freshwater river inflow increased salinity of lake

[Fatima]

Dear all,
I am working with an axisymmetric idealized lake. I added two freshwater river inflows with a constant temperature of 4 degrees centigrade (I activated LUVSrc and temperature and salinity tracers). The lake surface temperature is set to freezing point temperature, and the lake's salinity is set homogeneously at 14 PSU.
My lake depth is 145 m, and the 45 km length scale and average inflow velocity is 2.1 m/s (dx=90m and dz=0.16 m and f=0.033, river_transport= 1m^3/s).
Despite adding freshwater inflow with a constant temperature of 4 degrees Celsius, the salinity of the lake near the river's mouth increased by approximately 0.5 PSU.
I would really appreciate any help or suggestions.
Thanks a lot.

[jcwarner]

so the river inflows have salt = 0, correct?
are there any undershoots of sal? is the sal < 14 anywhere?
depending on the advection scheme, you can get over and under shoots, but the total mass should be correct.

[jivica]

what about temperature? Is it correct or do you have a strange result? Are you sure about the inflow direction you set (inflow not outflow from the domain)?

[Fatima]

Thank you for your reply.
There is no place with a salinity of less than 14 PSU. The river salinity is 0 PSU, and the river temperature is 4 degrees C.
Based on velocity fields, river directions are correct.
I changed my f=0, but still, i have the same problem with salinity. I attached velocity fields, temperature, and density vertical sections.
My current advection scheme is MPDATA.
Despite adding rivers with a flow rate of 1 m^3/s, there is no noticeable increase in the volume of water, there is a potential problem with water mass.
Should i change my advection scheme?
I would really appreciate any help or suggestions.
Thanks a lot.

[jcwarner]

where are you putting the rivers in at? are they from the lateral boundary or in the interior of the domain?
the LuvSrc need to come from masked areas, you cant just add them into an active grid cell.
If you want to add the source to an active grid cell, then try LwSrc.

[Fatima]

I defined rivers both in lateral boundary and mask areas (mask = 0), but I still have the same problem with LuvSrc.
I tried LwSrc (mask = 1), and the salinity increased (I attached a salinity vertical profile close to the river mouth).
I changed my settings and defined one inflow and one outflow. Salinity increased near the inflow, and salinity decreased near the outflow.
Do you have any suggestions?

[jivica]

You are close, think your river_direction and/or transport is wrong. Read about the rivers, John wrote a nice tutorial.

[wilkin]

You say ...

defined rivers both in lateral boundary and mask areas (mask = 0), but I still have the same problem with LuvSrc.
I tried LwSrc (mask = 1),

... but do you mean u,v or rho masks?

LwSrc points can be anywhere in the water mask_rho=1 but with i,j set by river_Xposition,river_Eposition in FORTRAN indexing convention for rho points.

LuvSrc points must be placed at u,v cell faces with i,j set by river_Xposition,river_Eposition in FORTRAN indexing for u,v. The cell face must be a land/sea boundary (which will have mask_u or mask_v zero but be adjacent to a rho water point). Then you need to set the sign of the transport so it flows into not out of the adjacent rho cell.

Have you read https://www.myroms.org/wiki/River_Runoff

[Fatima]

Thank you for your reply.
I did same settings for river definition. Salinity increased again. Is there any solution for increasing salinity?

[jcwarner]

ok. this looks like a simple test case.
can you tar up the ocean.in, *.h, and any files someplace that i can get?

[Fatima]

Thank you John,
I attached my roms files. It is a simple test case. When I defend outflow, Salinity decreases and vice versa.

[wilkin]

In bowl_safe_new2_rivers_u.nc the first river_Xposition index (501) is invalid FORTRAN indexing of rho goes from 0 to L (green points in this figure: https://www.myroms.org/wiki/Numerical_S ... _Technique) which for you is 0 to 500. The indexing of u-points (in red) is therefore 1 to 500, so 501 is not allowed.

Your file bowl_safe_new2_rivers_w.nc seems OK with sources at river_Xposition = 499 and 3.

Your river_transport is very small at 0.5 m3/s. For a LuvSrc inflow at the coast (2 m depth) with a cell width of dy= 80 m, that is an inflow velocity Q/(h*dy) of 3 mm/s. It might not be surprising that you don't see a significant change in tracer values, especially since you are using MPDATA which is very diffusive.

Other things I notice ... you have explicit horizontal mixing on temperature but not salinity. Since you are using MPDATA, explicit mixing added to the implicit embodied in MPDATA makes it even more diffusive and will further obscure an obvious temperature change.

I suggest you try a larger river_transport to see if you get a more conspicuous response, and a less diffusive advection shceme.

[jcwarner]

So i wrote a long post here, but it somehow got deleted. I will try to recover what i essence of what i wrote.

In summary, i ran your case and i see the salt decrease for the LwSrc as it should, with the source of water coming in at salt=0.
I ran your case with LuvSrc and i see the salt increase. The reason is that both of your point sources take water out of the domain. If you take water out, and specify the salt out =0, then no salt will leave. Therefor the salinity (concentration of salt) will increase in the domain.
If you have a box of water with salinity = 20, then you evaporate half of the water, the salinity goes up to 40 because the amount of salt stayed the same but the volume decreased.
If you set
LtracerSrc == T F ! temperature, salinity, inert
then the LuvSrc will keep the salt at 14.
The specifies to remove salt at the tracer concentration of the source location.

[arango]

John, did your post get deleted? That's weird. Only a couple of us have the permission privileges to do so. We have been having power failures recently, and it is possible that your post was lost because of it. I always use Firefox with history control to recover lost messages and text. It happened to me when I posted long, detailed messages in this forum.

[jcwarner]

I dont think it got 'deleted', but it never showed up. I wrote it, thought i hit the 'submit' button, and then it never showed up.
I am sure it was me, not pushing the correct post button and then closing the window.
Hopefully the main intent of my post is there.
-j

[Fatima]

Dear John,
Thank you for your complete reply.
I am currently working on a model where I’ve added two freshwater rivers, each with a discharge of 5 m³/s. The model is set to run for 40 days with a time step of 40 seconds. Some relevant conditions include:

The lake's salinity is set to 14 PSU.
The surface temperature is near freezing, while the river temperature is 4°C.
I haven’t included any forcing mechanisms or evaporation in the setup.
Despite the addition of the freshwater inflow, I’ve noticed that the model volume remains constant throughout the simulation. I’m trying to understand the cause of this behavior.

Could you please provide some insights into why the model volume remains unchanged despite the freshwater inflow? Any guidance or suggestions would be greatly appreciated.

Regards,
Fatemh

[jcwarner]

you need to make sure the flow is coming into the domain.
it can be tricky to identify the u- or v- locations for the inflows. the river point sources need to be at u- or v- masked points.
do you see the velocities increase at the discharge locations?

[Fatima]

Hi John,
I think I added two river inflows, each with a discharge of 𝑄=5 m^3/s, primarily directed in the u-direction. However, I have noticed two different velocity directions in the model, and I am uncertain whether these indicate inflows as expected.

I have attached the following files for your reference:
Horizontal and vertical velocity sections *near river locations),
Grid and initial condition files,
River file, and Log file.
In particular, I would greatly appreciate your guidance on ensuring the proper representation of the river inflows.

Thank you for your time and assistance. I look forward to your insights.

Fatemeh

[wilkin]

At https://www.myroms.org/wiki/Numerical_S ... retization scroll down to the small table that shows

Variable Interior Range Full Range

The valid index range for u-type points is i=1:L, and j=0:M.

You have specified u-face point sources (river_direction = 0) and i-coordinate positions of river_Xposition = 500, 0. The i=0 position is not valid and the source is not inside your domain.