2014-11-13_PERMIT FILE - C2010089A (2)

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.0 Drainage Sub Basins The area that drains to Pond NHN -001 is split into two main portions: areas that drain directly to Pond NHN - 01 and the areas that drain through the ditches (NHN -001 East and NHN -001 West). The area draining through the ditches is then divided into subwatersheds that each flow into different segments of the ditches. $ince these are temporary collection ditches, they will safely convey the 10 -yr, 24 -hr storm event of 2.00 inches. All runoff calculations utilized the curve number of 91. Table 2.05.3(4) -7 -2 denotes the subwatershed and associated areas. The subwatersheds locations are delineated on Map 2.05.3(4) -7. II subwatershed peak flow data was calculated using an emulation of the NRCS TR -55 method in the EDCAD software program. This emulator produces higher peak flow values than the original NRCS TR -55 - ogram, thus making it conservative. The NHN -001 East and NHN -001 West ditches were each modeled in EDCAD independently, with all segments and culverts linked together in each model. The SEDCAD output :ports are found in subsection 2.3 and 2.4. I+, sections were generated at a five foot interval along each ditch to determine the section of each segment with the smallest available flow cross sectional area. This smallest segment was then evaluated in tjhe SEDCAD (presented in subsection 2.3 and 2.4) to ensure proper cross - sectional area was available for the smallest cross sectional area present in each ditch segment. This flow cross sectional area also took into the required 0.3 feet of freeboard. Each ditch segment is installed at a single grade and with a single lining, meaning that the only variable along the segment that could affect ditch capacity is the flow section. Table 2.05.3(4) -7 -1 shows a comparison of the ditch segments' worst case flow cross sections Map 2.05.3(4) -7 to the SEDCAD determined ditch segment flow cross sectional requirements. APPENDIX 2.05.3(4) -7 PAGE - 3 - AUGUST 2013 (TR 04)