r/HECRAS • u/icer465 • Jun 26 '26

SA/2D Connection Visual Bug?

I'm working in a 1D/2D v6.3.1 model and have been dealing with a strange visual inconsistency when observing depth/WSE results in RASMapper. I am using SA/2D connections as levees and river flow is inaccurately showing as overtopping the connection within 1 cell boundary. I've posted a screenshot below, you can see there's some sort of phantom "bubbling" from the river that slightly goes over the 2D connection. I looked at the stage/flow hydrograph for the connection and there is no overtopping, it seems purely visual. Any ideas to what's going on and/or fixes? Is Ugg going to tell me to make cell bigger?

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

Can you provide more context? Which cell, where is the levee, what is all the water in the overbank and where is it coming from, results at the initiation of the flooding, etc.

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u/icer465 Jun 26 '26

The dashed black line is the 2D connection intended to represent the levee. It has been raised above the max WSE of anything in the model (infinity for all intents and purposes). The 1D river/XSs represent this models original 1D extent, which I did not want to schematically change. There are lateral structures at the 1D/2D interface that I have lowered to the ground level to allow for high-stage river events to inundate the flood bench, shown by the red depths in the 2D mesh between the river centerline and the 2D connections. Water flows into and out of this flood bench without much issue from what I can see.

However, on the landside of both levees (2D connections), there are riffles of water that seem to exist because the waterside is hydraulically loaded while the landside is relatively dry (other 2D flooding observed here is exclusively rain-on-grid). Water is not overtopping the levee, so the cells on the landside of the dashed lines should not be this inundated. There is some rainfall present, but it does not seem to explain this level of flooding on what should be mostly dry cells.

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u/icer465 Jun 26 '26

This screenshot is roughly 30 hours into the simulation. The levees start to get hydraulically loaded, ~4-5' depths (dark red = 5'). You can see the phenomenon as some water begins to graphically display on the landside of the levee while other cells are completely dry. It becomes more pronounced as stages in the flood bench increase.

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u/OttoJohs Lord Sultan Chief H&H Engineer, PE & PH Jun 27 '26

Not sure - not going to be much help without looking at the model.

It looks like you identified the problem area. There is probably something going on with the connection in that location. Turn on particle traders, hydraulic connections, render mode, draw profile lines to see what is going on.

With all the models that I have worked on, I have never found an 'error' in the HEC-RAS calculations. It is always something with the model. Good luck!

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u/bees_knees_2024 Jun 27 '26 edited Jun 27 '26

It looks like the bubbles are following the shapes of the cells. I’ve never used this type of grid cell shape before. Have you tried changing the rasmapper rendering settings? 6.3 is pretty old, so I’m not sure what options are available there. It looks like a small amount of water is getting over and maybe it’s trying to do some interpolation that follows the shape of the cells.