How to deal with the evaporation?

Dear all,
    I am trying to set up a 3-D model for a transient flow. But I have trouble with dealing with the evaporation. Because the evaporation varies with the groundwater table.How I import the evaporation in the "Flow Materials"?
   Someone had told me the interface manager IFM can help solve this problem. Can anyone tell me how to use the IFM programming?
   Thanks a lot for your help !

Convenient handling of head-dependent evaporation will be possible in the coming release 5.3. An equation editor can then be used to specify arbitrary equations for groundwater recharge/evaporation.
For IFM usage, please refer to the files ifm_for_programmers.pdf and ifm_example.pdf in the /doc directory of the FEFLOW DVD.