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Ambient temperature, water temperature, and ambient natural background temp

Martin Schueder, modified 4 Years ago.

Ambient temperature, water temperature, and ambient natural background temp

Padawan Posts: 52 Join Date: 10/8/13 Recent Posts
Hello,

I am encountering some extremely wrong model results (such as pH >14 and TIC <0) and I think it has something to do with my water temperature. I am confused about how to specify different temperatures in the Process parameters input tab. For instance, I have selected TEMPERATUR as an active process in my .0* file, and thus in the GUI I am prompted for the following:

- Air temperature (NatTemp)
- Ambient water temperature (Temp)

and therefore I am modeling:

- Water temperature (ModTemp)

Looking at pg 416 of the Process Library Description manual I see that:

- ModTemp = modeled temperature
- T = ambient water temperature
- NatTemp = ambient natural background water temperature

In the GUI I see that:

- Air temperature = NatTemp
- Ambient water temperature = Temp

I know the absolute temperature of water at my boundary conditions, and the absolute air temperature from physical observations. What I want is a dynamic computation of the temperature of each computational volume so that all temperature dependent processes occur at the appropriate rate. If it can be avoided, I do not want WAQ to compute this water temperature, and instead I want it to take temperature from FLOW. I believe the procedure is outlined here. Regardless of if I use FLOW or WAQ to compute “Temperature”, what I am unsure of is:

- The difference between the different temperature variables, as it appears the nomenclature is inconsistent (ModTemp, T, NatTemp, Temp are all used, but it appears T=Temp. Is NatTemp air or water?), what are the strict definitions of these variables?
- Which temperature variable the kinetic rates in WAQ are dependent on? The WAQ manual says T or ambient water temperature (pg. 217). If SwitchTemp=0, then T=ModTemp (Process Library Description pg. 417). Therefore, why would I specify Temp as a (constant/known time series) process parameter in the GUI if the ModTemp (which equals Temp) is being modeled?
- Which temperature it is that will be defined by the .tem file produced by FLOW when a .tem file is used as a forcing function? Should I define Temp as a constant process parameter, which is then overwritten by the forcing function commands I write in the .inp file?

I understand this post may be confusing and I apologize for asking such a rudimentary question. I very much appreciate your help.

Thank you,

Martin
Mathieu Chatelain, modified 4 Years ago.

RE: Ambient temperature, water temperature, and ambient natural background (Answer)

Padawan Posts: 28 Join Date: 12/13/12 Recent Posts
Hi Martin,
ModTemp (=modelled water temperature) is a state variable, while NatTemp (=air temperature) and Temp (=water temperature) are parameters. Finally, T is the water temperature as it is usually written in equations; in Delwaq, T=Temp.

Thus, Temp is the parameter affecting the rates of all (bio)chemical processes.

#1 If you model water temperature in Delwaq (=ModTemp) by activating the process TEMPERATUR, then you indeed don't need to specify a value for Temp.
(a) If SwitchTemp=0, then ModTemp = modeled absolute water temperature. Then, Temp = ModTemp, so that the temperature you model will be used to affect the rates of all (bio)chemical processes.
(b) If SwitchTemp=1, then ModTemp = modeled excess water temperature. Then, Temp = ModTemp + NatTemp, so that processes rates are affected by the absolute temperature.

#2 If you don't model water temperature in Delwaq, then you need to specify a value for Temp:
(a) a constant (called PARAMETER)
(b) a time-series (called FUNCTION)
(c) a spatial-varying time-series (called SEGMENT FUNCTION). Here you could use the result from your hydrodynamic simulation. You can either edit the INP-file directly, or select the *.TEM file via the GUI. In the INP-file, it will appear as a segment function:
SEG_FUNCTIONS
'Temp' ; name of segment function
ALL
BINARY_FILE 'your_hyd_run.tem' ; binary file


In case of doubt, just add Temp to your output and check its value!
Cheers,
-Mathieu.
Martin Schueder, modified 4 Years ago.

RE: Ambient temperature, water temperature, and ambient natural background

Padawan Posts: 52 Join Date: 10/8/13 Recent Posts
Hi Mathieu,

Thank you very much for this thorough explanation! I have done as you recommended in point #2(c) and have much improved results. I appreciate your time.

Martin
Mathieu Chatelain, modified 4 Years ago.

RE: Ambient temperature, water temperature, and ambient natural background

Padawan Posts: 28 Join Date: 12/13/12 Recent Posts
Very good news, I think that indeed #2c is the best way to include temperature forcing in Delwaq.
Happy modelling!
Cheers.