A Study on Impact of Bridge Construction on Channel Dynamics of the River Jalangi, West Bengal, India

(Balai Chandra Das )

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Abstract

River Jalangi is one of the three ‘Nadia Rivers’of West Bengal, India on left bank of which Krishnagar, the head quarter of the district of Nadia, is located. Two bridges were constructed on the river Jalangi at Krishnagar to host the national highway 34 (NH-34) and the Sealdah-Lalgola railway. A third bridge, the New Railway Bridge (NRB) was constructed to host the second track of the Sealdah-Lalgola railway. But unlike Old Railway Bridge (ORB) and Dwijendra Lal Roy Road Bridge (DLRB), NRB was designed in such a way that it created a huge obstacle to the flow of the river and made a great change in the channel morphometry. To assess the impact of the bridge construction on river channel morphometry and hydraulics, first hand data were collected before and after the construction of the bridge. Velocity distributions across the channel were measured using submerged-float method and found a directional change as well as change in magnitude also. Channel and flow asymmetry were calculated. It was found that because of bridge construction bed asymmetry, Channel Asymmetry and Flow asymmetry has increased considerably. Due to construction of the NRB, mainly because of its mid-channel dais, left bank-line at downstream has retreated 7 meter swallowing 1125 cubic meters of soil. Key Words: Pier, dais, Channel Asymmetry, Flow Asymmetry Introduction
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