Przemek Nalecki

I did that too - the time step icreases to about 4000d during the run and results are ~1.5e4 m3/d. I also ran the model with 1d time step which resulted in stable inflow rates of about 2.5e3 m3/d.

I am using Feflow 5.404, phreatic layer type, fairly detailed mesh.

Any suggestions of how to sort it out will be greatly appreciated.

I am running quasi steady-state model with rivers simulated as 1st kind with constraints (effectively high conductive drains). I ran the model for the same period of time (36500d) at various time steps:
-3650d
-365d
-36d
Looking at budget results, the 1st kind discharge rates stabilize at: ~6.4e4 m3/d (time step 3650d), ~1.5e4 m3/d (time step 365d) and ~4.3e3 m3/d (time step 36d) - which is quite a big difference.
Did anybody run into similar problems before?