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Evaluation of Potential Subsidence Impacts of Longwall Mining in the Spruce Stomp Lease Area <br />to Aquatic Life and Water Supply <br />Figure 7). Larger pools are found upstream of logjams/beaver dams. The bottoms of these pools <br />have accumulated fine- grained sediments. Over the Potential Project area, West Fork Terror <br />Creek has an average channel slope of 5.5 percent (see Figure 13). Within the Potential Project <br />area, typical average channel slopes range from a low of approximately 3 percent to 10.6 percent <br />(based on analysis of 100 foot reaches, see Figure 13). Based on a review of LiDAR elevation <br />information and site observations made during several 2012 site visits, there is significant <br />irregularity in channel slope and characteristics between sections within the Spruce Stomp Lease <br />Area. <br />A sediment transport analysis of West Fork Terror Creek within the Spruce Stomp Lease Area <br />was performed (see Appendix 2). The results of this analysis indicate that the creek generates <br />enough sheer stress under normal high flow conditions to move grain sizes which exceed the <br />average measured grain size. Abundant boulders which armor the creek's bed and banks exceed <br />the particle size that would be moved by normal flows. <br />III. Typical Channel Cross Sections <br />West Fork Terror Creek generally has a 5- to 15 -foot wide channel bed that is flanked by steep <br />banks that rise 1 — 3 feet above the channel bottom. In some areas, deeper pools have formed <br />with residual depths of 1.5 to 4 feet. During a September 2012 field visit, the channel riffles <br />typically had water depths of 0.3 — 1 foot (see photos in Appendix 3). <br />IV. Physical Habitat Description <br />Overall, West Fork Terror Creek in the vicinity of the Potential Project is diverse and provides a <br />range of microhabitats for the types of aquatic organisms typically associated with a trout <br />fishery. The channel includes well developed boulder dominated riffle -pool sequences with <br />cobble substrate. Riffle features range from confined, cascading water to broad (10 — 20 feet <br />wide) straight run channel shots. Many riffle sections have small side pools that provide refuge <br />for smaller organisms. Pools are typically limited to 1 — 3 feet in depth and no more than <br />approximately 20 feet in length (although typically much shorter). In addition to these features, <br />logjam/beaver dam features create deeper pools that filter through large and small woody debris. <br />121 - 014.000 Wright Water Engineers, Inc. Page 8 <br />January 2013 <br />