On May 18, Edappadi K. Palaniswami, the chief minister of Tamil Nadu, inaugurated the construction of the Kundah Pumped Hydro Electric Project (KHEP) in the Nilgiris.
The project’s financial outlay is Rs 1,650 crore and is expected to be completed in about six years. Once completed, it will be the third underground power station in Tamil Nadu and the largest hydropower-generating and pumping station in the state.
But a project of such size and complexity is not the only one at the moment in Tamil Nadu. The India-based Neutrino Observatory (INO) is strikingly similar to the KHEP project in layout, excavation and construction methodology, disposal of excavated muck and other characteristics. However, their purposes are vastly different. The KHEP will generate power, the INO will perform fundamental research.
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Nonetheless, both projects are considered important in the public interest.
But there are crucial differences in the way they are perceived.
The project components
The KHEP begins with a horizontal access tunnel leading to a large underground powerhouse cavern (98 l × 22 b × 42 h, all metres). The project also includes a head-race tunnel, a surge shaft, inclined twin pressure-shafts, penstock tunnels and a tailrace tunnel. Other appurtenances include a cable-cum-ventilation tunnel about a kilometre long, a tailrace surge shaft and a 500-m-long additionally driven intermediate tunnel (ADIT). All the tunnels will be about 7 m wide.
The KHEP is straddled between two extant reservoirs: the ‘upper’ Porthimund and the ‘lower’ Avalanche-Emerald. Its intake arrangements begin at the Porthimund while the tailrace tunnel debouches water directly into the Avalanche-Emerald.
The project has been designed to work in both generation and pumping modes. That is, water from the lower reservoir will be pumped back into the upper reservoir after power generation when the grid has surplus power. The tailrace tunnel will function as a headrace tunnel in the pumping mode.
The INO also consists of a horizontal access tunnel, about 2 km long, with an auxiliary tunnel, an ADIT, an intermediate tunnel and an additional tunnel. The main cavern will measure 132 l × 26 b × 32.5 h (all metres). There will also be three smaller cavern, each 8.6 l × 10 b × 3.5 h (all metres). The access tunnel will be about 7 m wide and other tunnels will be smaller.
The similarities
Both the projects are located completely underground by design, in the Western Ghats of Tamil Nadu. Their feasibility studies were undertaken by the Geological Survey of India (GSI) and the detailed project reports prepared by the Tamil Nadu Electricity Board (TNEB).
The projects are situated in similar geological and geomorphological milieus. The tunnels will pass through charnockite, migmatite gneiss and quartzo-feldspathic gneiss rocks, traversed by pegmatites and dolerite dykes. Geological weaknesses – such as foliation, joints, shears and intrusions – will be more or less similar, sans any sharp contrasts.
The general rock mass for both projects have been rated between ‘fair’ and ‘very good’ on the Q-system of rock mass classification. Their underground caverns will be built by excavating using the drilling and blasting methods. However, the KHEP involves a much larger volume of excavation – and more explosives to do so – than the INO. This is chiefly because the former needs more tunnels, vertical and inclined shafts and other arrangements.
Ecologically, the KHEP will have more green cover in its neighbourhood than the INO because it will be located in the Nilgiris – and in an area least prone to landslides, according to the GSI. The INO will be located in the Bodi Hills near Theni.
More specifically, both projects are located in the peripheral area of seismic zone II, as defined by the Bureau of Indian Standards. This zone has the lowest seismic risk in the country.
One technical difference between the two projects is that the rock cover for the INO will be considerably higher than that of the KHEP.
Special concerns about the INO
Given these details, how come activists and politicians raise ‘grave concerns’ about building the INO but keep mum about a similar project located between two reservoirs?
They have alleged that the excavation methods to be employed to build the INO’s cavern will damage the Idukki, Mullaperiyar and other reservoirs in the region. They have alleged that drilling and rock-blasting will precipitate extensive structural damages to houses located in nearby villages.
But unlike the KHEP, the INO is located 30-50 km away from reservoirs and its activities cannot affect them.
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On the other hand, the KHEP’s construction has been widely accepted and no objections have been raised whatsoever.
This dichotomy suggests that the INO is being opposed for reasons more political and procedural than technical. Otherwise, those who have an issue with the INO should have been similarly opposed to the KHEP.
It is painful that the Tamil Nadu site for the INO was picked because no other site in the country was as suitable. But the propaganda whipped up against it has created a misguided impression that the Government of India chose the Bodi Hills to frustrate the local people, the environment, water bodies in the area, etc. – as if it had a score to settle with the state.
Nothing could be farther from the truth.
V. Balachandran is former deputy director general of the GSI and a practising engineering geologist. He carries out natural hazard studies such as due to earthquakes and landslides.