This is a very simple question about the movement of unsaturated water, but I have made a mistake. Please help me

Hello everyone,

I’m a beginner,After learning some OGS tutorials, I start to use it myself.I am using the RICHARDS_FLOW module to calculate a simple unsaturated water flow problem, and the model can run, but I find that the final results are completely different from what I expected.

My idea is as follows:

The boundary conditions at all sides are no flow boundaries, and at the same time, there are no source terms. I have set up four layers of soil, and all the parameters of the soil are the same, except for the initial moisture content of each layer. The top layer of soil has the highest soil moisture content, and it decreases from top to bottom. I am using the VG(Van Genuchten) model to calculate the initial capillary pressure of each layer based on the initial soil moisture content. Due to the differences in initial moisture contents, the initial capillary pressure for each layer of soil are different. Under the driving force of capillary pressure, soil water will undergo movement.

The results are as follows:

I ran the model for 24 hours and visualized the output results using ParaView software. Unexpected results have occurred!The capillary pressure of the top soil layer has become negative,while the capillary pressure of the bottom soil layer has significantly increased.
The expected outcome was that, due to the higher soil moisture content in the upper layers resulting in lower capillary pressure and the lower soil moisture content in the lower layers resulting in higher capillary pressure, soil water would move downwards. Consequently, the capillary pressure would increase in the upper soil layers and decrease in the lower soil layers under the influence of capillary pressure. However, the obtained results seem to be completely opposite to the expected outcome. At the same time, I am puzzled by the occurrence of negative capillary pressure in the upper soil layers in the final results.
I don’t understand the cause of this result, whether it is due to a mistake in my thinking or a problem with my model setup, leading to a different outcome than expected.

Here, I attach all my input files and the parameters for each soil layer. I earnestly implore everyone’s help, as it is extremely important to me. I would like to understand the issue and correct it.
From top to bottom,soil parameters are as follows:
layer1: Maximum moisture content:0.41;residual moisture content:0.065;Maximum moisture saturation:1;residual moisture saturation:0.159;permeability :1.0228e-4m/s;initial moisture content:0.4;initial capillary pressure :312.55
layer2: Maximum moisture content:0.41;residual moisture content:0.065;Maximum moisture saturation:1;residual moisture saturation:0.159;permeability :1.0228e-4m/s;initial moisture content:0.3;nitial capillary pressure :1506.77
layer3: Maximum moisture content:0.41;residual moisture content:0.065;Maximum moisture saturation:1;residual moisture saturation:0.159;permeability :1.0228e-4m/s;initial moisture content:0.2;nitial capillary pressure :3540.81
layer4: Maximum moisture content:0.41;residual moisture content:0.065;Maximum moisture saturation:1;residual moisture saturation:0.159;permeability :1.0228e-4m/s;initial moisture content:0.1;nitial capillary pressure :17366.95
Each layer’s VG model parameters are as follows:
Maximum moisture saturation:1;residual moisture saturation:0.159;n=1.89;l=0.5;m=0.47;α=7.5.

Once again, I earnestly implore everyone to point out my issues. I sincerely thank you all in advance.
OGS_HHMM_test.zip (3.7 MB)