SSA Pipe Surcharge HGL @ Junction

[telze33]

I have set up a pipe network of an existing storm drain system for the upstream part of the network, and then there is proposed storm drain structures and pipes on the same network as well.  Regarding the flow calculations, the jurisdiction I am working in has a specific way that they calculate peak flows. So, I have inputted the peak flows as “external flows” at the junctions.  I want to the the HGL at the first 36” pipe and 1st junction, but the HGL jumps up and doesn’t seem to look correct on Junction 2.  Why is it doing this and how can I model it correctly so that the HGL is showing correctly?  What am I missing?  Below is a picture of what I am trying to explain above.  Thanks!

[Anonymous]

I am having the same issue, does anyone know how to resolve this?

[info]

Has this mystery been solved ?

[mzjensen]

The original post is pretty outdated, so I'm assuming that it got worked out. But for the more recent issues, I'd be happy to take a look at a project file if you post it.

[rmccollum]

There are multiple reasons why your HGL is so high, but the main reason is that you go from a 36" pipe with a flow capacity of about 53.7 cfs to an 18" pipe with a capacity of 8.4 cfs.  There are multiple design concerns with what is shown above with multiple potential solutions, but the system simply will not work if your Q goes above the Q of the 18" pipe.

Randy McCollum, PE

IMAGINiT Technologies

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