Win TR-20 Critical Duration Analysis

[TBrown33]

Please help.

My company has recently transitioned to upgraded software which included a jump from the old DOS based TR-20 to Win TR-20. In the old TR-20 I was able to perform a critical duration analysis and was hoping to do the same from WinTR-20, but I cannot figure out how and I cannot find it anywhere online. Most of my projects require the 100-year critical duration to be performed so it is very important that I can continue to do so. If anyone could pass along any information that would be tremendously appreciated!

 

[psmart]

Win-TR-20, like the old TR-20, is typically used with a 24-hour rainfall distribution. As far as I know, neither program has any provisions for a "critical duration analysis". This concept is normally associated with the Rational method, and not with the SCS/NRCS runoff procedure used by TR-20 and Win-TR-20.

Perhaps you're referring to a study that was done with Rational Method ... using HydroCAD ? See

http://www.hydrocad.net/rational.htm

Peter Smart
HydroCAD Software

http://www.hydrocad.net

 

[TBrown33]

psmart-

I know that TR-20 is typically resevered for the 24 hour storms, but in Illinois it is a requirement to run critical duration. We used TR-20 by running the 100 year storms according to Bulletin 70/71 (which is rain data accumulated by Huff and Angel in the Midwest) and attaching storm durations to the rainfall data. I was hoping I could do the same in WinTR-20 but I cannot find a place to adjust the storm duration. Thank you for the quick response though. Here is what our critical duration used to look like for the DOS TR-20 if that helps (the 1hr at the end of the line is just our name for the storm the actual duration is 6th column from the right)

7 COMPUT 7 050 050 0.0 3.56 1.0 1 2 01 1 1hr
ENDCMP 1
7 COMPUT 7 050 050 0.0 4.47 2.0 1 2 02 1 2hr
ENDCMP 1
7 COMPUT 7 050 050 0.0 4.85 3.0 1 2 03 1 3hr
ENDCMP 1
7 INCREM 6 0.5
7 COMPUT 7 050 050 0.0 5.68 6.0 1 2 04 1 6hr
ENDCMP 1
7 COMPUT 7 050 050 0.0 6.59 12.0 2 2 05 1 12hr
ENDCMP 1
7 COMPUT 7 050 050 0.0 6.97 18.0 3 2 06 1 18hr
ENDCMP 1
7 COMPUT 7 050 050 0.0 7.58 24.0 3 2 07 1 24hr
ENDCMP 1
7 INCREM 6 1.0
7 COMPUT 7 050 050 0.0 8.16 48.0 4 2 08 1 48hr
ENDCMP 1
7 COMPUT 7 050 050 0.0 8.78 72.0 4 2 09 1 72hr
ENDCMP 1
7 COMPUT 7 050 050 0.0 9.96 120. 4 2 10 1 120hr
ENDCMP 1
7 COMPUT 7 050 050 0.0 11.14 240. 4 2 11 1 240hr

 

[psmart]

I see - You were using a trial-and-error approach for determining the storm duration. This is harder to do with Win-TR-20.

You might want to look at HydroCAD. It includes the Bulletin 70 and 71 Huff distributions, and it's trivial to change the storm duration.


Peter Smart
HydroCAD Software

http://www.hydrocad.net

 

[TBrown33]

Is it harder to do or impossible? I have not found anyone else trying to do this online which is why I turned to hte forum. Also, the storm duration would effect the peak discharge and peak time when you are talking about how varied the storms are that I was trying to run wouldn't it?

 

[psmart]

If you use a custom rainfall table with Win-TR-20 you should be able to change the overall duration by adjusting the "Rainfall Table Time Increment".

As you noted, changing the duration will change the peak time and the relative intensity.

Peter Smart
HydroCAD Software

http://www.hydrocad.net

 

[TBrown33]

Thanks, I think this will work. You were a great help!