Numerical Simulation-Optimization for Channelization of River Kosi

Although flow in natural rivers is three-dimensional (3D), however, one (1D)-or two (2D)-dimensional models are often used in engineering practice for shallow open channel flow. In particular, when simulating a very long river of multichannel in cross section for a long period, 1D models (e.g., HEC-RAS) are more cost effective than 2D or 3D models, however, they are unable to simulate momentum exchange between main channel and floodplain, turbulence around engineering structures (e.g., bridges piers, spur dikes), and flow in highly sinuous channels (Duan et al, 2001.; Duan and Julien 2005). To overcome these limitations, engineers commonly enhance 1D model with empirical formulas to approximate energy losses attributable to in-stream structures o