TUFLOW Message 3991

TUFLOW Message
WARNING 3991: Negative depth at "a".

Alternate Message
N/A

Message Type
WARNING

Description
Numerical solution has resulted in a negative depth at specified location. This indicates that the model is unstable or unhealthy in this area.

Suggestions
Import the messages layer in to your GIS package. Check for the number and time at which these warnings occur. A few warnings at a single location or timestep in the simulation are not normally an issue. Persistent warnings however warrant further investigation. Check the following:

• Depth discharge curve for Q pits;
  
• Incorrect bed levels upstream or downstream;
  
• A large change in cross-sectional area;
  
• Very steep channel entering a gently or adverse grade channel;
  
• Sudden change in flow area (for example a culvert width entered in mm not m, 1200mm rather than 1.2m);
  
• Issues with 1D/2D linking (incorrect use of Z flag on culvert inlet / outlet);
• Too high a timestep; and
  
• Too small a nodal area.
  

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