TUFLOW Message 1991

TUFLOW Message
WARNING 1991 - ",a,": Negative depth at Node ",a,": "," y =",f7.2," Bed =",f7.2," Iter =

Alternate Message
WARNING 1991 - ",a,": Negative depth at Node ",a,": "," y =",f7.2," Bed =",f7.2," dh =

Message Type
WARNING

Description
Numerical solution has resulted in a negative depth at 1D node. This indicates that the model is unstable or unhealthy in this area. There are a number of possible reason for this to occur, the most common are:
Incorrect bed levels upstream or downstream;
A large change in cross-sectional area;
Very steep channel entering a gently or advers grade channel;
Sudden change in flow area (for example a culvert width entered in mm not m, 1200 not 1.2);
Issues with 1D/2D linking (incorrect use of Z flag on culvert inlet / outlet); To high a timestep; and
Low nodal area.

For a more detailed description on identify the start of instability please see Section 8.1.3 Tips for an Unhealthy 1D Domain and Section 8.1.4 Tips for Unhealthy 1D/2D Links of the TUFLOW manual (reference for 2010 version).

Suggestions
Identify start of instability and cause of instability and fix! See references above for guidance.

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