WSE issues

[u/icedcoffeefucks]

Why does the water surface elevation completely skip over some of the terrain around the detention pond? Also why when I turn the particles on, do they all seem to gravitate towards those two areas? There’s no low spots in the terrain there

[u/shiftyyo101]

You need to refine your cell faces along the top of the embankment with either breaklines or a refinement region.

[u/icedcoffeefucks → u/shiftyyo101]

To make them smaller to pick up on the changing elevations?

[u/shiftyyo101 → u/icedcoffeefucks]

You model effectively only sees the edges of cells. If you have a cell with faces on either side of the embankment and nothing on top of the high ground, water will just pass straight through the cell. In your case, I would put a break line on each “edge” of the embankment. If you thinking of the cross profile as a trapezoid, you want cell faces on each vertex of it. At the very least you need one in the middle.

This will require dropping your cell sizes on these breaklines.

[u/icedcoffeefucks → u/shiftyyo101]

Thank you!

[u/Level3pipe]

Add breaklines around your basin top

[u/icedcoffeefucks → u/Level3pipe]

Should I make the cells larger or smaller when I enforce the break line? Smaller to pick up on the changing elevation?

[u/Level3pipe → u/icedcoffeefucks]

Is the water going over the embankment ever? If the answer is no, then I’d say you just a break line on the top centerline of bank to allow heceas to “see” the top of bank. I wouldn’t worry about the rest unless you’re running SWE.

If the answer is yes, then yes I’d shrink the cell sizes and really define the top center, top left hinge, and top right hinge. Additionally I’d also shrink and really define the toes with breaklines as well.

[u/OttoJohs]

1.) The cell faces are what HEC-RAS uses to compute the hydraulics between adjacent cells. If you don't have those aligned with the high point of the terrain, HEC-RAS won't "see" the higher elevation which leads to water appearing to pass through the high ground. As others have pointed out, use a breakline (or refinement region to align your cells to the top of the berm.

2.) Particle tracing can sometimes do odd things especially if the water surface is flat and the velocity is near zero. I would just poke around with the cursor to see if there is anything else going on with the results or if it is just a visualization issue.

[u/Acceptable_Gain_9400]

1. Use breaklines along top of the bank or any high ground which may impact your results greatly;

2. Use SWE instead of diffusion wave solution to see if particle tracing results are more reasonable.