Impact of downstream boundary condition on 1D/2D model
I have a combined 1D/2D model where there is an upstream 2D flow area connected to a downstream 2D flow area with a 1D reach (due to presence of a bridge), and another 1D reach downstream of that (with more bridges).
I am using a constant stage boundary at the downstream-most XS and am running a sensitivity analysis on the starting WSE at this XS. I noticed that when I INCREASED the fixed WSE at this XS, it caused the WSE results in my upstream 2D flow area to become LOWER.
Can anyone speculate what may be causing this phenomenon?