Final Colloquium: Downstream Environmental and Socio-Economic Impacts of the Ranganadi Hydel Project in Northeast India" by Ms. Priyam Laxmi Borgohain, Lecture Hall, NIAS, 1630hrs

National Institute of Advanced Studies

Indian Institute of Science Campus



Final Colloquium



Title: Downstream Environmental and Socio-Economic Impacts of the Ranganadi

           Hydel Project in Northeast India

Candidate: Ms. Priyam Laxmi Borgohain

Advisor: Prof. Dilip R Ahuja

Date:  Monday, 30 July, 2018

Time:  4:30 pm

Venue: Lecture Hall, NIAS 


Abstract: The Brahmaputra Basin is identified as the ‘future power-house’ of the country. Consequently, the region is now witnessing rapid development of hydropower projects. At the same time, large dam construction faces strong opposition given their adverse environmental and socio-economic impacts. Arunachal Pradesh has the highest number of upcoming projects in the basin. One of the major concerns of dam building in this Himalayan state is their downstream impacts upon the riverine and riparian ecosystems of the lower floodplains of Assam.  Commissioned in 2002, the 405 MW Ranganadi hydel project (RHEP) is the sole operating hydropower scheme in Arunachal Pradesh. It is an inter-basin water diversion scheme that involves transfer of flow from the impounded Ranganadi River to an adjacent river – Dikrong, for power generation. This study analyzed the impacts of the hydel project upon the downstream hydrology and geomorphology of Ranganadi and Dikrong within the floodplains of Assam. The study further examined the associated socio-economic impacts upon the floodplain communities of selected downstream villages in the Ranganadi basin.  The two affected rivers displayed contrasting patterns of hydrological and morphological changes in the post-dam period. Annual median flows in the impounded and flow-deprived Ranganadi decreased by 63%, while the reduction in monthly medians ranged from 46% to 80%. The annual extremes showed higher reduction in the minimum water conditions. Unlike the pattern of change commonly demonstrated by impounded rivers, Ranganadi displayed attenuation of both high and low flows, indicating the influence of unsustainable water diversion for off-site electricity generation. At the same time, the flow-recipient river - Dikrong displayed 138% increase in post-dam annual flows. The monthly flows increased significantly by more than 30%. Dikrong, too, exhibited higher elevation in low flows compared to monsoonal high flows. Ranganadi exhibited decreased braiding and temporal narrowing channel pattern, while Dikrong displayed channel widening and an increasingly braided and multi-channeled planform. Sudden water releases from the reservoir, flash floods and sand casting were the major problems perceived by the downstream communities in the Ranganadi basin. Farming as a primary livelihood decreased, particularly in the left bank villages and especially post-2008 flash floods. The major adaptations observed were livelihood diversification and increased leasing of agricultural lands.


The downstream impacts of river damming have been aggravated by a complex overlapping of natural and anthropogenic stressors, and would become more unpredictable in the future given the cascade development of dams in both river basins. The study found the current flow release pattern of RHEP to be unsustainable, where downstream flows especially in Ranganadi have been mismanaged. Finally, this study emphasizes the recognition of downstream impacts in the Environmental Impact Assessment framework and a space for the downstream riparian to negotiate their concerns. It also recommends the implementation of environmental flow releases by old and new projects alike, especially in cases of inter-basin water diversion.


All are invited to attend

Tuesday, July 31, 2018