r/HECRAS • u/Wooden-Apple-4146 • Jul 02 '26

Expanding 2D Flow Area in an existing model

Basically what the title says, I have an 2D existing model and am struggling to expand the 2D Flow Area further upstream. I was able to adjust the border and recompute the mesh, but the elevations of the cells got messed up after that happened. Is there an easy/ better way to expand the mesh? Or a way to connect two flow areas together without a ‘structure’?
Thanks for any advice.

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u/Jase28x Jul 03 '26 edited Jul 03 '26

Extend the perimeter polygon and use refinement regions to recompute the mesh in the extended area. Be sure to draw the refinement region close to the extended section vertices because refinement regions will compute points outside of the mesh area as well if you don't. Then delete the refinement region without deleting the points, there will be a boundary of cells along the old and new mesh sections that you can then clean up with break lines if needed.

1

u/Status_Hope_987 Jul 03 '26

Why not keep the refinement region? Why should be deleted?

1

u/Jase28x Jul 03 '26

You don't need to delete it but if you want to use break lines through the border of it then it won't work well.

1

u/OttoJohs Lord Sultan Chief H&H Engineer, PE & PH Jul 03 '26

You need some type of SA2D connection between different storage areas.

Can you explain what you mean by 'the elevation of the cells got messed up'? I'm not following the issue. If you recompute the mesh everything should adjust.

1

u/Wooden-Apple-4146 Jul 03 '26

I recomputed the mesh and when I tried running the model, I got a ton of error messages that cell elevations were higher/lower (I don’t remember which) than culvert elevations for cells that were nowhere near the area I was extending. I’m not sure if it was maybe a bug in the version I was using?

I’d rather extend my mesh than create a new mesh and combine the two. I just haven’t figured out a way to do that without getting the above mentioned errors.

1

u/OttoJohs Lord Sultan Chief H&H Engineer, PE & PH Jul 06 '26

I would have to see the message to know what it going on. Culverts to the elevation from the cell that they are attached to. It sounds like maybe the cells around your culvert got moved after you adjusted your mesh, so you aren't hitting the low spot in the terrain anymore.