No structural damage to Bahunijhora multicellular box culvert bridge

Environment News

Recent incessant downpour caused havoc across the country.

Bhutan witnessed flash floods and road blocks disturbing settlements and road networks. Among them, the block at Bahunijhora stream in Pasakha caused major concern to the Pasakha Industrial Estate, the biggest industrial estate in the country.

The multicellular box culvert which was recently completed has been filled with debris washed down by the stream due to heavy rainfall for two consecutive days. It has cut off the road network at the industrial estate and for people of Pasakha and Samphelling gewog. The consignments to and from the industries have been on a halt for days. The block lasted for a few days raising eyebrows on the sustainability of the bridge which is not formally inaugurated. 

However, it has been assured that the multicellular box culvert bridge is intact and no structural damage is reported. Department of Roads (DOR) with assistance from industries, Police and Desuups have cleared the bridge which is now open for traffic.

DOR’s Project Engineer, Tshewang,  said that the assessment has been done and there is no major damage to the structure except the railing which was damaged during the clearing work by excavator.

The high intensity rainfall has flooded the debris which could not pass through the bridge resulting in overflow from the bridge. The engineer said that the bridge was flooded with debris for a few days.  The height and the length of the bridge actually allow the debris to pass through easily. “But the heavy rainfall was the main cause,” he said. The bridge which stands at more than 6m at the center can allow the debris to pass through the columns in between.

The six columns of the bridge are also undamaged. Structurally, the bridge would last for 50 years according to the design. The bridge is designed considering the impact from hydrology or the weather condition.

The gabion protection wall above the bridge has escaped minor damage according to the Engineer. However, full assessment will be done by DOR.

“The bridge was also aligned to connect to existing road which was not tall. The bridge has been designed after recommendations from geo-technical experts assessing the severity of the stream,” the Engineer said. Increasing the bridge’s height would mean that heavy vehicles cannot climb the steep arch to cross the bridge.

DOR now plans to clear the debris above the bridge before and after every monsoon to allow swift flow of the debris. Also, clearing work will be carried out whenever necessary during peak monsoon. The DOR’s office at Pasakha will monitor the situation frequently.

Bahunijhora’s multicellular box culvert has become important for the industries and the people of Samphelling gewog, serving as the main access route. Before the bridge was built, vehicles were diverted through unpaved road having to cross free flowing streams.

Bhutan Builders Private Limited constructed the bridge worth Nu 12mn with  grant from Asian Development Bank under South Asian Sub-regional Economic Cooperation (SASEC)’s Road Connectivity Project.

Krishna Ghalley from Phuentsholing

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