Total Discharge

Hello

I'm doing steady-state seeapge analysis of Nuozhadu Dam. I have a question about total discharge. I took 2 crossection in upstream and downstream but total discharges are different. 

Shouldn't the flow through all sections of the dam be the same? I show the crossections below and results. In A-A 18930 m3/day/m, in B-B total discharge 3690.

Why is this wrong

Thank you.