Numerical Simulation-Optimization for Channelization of River Kosi

Kosi is highly braided river and notorious for its vagaries. During its last two hundred years, it has been shifting laterally towards western direction. It has shifted across a width of over 100 km. The river Kosi has been provided with levees along the banks, at a width ranging from 6 km to 16 km to minimize further shifting of river. The general bed level at many places has risen by 0.1 to 3 m over a period of 50 years due to inadequate velocities in the river for carrying out the sediment. For the minimizing the silting and lateral shifting, it is desirable to explore the possibility of channelizing the river Kosi, which is thought to be one of the method by which the velocities in the river could be increased thereby increasing the sediment carrying capacity of the river. This paper presents the analysis of hydraulic aspects of channelizing the river by using 1D mathematical model HEC-RAS 4.1. Various channelization widths ranging from 800 m to 2000 m were examined keeping the bed profile unchanged and it is found that the channelization width of 1100 m would minimize aggradations and degradation of the river.