HYDRAULIC MODEL STUDIES FOR CHANNELIZATION OF RIVER KOSI FOR A REACH FROM CHATRA TO KOSI BARRAGE USING HOCKEY STICK SHAPE SPUR

Abstract

Channelization of a stream may be undertaken for making it more suitable for
navigation and to restrict water to a certain width to reclaim lands for other important purposes.
Another reason is to avoid inundation and spread of flood water over large stretches of flood
plains, which is also associated with sedimentation and related complications. The river Kosi
has been provided with levees along the banks at a width ranging from 6 km to 16 km to avoid
notorious shifting of the river. The average bed level in many places has risen by 0.1 to 2 m due
to insufficient velocities in the river required to carry the sediment. It is estimated that out of
about 187 million tonnes of sediment brought from Himalaya every year by the river Kosi, only
about 30% is transported to river Ganga and the rest is settled in the Kosi river belt. Due to
heavy inflow of sediment, major reaches of the River Kosi are braided and at several places it is
perched also. River engineers are apprehensive of increased attack of the river on the
embankments (levees) requiring higher maintenance cost. In view of this, channelization of river
Kosi is thought to be one of the methods by which the velocities in the river could be increased,
thereby increasing the sediment carrying capacity of the river. This would avoid settlement of
sediment in the river course and maintain the regime channel. Physical model studies conducted
to investigate the various options for channelizing the stretch of river Kosi from Chatra to Kosi
barrage are presented in this paper. For the maximum observed discharge of 15,586 m
3
/s, it was
seen that the hockey-stick shape spurs guide the flow of water with an average velocity of 3 m/s
and helps to form bed regime.