How to incorporate amount of rainwater in x1t?

[Aditya-Puru]

Hi there,
I am trying to run an X1t model of rock weathering due to rainwater, in which I need to specify amount of precipitation. How can I do that? From my understanding the setting the discharge rate will set the flowrate inside soil, but how can I specify something like 1200 mm of rain per year. 

Also please explain the 1kg free water we use as solvent. Does the amount of rest of the species mentioned in initial and fluid correspond to 1kg of free water?

Thanks.

[Jia Wang]

Hello,

You can specify flow within the system, but not outside. If you can assume that all the rain enters your system at 1200 mm/yr, you can set that as your discharge value. The discharge unit in the GWB is a volumetric flux, which is volume/ (cross sectional area * time). I think your rainfall measurement is already in the correct unit format but you should double check that. You can read a more detailed explanation on setting flow rates in section 3.2 in the GWB Reactive Transport Modeling guide.

You set the initial condition of your system in the Initial pane and the Fluids pane is where you set the composition of your boundary fluid chemistry. H2O is typically set as a free quantity since it is the amount of water present. In one node applications, such as SpecE8 and React, varying the water mass will change the bulk mass and volume of the system. In a reactive transport model, you set the bulk volume of your system by choosing the dimensions of your domain. 

If you choose units such as mmolal or mmolal, then the concentration set is relative to 1 kg of solvent water. Other units such as mg/kg is milligram of solute per kilogram of solution. Absolute units such as moles or grams are typically not recommended, as then you have to recalculate the total moles of a component if you change the size of your domain.

Hope this helps,
Jia Wang
Aqueous Solutions LLC

 

[Aditya-Puru]

Thanks a lot, that does help.