dual porosity model

A discussion forum for Hydrus-1D users.
Post Reply
padhi
Posts: 2
Joined: Tue Oct 11, 2016 6:02 am
Location: Japan

dual porosity model

Post by padhi » Fri Aug 30, 2019 4:53 am

Hello,

I am working with dual porosity model in Hydrus 1D for transient water flow and solute transport simulation.
Before running the transient simulation, I run steady state simulation and then use the water content in the soil profile at the end of steady state simulation run as the initial water content for my transient simulation.

It would be helpful if someone can clarify few things such as:

In the dual porosity model,
1. Moisture in the NOD_INF.OUT file is moisture in the mobile domain and Im.Moist. is water content in the immobile domain for that particular
node.
2. The initial water content in the profile.dat file is water content in mobile domain + water content in immobile domain.
3. Hence, nodal values of initial water content for my transient simulation will be Moisture + Im.Moist from my steady state simulation run.
4. for solute transport, my solute was initially present at a certain depth. The initial solute conc. that should be entered in the profile.dat file is
mass of solute per volume of liquid.
i.e., if the node is 0.5 cm, the water content for that node is 0.45 and initial conc. is 1(measured at that particular depth), then, initial solute
conc. that should be entered in the profile.dat file is 1(measured initial conc.)/(0.45(water content)*grid size(0.5) ) = 4.44

5. I use dual porosity (mobile-immobile) model with water content mass transfer
In the Water flow information section of SELECTOR.IN file, these are the input parameters : thr ths Alfa n Ks l thrIm thsIm
Omega
Here, thsIm is the water content in the immobile zone
In the Solute transport information section of SELECTOR.IN file, we have the parameters such as: Bulk.d. DisperL. Frac Mobile WC
(1..NMat)
Here, Mobile WC (1..NMat) is water content in the immobile zone. When dual porosity model for water flow is also simulated and thsIm is
defined in the in waterflow section, do I need to define Mobile WC (1..NMat) again?

Thank you

Jirka
Posts: 4733
Joined: Sat Mar 16, 2002 3:47 pm
Location: USA
Location: Riverside, CA

Re: dual porosity model

Post by Jirka » Fri Aug 30, 2019 9:00 am

Here are the answers:
1. Yes, that is correct.
2. Yes, that is correct. It is the total water content, which is then divided between mobile and immobile zone based on the ratios of porosities in the two domains. I.e., ThMob=ThetaTot*ParMob/(PorMob+PorImob), and ThImob=ThetaTot*ParImob/(PorMob+PorImob)
3. What’s described in point 2 is the only option available, if you want to specify initial water contents. This works fine if you have the mass transfer driven by the water content gradient. It is better to specify initial pressure heads (if you have the mass transfer driven by the pressure head gradient).
4. HYDRUS gives you an option to specify the solute transport initial condition either in terms of the initial concentration or the initial solute mass. How this is done is explained in the manual (I’m not going to repeat it here).
5. No, you do not have to, which is clearly indicated in the GUI (which states ThIm=0).

JS

padhi
Posts: 2
Joined: Tue Oct 11, 2016 6:02 am
Location: Japan

Re: dual porosity model

Post by padhi » Mon Sep 02, 2019 7:24 am

Thank you Prof. Jirka.
That helps a lot.

Padhi

Post Reply