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Hi,

I am modeling a supercritical flow in a river, with bedload transport.
Having a look to the results, at the inlet there is a non stable bed evolution. I set a constant solid discharge and 0 evolution at the inlet, but in the next node there is ~3 m of evolution. The separation between nodes is 1.5 m, so having a 3 m evolution with so little displacement is quite strange.

I attached a figure with this inestability.

Do you have an idea why these could be happening?

Regards,

Gonzalo

Hello,

maybe or most likely because your imposed solid discharge doesn't correspond to the sediment transport capacity calculated by Sisyphe, depending on the sediment transport formula you use.
Furthermore think of the physical behaviour of your system: e.g. do the boundary conditions describe what you observed or measured like "supercritical flow" and the "setting 0 evolution at the inlet"?

Best regards,
Clemens

Hi Gonzalo,

As Clemens suggests, you seem to prescribe a higher sediment flux then the flow can carry, causing sedimentation close to the boundary. However, on top of that you get oscillations in the sedimentation. It is difficult to determine from the image alone, but the obvious problem might be your time step. With a grid size of only 1.5m and supercritical flow, your time step will need to be well under 1s, I would think. Make sure the time step adheres to the cfl condition for both the flow and the sediment transport!