Relation between water content and pressure head in porous media

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madegeogr
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Joined: Wed Mar 13, 2019 8:17 pm
Location: Cyprus

Relation between water content and pressure head in porous media

Post by madegeogr » Wed Mar 13, 2019 8:48 pm

Hi,
I have recently started reading about porous media, and particularly single and double porosity models. I have seen that these models use either a transport equation for water content (θ) or pressure head (h). In case the pressure head (h) is calculated, I found several empirical expressions from Hydrus 1D tutorial, obtained from the retention curve, which can be used to calculate the water content. These expressions are non-linear expressions, thus it makes me wonder: how do you calculate the water content in Hydrus1D in case we know the pressure head. Do we use the same expressions? And if yes, are we solving inversely these non-linear expressions?
Thanks for your time

K

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

Re: Relation between water content and pressure head in porous media

Post by Jirka » Wed Mar 13, 2019 11:54 pm

While the retention curve may be a nonlinear function, it does not mean that we cannot directly calculate water content. Look at equation 2.29 of the manual, which is the famous VG equation, directly giving you water content as a function of pressure head. It takes only simple manipulation of this equation to express the pressure head as a function of water content.

J.

madegeogr
Posts: 6
Joined: Wed Mar 13, 2019 8:17 pm
Location: Cyprus

Re: Relation between water content and pressure head in porous media

Post by madegeogr » Thu Mar 14, 2019 7:51 am

Thanks Jirka for your response.
Initially this is what I also thought. The reason why I wanted to ask to be sure is because sometimes when you manipulate functions that involve powers of a quantity, you might have two solutions (e.g. +h or -h ).

Thanks again,
K

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