I am new to SMS-TUFLOW. I am having some problems with the model as every time when I delete or modify the boundary of the model, the model become unstable. For example, in this model, it ran smoothly before. But when I added two more polygon in the material, when I run it, the error pop up and said the Tuflow model is unstable. I checked the error message and it said "Negative V depth" "Negative U" .
I have the feeling I need to do some extra steps when I want to modify the boundary because when I rebuilt the model again with the extra polygon, it ran smoothly.