HydroCAD^® Stormwater Modeling - Since 1986

NJ-2023-Rain Event Lookup Table

The NJ-2023-Rain event lookup table was added in HydroCAD 10.20-3d to support updated stormwater rules for the state of New Jersey that take effect in 2023.  Customers using the Sheet flow procedure should update to HydroCAD 10.20-3g, in order to support different P2 values for each scenario.

The new rules provide tables of "adjustment factors" that must be used to adjust existing Atlas 14 rainfall data to better represent "current" and "future" conditions in each of county.  (For details see the partial PDF of the stormwater rules.)

These rainfall requirements are being supported in HydroCAD by way of a new event lookup table, which defines 2, 10, and 100-year events for each county at three different points in time:

Year-2000: Indicates existing data from NOAA Atlas-14, as published by NRCS and distributed in HydroCAD with the NRCS-Rain lookup table.  "Year 2000" indicates when Atlas 14 data was most recently updated for New Jersey. Rainfall data is expressed in inches with two decimal places.

Year-2020: These events are based on the year 2000 data (above), multiplied by the adjustment factors for "Current" conditions and rounded to two decimal places.  These events are intended to represent current-day rainfall conditions in the mid 2020's.

Year-2050: These events are based on the year 2000 data (above), multiplied by the adjustment factors for "Future" conditions and rounded to two decimal places.  These events are intended to represent projected rainfall conditions for 2050-2099.

After selecting the desired county, a total of nine rainfall events are defined:

2-year-2000, 10-year-2000, 100-Year-2000
2-year-2020, 10-year-2020, 100-Year-2020
2-year-2050, 10-year-2050, 100-Year-2050

By default, the rainfall events are grouped by target year, as shown above.  If desired, the sort order can be changed to "Name", which will group the events by return period.

In order to assist with the transition to the new rainfall data, it was decided to include the older year-2000 data for comparison.  If these events are not needed for any specific project, they can be easily deleted on the Rainfall tab.

In anticipation of ongoing changes to rainfall data, the events are named with the target year (e.g. 2020, 2050) instead of the "Current" and "Future" designations used in the rules.  However, this can be readily changed by renaming the events on the HydroCAD Rainfall tab.

When using the new lookup table, the appropriate rainfall distribution (NOAA C or D) is automatically selected based on the county.  This selection is exactly the same as the previous NRCS-Rain lookup table, but can be changed on the HydroCAD Rainfall tab if required.

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