J_2024 05 09_West Orange Stormwater Management Plan

Stormwater Management Plan Revision 0 2.0 2.1 Hydrology and Hydraulics HYDROLOGY AND HYDRAULICS Rainfall Data Rainfall Depths for Essex County were obtained from the NOAA National Weather Service Precipitation Frequency Data Server (See Appendix F). The SCS rainfall distribution for this project is NOAA 24-Hr Type D. See Table 2.1 for existing rainfall data. Table 2.1: Design Storm Frequency-Depth Return Frequency (yr) 24 Hour Depth (in) 2 3.42 10 5.20 25 6.44 100 8.71 Per the updated N.J.A.C. 7:8 regulations effective July 17, 2023, an adjustment factor for the respective county is applied for both the current precipitation (per N.J.A.C. 7:8, Table 5-5) and future precipitation (per N.J.A.C. 7:8, Table 5-6) for Essex County for the 2-, 10-, and 100-year return frequencies. The current and future adjusted 24-hour depths are used for stormwater modeling. The resulting design rainfall depths are shown below in Table 2.2. Table 2.2: Design Storm Frequency with Depth Precipitation Adjustment Factors (AF) Return Frequency (yr) Water Quality (WQ) 2 10 25 100 NOAA Atlas 14 (in) 1.25a 3.42 5.20 6.44 8.71 24 Hour Depth Current Current Future Adjusted AF AF (in) Future Adjusted (in) 1.01 1.03 N/A 1.06 4.07 6.36 N/A 11.58 3.45 5.37 N/A 9.23 1.19 1.22 N/A 1.33 a N.J.A.C. 7:8-5.5 requires the WQv storm to be 1.25 inches of rainfall in two hours. 2.2 Runoff Data HydroCAD-10 software was utilized to model the stormwater runoff at the site. The SCS TR-55 methodology was used for this model to calculate the pre- and post-developed runoff rates for storage design. Table 2.3 provides detailed information regarding curve numbers and land coverages for pre- and post-developed watersheds, respectively. Public Service Electric & Gas Company 2-1 Burns & McDonnell