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1999 Yaart Mine * 13-12 Drainage anASrdrmrnt Control Pkn •7 5.0 DITCH AND CULVERT DESIGN Hau! Road Ditches Runoff from haul roads located within the mining disturbed area will report to sedimentation ponds. The road-side ditches associated with these haul roads will be designed to contain the flow from the 10-yeaz, 24- hour storm event. As designed, the cut slope side of the haul road will serve as the shallow slope of the roadside ditch. Although the slope shown on the ditch designs is lOH:1V, in practice the slope will more typically be in the range of ]5-20H:]V. This design will increase the hydraulic radius of the ditch as well as provide for easy dearting of the ditch by graders. The steep slope sections of the roadside ditches will experience erosive velocities during the design storm event. Routine maintenance of the road and ditches will repair any erosion if and when it occurs. Armoring the ditches with lazge rip rap is not practical from an operational standpoint. Material from the road is constantly being moved into the ditches from the movement of lazge haulage equipment. Therefore, the ditches need to be maintained continuously. Rip rap placed in the ditches would last only a short time. As shown on Exhibits 13-11.3, Proposed Haul Road B Extension and 13-11.4, Proposed Haul Roads C & D, culverts will be installed at various points along the haul roads to limit watershed azeas, and daerebq, reduce peak Elows and velocities. In addition, rip rap will be placed below [he culverts to control velocities and control sediment prior to the runoff reaching the down-gradient sedimentation ponds. All ditches associated with haul roads located outside the disturbed azea will designed to contain the flow from the 10-yeaz, 24-hour storm event and control erosive velocities. Sedimentation control measures such as rip rap and straw bales will be installed, as needed. Design inputs and results for proposed haul road ditches are shown on the SEDCAD4 printouts located in Appendix 13-12.2, Haul Road Ditches SEDCAD4 Results. A summary of the ditch designs is shown on Figure 13-12.1, Ditch Design Schedule. Diversion Ditches All diversion ditches aze designed to safely pass the peak flow from the 10-yeaz, 24-hour storm even[. The ditch dimensions were determined using Manning's Equation for open channel flow. The diversion ditches will be grass-lined or armored, depending on flow velocities. Design results can be found in Appendix 13-12.1, Sediment Ponds SEDCAD4 Results. A summary of the ditch designs is shown on Figure 13-12.1, Ditch Design Schedule. Culverts The culverts axe designed to safely pass the peak flow Erom the 10-yeaz, 24-hour storm event. The culverts were sized using the U.S. Bureau of Public Roads nomograph. All culvert design inputs and results can be found in Appendix 13-12.2, Haul Road Ditches SEDCAD4 Results. Culvert locations aze shown on Exhibits 13-11.3 and 13-11.4. All new or proposed culverts are summarized on Figure 13-12.2, Culvert Schedule. 6.0 POST MINING CHANNELS The channel utility sub-routine contained within SEDCAD4 was used to design the postmine channels. The design methodology used in SEDCAD4 is based on the limiting permissible velocity method. If the actual design velocity is less than the permissible velocity, the channel is stable. Seneca Coal Company (SCC) uses two types of channel designs at the Yoast Mine: Montgomery Watrvn Mixing Group * 765 S. Union Boulevard Suite 460 * LnkewooA Calomrlo 80228 * (303f 763-5740 TR-30 Revised 03/07