I try to developed a simple 1D model of a prismatic channel. I used 2 rectangular XS and HEC-RAS links the left bank downstream to the right bank upstream (and the right bank downstream with left bank upstream). I hope you can help me because i can't make any proyect.
Sounds like the cross sections are not drawn in the same direction. HEC-RAS requires that the cross sections be drawn from left overbank to right overbank (facing downstream). If one was drawn right to left and the other drawn left to right, the scenario you described would happen. You can right click on the cross section that is in the wrong direction and switch direction. See post linked below: