Some unphysical phenomenon in the calculation example of DamBreak
As you can see in the above picture, there is no water in the area which I have marked out. That is not physical. Relative to the no water region, I think the dam break will also hapeen along the width of the tank(As shown by the arrows).
Why does this unphysical phenomenon happen? I guess maybe the pressure at the free surface is not zero, so the unphysical pressure gradient leads to this unphysical phenomenon. But I cannot be sure of that. Can anyone give some explanations?