The problem #

Overall Volume Accounting Error in 1000 m^3: 21377.

Overall Volume Accounting Error as percentage: 7.791

Please review “Computational Log File” output for volume accounting details

The cause #

The flow volume that goes in doesn’t equal to the flow volume that goes out. It’s almost certainly an issue of not setting the time step ( computational interval) small enough.

The smaller the mesh cell size is, the smaller the time step should be, or else you will get the accounting error above. The time step that works for a bigger mesh cell size may or may not work when the cell size is smaller.

The solution #

Just change the Computational Interval to a smaller value, and the error will disappear.