Because of the capillary force, is it necessary that the movement of the moisture is from bottom to top? It is not possible that the top to bottom is also there in unsaturated Zone?
As we are all aware that the Moisture Movement from top surface to bottom surface is due to gravity force. But doesn't capillary force work with that gravity force when moisture move from top to bottom in unsaturated condition?
In most models like MODFLOW, the flow in the vadose zone is considered vertically. However, if you see the literature, some researchers noted upward flow in the vadose zone. Interestingly, we can also have horizontal flow in the vadose zone because of capillary effects that have a significant effect on solute transport. at first, it seems strange. But we can explain all of these movements based on soil physics law.
Water potentials are the driving forces of the water movement in the soil. Water goes from higher potential to lower potential. Under unsaturated and non-saline conditions, the matric (or capillary) and gravitational potentials are the most important potentials in determining the direction of water flow. Therefore, if you want to find the direction of the flow between two points, you should calculate the sum of the matric and gravitational potentials in both points, and then you can find the direction. In the following paper, we discussed theoretically and experimentally why horizontal movement happened in the vadose zone and how is the velocity profile in the capillary fringe. Because of the impotence of the topic, it is selected as editorial choice and now it is open access for 3 months. (Experimental study on velocity and flow patterns in the capillary fringe)
Article Experimental study on velocity and flow patterns in the capi...
I think this topic will help you
https://www.google.com/url?sa=t&source=web&rct=j&url=http://www.soilphysics.okstate.edu/software/water/infil.html&ved=2ahUKEwihhLLrpr3pAhXADGMBHbbQAN8QFjADegQIAxAB&usg=AOvVaw0Plm-fxTGiByqv8prMvfe0&cshid=1589801383731
As per my understanding, both the forces work together but it also depends on the cross sectional area of the medium, where it makes the difference.
If the cross sectional area is small enough, then the Adhesion and Cohesion will be dominant which support the capillary force or else gravitational force will exceed.
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