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APPENDIX 2.05.3(4) -7 <br />NHN -001 DITCHES AS -BUILT <br />1.0 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 as -built for those ditches contains the drainage sub <br />basin information for the sub basins that feed the NHN -001 ditches, and a demonstration that <br />the ditches are sufficient to convey the flows in question. <br />During construction of the ditches, it was determined that roughly triangular ditches could be <br />built that would convey surface water runoff as effectively as the designed trapezoidal ditches <br />with a smaller total surface footprint. The original approved ditch designs can be found in <br />Appendix 2.05.3(4) -1. Additionally, as part of the Riprap used on segments of the ditches is a <br />product called Geoweb Cellular Confinement Systems GW30V. The Geoweb is a honeycomb of <br />plastic material that is staked to the channel bottom, and then filled with the appropriate sized <br />riprap. The Geoweb holds the selected riprap in place. A hydraulic analysis data sheet provided <br />by the manufacturer is attached to this appendix. It shows the velocity limits for the Geoweb for <br />some riprap sizes. The maximum velocity for GW30V with similar sized rock is around 10 FPS. <br />The highest velocity in the ditches is around 6.8 FPS. <br />Map 2.05.3(4) -7 shows the as -built route of the ditches. Map 2.05.3(4) -8 shows the standard <br />ditch geometry for the different segment types (shales and hardpans, armored, and '/2 culverts). <br />2.0 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 via ditches (NHN -001 East and NHN -001 West). The <br />area draining via ditches is then divided into subwatersheds that each flow into different <br />segments of the ditches. Since these are temporary collection ditches, they will convey the 10- <br />YR, 24 -HR storm event of 2.00 inches. All runoff calculations used the curve number of 91 that <br />was used in the currently approved permit. Table 2.05.3(4) -7 -1 shows the subwatershed flows, <br />and the subwatersheds can be seen delineated on Map 2.05.3(4) -7. <br />APPENDIX 2.05.3(4) -7 PAGE - 1- AUGUST 2013 (TR 04) <br />A,oplteri <br />ai , OeY .2013 <br />