Well, I’ve been saying I was going to do it. So I did it. In fact, it is one of the most often reasons someone visits the site. That I mentioned Intensity Duration Frequency (IDF) curves for London in a previous post has generated a lot of site activity for me. So, in return for the traffic I sat down and worked out a first attempt at the graphs.
Using Microdrainage and the Flood Studies Report (FSR) I cut out a lot of the hand work from the Wallingford Procedure (Rational Method). Their generate rainfall looks like this:
Pretty nice, eh? After a laborious bit of data entry and clicking it gives us everything we need to create a nice set of IDF curves.
So here it is, in all its glory, the IDF curve for London, UK in mm/hr:
Or, for you Americans, inches/hr:
Obviously I can take no responsibility for this information, or whatever you might do with it, but it does go a long way to pointing out why they get away with 6 inch pipes everywhere here. I’ve got an old IDF curve for Birmingham, AL somewhere so I might dig it out and do a little comparison. From memory though I believe they’re about 10-12 inches per hour in the 100 year storm. Quite a difference!
