TUFLOW Message 2991

TUFLOW Message
WARNING 2991 - Negative U depth at ",a,".

Alternate Message
WARNING 2991 - Negative V depth at ",a,".

Message Type
WARNING

Description
A negative depth has occurred at the cell side. This indicates the solution failed to converge at this point and is an indicator that the model may become unstable.

Suggestions
Import the messages layer in to your GIS package. A negative depth can be caused by a number of things, look at the _zpt_check file to see if there is a steep change in topography, the uvpt_check shows the Manning's n value at each cell side. Check this roughness suitable.
A negative depth can also be caused by a badly behaving boundary condition nearby, check if this is occurring near a boundary. This can be 1D/2D, a external 2d (such as a HQ boundary) or a 2D/2D boundary.
View the velocity vectors prior to the message are the flow patterns realistic.
This could also be an indicator of a timestep that is too large. However before reducing the timestep check the suggestions above!

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