Hello everyone!
I want to simulate the intrusion of freshwater via an infiltration pond in saline groundwater. Therefor I use the convective form of the transport equation (there had been some trouble with the dispersive form (
http://forum.mikebydhi.com/index.php/topic,2276.msg5172.html#msg5172)) with the Free-Surface approach.
The Infiltration pond is represented with a well-BC and a 1st kind concentration-BC.
In the most cases this works fine. But in scenarios with a low Infiltration rate or a high hydraulic conductivity, which come along with only a low rise of the hydraulic head in the area of the infiltration pond, the freshwater flows under the denser groundwater in the toplayer. (see picture)
[img width=200 height=50]http://i1383.photobucket.com/albums/ah315/Mieszko2/Schenkel_zps31fd5e6d.jpg[/img]
[sup]Cut through 3D-Model: Freshwater: violet; Groundwater: Red; Lines: Isolines of Nodal Darcy-Flux[/sup]
The density-contrast might be quite low, but considering the long simulationtime (>2000d) there should be a mixing with the water with lower density in the lower slices. Furthermore the isolines of the Darcy-Velocity and the hydraulic head are orthogonal to the surface, so that the mass should be transported with the flow. Thus this seems to be unphysical behavior of the model.
I tried vertical as well as horizontal refinement, a different solver and much more, but nothing fixed the problem.
Maybe someone encountered a similar problem? What couses this behavior of the model?
AS I said, this only happens with low rises of the hydraulic head.
Thank you
Cornelius
