Bridges in 2D

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Bridges in 2D

Ian Sharp
I have a long reach in which we wish to model the channel and overbanks with 2D.  However, there are several bridges which do not cross the floodplain so I am trying to figure out the best approach to model the bridges.  

My approach has been to model with 2D and then run short 1D reaches through the bridges and then return to 1D.  I am running into a mismatch at the 1D/2D interfaces (where flow enters or exits the 1D reach at a cross section).   This is especially prevalent at the downstream 1D section.  What I am experiencing is a sudden drop in velocity and a sharp rise in WSE.

I am wondering if anyone has experience with a similar situation and if there are any tips and tricks out there for how to handle bridges in the 2D environment.

Thanks!

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Re: Bridges in 2D

Jarvus
If you haven't already done so, go into the Options menu and turn on 1D/2D iterations.

If the water doesn't hit the bridge deck, you might try leaving the actual bridge out and modeling with 2D by adding the abutment to the terrain.  If you use really small cells, you can also add any piers to the terrain.  This has to be done outside of RAS.

You might be able to model the bridge by using a storage area connector and using culvert to represent the bridge opening.
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Re: Bridges in 2D

Ian Sharp
velocity DS of bridge

Thanks for the response Jarvus.  I have used the 1d/2d iterations and have found no improvement.  The image shows a typical example of what I am finding where the velocity at the downstream interface is zero in the 2D section.  
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Re: Bridges in 2D

Toby
Maybe try adding more cells at the 1d/2d boundary.  As a rule of thumb you don't want cells to change in size by more than 50% from one to the other, so try small regular shapped cells by the transition and a gradient in size from there.  Also could it be from a change in Mannings?
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Re: Bridges in 2D

Ian Sharp
Thanks Toby.  I have tried to add more cells and have also adjusted the roughness values to better match, but the problem remains.  I am wondering if there might be a problem that is occurring because I am only modeling the channel in 1D and not the entire floodplain (I am modeling 2D over the bridge approaches).
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Re: Bridges in 2D

guana
Maybe look at this:

http://hecrasmodel.blogspot.de/2016/05/bridges-in-2d-important-update.html

Combining 1D and 2D for modeling bridges in 2D areas was not considered. If you find out a good way, please share with us.
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Re: Bridges in 2D

Ian Sharp

Will do.  Thanks!

--
Ian Sharp, P.E., CFM
Project Manager/Engineer | JE Fuller/Hydrology & Geomorphology

Direct Line: 520-207-0008| [hidden email]

Tucson Office: 520-623-3112 <a href="http://|www.jefuller.com">|www.jefuller.com


From: guana [via HEC-RAS Help] <ml-node+[hidden email]>
Sent: Wednesday, October 5, 2016 4:05:02 AM
To: Ian Sharp
Subject: Re: Bridges in 2D
 
Maybe look at this:

http://hecrasmodel.blogspot.de/2016/05/bridges-in-2d-important-update.html

Combining 1D and 2D for modeling bridges in 2D areas was not considered. If you find out a good way, please share with us.


If you reply to this email, your message will be added to the discussion below:
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Re: Bridges in 2D

M. L. Harris
I'm experiencing a similar problem. Were you able to find a resolution?
M. L. Harris, P.E. | Water Resources Engineer
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Re: Bridges in 2D

Albrecht von Boetticher
I have the same problem with bridges in a combined 1D2D model. My bridges work fine in pure 1D and I only added a 2D flow area with a lateral structure upstream of the bridge...