Kosi Mahasetu: A Challenging Project On The Ever Shifting Kosi River. History and Project Timeline

Prime Minister Narendra Modi inaugurated the Kosi Rail Mahasetu (mega-bridge) today via video-conferencing.

The bridge connects Nirmali with Saraigarh. Nirmali was a terminus station of Darbhanga-Sakri-Jhanjharpur-Nirmali metre gauge section later converted to broad guage while Saraigarh station is located on the Saharsa-Forbesganj metre gauge route now undergoing gauge conversion.

This is a strategic rail bridge along the Indo-Nepal border. It will re-connect the Mithila and Kosi regions of Bihar besides providing an alternative route to the North East.

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The distance between Nirmali- Saraigarh will decrease from 298 km to 22 km as a result.


The actual cost of construction was Rs 516.02 crore. This rail link restoration was sanctioned by the Government of India in 2003-04 at a sanctioned cost of Rs 323.41 crore.

The Then Prime Minister Atal Bihari Vajpayee had laid the foundation stone for the construction of the bridge on June 6, 2003. The target date of completion set at that time was 2009-10.

CRS inspection

The first trial run on the bridge happened on June 23, 2020 after the project was completed with help of migrant labour. Following this, the CRS (Commisioner of Railway Safety) inspection of the bridge and the line between Saraigarh –Asanpur Kupha happened on August 13, 2020.

The CRS also conducted 110 kmph speed trials between Raghopur and Asanpur Kupaha stations on either bank of the Kosi River.

Post this, the CRS sanction was given for a speed 110 kmph between Saraigarh and Asanpur-Kupaha along with 80 kmph sanction over the Kosi Bridge.

Kosi Mahasetu – A Timeline and Key Features

Construction works of Kosi bridge New line (22 Km.) between Nirmali-Saraigarh section was included in the railway budget for 2003-04.

The sub-structure of Kosi bridge – 39 x 45.7m open web girders (OWG), was completed in 2010. The super structure of the Kosi Bridge besides four other bridges numbered no.4, 5, 6 & 7 were completed in 2013.

The west approach work from Km. marker 7.065 (from the centre line of Nirmali station to Km marker 8.700 and additional minor bridges work commenced in 2012.

For the east approachof the Kosi Rail Bridge, the work started on June 23, 2009 from Km marker 10.00 to Km marker 16.00. Works commenced on December 12,2009 from Km marker 16.00 to  Km marker 20.800.

Post that, earthwork and blanketing were completed in both the approaches of Kosibridge (39×45.7m OWG). This was followed by track linking from both approaches

Blanketing in east approaches has also been completed and is in progress in west approach. Track linking in the east approach has been completed and is in progress in the west approach.

Meanwhile, heavy floods in the year caused severe damage to substructure (especially the return walls) of two bridges -number 5 and 7. In addition, the approach of bridge number 7 was also washed out resulting in shifting of girder away from bearing.

Remedial Measures:

A slew of remedial measures were taken post the floods of 2017, first temporary and some permanent.

Temporary measures included

·         widening of pedestal of Roller end to house the bearing by 135 mm towards Saraigarh and seating of girder in proper location;

·         dismantling of dirt wall to clear the girder;

·         creating a gap between settled return wall and abutment to release the pressure on abutment at bridge number 5;

·         rebuilding of settled return wall of bridge number No.7 and raising of settled return wall of bridge number 5;

·         filling of stone dust in scoured portion of bridges

·         Slope protection by boulder creating and pitching.

After completion of the above works, the traffic over these bridges will be allowed at 10 KMPH with static patrolling and regular monitoring.

Permanent Measures included rebuilding of both the bridges on permanent diversion by increasing the waterway and providing 2×45.70 m open web girder (OWG) spans to cater additional discharge of water.

The work of rehabilitation of major bridges number 5 and 7 damaged due to heavy flood in August’2017 was completed and tracks linked despite the Corona pandemic slowing down works.

However, work on the bridge cum new line picked up again and trials happened on June 23, 2020 followed by CRS inspection and subsequent clearance for running trains on August 13, 2020.

This was followed by the speed trial on August 14 and the subsequent inauguration by the Prime Minister on Friday. 

The Shifting Course of the River Kosi – A Brief History

The river Kosi flooded the entire Kosi region of North Bihar by frequently shifting its course. Between 1921 and 1954 it shifted westward by about 50 km.

In 1934, the Kosi did not flow between Nirmali and Bhaptiahi stations.

A small bridge of 4×60’ span was provided across Kosi’s tributary river Tiljuga flowing near Nirmali. With the continuous shifting of the main channel of the Kosi the rail link between Nirmali-Bhaptiahi (Saraigarh) was washed away in 1934 during the heavy floods and severe Indo-Nepal earthquake.

As a result, train services were curtailed on this line. Further damage to the alignment in 1937 meant that train services had to be terminated at Nirmali.

The disruption of this route forced people of Nirmali area to take a circuitous route of 298 kilometres via Darbhanga-Samastipur-Khagaria-Mansi-Saharsa to reach their district headquarters.

Continuous change in the course of the Kosi made it tough to identify and plan a proper bridge location. This ensured that restoration of the erstwhile rail connectivity was delayed for decades together.

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About the Author: Raghavendra Rao

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