HEC-RAS 6.2 2D bridge modelling

[Anky Ip]

Hi Folks,

Apparently, HEC-RAS 6.2 has its 2d bridge modelling improved. Does anyone have any idea how it is different from 6.1? I have a model that 6.2 and 6.1 are giving me different results at one bridge location. The WSE upstream of the bridge is ~0.5m higher using 6.2. Nothing was changed. I was simply opened and ran the model with 6.2.

Thanks all in advance!

The official release notes:
“2D Bridge Stability
The simplified approach for including bridges in 2D meshes using 1D bridge curves has been improved. The method adjusts the bottom friction along the faces along the bridge to match the flow from the 1D bridge curves based on the head and tail water surface elevations. Unlike the previous approach in Version 6.1, the new approach preserves the advection and mixing terms and doe snot enforce the flow distribution based on conveyance. The new method in Version 6.2 has been found to be significantly more stable and robust compared to the approach in Version 6.1. ”

[Alison Lackie]

Hi,
Unfortunately I do not have a good answer for you, I just wanted to say I had a similar situation, and was trying to find out the details of how the computations differ between the two versions.

In my case, the disparity was resolved when a coworker reviewed my model and noticed that erroneously high mannings roughness had accidentally been applied to the bridge area; when that was resolved the disparity in model results was eliminated. However, we still do not know exactly why this was the case (as the version 6.1 results also used the ‘incorrect’ geometry file and produced different results). Based on my observation, it seems that the updated version is more sensitive to roughness, so you could try looking at that. Sorry I can’t provide a more complete answer.

[Author]

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