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Hello, I'm trying to model a model channel that we have at the lab.

I'm starting with a simple rectangular channel with a flat bottom and a steep slope. I've prescribed the discharge (555) and the depth at the upstream boundary and left it free (444) at the downstream boundary since it is a supercritical flow.

However I get this error:

DEBIMP: PROBLEM ON BOUNDARY NUMBER 2
GIVE A VELOCITY PROFILE
IN THE BOUNDARY CONDITIONS FILE
OR CHECK THE WATER DEPTHS.
OTHER POSSIBLE CAUSE:
SUPERCRITICAL ENTRY WITH FREE DEPTH
IN THIS CASE GIVE A POSITIVE DEPTH
IN THE INITIAL CONDITIONS
OR PRESCRIBE THE DEPTH AT THE ENTRANCE.


I have already prescribed the depth at the entrance, and also increased the depth along the channel, and made sure that all the nodes are wet, but I still get the same error.
If I increase the depth at the entrance enough then it runs, but I'm trying to see if I can produce the typical S2 and S3 water surface profiles, and for the prescribed depths I need at the entrance for that it produces the error.

Can anyone help me with that?
Thanks in advance.

Hello,

If you prescribe elevation at a boundary, the 1st idea for initial condition is to set it at the prescribed elevation.
Moreover, it is a good idea to prescribe an elevation at boundary higher the the bottom elevation.

With your input files, the bottom elevation at boundary 2 is 0.12 m whereas you prescribe a 0.04 m elevation at this boundary. Quite hard to do.

Hope this helps,

Chi-Tuan

Hi Chi-Tuan,

Thank you for your quick response, your suggestion solved the issue , I was mixing up depth and elevation, now I get the profiles I was expecting.

Thanks again,

Jonathan.