River Modelling

[andersonsoares]

Hi, I'm a graduate student and I am trying to modelling a river that goes from east to west of my grade, i put the flow as a point source (22 point sources side by side) and i am using roms_iview to check if the velocities corresponds with my input( river_transport), and this part its ok, but in the end of my river the u velocities sometimes is negative this represent a flow entering in the end of my river, and this is not expected.
I tried many lateral boundaries, I had the better result with this one:

! W S E N
! e o a o
! s u s r
! t t t t
! h h
!
! 1 2 3 4

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

LBC(isTvar) == Clo Clo rad Clo\ ! temperature
Clo Clo rad Clo ! salinity

Physical Parameters, Grid: 01
=============================

388800 ntimes Number of timesteps for 3-D equations.
20.000 dt Timestep size (s) for 3-D equations.
30 ndtfast Number of timesteps for 2-D equations between
each 3D timestep.
1 ERstr Starting ensemble/perturbation run number.
1 ERend Ending ensemble/perturbation run number.
0 nrrec Number of restart records to read from disk.
T LcycleRST Switch to recycle time-records in restart file.
72 nRST Number of timesteps between the writing of data
into restart fields.
10 ninfo Number of timesteps between print of information
to standard output.
T ldefout Switch to create a new output NetCDF file(s).
100 nHIS Number of timesteps between the writing fields
into history file.
0 nQCK Number of timesteps between the writing fields
into quicksave file.
F LuvSponge Turning OFF sponge on horizontal momentum.
F LtracerSponge(01) Turning OFF sponge on tracer 01: temp
F LtracerSponge(02) Turning OFF sponge on tracer 02: salt
5.0000E-06 Akt_bak(01) Background vertical mixing coefficient (m2/s)
for tracer 01: temp
5.0000E-06 Akt_bak(02) Background vertical mixing coefficient (m2/s)
for tracer 02: salt
5.0000E-05 Akv_bak Background vertical mixing coefficient (m2/s)
for momentum.
3.0000E-04 rdrg Linear bottom drag coefficient (m/s).
3.0000E-03 rdrg2 Quadratic bottom drag coefficient.
2.0000E-02 Zob Bottom roughness (m).
2 Vtransform S-coordinate transformation equation.
4 Vstretching S-coordinate stretching function.
5.0000E+00 theta_s S-coordinate surface control parameter.
4.0000E-01 theta_b S-coordinate bottom control parameter.
20.000 Tcline S-coordinate surface/bottom layer width (m) used
in vertical coordinate stretching.
1000.000 rho0 Mean density (kg/m3) for Boussinesq approximation.
157.000 dstart Time-stamp assigned to model initialization (days).
20170101.00 time_ref Reference time for units attribute (yyyymmdd.dd)
0.0000E+00 Tnudg(01) Nudging/relaxation time scale (days)
for tracer 01: temp
0.0000E+00 Tnudg(02) Nudging/relaxation time scale (days)
for tracer 02: salt
0.0000E+00 Znudg Nudging/relaxation time scale (days)
for free-surface.
0.0000E+00 M2nudg Nudging/relaxation time scale (days)
for 2D momentum.
0.0000E+00 M3nudg Nudging/relaxation time scale (days)
for 3D momentum.
0.0000E+00 obcfac Factor between passive and active
open boundary conditions.
F VolCons(1) NLM western edge boundary volume conservation.
F VolCons(2) NLM southern edge boundary volume conservation.
F VolCons(3) NLM eastern edge boundary volume conservation.
F VolCons(4) NLM northern edge boundary volume conservation.
14.000 T0 Background potential temperature (C) constant.
35.000 S0 Background salinity (PSU) constant.
1027.000 R0 Background density (kg/m3) used in linear Equation
of State.
1.7000E-04 Tcoef Thermal expansion coefficient (1/Celsius).
0.0000E+00 Scoef Saline contraction coefficient (1/PSU).
1.000 gamma2 Slipperiness variable: free-slip (1.0) or
no-slip (-1.0).

And my .h file:

/* momentum equations */

#define UV_ADV /* use to turn ON or OFF advection terms */
#define UV_LDRAG
#define ANA_BTFLUX
#define ANA_BSFLUX
#define ANA_HMIXCOEF

/* general options */
#define SOLVE3D
#define MASKING

#define ANA_STFLUX
#define ANA_SMFLUX

#define ANA_INITIAL
#define ANA_FSOBC

But sometimes the velocity in u direction (in top levels) get negative. And I am assuming that in the bottom the velocity can be negative.
what should i have to do to get a right distribuition of velocities in the end of my river (west side)?

[kate]

If you are imposing a river inflow on the eastern end, then you don't want a radiation condition there. If the western end is outflow, then that should have a radiation condition. Since your inflow is at the edge of the domain, you can use the river sources with a closed wall boundary condition or you can use a clamped boundary condition. Either way, you enforce the velocity as being purely incoming and you have to specify all the tracer values there.

[andersonsoares]

Sorry, the inflow is on the west end. As you can see in the figure, the west end is closed ( the inflow is right).
When I put radiation condition on the eastern end, the outflow get wrong direction.

If you are imposing a river inflow on the eastern end, then you don't want a radiation condition there. If the western end is outflow, then that should have a radiation condition. Since your inflow is at the edge of the domain, you can use the river sources with a closed wall boundary condition or you can use a clamped boundary condition. Either way, you enforce the velocity as being purely incoming and you have to specify all the tracer values there.

[kate]

Is it going unstable? There's nothing in the radiation condition that guarantees outflow in all cells. The outgoing transport should match (roughly) the imposed inflow from the other end.

[andersonsoares]

Is it going unstable? There's nothing in the radiation condition that guarantees outflow in all cells. The outgoing transport should match (roughly) the imposed inflow from the other end.

Kate, i would like to thank you for your help.

I will share what i choose as Lateral Boundary Condition and maybe this can be useful for someone.

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

LBC(isTvar) == Clo Clo rad Clo\ ! temperature
Clo Clo rad Clo ! salinity

And now, the u velocity looks better on eastern end (outflow).