Apply constant recharge rate of 300 mm/y at the top boundary of the domain

[SCH]

Hi All,
I want tp understand "Apply constant recharge rate of 300 mm/y at the top boundary of the domain",

-How we define domain? and how can we pply constant recharge rate of 300 mm/y at the top boundary of the domain?

thanks for your help

[dlparkhurst]

I assume you are using PHREEQC. With PHAST, there is a flux boundary condition where you would define the flux.

With PHREEQC, there is a specific relation between the flow velocity, the cell length, and the time step; specifically, the intersticial flow velocity is the cell length divided by the time step. So, you need to pick appropriate length and time. With PHREEQC, each cell has the same water volume, and water is moved to the next cell at each time step to account for advection.

[SCH]

Hi Sir,

- Thanks for your answer. Yes I'm using PHREEQC, let me know, if it's possible to combine PHREEQC with another software to use the boundary condition.

- if I have 300 mm by year, I can link with water volume in the solution parametre?

Thanks.

[dlparkhurst]

PHAST is a reactive transport model that uses a PHREEQC input files to define the chemistry for initial and boundary conditions. The domain can be 1, 2, or 3D; it assumes constant density and saturated flow. Phast4Windows is a beautiful graphical-user interface (written by Scott Charlton), which facilitates problem definition and running. Boundary conditions, time stepping, and grid definition are more flexible than PHREEQC.

In PHREEQC, SOLUTION 0 (infilling solution) should be the same volume as the water volume in all of the cells. 300 mm/y corresponds to an interstitial pore-water velocity for your porous medium. You must adjust your cell length and time step accordingly.

[SCH]

Thanks a lot

[SCH]

Sir,
I want to ask if I can therefore conclude that in PHREEQC, there is only my lithology and my concentrates in the solution which comes online in the simulation.

Somes parameters such as porosity, volume, density, rainfall, the proportion of lithologies in my waste rock, the hydraulic conductivity of the material are not taken into account in PHREEQC.

thanks

[dlparkhurst]

You can change the velocity by using cells of different lengths to account for changes in hydraulic conductivity. The time step is fixed, so the velocity is faster in longer cells and slower in shorter cells.