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February 1999 YaarlMine * 13-11 Drainage and SednnrntContmlPlon •7 5.0 DITCH AND CULVERT DESIGN • Haul 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- hout 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:IV, in practice the slope will more typically be in the range of 15-20H:1V. This design will increase the hydraulic radius of the ditch as well as provide for easy cleaning 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 large 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 Sc D, culverts wt71 be installed at vazious points along the haul roads to limit watershed azeas, and thereby, reduce peak flows and velocities. In addition, rip rap will be placed below the culverts to control veloaties and control sediment prior to the runoff reachiag the down-gradient sedimentation ponds. All ditches associated with haul roads located outside the disturbed azea will designed to contain the flow from the ] 0-year, 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 aze 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 event. 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 sutomazy of the ditch designs is shown on Figure 13-12.1, Ditch Design Schedule. Cult' s The culverts aze designed to safely pass the peak flow from the 10-yeaz, 24hour 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-]2.$ Haul Road Ditches SEDCAD4 Results. Culvert locations are shown on Exhibits 13-11.3 and 13-11.4. All new ox proposed culverts aze summarized on Figure 13-12.2, Culvert Schedule. 6.0 POST MINING CHANNELS All post mining channels were designed to safely pass the peak dischazge from the 10-yeaz, 24hour event Post mining channel dimensions were determined using Manning's Equation for open channel flow. All channel design inputs and results can be found in Appendix 13-12.3, Post Mining Channels SEDCAD4 • Results. PR-02 Neumd 3/OS Montgomery Watson Miung Groxp * 165 S. Union BonkoarQ Suite 460 * Iakervood Colorado 80228 * (303) 763-Sf40