I am using version 5.2 and I am modeling a 4.5 km wide island in 2D. The total width and depth of the cross section is 17 km and 6 km, respectively. The water table is at the ground surface.  The east and west of the Island (seafloor) is defined with a hydraulic head:

h = -alpha*(z-z_sea) where
alpha = (density_saltwater - density_freshwater)/density_freshwater=0.026
z = elevation
z_sea = 0

The upper boundary (the Island) is defined with a constant recharge and the lower boundary is defined as a no boundary.  I am starting off my model with saltwater (33 000 mg/l) throughout the cross section and running it until steady-state (head and local mass constant).  The freshwater saltwater transition zone is located at 900 to 2500 mbsl (1000 to 32800 mg/l contours). When I run the model to steady-state the hydraulic head is 36 m at an elevation of 63 m.  Is this the freshwater head?

I want to add a 600 m wide and 10 m deep lake at an elevation of 63 m above sea level to my model. I would like to do two simulations where I add the lake at (1) t=0 and at (2) steady-state.  How can I do this?
It looks like in version 5.3 you can choose head boundary conditions; hydraulic head, pressure, seepage face, saltwater head, saturation, and moisture content. How do you do this in version 5.2?

I would appreciate help with this problem

Anna
what do you mean by :
"When I run the model to steady-state the hydraulic head is 36 m at an elevation of 63 m"
if you're meaning that at an area which top surface is 63m a.s.l the groundwater level is 36m (i.e., 27m below surface) than yes, this is a fresh water head!

by the way, it would be interesting to see the cross-section, if you can attach it to your next post.

See attached the island.fem file.  Unfortunately the .dac is too big to attach so I am attaching it as island_steady.fem instead in another posting.  X = 0 is where y =63 m and h = 36 m

I am calibrating my model (by changing the hydraulic conductivity and longitudinal dispersivity) to different freshwater saltwater transition zone (TZ) locations.  This simulation has the TZ at 900 to 2500 mbsl.  When I run another simulation with another location of the TZ the hydraulic head at the elevation of 63 masl will be different.  This makes sense because from the Ghyben-Herzberg relation we know that:

z_s ? (?_f/( ?_s - ?_f))h where

z_s = depth below sea level
?_f = freshwater density
?_s = saltwater density
h = head in the fresh water measured from the sea level datum

Looking at the hydraulic head distribution at steady-state (see island_steady.fem) the east and west boundaries (of the island) are still as defined (as expected).  So you are saying that the hydraulic head for the rest of the cross section are freshwater heads? I should add that the z in the definition of my last post is z = elevation of the head boundary condition.

Is it as simple as when I calibrate to a certain transition zone all I need to do is to add my lake by setting a porosity of 1 and a high value for the hydraulic conductivity?  ShouldnÃ¢â‚¬â„¢t I set a certain hydraulic head at the ground surface?

Maybe this is supposed to be an unconfined problem?  Because what I would like to do is to set the hydraulic head = elevation where I add the lake.  Does anybody have comments on this?  What I would like to have is the groundwater table at the ground surface.

Anna
the steady state file as attached
I looked at the cross section.
1) why do you enter flux only to the  lower half of the boundary? and not to all the boundary (left and right)?
2)to get a head which is about the topography on your island you need to enter lower K's in the island domain, so water level could be rise.  either do it by change the isotrophy 1:10 at the island domain.
but you'll need a good excuse for that ...

3)after you raise the levels, you can enter a lake. you can do it by head boundary on the surface of the lake.

Good luck