This large regional model is being simulated for natural conditions - meaning, no pumping wells active - and when I run it, it completely floods. And it floods a lot!&#160; I suspected it could be my conductivity values, so I removed them and used the default FEFLOW values instead, just to check. Then I run the model and still floods, although not as crazily as before and not the whole model but around many of the BCs. I tried with conductivities Kx = Ky = Kz = 100 and the model still floods and in the same places.<br> So my problem is not just the conductivities but something else as well. In this stage of the calibration I am using the head constant BCs for the river network. Recharge enters the model thorough In/Outflow on top/bottom.<br> <br> So then I returned to the default conductivity of FEFLOW and tried to simulate using sepage face constraints in the BCs where flooded areas occurred in their neighborhood. No change occurred. It still flooded.<br> <br> I the started to simulate through different definitions of the 1st slice (all the remaining 31 ones are defined as Dependent). It just <strong>didn't flood</strong> when I defined the 1st slice as Phreatic, constrained head on top of model domain. But in this case the Imbalance was on the same magnitude of Recharge (10^6 when the magnitude of the BCs was 10^8), so it is a too large imbalance. In all the other possible options <strong>it flooded and in the same areas, always&#160;</strong>(such areas are always neighboring the BCs). The exception is when 1st slice was defined as Free, constrained head on top of the model . In these cases it still floods but only on a few nodes. However the Imbalance if the 1st slice is Free is less than 1 m3/d, which is too low.&#160;So what is going on and what solutions might be implemented?<br> <br> I am not willing to define constrained heads on top so I thought that defining constraints would be a solution. However when I click the nodes to apply the constraint, once I just click them once the window on top of the screen to define this constraint does not show up with m3/d, as it should but remains with the head units. Is this because I just click once in the nodes of the BCs? If not, then how sould I do it to define the constraints?<br> &#160;