Help, about the simulation of seawater-freashwater interface

Hi

    Recently, I finished a 3D density-dependent groundwater flow and mass trasport model near coastal areas by using FEFLOW software. There is confined aquifer underlying the sea boundary. Now the results about groundwater flow system is good, but the simulated interface between groundwater and sea water is very different with the common knowledge.  Normally, the interface at the bottom is towards the fresh water, but the interface in my results is towards sea water. I am not sure the results. Can any one give me a comment?

    I have detailed modelling results, but here, I cannot attach it. It's grateful that we can disucss it with E_Mail.

    Thanks!


      Hook

Hi,

What kind of boundary condition did you apply in your confined aquifer under the sea? Maybe there is a freshwater BC for the transport part?

Thanks for your reply. There are 6 model layers, the 1-2 layer near the coastal area is repsented as constant head/mass transport boundary condition. And the other part of the model at the upper boundary is represented as flux boundary.

The meida is hetergeneous. Steady flow/steady transport model is applied. It is found that different hydrogeology parameters will produce different salt-freash water interface. Sometimes the interface at the bottom is towards the sea, which is different from the knowledge of its real location.

According to your boundary conditions:
keep in mind, that FEFLOW will treat each flow boundary as a freshwater boundary (c=0) if you do specify any concentration at the inflow nodes or massfluxes.

Another thing you could check is whether or not your steady state transport solution has converged. To do that I normally run the modell as a transient one (or maybe steady flow / transient transport). I had made some bad experience with the steady state transport simulation. Espacially if you want to simulate a density driven flow (as you will have in saltwater intrusion) the solution will be much more stable and meaningfull in a transient / transinet model run.