## Problem 6.1

A discussion forum for book "Soil Physics with HYDRUS"
masegui
Posts: 4
Joined: Wed Apr 05, 2017 8:58 am
Location: United Kingdom

### Problem 6.1

Hi all,
I am working on example 6.1 from the book and it says at pag 307 " Then the imput was changed to 10 mmmol/L MgCl2". However when it sets the Mg concentration in the upper boundary is says 10 mmol/cm3 (pag 311 and Fig 6.57).

I am a bit confused, should it be 0.01 mmol/cm3 the concentration in the upper boundary if it was stated at 10 mmol/L in the experiment?

Many thanks.
Maria

Jirka
Posts: 4759
Joined: Sat Mar 16, 2002 3:47 pm
Location: USA
Location: Riverside, CA

### Re: Problem 6.1

The length units in the definition of concentrations do not necessarily have to be (although it is preferable) in the same units as length units for geometry and other variables. I discuss this in the "Units in HYDRUS" topic of the help (Other Topics).

"Inspection of the governing advection-dispersion equation shows that the concentration variable appears in most or all terms (except certain production and reaction terms). Consequently, the concentration [Mc/Lw3] does not necessarily have to be given in the same length units [Lw], as the transport domain [Ls]. However, one then needs to convert variables derived from concentrations (given above) to account for this mismatch of units (between concentration and length units)."

Additionally, one should be aware that HYDRUS assumes when displaying the concentration outputs that the units of concentration and length are the same.

J.

masegui
Posts: 4
Joined: Wed Apr 05, 2017 8:58 am
Location: United Kingdom

### Re: Problem 6.1

However, still I can't understand why the input concentration is stated at 10 mmmol/L in the explanation of the problem and when introducing the variables says 10 mmol/cm3.

Thanks
Maria

Jirka
Posts: 4759
Joined: Sat Mar 16, 2002 3:47 pm
Location: USA
Location: Riverside, CA

### Re: Problem 6.1

Both should be per liter. J.

masegui
Posts: 4
Joined: Wed Apr 05, 2017 8:58 am
Location: United Kingdom

### Re: Problem 6.1

Many thanks for the clarification Jitka

Regards
Maria