Informed that work on the Lower Subansiri Hydroelectric Project on the Assam-Arunachal Pradesh border had been “kept pending” since 2011 due to a local agitation, the National Green Tribunal (NGT) in December 2015 asked NHPC Ltd not to resume construction till safety issues were resolved. The Mini Ratna PSU has achieved over 30% progress in concretizing since.
When work was stopped in December 2011, show Central Electricity Authority (CEA) data, the Subansiri project had completed concretization of 5.75 lakh cubic metres (cum). By March 2019, concretization at Subansiri had increased by 1.85 lakh cums to a total of 7.6 lakh cums.
Some of the work — slope protection to arrest rockslide on both banks of the river, for example — commenced in 2014 before the stay order and the NGT permitted such measures for safety and protection of the public and property. But the Tribunal also categorically told NHPC “not to undertake any work on the main project except those that were related to urgent repairs and maintenance”.
Yet, records reviewed by The Indian Express show, massive concretisation has been carried out to construct the project’s extended spillway (see timeline), that has widened the dam base by over 100 metres.
A spillway is a structure for controlled release of dam water into the riverbed downstream. Additionally, the developer has nearly completed the construction of two cut-off walls under the dam base. These components were suggested in 2013 by a Dam Design Review Panel (DDRP), the recommendations of which are still being reviewed under an NGT order.
“Since the dam is incomplete, the river overflows the structure and erodes the riverbed downstream. So we concretized the riverbed to avoid damage to the dam foundation as per the recommendations of the design review committee. The construction of the spillway and the cut-off walls is not complete. This is protection work permitted under the NGT order,” said Executive Director Arvind Bhat, in-charge of the Lower Subansiri project.
Based on the report of a Tribunal-appointed Advocate Commissioner, the NGT in its December 2015 order specifically allowed the removal of construction material, upkeep of machinery, maintenance of roads and concretization of tunnels, along with any emergency maintenance work.
The Advocate Commissioner was briefed by NHPC officials at the project site but her May 2015 report did not record any threat to the riverbed downstream or requirement for spillway extension as a protection measure. Yet, by the end of 2016, the developer had used 1.75 lakh cum concrete, constructing a significant part of the extended spillway. Neither Bhat nor senior officials at NHPC’s Faridabad headquarters commented on why the PSU proceeded with construction as per the DDRP report, which continues to be under legal scrutiny.
Conceived to be the largest hydropower project of the country, the 2,000 MW Lower Subansiri project has been repeatedly red-flagged by experts and activists for its weak sandstone base, shallow foundation, inadequate quake resistance, absence of flood-control capacity, downstream impact on ecology and livelihood etc.
Observing that these safety issues could not be resolved despite numerous committees and that several modifications made to the original dam plan indicated serious problems with the project, the NGT in 2017 asked for yet another expert panel to consider the recommendations of all the previous panels as well as an alternative dam design.
While the NGT subsequently dismissed a petition that challenged the constitution of this panel on the ground of conflict of interest, the Supreme Court had sent the matter back to the Tribunal, instructing it to give a reasoned order. The next hearing is on July 25.