I have modeled a river with an upstream 2D flow area and a downstream 1D reach with a simple sequential connection. After 250 meters from the connection I have a weir with two gates.
I noticed that the velocities at the 2D flow areas edge (i.e. when there is the transition between 2D to 1D model) are very high but I don't understand why.
I tried to shift the connection a little more upstream but the situation doesn't change. I can't translate the connection much more upstream because I have a meander.
Probably the results don't change significantly for this variation of velocity, but I would like to know why this happen.