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Rainfall Intensity

Rainfall Intensity

Rainfall Intensity

(OP)
Where can I find values for rain intensity for Northern Illinois?  Are the values published for design (10 year storm)?

Thanks

EIT

RE: Rainfall Intensity

(OP)
Thanks for the info.

Now to really show my lack of knowledge...
I'm not designing anything as this is not my area of expertise, but trying to understand how stormwater volume is handled for roof/parking lot runoff.

Using the Rational Method (Q=CIA)

When using the intensity values listed in the documents above what duration should be used for a 10-year storm?

Also to clarify, are the intensity values listed in the previous posts typically used in design or do you typically find tc (time of concentration) then solve for Intensity?  

Thanks again.

EIT

RE: Rainfall Intensity

You need to determine the local requirements for drainage to design the drainage system. The information will come from the municipality

As to roof drainage, that is a plumbing issue. Refer to the link:

http://plumbingengineer.com/sept_10/drain_feature.php  

 
 
 

RE: Rainfall Intensity

Typically you find Tc and read your I off an IDF curve, then plug that I into Q=CIA.

Then if you go further down your storm network, recalculate the Tc, recalculate the I, and take the total watershed to that point as your A, instead of summing up the constituent Cs from upstream sub-watersheds.

 

Hydrology, Drainage Analysis, Flood Studies, and Complex Stormwater Litigation for Atlanta and the South East - http://www.campbellcivil.com

RE: Rainfall Intensity

(OP)
I see, I think I have it now.

So then the "storm duration" = Tc for the IDF chart?

Thanks

EIT

RE: Rainfall Intensity

Implicit in the "rational method" is the assumption that your storm is a flat hyetograph of constant intensity lasting exactly as long as it takes water to get from the farthest hydraulic point to the outlet.

So yeah.  "storm duration" = Tc for the RATIONAL METHOD ONLY.  Don't go mixing methods and start designing pipes for intensities assuming a 24 hour Tc.   

Hydrology, Drainage Analysis, Flood Studies, and Complex Stormwater Litigation for Atlanta and the South East - http://www.campbellcivil.com

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