2D Connections Stage/Flow Hydrograph Output Variables

[mowens]

Hi,

I was wondering if someone knew the difference between these flow outputs for my 2D connection. This culvert has a rating curve in it because it’s technically a siphon underground.

When I look at the Stage and Flow Hydrographs I get a lot of flow variables. What do they mean?

There is
– flow
– weir flow
– culvert flow
– outlet RC

What do they mean and why is my culvert flow negative?

[Jarvus]

Flow is total for the entire structure.
Weir flow is the flow over the top of the structure.
Culvert flow is flow through the culvert.
Outlet RC is flow from the outlet rating curve.
Negative flow usually means you have reversed flow from the tailwater side to the headwater side. For a long connection, it is possible for flow to be going one way over one part of the structure and the other way over a different part. It is also possible that the rating curve has not been entered correctly.

[mowens]

Thanks! That helps a lot!
I have a follow up about 2D connections:

When I run the model and look at my stage/flow hydrographs for any connections that are overtopping or about to overtop, my output looks like a little strange. The HW and TW Stage keep increasing but the the total flow and the culvert flow decrease. This doesn’t make sense to me that I would see a decrease in flow.

I have run the model with Inlet control, outlet control, smaller time steps, adjusted the mesh so the cells are bigger, changed the overflow computation method from from weir equation to normal 2D equation and none of those options have changed hydrograph and decreasing flow through the culvert during the storm event. I also tried running as DW and FM and changing the weir flow submergence decay exponent.

I have run the same culvert in a test 1D model using the same HW/TW elevation relationship and when I look at the 1D model my culverts can handle much more flow based on the WSEs.

I am not sure why the 2D model is doing this but maybe you have some insight as to why this is happening.

2D

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