Confined Aquifer/Positive Lower Boundary Head

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jchunter
Posts: 2
Joined: Sun Mar 08, 2020 7:13 pm
Location: USA

Confined Aquifer/Positive Lower Boundary Head

Post by jchunter » Tue Mar 10, 2020 7:38 pm

I have a question about how to represent the HYDRUS lower boundary conditions in a site with artesian conditions for the first saturated zone.

The site is located in the lower Mississippi delta, and is composed of a complex package of overbank and secondary channel deposits of clays, silts and fine sands. The first saturated zone lies approximately 10 meters below the surface, in an irregular body of fine sands. This zone is encased with low-conductivity clays and clayey silts. Wells completed in the saturated zone show potentiometric heads approximately 1 or 2 meters above the well screens (isolated in the groundwater zone).

I would like to use HYDRUS to evaluate the downward migration of conservative tracers from ditches and ponds (continuous sources) as well as surface spills (pulsed sources).

In the “Water Flow Boundary Conditions” box, under “lower boundary condition”, which option do you recommend?

Jirka
Posts: 4861
Joined: Sat Mar 16, 2002 3:47 pm
Location: USA
Location: Riverside, CA

Re: Confined Aquifer/Positive Lower Boundary Head

Post by Jirka » Tue Mar 10, 2020 8:50 pm

The pressure head BC, with the pressure head at the bottom of the domain. J.

jchunter
Posts: 2
Joined: Sun Mar 08, 2020 7:13 pm
Location: USA

Re: Confined Aquifer/Positive Lower Boundary Head

Post by jchunter » Tue Mar 10, 2020 9:19 pm

Thank you very much.

I take it that a "free drain" would not be appropriate.

Jirka
Posts: 4861
Joined: Sat Mar 16, 2002 3:47 pm
Location: USA
Location: Riverside, CA

Re: Confined Aquifer/Positive Lower Boundary Head

Post by Jirka » Tue Mar 10, 2020 9:52 pm

Let me quote from the help: "Free Drainage Water Flow Boundary Condition: A zero-gradient boundary condition can be used to simulate a freely draining soil profile. Such a situation often occurs in field studies of water flow and drainage in the vadose zone. This lower boundary condition is most appropriate for situation where the water table lies far below the domain of interest."

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