Nepal quake rekindles fears on Tehri dam, Jaitapur N plant

Bengaluru: The devastating quake in Nepal has revived the controversy in India over the Tehri dam in Uttarakhand that was commissioned in 2006-07 and a nuclear plant proposed to be set up at Jaitapur in Maharashtra.

Both the dam and the site for the nuclear plant were approved in spite of advice to the contrary by independent seismologists, the Rome-based International Association for Promoting Geoethics (IAPG) has said.

The 260.5-metre-high Tehri dam, the tallest in India, and the 9,900 MW nuclear plant, the world's largest, are among the controversial projects cited by IAPG in its latest publication "Geoethics, Ethical Challenges and Case Studies in Earth Sciences".

The two case studies from India "relate to future risks to engineering structures and concern fundamental ethical issues", Vinod Gaur, former director of Hyderabad's National Geophysical Research Institute and the author of the study, said.

The Tehri dam is located in the central Himalayan fold created by the Tibetan plate advancing southward over India at about two metres per century. Its 2.6 cubic km reservoir floods a narrow 30 km-long valley. Controlled release of reservoir water currently generates 1,000 MW of power.

According to Gaur, the Tehri dam was designed in 1972 when evidence of the ongoing deformation in the Himalayas was not available. The design was based on the assumption that a maximum credible earthquake at the site would have a magnitude of 7.2 on the Richter scale and a peak ground acceleration of 0.25g (where "g" is the acceleration due to gravity).

The project was the subject of three decades of debate due to concerns over the wisdom of constructing a major earth and rockfill dam in the Himalayas, which have seen three devastating earthquakes in the first half of the 20th century.

Gaur said that around the mid-1980s, the maximum credible magnitude was raised from 7.2 to 8.5 but the Tehri project's consultants retained the 0.25g value as the dam's design basis.

According Gaur, the dam should have been redesigned to withstand a peak ground acceleration of 0.56g, but the government gave the green signal for the dam's construction after ignoring the majority advice of an expert committee it had set up in 1996.

Four of the five members of the committee recommended a 3-D simulation of the dam for long-duration shaking appropriate for an 8-magnitude quake. Also recommended, before the beginning of construction, was a simulated dam failure analysis to evaluate the consequences of its hypothetical breach.

"No 3-D simulation responding to a great rupture beneath the dam has so far been undertaken," Gaur said. "The completed dam, therefore, falls short of the recommended compliance with international standards," says the IAPG report. "Thus, there is a real concern whether expert committee members have betrayed their ethical obligations to the public at risk from catastrophic damage in a future earthquake."

The IAPG case-study of the Jaitapur site says Indian authorities ignored the presence of a 35-km-long "possibly active fault" just 10 km south of the site in spite of concerns raised by scientists not involved in the project. ­"No paleoseismic investigations have been undertaken across this fault to determine when it last slipped," Gaur said, adding: "It has not been trenched to determine what magnitude earthquakes this fault may be capable of."

In response, the state-owned Nuclear Power Corporation has said that "all concerns have been accounted for" by its experts.

"The discounting of the possible occurrence of a damaging earthquake nearby is clearly imprudent," Gaur said, adding: "Should the fault slip, the nuclear plant would lie less than 10 kilometres from the rupture." "Shortcuts in seismic hazard assessments for nuclear power plants are not acceptable," Max Wyss, a renowned seismologist with Geneva's International Centre for Earth Simulation, has said in a commentary on Gaur's study. He fears that the cases reported in the IAPG publication "represent only the tip of the iceberg of similar cases worldwide, which raise serious questions about research integrity."

The 7.9 magnitude Nepal quake on April 29 has claimed over 7,000 lives and injured thousands more, besides causing large-scale destruction of houses and other buildings.