Cumulative impact and carrying capacity study of Subansiri Sub Basin including downstream impacts: final report

Central Water Commission (CWC), Government of India has undertaken the task of conducting, “Cumulative Impact and Carrying Capacity Study of Subansiri basin including Downstream Impact in Brahmaputra River Valley” with an objective to assess the cumulative impacts of hydropower development in the basin. Expert Appraisal Committee (EAC) for River Valley and Hydroelectric Projects of Ministry of Environment & Forest (MoEF) GoI has provided the Terms of Reference (TOR) for this study. IRG Systems South Asia Pvt. Ltd. has been awarded the study by CWC based on techno- commercial bidding. The study initiated from December 2011 involved extensive field data collection in different seasons to establish baseline status, data analysis and cumulative impact assessment, followed by recommendations for long term sustainable hydropower development in the basin. As per Central Electricity Authority (CEA) estimates, the basin has 6092 MW hydropower generation potential (60% load factor) with a probable installed capacity of 13767 MW. This potential is planned to be harnessed by setting up about 19 hydropower projects spread throughout the basin. Such a large-scale development expected to take place over a period of next 10-15 years in otherwise pristine area, can cause serious environmental impacts. EIA notification of September 2006, issued under Environmental Protection Act, 1986, has the provision of evaluating the impacts of individual projects of capacities 25 MW or more by SEAC/EAC before issuing environment clearances. However, in a situation where several projects are planned in cascade utilising the same natural resource; assessment of cumulative impacts is essential to plan development in environmental friendly manner and to mitigate and manage the impact comprehensively. Therefore, the current study of Subansiri Basin has been prepared with a view to provide optimum support for various natural processes and allowing sustainable activities.