Laserfiche WebLink
Peabody Sage Creek Mine —Drainage and Sediment Control Plan <br />Channel sections with shallow slopes or low flows are typically earthen or vegetated. Channels with <br />• steeper slopes or higher peak flows have traditionally been stabilized with rock riprap. <br />However, SCCC may construct vegetated channels with turf reinforcement matting (TRM) material <br />in place of rock riprap lined channels for channels that require some type of lining material. In <br />accordance with Rule 4.05.3, SCCC designed all operational runoff ditches and postmine channels <br />with a minimum freeboard of 0.3 feet. <br />Operational runoff ditch designs are summarized in Table 2.05.3 -E2 -5, Operational Ditch Design <br />Schedule; postmine channel designs are summarized in Table 2.05.3 -E2 -7, Postmine Channel Design <br />Schedule. The design demonstrations for the operational runoff ditches are presented in Appendix <br />2.05.3- E2.G -2, South Facilities Area (Portal Area) Operational Ditch and Culvert Designs; postmine <br />channel design demonstrations are presented in Appendix 2.05.3 -E2.I, Postmine Channel and Culvert <br />Designs. <br />4.2.1 Earthen Channel Design <br />The design methodology used in SEDCAD4 for earthen channels is the limiting permissible velocity <br />method. Permissible velocity is a function of the type of soil characteristics. If the actual design <br />velocity is less than the permissible velocity, the channel is stable. SCCC assumed sediment laden <br />water was used in the operations runoff ditch designs. Channel soil type and channel slope are the <br />• most sensitive parameters. <br />4.2.2 Vegetated Channel Design <br />Vegetated channels tend to become unstable when flow velocities exceed five (5) feet per second <br />(fps). Inputs to the channel utility sub - routine for vegetated channels include are as follows: <br />Peak Flow: The 10 -year, 24 -hour peak flow value is calculated with the hydrology component of the <br />SEDCAD model. <br />Channel Slope: Channel slope is a sensitive parameter. The steeper the slope the lower the <br />allowable velocity. The channel slopes were determined by direct measurement from the mine <br />permit maps. <br />Channel Geometry: Existing channels (constructed prior to 2007as part of the Seneca 11 Mine <br />reclamation plan) were generally evaluated assuming a triangular, or V- shaped, configuration, with a <br />3H: IN side slope. In certain situations, several postmine channels designs incorporated a trapezoidal <br />shaped channel with a bottom width of either three (3) or ten (10) feet and 411: IN side slopes. <br />Retardance Class: The reclamation seed mixture used in the reclamation plan results in a mixed <br />grass community. Consequently, the vegetation type selected as the model input is mixed grass. <br />• <br />2.05.3 -E2.17 <br />