Laserfiche WebLink
Stream Channel Parameters and Changes <br />Exhibit 55B Due to Longwall Mining-Induced Subsidence Page 11 <br /> <br /> <br /> <br />831-032.923 Wright Water Engineers, Inc. <br />December 2021 <br />of characteristics from photographs taken on selected stream channels in the area. <br />In 2020, WWE performed work relating to the South Prong stream channel through which we <br />gained site-specific knowledge of the hydraulic characteristics. As a result, we have updated our <br />channel geometry and refined our analyses of potential effect of longwall mining to incorporate <br />this experience. <br />The width to depth ratio, floodplain connectivity, substrate material, and channel slope provide an <br />understanding of the geomorphic context of the study stream systems. The hydraulic <br />characteristics provided in Table 3 result in existing width-to-depth ratios of 12 and 4 for South <br />Prong and Lion Gulch, respectively. As typically observed in headwater systems, the steep terrain <br />surrounding each study reach sets both streams within a confined valley. A confined-valley type <br />results in channels that are relatively entrenched, with little to no access to a broad floodplain. <br />Similarly, the existing terrain results in steeper channel slopes and stream substrate that can <br />withstand the higher velocities associated with the steep terrain. Together, these hydraulic and <br />geomorphic characteristics indicate that both study reaches consist of cascading stream channels <br />within the steeper sections and step-pool channel morphology where channel slopes are less than <br />4%. <br /> <br />