21 Stormwater Mgmt Report_082025

Release Number 55 (TR55), “Urban Hydrology for Small Watersheds”). Theoretical storms are modeled with the 24-Hour SCS Unit Dimensionless Hydrograph using the NOAA Atlas 14 Type D rainfall distribution and recurrence intervals of 2, 10, and 100 years. Hydrograph creation and routings are accomplished using the HydroCAD stormwater modeling program by HydroCAD Software Solutions, LLC. 2.1 Rainfall Data Rainfall data used in the stormwater calculations of this report are obtained from different sources based on the latest NJ stormwater management regulations (NJAC 7:8). The Water Quality storm event is based on the NJ BMP Manual Chapter 5 definition of having a total rainfall depth of 1.25 inches and a total duration of two (2) hours. Twenty-four-hour rainfall frequency data in Essex County for all other storms has been obtained from the Engineering Field Handbook NJ Supplement last revised August 2012 (developed from data contained in NOAA Atlas 14 Volume 2). Per amended NJ stormwater management regulations dated July 17, 2023 the precipitation depths for the 2-, 10-, and 100-year storm events are determined using adjustment factors applied to the NOAA Atlas 14 rainfall estimates. The rainfall depth values used in this project are listed in Table 2.1 and 2.2. TABLE 2.1 – Current Adjusted, 24-Hour Rainfall Frequency Data Event (year) 2 10 100 NOAA Atlas 14 Rainfall (inches) 3.44 5.22 8.66 Adjustment Factor 1.01 1.03 1.06 Current Adjusted Rainfall (inches) 3.47 5.38 9.18 TABLE 2.2 – Future Adjusted, 24-Hour Rainfall Frequency Data Event (year) 2 10 25** 100 NOAA Atlas 14 Rainfall (inches) 3.44 5.22 6.44 8.66 Adjustment Factor 1.19 1.22 1.25 1.33 Future Adjusted Rainfall (inches) 4.09 6.37 8.02 11.52 ** NJAC 7:8 does not contain adjustment factors for the 25-year storm. The factors listed have been obtained from NJ Extreme Precipitation Projection Tool (https://njprojectedprecipitationchanges.com/) in order to estimate the increased rainfall. ▪ Stormwater Management Report for Proposed Retail Store▪ 2 ▪ August 2025 ▪