A Peculiar HGL, any ideas?

I'm getting a strange HGL for a fairly simple run. Just running the flow routing module with an external inflow. Using Dynamic Wave with a 1 second time step, 15sec conduit lengthening time step, both normal flow limits. Why would manhole PL120 not be surcharging here? At one point I had several of these patterns at every other manhole. Any ideas of what I could try to determine the issue?

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  • Hi,

    I saw your model and think that there is an error in your Manning roughness coefficient for all conduits: 0.0013; it is a very low value. I changed it for 0.013 and the model seems to be an expected behaviour


    • Thanks, Rodrigo.  That was a good observation by you.   It also really does help his simulation results.

      • Yes, the switch between normal and St. Venant causing that behavior makes sense.

        An extra zero was the problem though, what a simple mistake that really skewed the results! Thank you Rodrigo!

  • I lowered the flow to 2 better show what is happening in your links.   You have a mixture of normal flow for steep links, flat bes slopes and intermediate bed slopes, the hgl has to change to have the same flow in all links.3293138902?profile=RESIZE_1024x1024

  • Hi, Please attach your model and I can comment.   The HGL does look odd to me as well.

    • Here is the model. The only inputs should be external inflow at the upper most junction and a DWF pattern downstream of this issue.

      • Hi, All that is happening is that the head has to build up those nodes with the spikes in the HGL to push the water downstream.

        • Hmm, I still don't understand how there can be a positively sloped HGL in the direction of flow. Between nodes PL119 and PL120 for example.

          • The flow is the same in each of  your links but the depths are different in each link, to get the same flow through each link you need to increase the HGL.  Some of the links are steep and use the normal flow equation and not the full St Venant which accounts for the odd slope to the HGL3293135444?profile=RESIZE_1024x1024

  • Are you using kinematic wave or dynamic wave for the solution?

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