Fezai,
It would be nice if you could share with us your files (all necesseray file to reproduce your simulation). You can zip them all and attach them here.
It will allow to see why you would have such a strange result on the discharges.
Without having seen your files, my initial thought would be that your friction is not correct (you have non-physical values for the friction law chosen), or that your turbulence/viscosity in not correct (you are working with mapple sirop instead of water
)
Sébastien.