Water temp responds too fast to air temp change

EFDC+
1

Dear EFDC users,

I am trying to calibrate the EFDC model against observed water temperature. We found the simulated water temperature responds too fast to air temperature change. The flow velocity and water surface elevation are reasonably calibrated. The problem is I found the following parameters are not sensitive relative to water temperature output:
- Minimum fraction of solar radiation absorbed in top layer
- Thermal thickness of bed
- Initial bed temperature
- Fraction of bed heat radiated back to water column
- Heat transfer coefficient between bed and water column

I am using Equilibrium Temperature thermal sub-model, since others gave me negative water temperature during winter period which is not real.

Any suggestions re which paramters to try are greatly appreciated,
Hailiang

2

One question we have is whether the heating up too fast is because the solar radiation values are not valid or is it a surface heat exchange issue?
If the latter then it is dominated by wind speed, wind direction and wind sheltering. If it is due to solar radiation then you need to check that your values appropriate – how did you come up with the values? Furthermore, what are your light extinction co-efficients and how did you determine them?

3

Thanks for the reply.
I do not think it is a problem of the solar radiation. We got them from monitoring station (the parameter global radiation). In addition, if I allow EFDC to calculate the solar radiation internally, I still see the fast water temperature reaction.

Also the wind speed and direction are also from monitoring station 30 KM from the study area. It seems the wind sheltering is a parameter to calibrate.

We do not have any data on light extinction coefficients, and used a value 0.5 for clear water light extinction, and found it is not sensitive to the water temperature.

I will feed back calibration progress with wind sheltering factor. Thanks

4

Hi Hailiang,
Your post caught my attention. I am facing similar problems as my simulated lake temperatures get negative in cold months (January through March) due to large amount of longwave radiation heat loss. I am using Full Heat Balance Mechanism right now. As you said, do you think using Equilibrium Temperature mechanism can take care of the negative temperature problem?
Please let me know your opinion and any particular suggestions about using this mechanism. Any idea where can I find a value for ‘Fraction of bed heat due to Solar Radiation radiated back to water column’ ?
I’m not using any wind sheltering and shading coefficient. And my evaporation is internally computed.

Thanks,
Rumana

5

Yes, Equilibrium Temperature (CE-QUAL-W2) submodel did eliminate the negative water temperature problem. But remember EFDC model currently does not include ice processes, so if you intend to incorporate these processes, EFDC model may NOT be the model to go. We finally choose CE-QUAL-W2 model for ice thickness simulation although it is a 2D model.

‘Fraction of bed heat due to Solar Radiation radiated back to water column’ is used as a calibration parameter, and we found it is not sensitive in our case. You may need to do sensitivity analysis to see what it impacts your model.

Hailiang

6

Hi Hailiang,
Thanks for your reply.
I’m modeling thermal stratification in Lake Ontario (February to August). I do not intend to do include ice processes. I was using Full Heat Balance Mechanism but it is giving me negative temperature (unreal) during February and March winter months.
I am looking into CALHEAT.for for understanding the mechanism of Equilibrium Temperature thermal sub-model. Is there any other module/routine or document I should look in to understand the mechanism and all equations?

Thanks,
Rumana

7

Not sure the ice distribution in your study area. The ice may impact your thermal stratification. You may need to check some references for your study area to see the impact of ice.

The CE-QUAL-W2 model manual may be another good source to check (http://www.ce.pdx.edu/w2/). EFDC (Equilibrium Temperature (CE-QUAL-W2 Method) )uses part of the CE-QUAL-W2 equlibrium temperature model. CE-QUAL-W2 is also written in FORTRAN, so it would not be a big problem if you can read EFDC code.

8

Hailiang,

I’m having the same problem. My model is too sensitive to the air temperature. I was wondering if you found any solution for this problem.

Thanks,
Amir

9

Amir,

Which heat option are you using ? Full heat balance or CEQUALW2 option ? Is it possible to send your model so that I could look at that ?

Best,
Janesh