Hello,
Rainfall is not in Telemac-2D version 6.1, though it is in Telemac-3D version 6.1, but it has been programmed in Telemac-2D version 6.2, that will be released at the end of July 2012, so not so far from now...
Though users have also been able to program it by themselves, it is however rather complicated to combine with point sources and tracers, so it is probably wiser to wait for version 6.2, and/or to use Telemac-3D in the while.
Jean-Michel Hervouet