2007-10-30_PERMIT FILE - C1982057

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January 2002 Seneca II-W South Expansion * Drainage and Sediment ContmlPlan • Page 8 5.0 HAUL ROAD CHANNEL AND CULVERT DESIGNS All haul road ditches were designed to safely pass the peak discharge from the 10-year, 24-hour event. The ditch dimensions were determined using Mannings Equation for open channel flow. All road side ditches will be gravel lined. All road side ditch inputs and results can be found in Appendix 2, Haul Road Channel and Culvert Designs. The design results and ditch locations are shown on Exhibits 13- 21.1, 13-22.1, 13-23.1 and 13-24.1. As shown on the ditch results, the flow velocities for all the road side ditches are less than 6 feet per second and will not require riprap. The culverts were designed to safely pass the peak discharge from the 10-year, 24-hour 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 2, Haul Road Channel and Culvert Designs. Haul Road J is designed as a relatively flat road and the location and length of road side channels and location of culverts is difficult to predict until the road is built. Given the difficulty to predict the location and length of the ditches, the ditches were conservatively designed to handle the peak discharge from the entire watershed above Haul Road J. Culvert J1 was also conservatively designed to handle the peak discharge from the entire watershed above Haul Road J and Haul Road I. Culvert J- 2 was designed to pass the peak flow from the entire watershed above the Pond 016 system, assuming worst case disturbed conditions. Additional culverts may be required along Haul Road J. These additional Culverts were conservatively designed to handle the peak discharge from the entire watershed above Haul Road J. Postmine drainage channel designs are presented in Attachment 20-1. • tYI1t~H * 165 S. Union Borrlevarrd, Suite 410 * L.ake:vood, Colorado 80228 * (303) 763-5140 TR-59 Revised 05/07