Culvert not conveying flow

[Dave Bigelow]

Hi Laurent,

I'm currently trying to implement a total of 18 culverts in my model, incorporating the coupled Itzi-SWMM model. The problem I'm having is that when I run the model, no flow is conveyed through the culverts. 

Looking at the output Space-Time Vector dataset with the drainage network results, the attribute "linkage_type", indicates that my junctions are "linked, no flow" (see attached photo). When I compare this with the attribute table from the tutorial, it indicates that the junctions are of linkage_type: "orifice" and "free weir". I also note that the culvert in the tutorial seems to work, as indicated by the non-zero "linkage_flow" in the drainage network results attribute table (see attachment).

I have been sure to include the dummy pipe (link) with outfall nodes linked to one of the junctions to comply with the SWMM rule needing them, as indicated in the tutorial.

I've scoured through the two SWMM .inp files (attached) and the two itzi parameter files (screenshot attached), and havent been able to identify what I am doing wrong to prevent the culverts from accepting flow! 

Note that in the .inp files, junctions J##a and J##b are associated with a particular culvert, with conduits C##a = the real culvert and C##b = the dummy pipe, with orifice O##.

Can you offer any guidance? Am I missing an important parameter somewhere?

Thanks for your help,

Dave

[Laurent C.]

Hi Dave,

The type of linkage depends on 3 values:

- The crest elevation,

- the head in the node,

- the water level in the cell of the surface model.

The first two  re in the table you attached. What is the water level at the surface at those points?

This could help identify the issue.

Regards,

Laurent

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[Dave Bigelow]

Thanks for your reply, Laurent :).

The water level at the cell overlying the culvert nodes depends on the model time step and the culvert of interest. Originally, they all start with a water depth of zero, and by the end of the simulation, they vary between 0.11 and 1.5 meters.

For example, the water level at the upper (input) node in the attached screenshot is zero (or no data) at t=5 minutes and then at t=90 minutes, the depth is 1.525 m. Also see the screenshot attached with the node information. at t=90 minutes, indicating no flow.

Is this what you're asking for?

Note that since I didn't have elevation data for all of the culvert inlets and outlets, I simply extracted the DEM values at those points. I don't suppose this relates to the issue though, since some of the culvert elevations were measured, and also did not convey any flow during the simulation.

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[Dave Bigelow]

Just bumping this thread, to see if anyone else has any thoughts!

[Behzad Jamali]

I’m not sure about this particular issue, but Sometimes simply reducing SWMM model time step might help. You should make sure that SWMM time step is four times smaller than surface model. That means SWMM will communicate with Itzi every four time step.