INVESTIGATION OF ARTIFICIAL CHANNELIZATION ON BRAHMAPUTRA RIVER BY NUMERICAL MODELING

Abstract

Brahmaputra river system is very complex because of its braided flow pattern and high sediment load. It is one of the most braided river in the world in which the width of the river extends up to 22 km. Constructing hydraulic structures like a bridge across the river along wide cross section will be difficult unless channelization works are provided. The first part of the study is developing a mathematical model for the river by using HEC RAS 4.1.0. Sediment transport capacity of the river has been done by using different method of transportation functions like Ackers-White, Yang and Engelend-Hansen methods. The result shows that Yang's method of transportation function gives a better result for Brahmaputra River when it is compared with the other transportation functions. From these transportation functions Ackers-White method of transportation function gives high value of sediment transport capacity and high value of change in channel invert. The second part of the study is to channelize the river by putting river training structures at selected nodal points. These nodal points are selected . based on the channel geometry and property in which channelization of the river can be possible. Some cross sections of the river are much braided in nature and it may not be economical to confine the flow over the whole reach of the river Flow guide bunds are adopted as a river training structure to confine and guide the flow to a gentle channel. Especially these structures are constructed on the banks of the river at bridge site locations to guide and confine the flow. Other structures which are adopted as channelization work are closing of secondary channels by putting bed bars, permeable • spurs, porcupine screens, Jack Jetty etc. The change of flow parameters have been compared before and after channelization of the river. There is an increase of velocity, shear stress, and sediment capacity at the cross section in which channelization is made' and up to a certain distance downstream of it. The water surface elevation also increases in the upstream sections up to a certain distance depending on the magnitude of the waterway and depth of channel.