Hi csena,
(1) you should use your choice (iii), the 2nd kind (Flux) boundary condition
To apply the recharge value in the way you described, several steps are necessary:
(1) first, you need the upper topographic boundary as a line (shp, ascii)
(2) second, you need a pow-file where you define a power function (time-varying function for the reacharge) for every node.
(3) You have to create a database-file where you specify the x,y-coordinates of these nodes and the respective number of the pow-function (syntax per line: x,y,pow-ID)
As a further prerequisite, the nodes of your mesh have to be identical with the nodes you described in these file.
You can then use the JOIN-tool with DATA-option to assign the Pow-ID's to the nodes. Choose the option "1D-Interpolation" in the upcoming dialog and set and set a reasonable high "Distance for non-interpolated data points". Load the pow-file in "Time-vaying function ID's" and load the database file with "Import powerfunction IDs". Finally click appply to start the assignment.
Annotations:
- Since the 2nd kind BC is mathematically applied to the edges of the cells and not to the nodes, there will be a minor "smearing" of your assignment between the nodes. Usually it should not matter.
- This procedure can be easier if you do not strictly define a pow-function to every single node. Alternatively, you can simply define the recharge for a small number of points on the border, and let FEFLOW the missing pow-functions by interpolation.
