Mangdechu project designed to withstand major quake

Hydropower: Clearing rising apprehensions surrounding the safety of Mangdechu hydropower project (MHP) from earthquakes, the authority claims that the project is safe and will be stable in the event of an earthquake, because of inclusion of earthquake parameters in the structures.

“Bhutan should not worry because the earthquake parameters loading on the project structures are taken on the higher side,” the project’s managing director, AK Mishra said.

An inclusion of earthquake parameters means that the project could withstand a major earthquake of magnitude eight at a 15km depth, according the project’s DPR conducted by National Hydroelectric Power Corporation (NHPC), India.

This is as per the findings of IIT Roorkee’s study conducted for MHPA and approved by the national committee for seismic design parameters.

“Going through the seismic data and seismotectonic set up of the area, it is inferred that main central thrust (MCT), a major tectonic feature of the area, is capable of generating a maximum credible earthquake (MCE) of magnitude eight at a depth of 15km from the project site,” the report stated.

MCE is defined as an earthquake of maximum magnitude likely to be produced at the site under currently known seismotectonic framework.

“MCE occurs generally only once in 100 years and, even if the earthquake occurs, the project is still safe,” the project’s chief geologist, Pankaj Punetha, said.

The area of study on seismotectonic set up and earthquake data covers from Sikkim in the west to Arunachal Pradesh in the east, and Tibet in the north to Meghalaya in the south.

The report states that, in case of MHP, MCT is inferred as major source of threat to the project.  Other sources of major threat are main boundary thrust, Dhubri fault and Dauki fault zone, each of which are likely to cause an earthquake of 7.5 magnitude. The depth of these sources stands at 15,154 and 256km from the project area respectively.

Based on the project’s location at seismically active area, earthquake parameters were incorporated in the design of the project.

AK Mishra said re-enforcement and support system design consider the effect of earthquake and accordingly the system is designed in a conservative manner. 

“The maximum impact of earthquake comes on those structures, which are above the surface, while those below the surface are least affected,” AK Mishra said, adding that the hydro-mechanical like gates are designed for extra loading due to earthquake. 

Economic affairs minister, Norbu Wangchuk also said that the project would be safe from earthquakes.

“We put in all science and technology in dams as far as possible to protect the project from earthquakes; so I believe it’s safe,” Norbu Wangchuk said.

Meanwhile, MHP has suffered no damage from the tremors that the recent earthquakes in Nepal triggered.

“After the major earthquakes in Nepal, no movement was recorded in any of the geotechnical instrument installed in the various civil structures, showing them to be absolutely safe,” Pankaj Punetha said.

Pankaj Punetha also said that, even during the construction, additional geological and geotechnical investigations are undertaken as and when required to ensure stability and safety.

The recent assessment data for stability and safety conducted since 2014 also reveal that Factor of Safety (FoS) is sufficient to ensure the project stability during the earthquake.

In case of the MHP, every component records more than FoS 1.39-2.78 value, he said.

By Tempa Wangdi

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