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HydroCAD Stormwater Modeling - Since 1986

NOAA Atlas 14

What is Atlas 14?

NOAA Atlas 14 contains the latest rainfall data for much of the United States, and generally replaces the older data published in NWS Technical Paper 40 (TP-40).

How do I use Atlas 14?

If your stormwater regulations require the use of Atlas 14 data, you need to examine the regulations very carefully to determine exactly how the data should be used.  There are several alterative ways to "use Atlas 14", so you need to be clear about your requirements before you can properly setup your model.

Note: These alternatives apply specifically to the SCS/NRCS runoff procedure.  If you're using the Rational method there are fewer options to navigate, and you can generally skip ahead to download local PFD data.

Alternative 1 - This alternative uses the 24-hour precipitation depths from Atlas 14 in conjunction with one of the traditional rainfall distributions, such as the Type II.  In this situation the only data you need from Atlas 14 are the 24-hour depths, which can be entered by hand, loaded from the Atlas 14 lookup table, or downloaded from online sources for your specific project location.  The key feature off this alternative is that you continue to use the traditional rainfall distribution for your location in combination with the new event depths.

Alternative 2 - This approach uses the Atlas 14 event depths, just like alternative 1.  But instead of using the traditional rainfall distribution (e.g. Type II), it uses one of the new rainfall distributions for your local area, such as the NOAA_A/B/C/D, NRCC_A/B/C/D, or MSE 3/4 distributions developed by the NRCS.  These distributions are included in HydroCAD-10 build 14, along with a new Atlas 14 lookup table that will automatically define your events with the appropriate rainfall distribution and depths.

Alternative 3 - This approach uses the new Atlas 14 event depths, just like the previous alternatives.  But instead of using a predefined rainfall distribution, a custom synthetic rainfall distribution is also created based on local rainfall data from NOAA, NRCC or other sources.  This is the most complete implementation of the new rainfall data, in that you're using a site-specific rainfall distribution.  Details here.

For further information read about rainfall setup options.


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