No runoff generated with "Atmospheric BC with surface runoff" – is this normal?

[Rabeb Dridi]

Hello,
I’m running a HYDRUS-1D simulation where I defined the top boundary condition as "Atmospheric BC with surface runoff". However, when I check the T_Level.out file, I see that RunOff = 0 throughout the entire simulation.
I also checked the pressure head at the soil surface (hTop), and I noticed that all values are negative during the simulation period.
Additionally, the weather and irrigation conditions during the simulation were relatively mild:
Precipitation was low and occurred infrequently.
Irrigation was applied via drip, in small but frequent doses.

Given this, I’m wondering:
Is it normal that no surface runoff occurs under these conditions, even when "Atmospheric BC with runoff" is selected?
Does the negative hTop confirm that the soil surface is always unsaturated, and therefore all water infiltrates (0-20cm : sandy clay loam)?

Thank you for your help!

[Jirka]

When this BC is used, runoff is generated when surface ponding (i.e., h>0) is reached. Since hTop remains negative during the simulation, such a situation did not occur, and runoff was not generated. J.