Hello,
Inside Telemac, the flowrate is negative at entrances and positive at outputs, this is due to the fact that we always have a normal vector to the boundary pointing outwards. This is for internal computations, and the flowrate given at entrances by the user is positive, which is more natural, hence what is given on listings is the contrary of what I say here (the listing says >0 : entering, <0 : exiting). Any difference between flowrates at entrance and exit may be due to unsteady flow. You need also to have the keyword : CONTINUITY CORRECTION : YES in your steering file to have a correct evaluation of flowrate at the exit. The relative error in volume is computed in bilan.f (library telemac-2D). The relative error is roughly all the water lost divided by the mass in the domain (see the subroutine for details).
With best regards,
Jean-Michel Hervouet