Laserfiche WebLink
Introduction <br /> Pond NHN-002 at the New Horizon North Mine is designed to capture and contain the runoff <br /> from the 10-YR, 24-HR storm event as part of sediment control at the mine. This appendix <br /> contains design specifications for Pond NHN-002 and its feeding ditches, NHN-002 North and <br /> NHN-002 South. Included in these designs are the stormwater runoff values for the 10-YR, 24- <br /> HR event that the ditches and pond must contain and control, and the 25-YR, 24-HR event that <br /> the pond must pass safely through its emergency spillway. <br /> Stormwater Data <br /> Pond NHN-002 is the sediment pond for the stormwater drainage watershed SW2 shown on <br /> Map 2.05.3(4)-1. Runoff from this area flows entirely to the ditches that feed Pond NHN-002 or <br /> the pond itself. Map 2.05.3(4)-9 shows the breakdown of SW2 into subwatersheds that each <br /> feed a separate part of the Pond NHN-002 stormwater control system. SW2-A feeds NHN-002 <br /> South, SW2-B feeds the pond directly, and SW2-C feeds NHN-002 North. Table 2.05.3(4)-8-1 <br /> shows a summary of the runoff values for each subwatershed. This data can also be seen in <br /> SEDCAD models located in this Appendix. In addition to the subwatersheds, Pond NHN-002 <br /> also will handle pit pumping, which can be seen in the Table 2.05.3(4)-8-1. The10-YR runoff and <br /> peak flows are from SEDCAD Model 1 (As shown later in this Appendix); the 25-YR peak flow is <br /> from SEDCAD Model 2 (As shown later in this Appendix). <br /> Table 2.05.3(4)-8-1 <br /> Subwatershed Area 10-Yr, 24-Hr 25-Yr, 24-Hr <br /> Acreage Peak Runoff Peak Runoff <br /> Discharge Volume Discharge Volume <br /> (cfs) (ac-ft) (cfs) <br /> SWS2-A 23.33 23.96 2.24 <br /> SWS2-13 35.20 39.23 3.43 <br /> SWS2-C 28.83 27.37 2.76 <br /> Pit Pumping* N/A 2.01 0.16 <br /> SWS2 Combined 87.36 1 91.13 8.60 113.40 11.23 <br /> *Pit pumping is the same regardless of storm size <br /> APPENDIX 2.05.3(4)-8 PAGE -3 - January 2015 (TR-09) <br />