Mass balance issue with 'surface layer' boundary

The HP1 code incorporates modules simulating
(1) transient water flow in variably-saturated media,
(2) transport of multiple components, and
(3) mixed equilibrium/kinetic geochemical reactions.
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SiyanW
Posts: 3
Joined: Wed May 27, 2020 9:46 pm
Location: USA

Mass balance issue with 'surface layer' boundary

Post by SiyanW » Tue Jun 30, 2020 10:27 pm

Dear Jirka and Hydrus users,

I am running Hydrus 1D to simulate water retention performance for a rain garden (a type of green infrastructures) using my field measured inflow data during a storm event. It's a straightforward model assuming no evaporation and transpiration during the storm event. The upper boundary condition was set to be atmospheric BC with a surface layer (max h at the surface is 25cm), and the lower boundary is set to be free drainage.

My question is about the discrepancy I found in the T_level.out file after successfully ran Hydrus with the input. I understand that many users have posted questions about mass balance calculations. I had read them carefully before I posted my question here, but the existing posts still cannot help me figure out my issue (I have also successfully run ’pond3‘ example and validate the mass balance calculation Jirka posted at viewtopic.php?f=4&t=3122&p=11441&hilit= ... nce#p11441).

My issue is that sum(rTop) at the last time step is not equal to sum(vTop)+hTop+sum(RunOff) at the last time step in my case. Since I have set evaporation and transpiration to zero, the potential inflow will either be infiltrated or pond at the surface or overflow to be runoff.

However, in the T_level.out file as I attached here, at the final time step:

sum(rTop)=137.48 cm (it's negative but to simplify I only keep the absolute values for all results here and below)
sum(vTop)=52.356 cm
hTop=4.1395 cm
sum(RunOff)=31.271 cm

the discrepancy between potential inflow and the sum of the rest of the three - sum(vTop),hTop,sum(RunOff) is:
sum(rTop)-sum(vTop)-hTop-sum(RunOff)=49.714 cm
There is 49.714 cm water missing in the mass balance and the relative error is 49.716/137.48=36%, which is not reasonable at all.

I have checked the mass balance inside the flow domain as well. Based on T_level.out file,

Volume(start)=19.82 cm
Volume(end)= 23.13 cm
therefore the changes in storage is 3.31 cm

This changes in storage matches the results calculated from sum(vTop)-sum(vBot)=52.356-49.046=3.31 cm,
However, if I checked the results based on sum(rTop)-sum(RunOff)-hTop-sum(vBot)=137.48-31.271-4.1395-49.046=53.0235 cm. This indicates changes in storage is 53.0235 cm.

I have also checked the values of WatBalR and WatBalT in the Balance.out file. They all look satisfactory. Am I missing something here? Could you please take a quick look at my attachment and help? Much appreciated!

Thanks!
Siyan
Attachments
20170525event_copy.zip
(110.93 KiB) Downloaded 2 times

Jirka
Posts: 4961
Joined: Sat Mar 16, 2002 3:47 pm
Location: USA
Location: Riverside, CA

Re: Mass balance issue with 'surface layer' boundary

Post by Jirka » Tue Jun 30, 2020 11:37 pm

The code was not meant for conditions when the entire profile is fully saturated and simultaneous atmospheric and free drainage BCs. However, we can handle that as well. Try the attached updated code. J.

sum(rTop)=137.48 cm (it's negative but to simplify I only keep the absolute values for all results here and below)
sum(vTop)=52.54 cm
hTop=23.58 cm
sum(RunOff)=61.36 cm
sum(rTop)-sum(vTop)-hTop-sum(RunOff)=0 cm
h1d_clci.zip
(1.12 MiB) Downloaded 5 times

SiyanW
Posts: 3
Joined: Wed May 27, 2020 9:46 pm
Location: USA

Re: Mass balance issue with 'surface layer' boundary

Post by SiyanW » Wed Jul 01, 2020 1:44 am

Thank you very much, Jirka. However, I have a follow-up question relates to the folder you attached. It might sound stupid but I am not sure whether the attached exe files should be executed in the command prompt or should it be open by double clicking the exe file directly? I am asking because I was unable to open the two exe files anyway. Thanks again!

Additionally, I noticed that in most of my simulations, the soil moisture content is close to saturation (basde on soil moisture measurement in the field). Is it possible to run all of these simulations through Hydrus?

Thanks,
Siyan

Jirka
Posts: 4961
Joined: Sat Mar 16, 2002 3:47 pm
Location: USA
Location: Riverside, CA

Re: Mass balance issue with 'surface layer' boundary

Post by Jirka » Wed Jul 01, 2020 3:01 am

You need to copy these files into the HYDRUS folder (where the HYDRUS software is installed). J.

SiyanW
Posts: 3
Joined: Wed May 27, 2020 9:46 pm
Location: USA

Re: Mass balance issue with 'surface layer' boundary

Post by SiyanW » Wed Jul 01, 2020 4:09 am

Thank you so much, Jirka. It works now! :)

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