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APPENDIX 2.05.3(4) -7 <br />NR/, ,t?.OKO 001 DITCHES AS -BUILT <br />1.0 In aduction -Vpi " � N <br />Pon 001 is fed by two collection ditches running along the west and east sides of the south <br />drainage basin of the New Horizon Mine. These ditches were designed as part of the original <br />permit application and were constructed in January 2013. This as -built for those ditches <br />contains the drainage sub basin information for the sub basins that feed the P 001 ditches, <br />and a demonstration that the ditches are sufficient to convey the flows in question. l� �f <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. Additionally, as part of the Riprap used on segments of the <br />ditches is a product called Geoweb Cellular Confinement Systems GW30V. The Geoweb is a <br />honeycomb of plastic material that is staked to the channel bottom, and then filled with the <br />appropriate sized riprap. The Geoweb holds the selected riprap in place. A hydraulic analysis <br />data sheet provided by the manufacturer is attached to this appendix. It shows the velocity limits <br />for the Geoweb for some riprap sizes. The maximum velocity for GW30V with similar sized rock <br />is around 10 FPS. 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) -B shows the standard <br />ditch geometry for the different segment types (shales and hardpans, armored, and'/ culverts). <br />2.0 Drainage Sub Basins ,,00 <br />The area that drains to Pond 001 is split into two main portions: areas that drain directly to Pond <br />N)�i -001 and the areas that drain via ditches (NHN -001 East and NHN -001 West). The area draining <br />via ditches is then divided into subwatersheds that each flow into different segments of the <br />ditches. Since these are temporary collection ditches, they will convey the 10 -YR, 24 -HR storm <br />event of 2.00 inches. All runoff calculations used the curve number of 91 that was used in the <br />currently approved permit. Table 2.05.3(4) -7 -1 shows the subwatershed flows, and the <br />subwatersheds can be seen delineated on Map 2.05.3(4) -7. <br />APPENDIX 2.05.3(4) -7 PAGE - 1- 2013 (TR 04) <br />