Subansiri dam construction: A threat to Elephant Migration
Guwahati: One thousand five hundred fifty-eight hectares of elephant habitat across the river Subansiri have been lost due to NHPC’s dam construction infrastructure, says a Wildlife Institute of India (WII) report.
“Notwithstanding the potential impacts of the dam operations, major establishments of the NHPC have already caused considerable habitat loss for elephants and other wildlife. In doing so, the once intact and contiguous stretch of elephant habitat across the river Subansiri has been seriously undermined. Other than the narrow strip of the corridor along the Geuka nadi, the east–west movement of elephants across the Subansiri River seems difficult in the present scenario. The NHPC establishment, including that of the residential complex, office, school, and other open space used for recreational purposes, has caused both habitat loss and poses a hindrance to elephant movement.” says a Wildlife Institute of India(WII) report on “Plan for Ensuring Safe Passage for Elephants between Panir and Dulung Reserved Forests in the downstream of Lower Subansiri Hydroelectric Project”.
The Lower Subansiri Hydroelectric Project of the NHPC was initially conceived in 2001 and the project activities commenced in 2003. As the project site is ecologically rich, numerous environment-related concerns were flagged.
The project was referred to the Standing Committee (SC) of the National Board for Wildlife NBWL. During the 72nd meeting of the SC-NBWL, it was decided that WII may conduct a study to “prepare a plan ensuring the free passage of elephants across Panir Reserved Forest and Dulung Reserved Forest.”
The WII’s study pertains to the assessment of elephant use of the Dulung- Subansiri elephant corridor and the preparation of a plan to ensure free east-west passage of elephants across River Subansiri. Dulung Subansiri corridor is one of the 14 identified corridors in northeast India.
“As elephants are recognized as an umbrella species in biodiversity conservation, a functional elephant corridor should benefit biodiversity in general. Although the corridor is functional, it is tenuous and would require urgent steps to strengthen it,” the report says.
“NHPC has established office premises, a residential complex and associated secondary infrastructure right in the elephant habitat. In the long-term interests of the corridor for elephants and other wildlife, these establishments need to be decommissioned in a phased manner. While habitat loss itself is a recognized threat, losing important areas to development is a major challenge. With prudence, NHPC’s secondary establishment could have been planned far from the corridor,” the report says.
The report which was discussed during the 77th meeting of the Standing Committee of the National Board for Wildlife in January this year had expressed concern about the potential adverse effects of hydro-peaking operations on the Dulung-Subansiri elephant corridor including the risk of flash floods separating elephant herds and altering the dynamics of river islets.
It recommends restraining hydropeaking until a comprehensive hydrological modelling study is conducted to assess the impacts on elephants and their habitat.
Hydropeaking refers to the practice of varying the flow of water released from a dam to generate electricity in response to changing demand.
The Dulung-Subansiri elephant corridor provides vital connectivity for elephants across the river Subansiri. The connectivity is between Panir Reserved Forest in Banderdewa Forest Division, Arunachal Pradesh and Dulung Reserved Forest of Lakhimpur Forest Division of Assam located on the west bank of the River Subansiri and the Subansiri Reserved Forest of Dhemaji Forest Division located in the east bank of the river Subansiri.
Assam harbours nearly 5,700 elephants. During the last decade (2009-2020) Assam has also lost 116 elephants due to electrocution, 32 elephants due to poisoning, and 62 elephants due to rail collisions, illustrating the magnitude of the increasing human–elephant conflict situation in Assam.
During the site surveys by WII, the elephant signs were found to be widespread. “The signs, ranging from old to relatively new (a few weeks before the survey), indicate intensive use of certain islets, including the Joba/Jobabari Chapori.
From the signs, it is also certain that the islets in the Subansiri River are not only used for passage but also as habitat for prolonged stays. The survey team came across ample signs of young elephants, making it evident that even the family herds use the corridor,” the report says.
The WII has recommended that from the long-term standpoint of elephant conservation and mitigation of the human–elephant conflicts in the Assam–Arunachal Pradesh landscape along the Himalayan foothills, maintaining habitat contiguity is paramount. “For elephants distributed along the Himalayan foothills, the Dulung Subansiri elephant corridor is critical and, thus, needs to be immediately notified and marked on the ground. In the long-term interests of elephants and other wildlife in the region, the State of Assam in consultation with the Arunachal Pradesh Forest Department should explore the options of notifying the Kakoi R.F– Dulung R.F as a Wildlife Sanctuary or Conservation Reserve by including a demarcated elephant corridor area.
The minutes of the 77th meeting of the Standing Committee of the National Board for Wildlife in January reveal that the Director of the Wildlife Institute of India mentioned that during peaking when all the eight turbines would be functioning there would be a sudden increase in the flow of water from the dam up to 1.5 m high which would take away the elephants crossing the river.
The minutes also reveal that the Member Secretary of the National Board for Wildlife had informed about his meeting with the NHPC officials on January 29 wherein they requested not to accept the last recommendation made by the WII as their main process involves hydro-peaking operations.
Impact of Hydro Peaking
The report further expresses concern about the potential adverse effects of hydro-peaking operations on the corridor, including the risk of flash floods separating elephant herds and altering the dynamics of river islets. It recommends restraining hydropeaking until a comprehensive hydrological modelling study is conducted to assess the impacts on elephants and their habitat.
The hydro-peaking scenarios that were provided by NHPC to WII indicate a rise in water level by around 2 meters with a concomitant increase in the water velocity in and around the demarcated corridor area. The potential threats of this indicated hydro-peaking scenario to elephants are twofold: (i) Despite being good swimmers, elephants, particularly the calves and young elephants are vulnerable to flash floods that could sweep elephants away, resulting in separation and even drowning. (ii) recurrent incidences of elephants being swept during river crossing could trigger behavioural avoidance of the vulnerable stretches resulting in functional loss of the corridor.
“It is evident that any drastic and frequent modulation in the river flow would be inimical for the Dulung-Subansiri elephant corridor, which is an extremely crucial link in maintaining the continuity of elephant habitats along the Himalayan foothills in the northeastern region,” the report says.
Peaking operations resulting in a sudden increase in water depth by nearly 2.0 meters and accompanied by velocity could increase the risk of elephants, particularly calves, getting swept by flash floods.
The report further says peaking-related fluctuations in the water level could affect the stability of riverbanks and possibly trigger erosion in riverbed grassland. Erosion may expose roots, resulting in the loss of nutrients and stability of the riverbank. “Further, abrupt fluctuations in water levels may displace seeds and impede the natural process of germination and growth of grassland plants. This can lead to irregular and sporadic growth patterns, negatively impacting the overall vegetation downstream of Subansiri,” it says.
The Dulung-Subansiri elephant corridor with its diverse amphibian and reptile species, including threatened turtles and tortoises, is particularly vulnerable to threats like habitat modification and biotic pressure. “Hydropeaking, in particular, can significantly impact the basking sites of reptiles and amphibians. Sudden changes in water levels can submerge basking rocks and logs, forcing these turtles and tortoises to seek alternative sites that may be suboptimal or expose them to predators potentially leading to population decline,” it says.
