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Appendix Exh7 -14F <br />West Pit Fill Ditch and East Taylor Pond Ditch <br />These ditches form the system that drains 187.8 acres including currently disturbed and <br />reclaimed areas into West Pit Pond - 008A. The West Pit Ditch is the longest and the <br />major component. The West Pit Coal Road Ditch is a ditch that intercepts and diverts <br />47.7 acres in the uppermost portion of this watershed away from the Work Area <br />Sediment Pond watershed and into the West Pit Pond watershed. It drops into the <br />headwaters of the West Pit Fill Ditch, which conveys this flow and another 53.2 acres, <br />mostly currently disturbed, toward the West Pit Pond. Along the way, about 1,000 feet <br />before the flow is released to the West Pit Pond, the West Pit Fill Ditch is joined by the <br />East Taylor Pond Ditch coming in from the south, collecting another 60.5 acres of mostly <br />reclaimed land. Finally flows from 13.9 acres of reclaimed land and 12.5 acres of <br />undisturbed lands join the West Pit Ditch about 200 feet above West Pit Pond, and the <br />combined flows proceed to the pond. Layout, tributary areas and ground cover <br />conditions that determine the runoff curve number (CN) for the three ditches are <br />presented on Figures 14F -1 and 14F -2. The runoff curve numbers used in the analysis <br />were taken from the approved values for the various stages of reclamation per TR -73. <br />For most of the system, the design storm is the 100 -year, 24 hour storm as specified in <br />Rule 4.09.2 because the ditches are within and drain runoff from a valley fill. The one <br />exception is the uppermost ditch, West Pit Coal Road Ditch, which is not within the <br />valley fill. To satisfy Rule 4.09.2, the 100 year flow from this uppermost segment is <br />included in the overall system modeling, but the ditch itself is designed for the 10 year 24 <br />hour storm. The attached SEDCAD run based on the 10 yr storm therefore applies only <br />to this uppermost ditch segment. <br />The West Pit Fill Ditch is a rip -rap lined ditch due to the gradient (10% to 25 %). It has a <br />trapezoidal section of 10 -foot bottom width and 3H:1 V side slopes. The West Pit Coal <br />Road Ditch (which is the upper reach of the West Pit Fill Ditch) is the south shoulder <br />road ditch for that haul road, modeled as a vegetative lined channel. The East Taylor <br />Pond Ditch is a triangular ditch with 3H:1 V side slopes with a lesser gradient (5 %) that <br />also allows the use of a vegetative channel lining. Required rip -rap sizing was <br />determined as described in the introductory text on pages Exh. 7 -14 -1 through 7 -14 -4. <br />Adequacy of vegetative lining is determined directly from the SEDCAD output. <br />Design changes are only being proposed for a 300 -foot segment at the uppermost end of <br />the West Pit Fill Ditch, to allow a proper tie -in to the previously constructed lower <br />segment. Most of the other ditches in this system are at or near bond release, and no <br />physical changes are proposed for them. However, because the previous modeling <br />included the entire system tributary to the West Pit Pond, it was necessary to re -run the <br />modeling for the entire tributary watershed. <br />The SEDCAD modeling for the ditch system is presented on the following pages. The <br />uppermost ditch in the main stem, West Pit Coal Road Ditch, is designed for the 10 year <br />Exh.7 -14F -2 Revision Date: 9/12/2012 <br />Revision No.: TR -96 <br />