What rainfall method to use with NRCC rainfall? 1

[pjhealy]

A local town is proposing regulations that will require stornwater management facilities to be designed to handle the "extreme precipitation" shown in the "Atlas of Extreme Precipitation in the Northeastern United States" published by the Northeast Regional Climate Center (at Cornell).

Since I will not be using TP-40, what rainfall distribution should I use? Is this explained in the Atlas? or does it use a new distribution model?

Patrick

 

[RWF7437]

1. Get a copy of the proposed regulation.
2. See if it tells you what distribution to use.

If not, ask the agency proposing the regulation to tell you. Better yet, get them to give you an example of the calculations they expect to see.

3. Did you mean "NRCS" rather than "NRCC"?

good luck

 

[pjhealy]

NRCC = Northeast Regional Climate Center. It is apparently located at Cornell University.

http://met-

http://www.cit.cornell.edu/

I was reading from the proposed regulation when I posted my question:
"Stormwater facilities shall be designed to handle
the extreme precipitation as shown in the "Atlas of
Extreme Precipitation in the Northeastern United
States" published by the Northeast Regional Climate
Center,"
and yes, I ordered the refernced publication.

Presumably the atlas (ala TP-40) will show the extreme rainfall for a given locale for a given time period, 24-hours, 12 hours, 1 hour, etc.

Do you know whether it will use an NRCS-type distribution curve (curves are predefined in HydroCAD: Type I, Type II, Type IIA, Type III), or will we have to create new distribution curves for each event. If the latter, I must allow time in my proposal for these additional services.

Patrick

 

[RWF7437]

I live in Oregon so, no, I can't answer your questions. But, the Agency proposing the requirement must ! It is their duty; not yours or mine. Telling someone to "design for the 100 year storm", is meaningless without specifying the duration, rainfall pattern and method to be used. It should also explain other details such as, acceptable values of roughness, Curve number, etc., etc.

An example can answer these questions most efficiently. Ask for one. Indeed, insist on one.

good luck

 

[psmart]

HydroCAD also includes a "Constant Intensity" storm that *might* be applicable, but you really need to get more info as RWF7437 recommends. Unfortunately, the regulations may be incomplete. It happens pretty often. Don't be afraid to push for clarification. Knowing what runoff methodology is required (SCS, Rational, etc.) might shed some light on this.