco, [nc., November 28, 2003). Reclamation of Historical Use Area Upon completion of the mining operations at the Dalton Pit, Sandco proposes to complete the reclama- tion of the stream channel. Riverbank areas, access ramps, and stockpile areas wilt be stabilized with cottonwood and willow plantings (Sandco, Inc., Revised Reclamation Plan, Exhibit E, July 14, 1999). The effected river channel will be graded to remove isolation dikes and haul roads, the natural channel will be restored as best as possible, and grass seed will be planted where necessary (Colorado Division of Minerals and Geology, Revised Notice, Reclamation Summary, Permit number M-87-064, June I, 2999). Banks will be graded to a slope of 3:1 or less, and annual surveys of the river profile and cross sectional perspectives will be done (U.S. Army Corps of Engi- neers, letter to Sandco, [nc., November 28, 2003). Riverbank conditions will be recorded and photo- graphed, and vegetation, wildlife, and habitat condi- tions will be documented. Future Use Area The future use area consists of an off-channel gravel mine to extract sand and gravel materials. The extraction will occur during the winter months of November through March. The mining or extraction of the materials will be confined to the boundaries of the future use area (figure 3). The future use area will have a minimum of 300 ft of separation from the Animas River, and a maximwn of 500 ft of separation (Sandco, Inc., Permit Application, Regular 112, Amendment, April 18, 2004). Excavation of the lake pit will begin at the south end of the future use area with removal of the top soil to be stockpiled for reuse during reclatnation. Approximately two acres per year will be stripped to expose the sand and gravel deposit. The backslopes of the lake pit boundaries will be made to a slope not steeper than 1 ft vertical l0 3 fl horizontal. Excavated slopes that arc temporary (between the yearly excava- lions within the pit) will be made to approximately l ft vertical to 1.5 ft horizontal This procedure wilt be followed on a yearly basis until excavation is completed to the full extent of the lake pit boundary (figure 3). Construction of the future use area will be compatible with wildlife and aquatic habitats. The lake will ultimately be about 35 ft deep; therefore, there will be deep water for water fowl and fish habitat. There will be alternating shallow water areas along the banks to provide for aquatic plants, spawning beds, wading birds, and macroinverte- brates. Lake shore wetlands will be constructed to provide for terrestrial wetland plants and animals. Riparian woodlands between the Animas River and the future use area will not be disturbed (figure 3). Seasonal River Crossing A seasonal river crossing will be used to access the future. use area from [he Sandco Plant; the river crossing will occur at cross section SC-l l (figure 4). 'Che seasonal river crossing will be in-place only during the low-flow months of November through March. Up to 8 culverts, 4-fr diameter will be placed in the river and a road bed of unconsolidated materials will be packed as a road surface over the culverts. The culverts will protrude from the sides of the road bed, and the slopes of the embankments will be about 1 ft vertical to 5 ft horizontal. The crest of the road grade will be about 6 ft above the channel bottom. Hydraulic computations of the flow capacity of the culverts were done for this report. Two computa- tions were done that are important for the seasonal river crossing: (I) Maximum culvert capacity where the river stage reaches the tops of the culverts, and (2) Maximum culvert capacity where the river stage over- flows the road crest. For computation (1), using 8 culverts of 4 ft diameter and pipe lengths of 25 ft, the total river discharge (Qt) was computed to be 510 fr3/sec such that the headwater depth (1'h) was exactly 4.00 ft (figure 5). The flow in each pipe would be 63.75 ft3/sec. For computation (2), the total river discharge (Qt) was computed to be 838 ft3/sec such that road ^ow (Qr) was 0.16 ft3/sec (figure 6). The flow in each pipe would be 104.7 ft3/sec. Streamflow discharges in the Animas River at Durango during winter months can range fran 103 to 844 ftj/sec (table 2). The higher (lows may affect the S ~L Southaaast Hydro-Logic 5 W°_'_