New Delhi: On September 17, Prime Minister Narendra Modi will be celebrating his 69th birthday at the Sardar Sarovar Dam in Gujarat once again. Incidentally, the celebrations will coincide with the dam reaching its highest ever level.
The dam has been inching closer to its upper limit of 138.68 metres above sea level and is expected to attain that level – for the first time ever – on Tuesday.
But concerns over the safety of reaching such levels remain. The Hindu reported on Sunday that tremors have been felt in villages around the dam. Locals have claimed hearing ‘blast-like’ sounds and feeling the earth shake.
“The blasts are so loud that they could be heard even 6-7 km away. It’s like one you would hear from a mine, that would send birds flying away. Even at the site of rehabilitation, tremors are being felt. We have never experienced them in the region before.” Bharat Mandloi, a farmer from Ekalbara told the English daily.
The phenomena that could be causing these tremors is known as reservoir induced seismicity. When a reservoir is filled with water it increases the pressure exerted on the earth in the area of the reservoir. The pressure can sometimes be so much that it can lead to movement in tectonic plates below the surface even causing them to shift.
The water itself is also a significant factor as it percolates below the surface into cracks and crevices. It can lead to the widening of these cracks and crevices causing instability below the surface. Water can also act as a lubricant making it easier for rock plates to slip.
Studies have also found that there is a ‘pronounced increase’ in seismicity when a reservoir is filled for the first time. The Sardar Sarovar Dam is going to be filled to the brim for the first time on Tuesday.
A recent study has found that after the floods last year in Kerala, the risk of reservoir induced seismicity has increased for the dams of the state. It concluded that if the gates of the dams in the state were not opened as they began to fill to capacity, seismic activity would have occurred during the floods.
In 1967, Koyna in Maharashtra suffered the most severe earthquake which has been attributed to reservoir induced seismicity. One of the largest dams of the time was constructed in Koyna in 1962.
However, studies have also pointed to the 1967 earthquake being an isolated event not related to the reservoir.
Another cause for worry is the rapid filling up of the reservoir at the insistence of the Gujarat government. According to the dam safety manual, in 48 hours not more than 30 centimetres of water should be filled. But, in a hurry to fill the dam to the brim the Gujarat government doubled the pace to 60 centimetres in 48 hours.
According to Himanshu Thakkar who is the coordinator of the South Asia Network of Dams, Rivers and People – a network of organisations and individuals working in the water sector – the filling up of the dam with the monsoon still around, can also pose the risk of flooding.
“The monsoon is not over yet. A dam should be filled to capacity when the monsoon is over. Now, what if there is more rainfall in the next few days? Where will the water go? That will increase the risk of flooding for villages around the dam,” he said.
Sagar Rabari, who is founder president of the Gujarat Khedut Ekta Samiti – a farmer’s body based in Guajrat – believes that there is no great achievement in filling a dam to the brim. “The point of a dam is to make water available for people to be able to use it. It is not simply enough to store it and not have the infrastructure to take it to people,” he said.
According to Rabari, the figures pertaining to Sardar Sarovar dam released by the Gujarat government reveal that the state has not used the water that was allocated to it. “The figures that they have released, do not account for about 32% of the water that was allocated to Gujarat. Where did the water go?” he asked.
In 2017-18 Gujarat was allocated 4.8 million-acre feet of water by the Narmada Control Authority while the state only used 3.25 million-acre feet. In 2016-17 too, the state only used 2.95 million-acre feet of water as opposed to the 9.79 million acre feet allotted to it.
“I don’t understand the big achievement of filling the dam to its full capacity when people are not able to use the water,” Rabari said.