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Pond NHN-001 East and West Ditch As-Builts <br />Introduction <br />Pond NHN-001 is fed by two collection ditches NHN-001 West and NHN-001 East running <br />along the west and east sides of the south drainage basin of the New Horizon Mine. These <br />ditches were designed as part of the original permit application (see Appendix 2.05.3(4)-1) and <br />were constructed in January 2013. This appendix includes the construction certification <br />documentation for both ditches and demonstrates that both ditches as -built are sufficient to safely <br />pass the flows from a 10 -yr 24 -hr event. Table 2.05.3(4)-7-1 provides the as -built conditions of <br />each segment by station. The as -built condition of both ditches, including cross-sections and <br />station information, are presented on Map 2.05.3(4)-7. <br />This as -built documentation supersedes ditch design information presented in Appendix <br />2.05.3(4)-1 for the segments shown on Table 2.05.3(4)-7-1. For any future extensions of the <br />NHN-001 East and West Ditches outside of the stations listed in Table 2.05.3(4)-7-1, they will <br />be constructed to the specifications outlined in Appendix 2.05.3(4)-1. <br />During construction of the NHN-001 East and West Ditches a rip -rap substitute was installed <br />called Geoweb Cellular Confinement Systems GW30V (Geoweb). Geoweb is a honeycomb of <br />plastic material that is staked to the channel bottom and then filled with the appropriate sized <br />riprap to substitute for a rock lined channel. The Geoweb material holds the selected rip -rap in <br />place and limits velocities in the same manner as a rock -lined channel. SEDCAD outputs for the <br />NHN-001 East Ditch indicate a required D50 of 1.5 inches to 3.0 inches, depending on the <br />segment, for velocities ranging from 3.77 fps to 6.08 fps. SEDCAD outputs presented for the <br />NHN-001 West Ditch indicate a required D50 of 1.5 inches to 3.0 inches, depending on the <br />segment, for velocities ranging from 3.37 fps to 4.72 fps. The hydraulic analysis data sheet <br />provided by the manufacturer demonstrates the velocity limits for the Geoweb for a select set of <br />riprap sizes. The range of velocity for GW30V with similar sized rock is 11.69 to 12.01 fps. The <br />highest velocity in both the East and West ditch is 6.08 fps; therefore, GW30V was selected and <br />installed as a substitute for 1.5 to 3.0 inch rip -rap material. The installation details for the <br />Geoweb is presented in Figure 2.05.3(4)-7-1. <br />Drainage Sub Basins <br />The area that drains to Pond NHN-001 is split into two main portions: areas that drain directly to <br />Pond NHN-001 and the areas that drain through the ditches (NHN-001 East and NHN-001 <br />West). The area draining through the ditches is then divided into subwatersheds that each flow <br />into different segments of the ditches. Since these are temporary collection ditches, they will <br />safely convey the 10 -yr, 24 -hr storm event of 2.00 inches. All runoff calculations utilized the <br />curve number of 86. Table 2.05.3(4)-7-2 denotes the subwatershed areas and cumulative peak <br />flows. The subwatersheds locations are delineated on Map 2.05.3(4)-7. <br />Appendix 2.05.3(4)-7 Page 1 April 2016 (PR -01) <br />