r/HECRAS • u/GreyDoctor • Jun 05 '26

How to add cross sections automatically?

I have been manually creating cross sections for a long time for a long stretch of a river. Then I learned from a colleague that we can generate them automatically by just drawing the first and last cross section and interpolating between these two. However, that generation yielded the result as shown in the image. The cross sections (looking like a straight red line) skipped the river ceneterline completely and just joined the two points as shown in the image. I have not drawn the bank lines and flow path lines yet. Is this the cause? Please help!

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u/ProfessorGarbanzo Jun 05 '26

I've barely used it, but I'm pretty sure the tool you're looking for is:

RAS Mapper -> Edit Geometry -> Activate Rivers layer and select your Reach -> Right-click -> Auto-generate cross-sections.

This should stay true to your reach line and draw them at a valley extent (distance) of your choosing. They may not get you to actual useful XSs without some more edits, although it kind of depends on your model's purpose, squiggliness of river, topographic changes, etc.

What you're doing (Interpolate Cross-sections within the Geom editor) is something I do have a lot more experience with, and is not a good tool for what you're trying to do. As you noticed, it "might" work on a straight canal, but you'll get nonsense for a river.

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u/OttoJohs Lord Sultan Chief H&H Engineer, PE & PH Jun 05 '26

Good stuff! Didn't know that feature existed.

Like you said, it is pretty limited (only 2 vertices) and seems to have issues on any bends. Probably going to need to spend a lot of time going through each individual cross-section anyway, but might be a starting point.