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Bigger floods and increased erosion due to climate change are threatening and damaging river bridges in Bihar, in some places forcing people to fall back on temporary pontoon bridges

Close to 60 boats are used to build a pontoon bridge as two permanent bridges collapsed because of floods. (Photo by Alok Gupta)

Close to 60 boats are used to build a pontoon bridge as two permanent bridges collapsed because of floods. (Photo by Alok Gupta)

Every January, fishermen at Beldour and Chautam administrative blocks in Khagaria district of Bihar take part in the rather strange practice of donating boats at the confluence of Koshi and Bagmati rivers. They collect close to 60 boats, place them in a straight line connecting the riverbanks and build a temporary pontoon bridge.

“These boats are pillars and we are going to construct a bridge over it,” local boatman Gopal Yadav said. “Keeping a straight line matters or else heavy vehicles that will ply on this bridge will drown,” he added, showing of his newly acquired engineering skills. The villagers complete construction of the pontoon bridge within a fortnight by laying bamboo poles tied with ropes over the boats.

Local villagers started making this bridge, locally known as Nauka Setu (boat bridge), every year since 2011 after the nearby concrete bridge, BP Mandal Setu, and a steel bridge over the rivers collapsed due to the heavy flow of the rivers. The pontoon bridge saves the villagers a detour of nearly 150 km to reach Supaul and Madhepura districts in Bihar and also to reach Nepal.

Although small buses, cars, loaded vans and even government vehicles bumpily cross this Nauka Setu, no scientific study has ever been done on how much load the bridge should be allowed to carry. The boat bridge is risky and can collapse anytime, according to Amarendra Sinha, block development officer of Beldour. This bridge is closed or dismantled from May to December when both the rivers are in spate. “But the villagers have no option because it’s the only mode of transportation for nearly a million people from January to May,” Sinha told

Bridges and climate change

Bridges getting washed away due to floods and riverbank erosion is becoming more common in Bihar as severe weather conditions increase in frequency because of climate change. This leads to hardship for large numbers of people, who are in some places trying to cope by making temporary bridges of doubtful safety.

The Bihar state government in 1991 constructed the concrete BP Mandal Bridge to connect Khagaria with the rest of the province. “Engineers artificially created the confluence of Koshi and Bagmati rivers to pave way for construction of the bridge,” river expert Dinesh Mishra told

Ever since it was inaugurated, the bridge faced mild to severe damage to its pillars due to unpredictable water flow. Finally on August 29, 2010, the Koshi River washed away around 10 pillars of the bridge. The district administration declared the bridge to be dangerous and closed it till further notice. Several efforts were made to repair the bridge but the strong current of the river foiled every attempt.

The government then decided to construct a steel bridge some distance away from the BP Mandal Bridge. The 566-metre bridge built on steel piles was constructed at a cost of Rs 1.7 million (USD 25,337) and inaugurated on June 8, 2011.  Local residents named it the caterpillar bridge as it had as many as 92 pillars to withstand the strong currents of the Koshi and Bagmati rivers.

On July 16, 2012, the new bridge too succumbed to the strong current of the rivers. A 200-metre portion of the bridge was washed away. Government engineers tried to retrieve the bridge by pulling it up by ropes and chains but failed to prevent it from being washed away repeatedly.

“While the steel pile bridge is beyond repair, the Mandal bridge is being repaired again,” Satyendra Kumar, superintendent engineer of the water resource department of the Bihar government, Khagaria division, told The repair was supposed to be completed by 2016. Now, “repair work is still going on and it will take another one year to complete it,” Kumar estimates.

Many bridges in danger

These two bridges are not the only ones in the state that have suffered massive damage because of raging rivers that are changing course more frequently. In Bhagalpur, the 4.7 km Vikramshila Setu on Ganga River, the third-longest river bridge in India – connecting the districts of Purnea and Katihar – is also suffering massive damage.

In the same region, the 1.8 km Koshi Mahasetu inaugurated in 2012 is facing a threat because of a weakening guide dam on the eastern part of the bridge. This is also threatening to submerge at least five villages. The bridge was built to save travel time by nearly five hours between Madhubani and Supaul districts. A similar bridge between the two districts was destroyed in an earthquake in 1934. After that, it took the government 78 years to connect the two districts.

A government vehicle crossing the pontoon bridge. The washed away concrete bridge can be seen in the background. (Photo by Alok Gupta)

A government vehicle crossing the pontoon bridge. The washed away concrete bridge can be seen in the background. (Photo by Alok Gupta)

In the case of Koshi Mahasetu, the situation is so alarming that Deputy Chief Minister of Bihar Tejaswi Yadav wrote a letter to federal transport minister Nitin Gadkari to immediately help the state to strengthen the guide dam. Yadav in his letter has mentioned that even the Central Water and Power Research Station has recommended repairing the eastern guide dam to protect the Koshi Mahasetu from damage.

Alarm bells started ringing for the Vikramshila Setu after its pillars started crumbling. A team of retired engineers from Tilkamanjhi University voluntarily inspected damaged pillars 15 and 16. One of the engineers, Ashok Kumar Sinha, told, “Pillars number 15 and 16 have gone down by 15 mm. A major portion of wall around the pillars has been washed away triggering collapse threat of the bridge due to erosion caused by the Ganga.”

Expert advice

The Bihar government consulted Nayan Sharma, a professor at the Indian Institute of Technology at Roorkee to seek a solution to protect the BP Mandal Setu and the adjoining steel bridge.

Sharma points out that he gave warning to the state government regarding the imminent adverse impact of climate change and erratic flow of rivers on both the bridges. “It’s not only about these two bridges; other bridges constructed over the rivers in Bihar need to braced to the changing rainfall and flood patterns,” he told Sharma says that in his report he advised the state government to immediately strengthen the pillars of both bridges, as strong currents of the Koshi and Bagmati rivers are weakening the pillars of the bridge.

Sharma also studied in detail severe erosion caused by the Ganga in Vikramshila. In his research paper, he says that at the point around 3.5 km downstream of Vikramshila Setu, there has been 1,100 metres of erosion between 2003 and 2011. The high rate of erosion makes it probable that the river will weaken the pillars of the bridge. “It needs a further detailed study,” he reiterates.

Erosion is also threatening the Bhagalpur College of Engineering and Bihar Agriculture University buildings, national highway 80 and Fatehpur Masjid, his report says. “These are the findings of 2011. The situation has changed for the worse and the state should immediately take action to control erosion,” Sharma warns.

River expert Mishra points out that apart from climate change affecting the flow of rivers, the engineering of BP Mandal and steel bridge were also defective. “First, constructing a bridge at the confluence of rivers itself was a risk. Second, the engineers tried to flow Bagmati through Koshi River,” he explains.

Forced confluence

The Koshi-Bagmati confluence did not naturally exist at Khagaria, he claims. “Engineers created the confluence. Since Bagmati is at higher level and Koshi at a lower elevation, the former should have been merged with the latter,” he says. The result of this was that sedimentation increased in the lower Koshi riverbed. It increased water flow in both the rivers, causing stress on the pillars of the bridges.

Both Mishra and Sharma accept that bridges over the rivers are important for transportation. But the climate change and disaster management components need to be taken into consideration to avoid damage and inconvenience. “It’s important that old bridges are readied to meet the unpredictability of rivers,” Sharma cautions.

Bihar is constructing a large number of bridges under the Chief Minister’s bridge plan that funds construction of small bridges under the cost of Rs 2.5 million. The state has spent nearly Rs 191.5 billion for construction of a large number of bridges under the scheme. A majority of these bridges are over rivers.

Anil Kumar Sinha, vice chairman of Bihar State Disaster Management Authority, accepts that old bridges constructed over the rivers in the state do not have any preparedness for disasters. “We are also aware of how bridges failed on confluence of Koshi and Bagmati rivers,” he says.

Sinha says that in 2014, the planning and development department of the state, keeping in view disaster management and climate change, issued a directive, making it compulsory for every department to ensure the disaster management component in taken into consideration in all works.

Bihar has added the climate change component for the proposed Ganga expressway project. Experts are awaiting similar action for old bridges over rivers. Sinha says that efforts are underway to protect the bridges but they will take some time to take effect.

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