IDF A,B,C Coefficients vs SCS Storm Distribution 1

[Ryb01]

Hello All,

I recently had a conversation with a colleague of mine regarding converting rainfall intensities from A,B C coefficients of the rational method to rainfall depths to further generate a SCS storm distribution.

I had never heard of this before and I would question the accuracy of doing so..however, I wanted to open up a discussion see if....
1) Is this possible?
2) If yes, where could I find referece material?
3) Are there limitations and/or concerns of doing this?

Thank you in advance. Any help in this matter would be greatly appreciated.

 

[psmart]

As a guess, your colleague is generating a so-call "Chicago storm", which can be defined based on Rational coefficients. A number of H&H programs, including HydroCAD, have this capability. Basically, it's a nested storm, with the highest intensity usually placed at the center of storm.

The applicability of a Chicago-style storm is generally specified by the local stormwater regulations.


Peter Smart
HydroCAD Software

http://www.hydrocad.net

 

[Ryb01]

Hi Psmart,

Yes agreed, however, would it be possible to create, for example a 100-year Chicago storm to a 100-year SCS?

My thoughts would be you would have to do a bit of math to break down the Chicago storm into unit intervals to be determine a total rainfall depth and then apply to the SCS distribution? Could you do this?

 

[psmart]

A Chicago-style storm and the standard SCS distributions are all mass curves. There's no need to convert between them, since they're already in the same basic format.

Regardless of the origin of the mass curve, you can evaluate the IDF data for a duration of 24-hours to get a total depth for use with any of the mass curves. There's no need to "break down the Chicago storm". Just evaluate the 24-hour depth directly from the IDF coefficients.

Peter Smart
HydroCAD Software

http://www.hydrocad.net

 

[Ryb01]

Thank you Peter. Your help is much appreciated.