rainfall time series

Hello,
I want to create a time rainfall time series and use it as a boundary condition in a 2D model. I have a few questions:
1) what would be the righ unit clas to use? velosity [m/d] volume [m3]?
2) The value of hydraulic conductivity I use is low, so actual infiltration rate will be much lower then the rainfall rate. What happens to the runoff in the model?

Thanks in advanced,
Matan

If infiltration lower than raining, the Head will increase and even exceed the top, in that case, you need to decide to how to deal with this, and use "Head limits at the model top".
One of the options is to remove the water.
Please see: http://www.feflow.info/html/help75/feflow/08_ProblemSettings/Flow/free_surface.html