Assam: Subansiri river dries up after landslide blocks dam diversion tunnel at Gerukamukh

North Lakhimpur: The Subansiri River dried up suddenly on Friday morning, causing widespread panic among the people of north Assam’s Lakhimpur district.

The blockade on the No. 1 diversion tunnel of National Hydro-electrical Power Corporation (NHPC)'s Subansiri Lower Hydroelectric Power (SLHEP) plant's dam on its left bank is suspected to be the cause of the river drying up.

The diversion tunnel has been diverting the flow of the water of the Subansiri through a two-km long course from the dam site to the downstream of the river. This diversion keeps a normal amount of water in the downstream areas of the river. The blockade on the diversion tunnel was caused by a landslide last night.

"Out of 5 numbers 9.5m diameter diversion tunnels, the only diversion tunnel number 1 in use, has been blocked due to landslide at about 11:30 am today. The other 4 numbers of diversion tunnels had already been blocked earlier. As a result, the river flow to the downstream is highly reduced," NHPC said in a statement.

"The dam spillway bay level is 145m msl. The present river flow of 997cum/sec is being stored in the reservoir and water level of the reservoir is increasing. At 1 pm, the water level reached 139m. It is expected the water level to reach 145m by the evening and the river will again flow through the spillway to the downstream normally," NHPC added.

As the river dried up suddenly due to the blockade, there is a fear of the diversion tunnel breaching by the blocked water and resulting in a disaster similar to the one that recently occurred in Sikkim.

The SLHEP dam, which is scheduled to become operational from January 2024, has been a cause of concern for the public here as repeated landslides have hit its construction work periodically.

 These recurring landslides indicate the fragile nature of the terrain where the hydropower dam is being constructed. Though the dam is claimed to be safe by the NHPC, its site on the hills is not.

The NHPC allegedly did not conduct any geological assessment of the dam site while taking over the charge for SLHEP from the Brahmaputra Board.

The sudden drying of the Subansiri has also raised concerns about the biodiversity of the river in the downstream area.

 Subansiri has a population of endangered Gangetic Dolphins and Golden Masheers, which face an imminent threat of being wiped out due to the current situation.

The Subansiri, which presently flows just 5 kilometers away from the district headquarters of North Lakhimpur, could cause widespread devastation if the situation is not addressed immediately.

The district administration has issued a warning to people living near the river to move to safer areas. NHPC officials are working to clear the blockade on the diversion tunnel and restore the normal flow of the river as soon as possible.