Ineffective Flow in 2D model

[Kendall Rees]

Hello, I have a 2D model for some proposed bridges over a confluence of 2 streams. I have struggled with defining ineffective flow stations and elevations in the bridge editor due the geometry of the channels and the location of the bridge. I have a couple of questions: 1) if I am using a 2D model, do I need to define ineffective flow regions in the bridge editor and 2) can I use the 2D results to determine the location of the expansion/contraction regions instead of using the method with ratios outlined in the manual? It is having a significant impact on my WSE between the different proposed bridge sizes.

[Luis Partida]

Hi Kendall, this website isn’t great when I have pasted links in the past. Google “modeling bridges inside 2D flow areas HEC” and a page should pop up where they go into great detail on what is going on with the entire process.

[Chris Goodell]

Hi Kendall. If your bridge abutments (as defined in the SA/2D editor) significantly blocks the bridge opening, then yes, you should include ineffective flow areas under the options menu item in the SA/2D editor. They will impact the bridge HTAB curves which are used to simulate the force impact of the bridge in 2D equations. And yes, it’s a good idea to use the 2D results to help inform how you would set up the ineffective flows (better that than to use the old “ratios” method.

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