oscillating head at a well

Hello all!

Has anyone any experience with oscillating heads at the node of a well (4th BC)?

I’m handling a 3D modell with several slices and a river running through the modell domain. By running the transient modell the hydraulic head at the well oscillates. The aquifer consists of 3 layers (3/ 7/ 1 m thickness; similar conductivities). The well is applied as a multilayered well with Q=0 at the 2nd and Q=340 at the 3rd slice. I tried to avoid this error by adding 1 very thin layer above the 2nd and 1 under the 3rd slice, but it didn’t work.

By the way, the pumping rate is realised at every time step, as I checked with the budget analyzer.
What else could be the reason for this problem??

I appreciate your advices! Thanks!
Stefanie 

Some ideas to help you :

Is the oscillating head close to the interface between two layers?
May be you could change the hydraulic conductivity (increase hydraulic conductivity in the 3rd layer) to test if you have always that problem

How many days are you using for one run of your model? maybe it's not enough

Have you checked your free surface definition in the Problem definition menu, what is the "free surface definition" for the 3rd layer, where you put Q=340

Best regards