The multi-cellular culvert box bridge at Bhawanijhora, Pasakha is frequently submerged in the flashfloods caused by heavy rainfall, leaving people cut off for few hours to few days. The height of the bridge is 6 meters and the capacity of the bridge is 40 metric tonnes. The construction started in March 2018 and completed in May 2019.
Project Coordinator of SASEC project, Phuentsholing, Kinzang Wangchuk, said that they are concerned over this issue and the project has consulted with all the relevant stakeholders, including ADB and the ministries.
He added, “The department has formed a team comprising of engineers to find out the causes. It was a disaster, but it is an uncertainty geologically. The finding by the team states that it was all triggered by heavy rainfall and the team has noticed a lot of tension cracks in the uphill valley.”
It was found that slippage was high due to heavy rains, and because of that the whole tension crack had shifted down which made the hillock to move down causing a flashflood and leading to the submersion of the bridge, he added.
He said that they forecast a flood-return for every bridge, whereby if the return flood period of bridge is 100 years, then obviously the structure height of the bridge has to be high. Therefore, the multi-cellular culvert box bridge was constructed for the return period of 10 years, he said.
However, “The flood-return which was supposed to come in 10 years has hit the bridge at once this year. So the team has concluded that it was all because of the heavy rainfall and it coincided with flood-return,” he added.
In addition, he said that they do not anticipate such floods next year, whereby no such issues will be aroused and the highest pattern of the rainfall was this year as per the metrology department.
Even to use that bridge in future is in question, he said, adding that since the hillock, itself, is an uncertainty, even the neighboring villagers may have to evacuate in the long run.
He said, “Because of that impact (submerged bridge), the tendering of Land Custom Station at Pasakha has been put on halt by Phuentsholing Thromde.”
Meanwhile, he shared that for any project, they would do risk identification, he said.
In addition, he also said that for ADB projects, a team comprising of expertise from various agencies would comment unlike GoI and RGoB projects. All the due process were done, he said, adding that going through the PPTA report, they were given two options to construct the bridge at Bhawanijhora with given reasons.
They suggested that, if we have enough budget then it would be best to construct a fly-over long span bridge while if at all we cannot do that, then the multi-cellular culvert box is the only option.”
However, he said that they did not know what decision took it to opt for the construction of multi-cellular culvert box bridge at Bhawanijhora. Maybe due to budget constraint in due process, he added.
The designer stated that based on the recommendations of the PPTA report, they have done all the designing of the current bridge. He said, “As per PPTA report, they have not done sub ground drilling before, they have just taken from the surface geological patterns. There could be any uncertainty in the area geologically.”