HEC-RAS 3D Modeling 1

[GarySki]

What are the advantages of 3D modeling? We have a project where it was suggested that 3D modeling may be necessary since we are proposing to grade around some existing trees that will remain in place. They are currently along the bank but will end up in the middle of the river. Can't we make reasonable assumptions as to velocity/erosion and continue to use HEC-RAS as a 1D model? Why do we need 3D? It seems like overkill to me. Anybody use 3D on a regular basis?

 

[RWF7437]

Are you possibly confusing two different things? As far as I know HEC-RAS is, and remains, a 1D hydraulic model. That is, it can only model flow in one direction and has no ability to account for things like backflows, eddies, whirlpools and the like. However, it can present the results of the calculations in a kind of 3D picture, such as an isometric view of the river profile. It is probably also possible to import the results into ACAD Civil 3D to make a "pretty" picture of the results. But I am NO ACAD expert so perhaps I'm saying this incorrectly ?

I hope others with better knowledge of both HEC-RAS, HEC-Geo RAS, and AutoCad weigh in on this to explain it better than I have.

good luck

 

[GarySki]

Apparently 3D is some add-on software that works with HEC-RAS. I'm just now trying to understand what it entails. I've worked with AutoCAD Civil and 3D earthworks calcs before but had not heard of 3D hydraulic modeling until this morning. I'm told 3D can evaluate velocities more precisely.

 

[RWF7437]

" I've worked with AutoCAD Civil and 3D earthworks calcs before but had not heard of 3D hydraulic modeling until this morning. I'm told 3D can evaluate velocities more precisely."

Have you worked with HEC-RAS or HEC-Geo RAS before ?
How precisely do you need to know velocities and is this precision really worth the extra time and expense needed to achieve it ?

I suspect the answer to the second question is NO, because the flows you will be using are probably no more accurate than plus or minus 50%.

good luck

 

[sammyk]

You peaked my curiosity, so a quick google search found these links.

http://www.flow3d.com/

http://www.usbr.gov/pmts/sediment/k...hree-Dimensional Hydraulics of Rock Weirs.pdf

Looks quite expensive, and far beyond a HEC-RAS analysis. Heck, it looks you need a PHD in Fluid dynamics to do these studies.

 

[RWF7437]

Try this link...it's a lot cheaper than 3D modeling

http://civil3drocks.blogspot.com/2006/08/hec-ras-tools-for-civil-3d.html

 

[GarySki]

Thanks guys. You confirmed my suspicions. To answer your question, I've only worked with HEC-RAS a little bit. I understand it but am not proficient with all its nuances. I'm more familiar with the Rational Method and mannings. Their results are only as good as their input and can be manipulated quite a bit based upon the assumptions. I suspect HEC-RAS is the same. I agree, it's not worth the headache to save a few trees. I'll just get a good soil erosion rep on board and take our best shot at saving the trees. If they are washed out, it wasn't meant to be.

Thanks again! Gary