Effect of Channel Width Contraction at Bogibeel Bridge Site on the Morphology of the River Brahmaputra

Abstract

The purpose of construction of bridge over the river or stream is to ensure and facilitate the smooth communication over the waterways. However, in certain engineering designs of bridge, a significant portion of waterway is occupied by the piers placed on the river bed and approach road build on the river bed. This results the constriction of the natural waterway. When the waterway is constricted because of the construction of bridges, it results detrimental effects on the morphology of the streams. The major consideration of the paper is to study the effect of constriction of the natural waterway on the river bank morphology and river island due to bridge construction. In this study, 4.94 km long Bogibeel Bridge constructed over the river Brahmaputra is taken into consideration to study the morphological changes in its upstream and downstream portion of the river reach due to the constriction of the waterway. With the completion of the construction of the piers and approach road of Bogibeel Bridge, some significant morphological changes have already been observed. The satellite imageries of the area over two decade clearly indicates the changes that took place in the river bank morphology due to the construction of the bridge structure on the river bed. Some significant gradual modification in the river bank as well as on the permanent river island is identifiable with the progress of the bridge construction. The portions of the river bank which recede alarmingly due to changes in the configuration of the river channel have been identified to take up effective and sustainable measures to reduce or stop the current erosion.