Well as constant head

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tjoudega
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Location: Austria

Well as constant head

Post by tjoudega » Wed Jun 03, 2020 11:56 am

Hello,

I am modelling in 3D-layered. In accordance with Tutorial Test 8, I want to model the pumping well as a constant head boundary. But because I would like to have this well in the middle of my domain, I have cut out a cylinder (with a radius of 30cm, as is our real pumping well screen) from the domain as an opening. This way, the well screen is now a domain boundary that I can assign a constant head to. (See attachments.) The constant head in the well is lower than around it, creating a drawdown and a flow through the "well screen" - the opening in the domain - that is realistic to our field site.

My question is: In Hydrus, would this be an acceptable way to model a pumping well?

Thank you,
Thomas
Attachments
Opening - Well.png
Opening - Well.png (1.35 MiB) Viewed 1142 times
Boundary - Well.png
Boundary - Well.png (1.92 MiB) Viewed 1142 times

Jirka
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Location: Riverside, CA

Re: Well as constant head

Post by Jirka » Wed Jun 03, 2020 3:33 pm

Hi Thomas,

Yes, you can certainly do it this way. My question is whether you need a 3D domain. Note that we have developed some tools (e.g., the reservoir BC) in 2D, which greatly simplify dealing with pumping or dry wells in 2D. Please note that you can find (and download) several examples involving the reservoir BC (and its use for wells) on the HYDRUS website at:
https://www.pc-progress.com/en/Default. ... eservoirBC

Two of these examples were reported in:
Šimůnek, J., M. Šejna, and M. Th. van Genuchten, New Features of the Version 3 of the HYDRUS (2D/3D) Computer Software Package, Journal of Hydrology and Hydromechanics, 66(2), 133-142, doi: 10.1515/johh-2017-0050, 2018.

Additional, more complex examples can be found at:
https://www.pc-progress.com/en/Default. ... ib-Drywell

Note that these simulations were reported in:
Sasidharan, S. A. Bradford, J. Šimůnek, B. DeJong, and S. R. Kraemer, Evaluating drywells for stormwater management and enhanced aquifer recharge, Advances in Water Resources, 116, 167-177, doi: 10.1016/j.advwatres.2018.04.003, 2018.

Jirka

tjoudega
Posts: 13
Joined: Mon May 22, 2017 3:41 pm
Location: Austria

Re: Well as constant head

Post by tjoudega » Wed Jun 24, 2020 10:06 am

Hi Jirka,

Thanks for good tip. There is one thing I can't wrap my head around, which is the injection in 2D domains. Injection in 2D domain in Hydrus go by L/T, in my case m/hour. If I have an injection of a certain amount of cabic meters/hour, how do I convert this to the 2D domain? What is the "area" I have to divide through? Is this the area occupied by the node I am injecting into?

Thanks,
Thomas

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

Re: Well as constant head

Post by Jirka » Wed Jun 24, 2020 2:26 pm

Qp is the pumping rate (positive for removal of water, negative for adding water) ([L2 T–1] or [L3 T–1] for two-dimensional and axisymmetric systems, respectively). See Figure 2.7 in the technical manual or Fig. 1 in:
Šimůnek, J., M. Šejna, and M. Th. van Genuchten, New Features of the Version 3 of the HYDRUS (2D/3D) Computer Software Package, Journal of Hydrology and Hydromechanics, 66(2), 133-142, doi: 10.1515/johh-2017-0050, 2018.
JS

tjoudega
Posts: 13
Joined: Mon May 22, 2017 3:41 pm
Location: Austria

Re: Well as constant head

Post by tjoudega » Thu Jun 25, 2020 9:04 am

I am sorry, I was referring to injection of solute by internal nodes. In my field test we injected 1 cubic meter/hour for 20 minutes. But I can't put in a volume of water, only a flow (m/hour). What are your thoughts on this, is there any set way how to convert this?

Thanks,
Thomas

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

Re: Well as constant head

Post by Jirka » Thu Jun 25, 2020 6:52 pm

What you say is not correct. The units for internal node recharge are [L2/T] (see the figure below) and [L3/T] in 2D and 3D, respectively. J.
NodalRecharge.png
NodalRecharge.png (18.53 KiB) Viewed 102 times

tjoudega
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Location: Austria

Re: Well as constant head

Post by tjoudega » Fri Jun 26, 2020 8:57 am

I have a pulse injection of 20 minutes. Somehow I could never get "Pulse length" to work in 2D: Even if put 0.333 hours in that field (Flow and Transport Parameters), the injection would happen continually, all the way through for the entire run time of the model. I am not sure if this is an error or something that is inherent to working in 2D, or if I am doing something wrong, but it is for this reason that I have taken to use a Time-Variable Internal Flux Sink/Source (when working in 2D), which you can specify in the Initional Conditions tab. This way, I can set a pulse length at Var. Fl4, so that I don't have a continuous injection when I don't want it. However, this flux is in L/T (see figure below). Is there any way I can insert a flux in L2/T in this way?
flux v4.png
flux v4.png (65.74 KiB) Viewed 100 times

Jirka
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Location: Riverside, CA

Re: Well as constant head

Post by Jirka » Fri Jun 26, 2020 8:29 pm

I'm pretty sure that "Pulse Duration" works OK if you use this option correct. Note the definition in the User Manual: " Pulse Duration: Time duration of the concentration pulse. Concentrations (flux or resident) along all boundaries, for which no time-variable boundary conditions are specified, are set equal to zero for times larger than the "Pulse Duration".

If you select the node to be " a Time-Variable Internal Flux Sink/Source", then values from Var.Fl4 are interpreted as being in units of [L2/T].

J.

tjoudega
Posts: 13
Joined: Mon May 22, 2017 3:41 pm
Location: Austria

Re: Well as constant head

Post by tjoudega » Wed Jul 01, 2020 10:34 am

Okay, that is good to know!

One last question about 2D: In our team we have noticed (hopefully correctly!) that Hydrus uses a linearized approximation for top-down 2D models, meaning we don't have a good representation of flow near wells with a large drawdown. Is there any way to turn this linearization off?

Thank you for your time, we really appreciate it. We have struggled for the last few weeks in Hydrus but your replies to this thread help a lot!

Kind regards,
Thomas Oudega

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

Re: Well as constant head

Post by Jirka » Wed Jul 01, 2020 5:53 pm

I'm not sure what you mean. Linear distribution of the pressure head on the boundary representing the well (in the reservoir BC)? What else would you suggest than using the hydrostatic pressure head? J.

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