Shallow water flows in multiply connected open channel network are frequently encountered in hydro-environmental problems. Simulating such flows practically reduces to solving the 1-D shallow water equations (1-D SWEs) in locally 1-D open channel networks. A key in solving the 1-D SWEs is physically consistent numerical treatment of junctions and bends, which has not been discussed in depth in the conventional researches. This paper performs numerical comparisons of shallow water models with different internal boundary conditions (IBCs) at junctions and bends, focusing on their applications to real problems. The computational results show significant impacts of the IBCs on the simulated hydraulic processes, such as flow transition, flood arrival time, and peak discharge.