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NHN-002 Ditch Designs <br />Two ditches will convey stormwater runoff to Pond NHN-002: NHN-002 North and NHN-002 <br />South. Each of these ditches has been designed to convey the 10 -YR, 24 -HR event flow to the <br />sediment pond. Table 2.05.3(4)-8-1 shows the peak flows for the subwatersheds that feed each <br />ditch. Subwatershed SW2-A feeds NHN-002 South, while SW2C feeds NHN-002 North, leaving <br />the remainder of SW2 (SW2-B) draining directly into Pond NHN-002. Map 2.05.3(4)-9 shows the <br />anticipated route for each ditch as well as the subwatersheds. Both ditches are designed to use <br />a trapezoidal cross section with sideslopes no steeper than 2H:1V. This design will facilitate <br />ease of construction given the size and length of the ditches. <br />Map 2.05.3(4)-9 shows the route of both NHN-002 North and NHN-002 South ditches, profiles <br />with the anticipated grades of the ditches, and design details and criteria for each. It is <br />anticipated that only one portion of the NHN-002 South will be steep enough to require riprap or <br />plastic lining. The remaining segments of NHN-002 South and all of NHN-002 North will have <br />excavated overburden as their lining. <br />SEDCAD Model 1 shows the ditch designs based on the appropriate subwatersheds and <br />channel lining. Also included at the end of Model 1 is a demonstration of the NHN-002 South <br />ditch with plastic for lining as opposed to riprap on the steep portion. <br />APPENDIX 2.05.3(4)-8 PAGE - 8 - September 2014 (TR 06) <br />