Simulating abstraction from a surface water body

Hi there,

I am simulating a mining pit with known water table that has been used for abstraction over a long period. Hence I would like to combine an interior constant head boundary condition on the mining pit with abstraction in the middle. Usual constant head BC leads to unreal inflow from the surface water body into the well from the surrounding pit creating additional amounts of water and therefore messes up the water balance.

I am wondering if a transfer BC with in-transfer rate = 0 would help out.
Any suggestions are welcome. My model is 3D multi-layer.

Thanks in advance

Your description seems vague to me: its not clear what you are attempting to simulate.  What does "abstraction from the middle" mean?  My guess is that you're simulating the pit lake level with fixed head and you have an "abstraction well" node in the center of the lake.  If this is so, feflow is not the tool for you since this is a surface water problem which is probably can be solved using a spreadsheet.  There must be more to the system if you are using FEFLOW.

Yes your assumption is correct. I am using a transfer BC (in-transfer = 0) in the pit and an abstraction well in then center of it. In order to simulate the body of the pit i am using a very high K leading to (almost) no draw down around the well. It seems to be working fine so far, although I know it might not be the most correct solution. Hence I was wondering if anyone has further suggestions.

if the lake level in the pit is not changing, then a steady state without the cauchy (transfer) bc makes more sense: the well extraction would be equal to the rate of inflow to the pit zone represented by the high K

Pete

ok, I think I get it.  You're probably using cauchy nodes to simulate net evaporation from the lake surface.  But, you should be able to compute that rate knowing the evap rate and area of the lake and that should be equal to the cauchy discharge.  A more realistic and numerically stable approach would be to either add the net evap rate to the abstraction rate for the well or simulate net evap using negative recharge at the lake surface in conjunction with the abstraction well.

Pete

As an alternative to your described lake model, you could contact DHI to obtain the lake IFM.