Hello,
I would suspect that you have very shallow zones and that you are adding forcing terms in those shallow or dry zones. It is similar to what happens with wind and for wind we have introduced a threshold depth for that. You can try to modify subroutine prosou.f, changing lines 737 and 738, where the forcing terms are added, by something similar to what is done on wind at lines 353 to 359. I agree that in the future we should do that once for all for everybody and add a corresponding keyword, but well this is where we are now.
With best regards,
Jean-Michel Hervouet