Root solute uptake in dual permeability model

[YOON]

Dear all,
I am currently working on a modeling study using dual-permeability model(physical non-equilibrium) and have a question.
I am attempting to estimate the solute concentration of the root water uptake in the dual-perm model. However, I have noticed some discrepancies between the results of cvRoot and sum(cvRoot), where the values in cvRoot seem greater than what they should be.
I have tried to estimate sum(cvRoot) using cvRoot as the cumulative sum of the average cvRoot between two-time steps multiplied by the length of the time step, and it seems that the estimate is larger than sum(cvRoot) in general.
I also found a relationship between the {estimated sum(cvRoot) for the final time step} / {the reported sum(cvRoot) in solute1.out file for the final time step} and w (the ratio of fracture) based on the results gathered from numerous model runs using different parameters. It appears that these two variables exhibit a certain clear relationship as depicted in the attached figure. I would appreciate any insights or explanations regarding this phenomenon.

<img src="https://drive.google.com/file/d/1CzZYL- ... drive_link">

Best regards,
Yoon.

[YOON]

I'm writing again since I haven't received a response yet.
If anyone could offer assistance, it would be greatly appreciated.
Thank you.

[Jirka]

One of the assumptions in the dual permeability model is that root water uptake occurs only from the matrix (by setting qTopF=0; a fraction of uptake from fractures). At each time step, the code calculates RWU from both domains (even though it is zero from the fracture domain), and integrates cumulative RWU.
For water:
qTopF=0. ! =0: only matrix
TPotM=TPot*(1.-qTopF)/(1.-wF) ! potential transpiration
TPotF=TPot*qTopF/wF

vRootT=vRoot*(1.-wF)+vRootF*wF ! actual total RWU=RWU from matrix + RWU from fractures
CumQ(4)=CumQ(4)+vRootT*dt ! cumulative total RWU
For solute :
CumCh(5,jS)=CumCh(5,jS)+cvChR(jS)*dt*(1.-wF) ! uptake from matrix
CumChF(5,jS)=CumChF(5,jS)+cvChRF(jS)*dt*wF ! uptake from fractures

J.