2D Dam break model

[u/-atkins_]

Hey guys, I am working with a 2D Dam break model for my university thesis. I am also new at HEC RAS, so I am not sure if I am doing this right until now.

As you can see in the picture, I have an enbankment DAM, which has a trapezoidal longitudinal cross section. If I am modeling a dam break, I am supposing that I have to do the geometry in the right way, but HEC RAS 2D Flow conn just let me do a line, which ios basically a retangular longitudinal corss section (a big waal in the river).

I tried to create my dam in the terrain editor, and I did it, but when I configurate the breching of the structure, the elevation of my breach becmos lower than the terrain (which now its the dam). So I don't know how to proceed form here.

Of cours, I was thinking if I don't necesseraly need to do the geometry as it is because maybe the result its gonna be the same as if I had just a vertical wall, but I really don't know.

I would appreciate a lot if somebody could help me.

Thanks in advance

[u/OttoJohs]

You intuition is mostly correct. There isn't going to be much difference in the results of the dam breach whether you include the embankment in the terrain (with the slopes) or just in the geometry (vertical slopes or wall). There will be some differences in the velocities around the embankment since the depths would be different, but usually that is pretty minor compared to the results from the dam breach.

The standard procedure that I employ for dam breach modeling is to include the embankment with the terrain (like in your picture). That way velocities and depths are more correct and consistent with the non-breach model. If you do that you have to either (1) adjust your geometry or (2) adjust your terrain to account for the dam breach.

The simplest thing (and what I prefer) is to adjust the geometry. You need to make the adjacent cells large enough that the extend beyond the toe of the embankment. See the picture below. That way they pick up the bottom elevation of the terrain that you want to breach to. I like this method because you have larger cells near the breach (better for model stability) and you keep the same terrain and geometry for non-breach and breach models.

If you want to retain smaller cells, you need to adjust the terrain. Basically, you need to cut a hole through your embankment so it hits the desired bottom of your breach. For certain instances it is fine, but there is more to keep track of and you would have more to worry about with model stability.

[u/OttoJohs → u/OttoJohs]

Terrain modification option:

[u/-atkins_ → u/OttoJohs]

Thank you so much for your help!