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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 />