J_2024 05 09_West Orange Stormwater Management Plan

PSE&G West Orange Switching Station West Orange, NJ Stormwater Management Report As in the pre-development analysis, the time of concentration (Tc) was determined using the hydraulically longest flow path. The Tc flow paths within the area of disturbance are identified on the Post Development Drainage Area Plan located in Appendix D. Tc flow paths under post-development conditions were also extended to ‘‘Analysis Point A.” HydroCad output under Post-Development conditions for the 2-year, 10-year, and 100-year, 24 hour storm events is included in Appendix E and summarized in Table III-5. Table III-5 Post-Development Runoff Rates and Volumes at Analysis Point A Storm Event Runoff Volume (acre-ft) Peak Runoff Rate (cfs) 2-year, 24-hour 10-year, 24-hour 100-year, 24-hour 2.379 4.371 8.685 21.97 39.70 75.50 NJDEP 0.460 9.30 Table III-6 provides a comparison between pre-development and post-development runoff conditions for each design storm. As shown in Table III-6, projected peak runoff rates and volumes under post development conditions are expected to be less than under pre-development conditions for each storm event. Table III-6 Pre and Post Development Total Runoff Volumes and Peak Rates Storm Event 2-year, 24-hour 10-year, 24-hour 100-year, 24-hour NJDEP Pre - Tota Discharge Volume Peak Runoff [acre-ft] [cfs] 2.684 23.25 41.95 4.777 9.133 79.82 0.541 10.16 Post - Total Discharge Volume Peak Runoff [acre-ft] [cfs] 21.97 2.379 39.70 4.371 8.685 75.50 0.460 9.30 Figure 4 shows the pre and post-development hydrographs for the 2-year, 24-hour, 10year, 24-hour, and 100-year, 24-hour storms at Analysis Point A. The graphs show that runoff flows under post-development conditions do not exceed at any point in time those under pre-development conditions. Table III-6 shows that the 2-year, 24 hour peak runoff for the post development is less than predevelopment. Therefore, at a minimum, 100 percent of the average annual pre­ construction groundwater recharge for the site has been maintained. TRC Engineers, Inc. 13 March 2012