Hydraulic conductivity under hysteretic SWCC with air entrapment consideration

[MoamenM]

Dear to whom it may concern,

I ran three simulations: 1-using nonhysteretic drying curve; 2-using nonhysteretic main wetting curve (after air entrapment) and; 3-using hysteretic SWCC, where drying properties were from point #1 and wetting properties were from point #2. I used the hysteresis model by Lenhard et al. (1991). I assumed that the saturated hydraulic conductivity for drying curve and wetting curve are the same.

In the attached photo, I plotted the SWCC and HCF (vs. water content and vs. suction). The figure plots the theoretical SWCC and HCF hysteresis envelope, and also plots the data points from all three Hydrus simulations. Blue data points are from the simulation using nonhysteretic drying curve. Green data points are from the simulation using nonhysteretic wetting curve. Red data points are from the hysteretic simulations.

My question is: why the data points (of the hysteretic simulation) fit within the envelope when hydraulic conductivity vs. water content is plotted; whereas when its plotted against suction, the data point divert away from the envelope (i.e., in the HCF vs. suction, the data points are below the theoretical wetting curve) ?
Notice that mass balance error for all three simulations are below 1%.

I would appreciate an explanation. I hope that I have elaborated my request clearly.

Thanks