Volume not conserved.

[WencaiZhou]

Hi,
I am running ROMS on a semi-enclosed embayment with result output at each time step (10 seconds), and the result shows that volume is not conserved as I compute the volume fluxes at the four boundaries of a water column, of which the grid size is 555 m * 567 m. The sea surface level of the water column is controlled by the M2 tide with amplitude roughly 2 m, but the total boundary volume flux stays positive all the time, indicating that the volume of the water column is continuously increasing (see the image below).



Is the grid too big to test the volume conservation, or there is some other issue missed? Any suggestion is welcomed and appreciated.

Cheers.
Wencai

[kate]

I can't see your image.

I don't usually worry about volume conservation, but I don't generally have major draining or filling over time, just ups and downs. What are your boundary conditions?

[WencaiZhou]

variation of SSL vs. total boundary volume flux of the water column.

zeta_Q.png (20.65 KiB) Viewed 3866 times

Hi kate,

I have uploaded the image to attachment, and the lateral boundary condition type is shown below:

! Set lateral boundary conditions keyword.
! W S E N
! e o a o
! s u s r
! t t t t
! h h
!
! 1 2 3 4

LBC(isFsur) == Cha Clo Cha Cha ! free-surface
LBC(isUbar) == Fla Clo Fla Fla ! 2D U-momentum
LBC(isVbar) == Fla Clo Fla Fla ! 2D V-momentum
LBC(isUvel) == Rad Clo Rad Rad ! 3D U-momentum
LBC(isVvel) == Rad Clo Rad Rad ! 3D V-momentum
LBC(isMtke) == Gra Clo Gra Gra ! mixing TKE

! Set lateral open boundary edge volume conservation switch for nonlinear model and adjoint-based algorithms.
VolCons(west) == F ! western boundary
VolCons(east) == F ! eastern boundary
VolCons(south) == F ! southern boundary
VolCons(north) == F ! northern boundary

The water column where I test the volume conservation is far away from the open boundaries of the study area, so I think it may have little to do with the boundary conditions, isn't it?

Cheers.
Wencai

[yj7054]

Hi, I also hold the same confusion with you, so did you figure out your problem?
How to check the volume conservation?