Hi,

I am conducting simple simulations using multi-layer pumping wells. For your review, the model domain and other settings are shown in the attached.

Two cases are considered:

- Case 1. The model is solved by assuming the aquifer is confined.

- Case 2. The model is solved as an unconfined aquifer system: Slice #1 is set as "Phreatic" and Sy=0.1

Cases 1 and 2 use the same settings except the aquifer type.

[Case 1]

The simulation of Case 1 run well (e.g., dt increased from 1.0e-5 (a few steps at the beginning) up to 31day), and the modeled hydraulic heads look ok (see the attached).

[Case 2]

For Case 2, the model has difficulties in solving the unconfined well problem. The length of modeled time-steps stays at 1.0e-5 day, which is too small to run for the whole modeling period. My understanding of key difference between Cases 1 and 2 is the magnitude of relative conductivity (k): k= 1 constant for Case 1 while k= variable for Case 2, depending on the elevation of water table in model elements (saturation degree). In Case 2, the residual water depth is set as 0.25 (about 10% of the layer thickness).

My question is what causes the convergence difficulty in Case 2?

Could you share any ideas, suggestions, or experience to solve this issue?

Cheers,