INDIA: Quake Triggers Narmada Dam Safety Debate

By Ranjit Devraj Reprint | | Print |

Ranjit Devraj

NEW DELHI, Jan 30 2001 (IPS) - The devastating earthquake in India’s western Gujarat state has revived the debate about links between seismicity and big dams, with anti-dam activists saying this has raised questions about the safety of the Narmada dam.

Famous anti-Narmada dams activist Medha Patkar has cited statements by a section of Indian seismologists who say that the Jan. 26 quake, which has killed at least 20,000 people, proves that the multi-billion dollar Sardar Sarovar dam is sited in a highly seismic zone.

The dam, located in Gujarat, is the first of 30 big and more than 3,000 dams to be built under the Narmada Valley project across the Narmada river, which flows across central India and into the Arabian Sea.

Patkar’s over 15-year-old campaign, Save the Narmada Movement, better known by its Hindi initials NBA, claims that the social, environmental and economic costs of the project are greater than the projected benefits. In October 2000, India’s Supreme Court lifted a four-year halt on construction of the Sardar Sarovar.

“We will have to explore more accurately the extent and magnitude of the areas prone to seismic activities in India,” said an NBA press note signed by Patkar.

She quoted two leading Indian quake experts, one of them saying that the Gujarat earthquake is “likely to trigger off tectonic activities in the Narmada-Son Lineament.”

The Narmada-Son Lineament refers to the meeting of two natural geological faults — one running along the Narmada and into the Arabian sea, the other, along the Son river in the area.

Another NBA activist, Sanjay Sanghavi was quoted in newspapers Tuesday as saying that the Sardar Sarovar is located in a “seismologically very sensitive and a geologically disturbed area.”

“In such a situation, the Reservoir Induced Seismicity (RIS) becomes extremely significant,” he added. According to some quake experts, large dams are known to trigger seismicity because of the large volume of water impounded in their reservoir.

Leading Indian seismologist Harsh Gupta of the National Geophysical Research Institute in southern Hyderabad city, agrees with the NBA.

According to Gupta, the best known example of dam-induced seismicity is the Koyna dam in western Maharashtra state, which adjoins Gujarat.

The Koyna dam area was rocked by a devastating quake in December 1967, which killed 200 persons. That temblor ranked as the world’s biggest quake triggered by a reservoir.

The region has experienced more than 100,000 tremors since 1963 when the 103-metre-high dam was built. Seventy of these were moderate ones, measuring more than 5 on the Richter scale, while the worst in 1967 recorded 6.3.

Experts have raised concern again, after a series of tremors recorded at the site in March, April and September 2000.

Another leading Indian geologist, Arun Kumar Singh said that there have been at least 20 instances of reservoir-induced seismicity in India.

However, well-known earth science expert, V. Subramanian of the Indian Institute of Technology in Maharasthtra’s capital Mumbai, disagrees.

He was quoted as saying in newspaper reports Tuesday that though the Narmada project lies over a geological fault, there was no possibility of an earthquake being triggered by the dam.

“The pressure exerted by the weight of water in a reservoir is just not enough, because the reservoir is spread over a very large area. Even the largest dam is just not significant enough to trigger an earthquake,” he said.

Janardhan Negi, emeritus scientist at the Hyderabad geophysical institution, too disputes the theory of big dams triggering quakes. He points out that only 32 out of 40,000 large dams worldwide have triggered any tremors — a figure that he says is insignificant.

The Koyna region appears to be quake-prone, he adds.

Another big dam at the centre of the quake-dam controversy is the 260-metre-high, rockfill Tehri dam being built in the central Indian Himalayan foothills.

Experts agree that the region is a seismic hotbed and was the site of a six plus temblor that killed over 1,000 people in October 1991.

The dam, sited close to the historic Tehri town in northern Uttaranchal state, is less than 100 km within the epicentre of that quake.

The Uttaranchal district of Chamoli was struck by another quake in March 1999 that killed over 100 people. The epicentre of this quake was 125 cm from the Tehri dam location.

But the Tehri Hydro Development Corporation, which is implementing the project, insists the dam’s design has been extensively analysed by expert institutions in India and Russia.

The corporation claims that the dam can withstand quakes as high as eight on the Richter scale.