bed shear stress as a model output

[Carolyn Cload]

good afternoon,

for the modeling work I am doing, it seems to be fairly important to have an estimate of the bed shear stress in the channel so that i can calculate Sheilds stress, as this is a key parameter in bifurcation stability. 

I know that it is one of the cell properties in the Point Info window but that just gives a value for a single cell at one point in time. Is there a way to obtain bed shear stress for the whole model as an output? 

I could probably estimate it using bed slope and hydraulic radius but if it is possible to obtain the calculated values directly that would be really helpful. 

thanks again for all your help

Carolyn 

[Tom Coulthard]

Hi Carolyn - it can be output as per water depth etc.. but code would need to be changed. If you want to do that I can tell you which line to change… you’d need to download the source and visual studio (free version works)

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From: caesar-...@googlegroups.com <caesar-...@googlegroups.com> on behalf of Carolyn Cload <caroly...@gmail.com>
Sent: Tuesday, April 28, 2026 4:13:10 PM
To: caesar-lisflood <caesar-...@googlegroups.com>
Subject: bed shear stress as a model output

 

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[Carolyn Cload]

Hi Tom, 

Yes please. I am not great at coding but it would save a lot of time and extra calculations so worth a try. 

Thanks 

Carolyn 

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[Tom Coulthard]

OK change line 8276 from

            if (typeflag == 15 && tempcycle > 0) FILENAME = "d50top" + Convert.ToString(Convert.ToInt64(tempcycle)) + ".txt";

to             if (typeflag == 15 && tempcycle > 0) FILENAME = "Tau" + Convert.ToString(Convert.ToInt64(tempcycle)) + ".txt";

then change from 8397 change

 else
 {
     sw.Write(d50(index[x, y]));
     sw.Write(" ");
 }

TO:

 else
 {
     sw.Write(Tau(index[x, y]));
     sw.Write(" ");
 }

This basically hijacks the D50 top layer output and turns it into the shear stress. As in you need to check off save d50 in the save drop down menu...

May not be perfect but should work. 

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[Carolyn Cload]

hi Tom, 

thank you for this. I have opened the Caesar Lisflood 2.0.cs file in visual studio and made the changes as you said. When I tried running it, there was an error for line 8398 and I had to remove the word "index" and square brackets [ ] so it now says   sw.Write(Tau[x, y]) which is the same syntax as references to Tau in other parts of the code. 

took me a while to get it working (the input files all needed to be saved in the same folder as the exe file and I didn't know where that was for a while) but it is running now and outputing Tau files instead of d50. So thank you very much for your help. 

[Tom Coulthard]

Oh great - and sorry if I gave you partially right advice! 😅 

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From: caesar-...@googlegroups.com <caesar-...@googlegroups.com> on behalf of Carolyn Cload <caroly...@gmail.com>

Sent: Thursday, May 7, 2026 4:36:21 PM
To: caesar-lisflood <caesar-...@googlegroups.com>
Subject: Re: bed shear stress as a model output

 

To view this discussion visit https://groups.google.com/d/msgid/caesar-lisflood/93f4b942-8062-4004-b8d8-d39418a58ac1n%40googlegroups.com.