Kinematic wave modeling: Free outfall depth

[andy_a]

Hello!

I tried to run a simple SWMM 5.0.006 model with a free outfall using kinematic wave. The result seems illogical as the depth of the free outfall is almost always constant and equal to that of the maximum depth of the connected conduit regardless of the depth of flow in the conduit (e.g. half-full).

The depth at the outfall however goes back to zero when the connecting conduit is emptied.

For comparison purposes, I tried running the model using dynamic wave. The result seems logical where the depth at the outfall varies with the depth in the connecting conduit.

Can somebody please explain to me what is happening with the kinematic wave model?

I look forward to the group's reply.

Thanks a lot!


andy_a
eliseo.jr.ana@vub.ac.be
brussels, belgium

[Buddy]

In EPA SWMM help you can find the explanation after looking for the keyword outfall.
Outfalls are terminal nodes of the drainage system used to define final downstream boundaries under Dynamic Wave flow routing. For other types of flow routing they behave as a junction.
A outfall is treated as a junction in kinematic wave modeling, so the water in network can only flow out as overflow a junction.
SWMM 5.0.011 have revised it.