Hi suruchigeo,
The problem is that the boundary you specified in bnd11 file is defined as Open for chainage 1526.960 and this point is not actually at the most upstream part or most downstream part of your branch(river). In fact, you can have maximum two open boundary conditions for a branch.
If you describe more detailed what you want to do, maybe we can give you a more detailed solution. Until then, I suggest you to use in the upstream part of your river(branch) Inflow discharge and in the downstream part Q-H relationship if you don't know the variation in time of the water level at that specific point. If your river ends up in sea or in a lake, you can probably use WL open boundary condition (as constant or as a time series), or in any other cases when you know the water level at the downstream location.
Regards,
Aurelian
