I saw one reference to time of concentration in which the point you are discussing is called "the point of interest."
Depending on the size, as long as you are consistant in how you work, you should get a workable model.
I use ICPR all the time. I am still new to it, but I echo the response to cut down the calc time. It seems that culvert flow or flow when the pipe ends are submerged makes it a little unstable. Less calc time has fixed it for me. Good luck.
Ask Hanson pipe for a catalog. There is a lot of information in there and they gave me mine for free. Tell them you design with RCP and give a work address.
I use ICPR and faced the same problem about the manual. The manual is online in the help files. Well, I just completed the ICPR seminar and I expect anyone would have a difficult time learning it without the seminar. Come on down to Florida for a couple of days.
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