I am getting the following error message on a certain drainage project:
"Time of Concentration Outside Rainfall Table"
I have checked all of my drainage areas and all have a manually entered Tc of anywhere between 4.9 and 15.2 minutes, well within my library's rainfall data. My minimum Tc is set at 5 minutes. The one area that I have a Tc of 4.9 processes using the minimum of 5 minutes, which is what I expect. All of the others seem to produce normal results with their larger Tc's.
Should I be concerned about this error message?
Josh Mauritz
MS v08.11.05.17
GPK v08.11.05.39
Josh
We have partially identified the problem. This error only occurs when the intensity works out to zero which means that the Tc works out to zero. Something odd is happening when you use the weighted method that is forcing you into this odd situation. We are in the trail to debuggin the network so we can track where the zero is popping out and then we can hopefully discover where (if any) the error in the drainage network lies.
In the mean time you should be bale to proceed with the weighted checkmark turned off without any ill effects. If your reviewing agency requires the weighted calculation then, hopefully we can finish the debug process before you have to submit any reports for review.
Robert GarrettSenior Product EngineerBentley Systems Inc.
Robert,
Thanks. You will find a zipped folder on your ftp site. I appreciate your time.
Josh - This just in from the original developer of the drainage program.
" If he is using the weight TC option, we might need to find out if he has some huge discrpancy in the areas and c values that is screwing up this weighting."
If you are inclined to then send me your DGN, GDF & drainage library. I will also need the GPK if any nodes are based off an alignment along with tin/gsf files and superelevation DGN file if they are used.
You can post on ftp://ftp.bentley.com/pub/incoming if they are too big for email
Dan,
Thanks for your help. I took a look at my file using your/other's suggestions. Here is what I have concluded:
An Area report shows all Tc's used to be between 5 and 15.2 minutes - Seems OK, but error message still appears.
Links From and To node Cumulative Tc report show Tc' s of between 5 and 15.77 minutes - Seems OK, but error message still appears.
My normal preferences use the "Weight Time of Concentration" under Intensity Options. If I uncheck this and then design my network, the error message goes away. However, then I don't think my results are correct.
Any suggestions?
Well in Texas, 14 thousand minutes isn't a long time to wait for it to rain... ;-)
But if your Tc is actually less than 5 minutes or more than 10 days, the easiest way to locate it is run the Report Builder and output the Tc values into a csv file, then use Excel to highlight the times outside that range.
Based on Robert's suggestion, output the Area variables to check that a drainage area isn't the offender. Based on what Alex says, ouput the Links's "From Node" and "To Node" cumulative Tc values as the offending Tc value could be inside a pipe or ditch.
Sometimes we use "fake" areas just to get a link or node connected to the system and we have to use a Q=.001cfs, if we forget the to leave that in and design/analyze the network the resulting Tc is huge. An excel conditional formatting statement should highlight the offender for you.