IDF Curves 1

[kazzy]

Say you have a catchment and you know the maximum flow that can go through the pipes. Which IDF value would you state as the event that can flow through this network? I.e. say the intensity is 30mm/hr this could correspond to a 2 year 10min storm or a 100year 1 hr storm:

http://www.idfcurve.org/chart_samples/chart_samples.aspx

Which is the best to choose and why?

 

[TerryScan]

I would choose whichever curve is the regulatory standard in your location for storm sewer design.

 

[gbam]

kazzy - the design storm frequency and duration is set by local or regional regulations as TerryScan stated above. There are soooo many different combinations of storms and etc.. that governing agencies set their guideline.

 

[LincolnPE]

Typically in municipal design, the majority of the storm sewer network pipes are sized for the Minor Storm events. The Minor Events are typically the 2yr or 5yr. That's because it is not economically feasible to size the network for the Major Events. The Major Design Event is typically the 100 year, and is typically carried on the street surface, within the ROW, with safe freeboard relative to structures.

 

[Ryanemma]

The municipality usually has in the stormwater ordinance which storm to use for design purposes. I always design for a 25 year storm. Once you know the storm, the time of concentration will dictate the correct duration and thereby rainfall to use.

If there is no guidance on the storm frequency to use, pick what storm event you are comfortprable with.

 

[beej67]

Around here, it's not uncommon to see municipal storm sewers designed for the 25, and culverts designed for the 100. Depends a lot where you're at.

If you're trying to back your way in to determine what the capacity storm is for your culvert, then solve for flow using Manning's or whatever, check inlet/outlet control, and plug that into the Rational Equation to determine capacity intensity. Then determine your Tc and read up on your idf curve to determine the capacity storm.

Hydrology, Drainage Analysis, Flood Studies, and Complex Stormwater Litigation for Atlanta and the South East -

http://www.campbellcivil.com