How to disable a junction but keep it in the geometry?

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How to disable a junction but keep it in the geometry?

Jaison
Hey guys,

Thank you in advance for any help. I do a lot of FEMA modeling and according to their guidelines they do not allow junctions in HEC-RAS models. Is there a way to keep a junction in geometry but disable profile smoothing and other features that involve a junction? We have to treat every stream like different entities for flood mapping unless coincident peaks can be proven. Very rarely the case. I ask because a feature like this would help resolve topology errors (connecting lines for the NFHL layer) when putting all the streams together for the final LOMR or study. Just less work for the GIS team.

Thanks!!!
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Re: How to disable a junction but keep it in the geometry?

Luis Partida
Usually the peak flow from the incoming tributary is just added to the main rivers cross section at the intersection of the trib and main river
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Re: How to disable a junction but keep it in the geometry?

cameron
You shouldn't just add the peak flows unless they have coincident peaks. Usually the flow downstream of a confluence does not equal the sum of the trib and the main stream flow upstream of trib.

A lot of FEMA studies are done using peak regression flows or hydrographs that have been calibrated to regression flows as there is no other calibration data.

The answer about turning off junctions is, it is not possible. Once a junction is placed, you will need to specify reach names and junction inputs.
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Re: How to disable a junction but keep it in the geometry?

Lonnie A
In reply to this post by Jaison
This is how I avoid use of junctions in unsteady. It might be possible to do something similar with 1D but I haven't tried it.
http://hecrasmodel.blogspot.com/2018/12/using-hec-ras-storage-area-and-lateral.html
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Re: How to disable a junction but keep it in the geometry?

Luis Partida
In reply to this post by cameron
Its more rare to find an unsteady state FEMA model than a steady state. In most cases the peak flow (especially for small tributaries) is just added to the flow intersection and the junction trib is ignored. Obviously if you are doing an unsteady state model theres no need to do this. Thats common sense. As Lonnie said there is ways to remove HEC-RAS junction modeling by utilizing either SA or 2D flow area. That is more advanced and people are barely picking up on this old trick now