Water balance

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Posts: 12
Joined: Tue Feb 12, 2013 3:22 pm
Location: Spain

Water balance

Post by j.valdes » Fri Dec 04, 2020 7:18 am

Dear all,
I’d like to share some results from Hydrus-1D, just to know if someone could provide me some hint about what’s happening.
Main features of the model are:
- Water, vapor and heat model. No transpiration
- Time units: days. 3651 days (10 years)
- 4000 cm (40 m) profile.
- Pressure head of 7 m at the botton (there is water table at 33 m depth)
- Atmospheric BC with Surface runoff at the top
- Temperature BC for both botton and top for the heat model.
- Only 1 subregion for water balance
Main results for the water balance (units in cms) for the complete simulation period:
- CumActSurf, sum(Vtop), -329
- CumActBot sum(vBot), +32
- sum(Runoff), 0
- WaterVolume change in the whole profile, 622(t=end)-271(t=0)=351
- sum (Infil), 694
- sum (evap), 602
- Precipit 641

- Difference between sum(infil) and sum(evap) (i.e. +602-694= -92cm) = should not be equal to sum(vTop) (i.e, -329cm )?
- Sum(vtop) +sum(vBot) (392(into the domain)+32(into the domain)=424 cm) should not be equal to difference in volume for the whole profile(i.e, 351 cm)?
- Even that precipitation is sinusoidal variated by HYDRUS, there is no-runoff, which sounds somehow strange

Any tip about these results??
I attached the complete model just in case someone wants to make a deeper look.
https://drive.google.com/file/d/1KBSxUa ... sp=sharing

Thanks in advance

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Joined: Sat Mar 16, 2002 3:47 pm
Location: USA
Location: Riverside, CA

Re: Water balance

Post by Jirka » Fri Dec 04, 2020 6:51 pm

I do not have time to look at your simulations. Check out the reported water balance in Balance.out file. HYDRUS reports both absolute and relative mass balance errors in this file. If these are small, then the mass balance calculations in the run are OK, and your own calculations (on side) are wrong. J.

Posts: 12
Joined: Tue Feb 12, 2013 3:22 pm
Location: Spain

Re: Water balance

Post by j.valdes » Fri Dec 18, 2020 6:29 am

Checking the Balance.out file was the first step I made after detecting the problem and before adressing the question into the forum. There was no problem there.
After making some test, I would like to share my point of view about what is happening for other Hydrus users:
- sum(Infil) variable does consider water entering in vapor and liquid form. I concluded that because it's impossible to have 694 cm of infiltration when the precipitation is 640 cm.
- In the same way, sum (Evap) does consider both water phases. I concluded that after running the same moddel without vapor component. In that other model without vapor the evaporation was 325 cm so the hugh increase in the evaporation (from 325 to 602 cm) must came from the vapor phase.
- However, sum(vTop) does not included the vapor phase, so it considers only the movement of water through the top boundary considering the components included in the liquid water flow process. If the sum(vTop) considered the vapor, it should be equal to the difference between sum(Infil) and sum(Evap).
-The water balance from the Balance.out file, considers only the components from the liquid water flow process. I concluded that because the water balance along the complete period is in agreement with sum(vTop) and sum(vBot), which do not consider the vapor process, as stated before.


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