Posted Tue, 29 Jul 2014 09:00:01 GMT by Ben Mauck PhD Student

I have been receiving Error message 25 that the levels have exceeded the maximum level and warning 47 that the levels has fallen below the slot. I have lookup the these errors and they all seem to say that the model is unstable, mainly due to inconsistencies in the bed level or boundary conditions?  How can I rectify this instability? Would defining the cross sections at river junctions help?

Thank you
Posted Mon, 04 Aug 2014 10:07:35 GMT by Mathieu Hellegouarch
Hi Ben,

Yes, that seems to be due to instabilities. If you get warings in the log file indicating that bed levels are different at rivers' junctions, then you should indeed try to correct these discrepancies of bed levels. To do that, you can indeed add cross sections at river junctions, and then adjust their levels.

You can also look at the results at the first time steps: if there is a big change in the results between the initial conditions and the following time steps, it may also be cause of instabilities. In that case, this has to be avoided by improving the initial conditions.

There are other things that can help to improve the stability, but an important one is the time step: depending on the spatial discretisation and the geometry of the river, you may need to decrease the time step to e.g. 1 s. So you can also consider reducing this time step, for example if you kept the default value.

Best regards,

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