Error opening Hydraflow files for Civil 3D 2023

[amr_bazaraa]

Files saved in Hydraflow cannot be opened again. Whenever you try to open the stm file, you get the error message "Error loading ...*.stm"

The Hydraflow file contains only a few pipes and has a size of less than 15 KB, so size is not an issue.

I have tried saving 4 different files and non of them can be opened again.

Hydraflow files and Civil 3D are the same 2023 version

Attached is the error I get and the original file

[matt_anderson_pe]

Likely too old.

The header of the STM file is:

""Storm Sewers for AutoCAD Civil 3D 2015"

[amr_bazaraa]

Hi Matt,

That is a very good observation but how is that possible, I do have Civil3D 2023 and I am launching Hydraflow from my current Civil3D 2023. Is it possible that a Civil3D 2023 opens Hydraflow 2015. Sounds very strange. Don't you agree?

I open Hydraflow from Civil3D 2023 by choosing from the menu, Analyze / Design / Launch Storm sewers (Hydraflow) 

Any suggested solutions?

[pendean]

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@amr_bazaraa wrote:

...I open Hydraflow from Civil3D 2023 by choosing from the menu, Analyze / Design / Launch Storm sewers (Hydraflow) 

Any suggested solutions?

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Have you seen this yet

https://help.autodesk.com/view/CIV3D/2023/ENU/?caas=caas/sfdcarticles/sfdcarticles/Open-file-error-w...

And what if you...

https://help.autodesk.com/view/CIV3D/2023/ENU/?guid=GUID-5E6FCD9D-2A93-4AD5-A1E4-48077FA36CC3#:~:tex...

[matt_anderson_pe]

At some point after Autodesk purchased Hydraflow, the file format was modified, but Hydraflow File>Open was not backward compatible. 

Interesting to use SSA to import, and then export to STM to upgrade the process.

[lim.wendy]

Hi Amr,

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[athompson65Z89]

I'm encountering a similar issue. Using Civil 3D 2024, I exported a pipe network in December of 2025 and everything is fine to edit the Hydraflow. However, if I export the same network today, it will not let me make global edits in Hydraflow.

Additionally, I've noticed the exported STM from December 2025, if you look at it in notepad, the top line reads "Storm Sewers for AutoCAD Civil 3D 2015", whereas the export from today reads "Storm Sewers for AutoCAD Civil 3D 2012". I'm not opening the file in a different version as c3d2024 is the only version I have installed on my computer.

I cannot find anywhere in settings, etc. where a export version would be set.

Here is a comparison of the same network being exported. The format is different and it has changed some of my values.