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Dissolved Oxygen > Saturation

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Fernando Aguilar, modified 4 Years ago.

Dissolved Oxygen > Saturation

Youngling Posts: 22 Join Date: 2/7/13 Recent Posts
Hi all,

I'm trying to simulate eutrophication in a reservoir, but I'm having different problems. One of them is related to dissolved oxygen: after running the model, the dissolved oxygen values increase a lot and they are bigger than saturation concentration. What can be wrong?

I can share my substance file but I'm taking in account these processes:

- Algaes (1, 2 or 3 different species).
- NH4
- NO3
- SI
- PO4
- Water temperature (Hydrodinamics output)
- Salinity (Hydrodinamics output)

Any tip?

Thanks in advance,
AM
Arjen Markus, modified 4 Years ago.

RE: Dissolved Oxygen > Saturation

Jedi Knight Posts: 235 Join Date: 1/26/11 Recent Posts
Well, the dissolved oxygen concentration can in fact get higher than the saturation level and I would indeed expect it to happen in a eutrophic situation: the algae are producing oxygen and this cannot be exchanged with the atmosphere fast enough. Some questions: do you have the reaeration process turned on (check in the .lsp file)? And what kind of oxygen levels do you get?
FA
Fernando Aguilar, modified 4 Years ago.

RE: Dissolved Oxygen > Saturation

Youngling Posts: 22 Join Date: 2/7/13 Recent Posts
Hi Arjen,

Thanks for your quick answer. I mean that the values are much bigger: Saturation level is around 10 and dissolved oxygen becamoes around 200.

Yes, I have reaeration process already active and I've change reaeration transfer coefficient with a value of 0.75. Do you need more info?

Regards,

Fernando
AM
Arjen Markus, modified 4 Years ago.

RE: Dissolved Oxygen > Saturation

Jedi Knight Posts: 235 Join Date: 1/26/11 Recent Posts
Hm, that sort of concentrations is way too high indeed. Can you tell me what concentrations of algae you get, the typical depth of the system and the flow velocities? What reaeration option are you using (the switch I mean)?
FA
Fernando Aguilar, modified 4 Years ago.

RE: Dissolved Oxygen > Saturation

Youngling Posts: 22 Join Date: 2/7/13 Recent Posts
Hi again,

Algaes: We are calibrating them, but for instance in Blue greens, starting in 0.03 we get values of 0.6 max. However we had models where algaes dies and oxygen still grow a lot.
Depth: It depends, but it is up to 30-35 m.
Horizontal velocity: up to 0.04 m/s
Vertical velocity: Around 3x10-5
Rearation: I tried 1, 2 and 5.

Thank you!

Fernando
AM
Arjen Markus, modified 4 Years ago.

RE: Dissolved Oxygen > Saturation

Jedi Knight Posts: 235 Join Date: 1/26/11 Recent Posts
Hm, nothing really extreme. So concentrations of 200 and more are definitelty not to be expected. This requires some further investigation. We will be contacting you.
Christophe Thiange, modified 4 Years ago.

RE: Dissolved Oxygen > Saturation

Jedi Knight Posts: 125 Join Date: 11/15/12 Recent Posts
Fernando,

Are the DO concentrations relatively uniform or does the ~200 max occur in a specific part of your model?
Do you have drying cells in your model (as a consequence of dam operation for instance)?
Can you provide the balance output (*.prn file) without lumping the processes contribution? (Output options > Balances: check Extended mass balances and uncheck lump contribution of processes.)

If the cause is a mis-configured process, then the balance output should help identify the culprit.
FA
Fernando Aguilar, modified 4 Years ago.

RE: Dissolved Oxygen > Saturation

Youngling Posts: 22 Join Date: 2/7/13 Recent Posts
Hi Christophe,

Yes I have some drying cells. This values are only in a certain part of the reservoir (but is one of the most important).

I have attached you the file you want.

Thank you,

Fernando
Christophe Thiange, modified 4 Years ago.

RE: Dissolved Oxygen > Saturation

Jedi Knight Posts: 125 Join Date: 11/15/12 Recent Posts
This values are only in a certain part of the reservoir

Could you elaborate on this? Is there a smooth gradient or are the high concentrations really limited to specific segments? From your prn file I see you have observation station (57,111) and stations (57,112) (layer 1 to 35). Can it be that you see high DO values for (57,111) and not for the (57,112) stations? Assuming (57,111) is an average over all layers, that would mean values are summed instead of being averaged. But there's a lot of guessing here emoticon Can we have a look at your inp, lst and lsp files as well?
FA
Fernando Aguilar, modified 4 Years ago.

RE: Dissolved Oxygen > Saturation

Youngling Posts: 22 Join Date: 2/7/13 Recent Posts
Hi Christophe,

Yes, You can see a map of the reservoir (layer 8). I have to say that this is a Z model. I send you a chart of layer 8 and average.

In (57,111) I see the averaged (that is true, I sometimes see summed values instead average but not in this parameter).

I've attached you these files.
FA
Fernando Aguilar, modified 4 Years ago.

RE: Dissolved Oxygen > Saturation

Youngling Posts: 22 Join Date: 2/7/13 Recent Posts
And lsp...

Attachments:

Christophe Thiange, modified 4 Years ago.

RE: Dissolved Oxygen > Saturation

Jedi Knight Posts: 125 Join Date: 11/15/12 Recent Posts
Hi Fernando,

I noticed some balance errors in your prn file. Not sure what the cause is, but since you are using z-layers and have some water level fluctuation you should certainly activate the emersion process.

From section 7.3.1.1 of the input file description manual

Hydrodynamic models in 3 dimensions using strictly horizontal layers, so called Z-layers,
may feature a water surface that travels through layer interfaces when water level rises or
falls like in dammed lakes. You will then need:
CONSTANTS ACTIVE_Emersion DATA 1.0 ; switches process 'on'
CONSTANTS ZThreshold DATA 0.01 ; threshold in m.

This switches the Emersion process on. This process joins the top layer with the layer
underneath if layer thickness is lower than ZThreshold and makes the new layer the top
layer. At flooding the reverse happens. If the thickness is over ’ZThreshold’ more than the
thickness of the layer underneath, then a new top layer is formed. If you are not using this
process, unpredictable results may occur for incomplete water columns.


Did you do a "continuity" simulation? Any errors in there?

If activating the emersion process does not bring any improvement, it would really help to have all of your model input. If you need an ftp to transfer it, contact me at firstname dot lastname at deltatres dot nl.
Michel Jeuken, modified 4 Years ago.

RE: Dissolved Oxygen > Saturation

Jedi Knight Posts: 156 Join Date: 1/21/13 Recent Posts
I would like to add that I recently discovered that flow doesn't write the correct label to the hyd file in case of a z-model. At the geometry label, the z-layer tag was not automatically written. With the tag present the GUI writes these extra parameters automatically.

The line in the hyd-file saying
geometry  curvilinear-grid

should be
geometry  curvilinear-grid  z-layers


The manual actually stated that you had to add that tag by hand. I've fixed this in revision 4592 of Delft3D FLOW, so it will be written automaticly from that version on.

Michel
FA
Fernando Aguilar, modified 4 Years ago.

RE: Dissolved Oxygen > Saturation

Youngling Posts: 22 Join Date: 2/7/13 Recent Posts
OK Michel. Thanks, I'll take a look.
FA
Fernando Aguilar, modified 4 Years ago.

RE: Dissolved Oxygen > Saturation

Youngling Posts: 22 Join Date: 2/7/13 Recent Posts
Hi again,

I have been checking my outputs in particular Continuity. I have noticed that Continuity values are very high as you can see in the figure attached. It is supposed to be around 1, right?

If you need something else maybe upload my files somewhere is a good idea.

Cheers,

Fernando
Christophe Thiange, modified 4 Years ago.

RE: Dissolved Oxygen > Saturation

Jedi Knight Posts: 125 Join Date: 11/15/12 Recent Posts
Hi Fernando,

Indeed, the continuity concentrations should remain 1 g/m3. In the figure you attached it reaches a max of 30, which means the concentrations of other substances will be multiplied by 30 too!

There isn't much that can be done without the whole input set, so I suggest you send me an email (see previous post) so I can provide you with an ftp for file transfer.
Christophe Thiange, modified 4 Years ago.

RE: Dissolved Oxygen > Saturation

Jedi Knight Posts: 125 Join Date: 11/15/12 Recent Posts
Hi Fernando,

You used discharges with negative fluxes (extractions) in your FLOW model but did not include them in WAQ.
The volume of your system decreases while no corresponding mass is removed, hence the rising concentrations.

When loading the hydrodynamics in the WAQ GUI, all your FLOW discharges will be listed. You can set the concentrations of the outgoing discharges to zero as these values will not be used, but leave the flow discharge values unchanged.

Try running your model like that and look at the continuity concentrations.
FA
Fernando Aguilar, modified 4 Years ago.

RE: Dissolved Oxygen > Saturation

Youngling Posts: 22 Join Date: 2/7/13 Recent Posts
Thanks Cristophe. If I do that the Continuity seems to be OK, around 1. But I take these discharges away because, If i put 0 in the concentrations I have realised that values are getting higher and higher, like Dissolved Oxygen. Take a look in the figure I've attached. I'll upload you the model again, ok?

Thanks.
FA
Fernando Aguilar, modified 4 Years ago.

RE: Dissolved Oxygen > Saturation

Youngling Posts: 22 Join Date: 2/7/13 Recent Posts
Hi Christophe,

It helps me a lot! The values are a bit higher than reals but they are around 30-40 max. so now it's not so bad.

I hadn't added Continuity simulation but now I do.

I'm going to do some tests and I'll let you know if I have more problems.

Thank you so much
FA
Fernando Aguilar, modified 4 Years ago.

RE: Dissolved Oxygen > Saturation

Youngling Posts: 22 Join Date: 2/7/13 Recent Posts
OK, if you need further information I can send you any config file you need.

Cheers,

Fernando