Varying offset from Feature
I would start with the grading tools. You can create a grading criteria very easily to grade to surface at 3:1
If the top of bank is known and the the flow line is known there is no grading to be done, just add the two FL to the surface.
Joe Bouza
Did you find this post helpful? Feel free to Like this post.
Did your question get successfully answered? Then click on the ACCEPT SOLUTION button.
Are you looking to locate the Flow line?
Joe Bouza
Did you find this post helpful? Feel free to Like this post.
Did your question get successfully answered? Then click on the ACCEPT SOLUTION button.
If the line are fixed the project 3:1 a distance beyond the Flow line the extract the 3:1 surface elevations to the flow line.
This may differ then your Known elevations.
Maybe you are trying to locate the flow line ? if this is the case
grade to each known elevation AT 3: 1 , Then add transition in between, since they are 3: 1 the transition will and your FL will be located
Almost forgot. to do this you answer NO when asked to apply to entire FL
Joe Bouza
Did you find this post helpful? Feel free to Like this post.
Did your question get successfully answered? Then click on the ACCEPT SOLUTION button.
this is the part I dont get. If you know the elevation of the channel and the top of bank is fixed, the slope is what it is
anyway, the green lines are the known channel ele at 3:1, the yellow is the fixed top of bank FL. after you place the grading slivers, then in the grading tool bar drop down pick transition and pick the top of bank FL between the slivers
Joe Bouza
Did you find this post helpful? Feel free to Like this post.
Did your question get successfully answered? Then click on the ACCEPT SOLUTION button.
Is the flow line in a constant position?
Joe Bouza
Did you find this post helpful? Feel free to Like this post.
Did your question get successfully answered? Then click on the ACCEPT SOLUTION button.
Hi,
If I understand you correctly this is what I do.
1. Import your flow line points through a point file and add it to a point group. (If you can use dynamo that would be great)
2. Offsett your flow line polyline either side (say 1m)
3. Convert the two lines to feature lines at an elevation you like. These are dummy feature for our work.
4. Create a surface and add the two FL as breaklines
5. Then add the point group to the surface. Now you will have the flowline elevations on the surface
6. Convert the flow line polyline to a feature line. Get the elevations from the surface but avoid adding elevation points at intermediate break points and set relative elevation to 0.
7. Now when the elevations of the flow line change as a result of hydrological reasons, remove old points and add the new points to the same point group. If the changes are minimal you can manually update the points.
8. This will update the surface and ultimately the flow line feature line because it has relative elevations to the surface.
Based on your description, you want to grade to a feature that has a varying offset and elevation. This, unfortunately, (or fortunately, depending on how you feel about grading objects) cannot be done with a grading object. You can do it with a corridor, using an assembly that uses the link slope to elevation generic link.
Christopher T. Cowgill, P.E.
AutoCAD Certified Professional
Civil 3D Certified Professional
Civil 3D 2026 on Windows 11
Please select the Accept as Solution button if my post solves your issue or answers your question.
Pardon, that wasn't what I meant.
If you are looking to locate it, then there is a bit more to do.
Make a temp grading and surface from the top of bank., set the tessellation to something reasonable, and grade at slope for arbitrary length beyond where the flow line is expected.
the feature line for the flowline is initially placed with the known elevation snapped to the the tessellation ray. have a Feature line label style that displays vertex and slope. each vertex coincides with a ray. anywhere along the ray is 3:1 , grip edit the unknowns to a ray until the flowline slope is satisfied.
Not perfect but you will get what you need in relatively short order
Joe Bouza
Did you find this post helpful? Feel free to Like this post.
Did your question get successfully answered? Then click on the ACCEPT SOLUTION button.
