The 2000 MW Lower Subansiri hydroelectric power Project, proposed to come up at Gerukamukh of Assam Arunachal border is the first large hydroelectric project to be constructed in the Subansiri river basin.

The Lower Subansiri hydroelectric power project (LHSEP) is the part of an ambitious plan of government of Indian to generate 50,000MW. The program was initiated in May 2003. The Central Electricity Authority (CEA) has taken up pre-feasibility studies of 162 projects as part of this initiative, among which a total 5,600MW was planned on Subansiri River.

The LHSEP is designed as a run-of-the river power project on the lower reach of Subansiri River, a tributary of River Brahmaputra. River Subansiri flows from Arunachal Pradesh into Assam where it joins the Brahmaputra.

The Subansiri hydropower project has three components, namely the 2,000MW Upper Subansiri, the 1,600MW Middle Subansiri, and the 2,000MW Lower Subansiri. The Lower Subansari HEP received clearance from the government in August 2003, following which NHPC started developing the project.

The Northeast of India has been identified as India’s ‘future powerhouse’ [1]. In 2001, the Central Electricity Authority CEA), India has identified 168 large hydroelectric projects with a potential of 63,328 MW in the Brahmaputra river basin [2]. This includes 22 projects having potential of 15,191 MW in the Subansiri river basin. The 2000 MW Lower Subansiri Hydroelectric Power Project, proposed to come up at Gerukamukh, Assam pose a real threat to the freshwater biodiversity of the downstream of Subansiri river basin by the regulation of the river through diversion, impoundment and reducing water discharge to the downstream [3].

The construction of Lower Subansiri started in 2005 and was due to be completed in 2010. However, the project has been delayed because of strong opposition over its potential environmental impact. It is alleged that the dam is located in a seismic zone but it is significantly under-designed to resist earthquakes. The fluctuation of water level in the river is also feared to affect the ecology in the lower Subansiri region in future.

The project has displaced many families, but it is claimed that it will displace many more people residing downstream of the project because of ecological changes endangered by the project. The project is also alleged to affect cultivation and cattle graze in the downstream area. In December 2012, NHPC set up an independent dam design review panel to facilitate the progress of the project while taking into account the issues advanced against the dam from different quarters [4] There is also strong opposition from Assam. As Assam is located on the downstream of the project, protesters have been arguing that the state will bear the brunt of environmental impact. They are also concerned over the safety of the dam as the project is located in a seismic zone [5].

The Lower Subansiri hydroelectric power project (LHSEP) is the part of an ambitious plan of government of Indian to generate 50,000MW.

The Subansiri hydropower project has three components, namely the 2,000MW Upper Subansiri, the 1,600MW Middle Subansiri, and the 2,000MW Lower Subansiri.

The cost of Lower Subansiri project was originally estimated to be INR62.85bn ($1.16bn) at 2002 price level but has since been revised to INR106.6bn ($1.97bn) at 2010 price level. The project cost is expected to further go up because of the delay.

The project cost is being met through 70% equity and 30% debt financing by the provision of a term loan. The central government is providing budgetary support as part of the equity component.

The LHSEP consists of a concrete gravity dam, which will be 116m high from the river bed level and 130m from foundation. The length of the dam will be 284m. The gross storage capacity of the reservoir will be 1.37km3.

The power house will be equipped with eight 250MW Francis turbines located on surface on the left bank of the river. It will also have eight horse shoe shaped head race tunnels (diameter 9.5m and length varying from 608m to 1,168m), eight horse shoe shaped surge tunnels (diameter 9.5m and length varying from 400m to 485m) and eight circular penstocks (diameter varying between 400m and 485m, and length between 7m and 9.5m). A tail race channel (35m long and 206m wide) will take the water discharged by the turbines back to the river [4].