The downstream impact of dams in the Brahmaputra river basin has been a major issue of concern in recent years in Assam and Arunachal Pradesh (AP), even as plans unfold to develop at least 135 large hydropower projects to produce approximately 57,000 MW of electricity in AP alone. The past three months have seen major developments on the issue. Both an Expert Committee of Academics and a House Committee of the Assam Legislative Assembly submitted reports in June and July 2010 respectively, raising serious questions on the viability of upstream mega dams, with the under construction 2000 MW Lower Subansiri project being particularly in focus.
On August 12, the Rajya Sabha saw a lively discussion on the issue in response to a calling attention motion by MP from Assam, Birendra Prasad Baishya. On September 10, Union Environment Minister Jairam Ramesh held a public consultation on the issue in Guwahati as a follow-up to an August meeting with a delegation led by the Krishak Mukti Sangram Samiti, a major peasants’ movement in Assam.
Over the past few years, downstream impact concerns raised in the North-east include: loss of fisheries, changes in beel (wetland) ecology in the flood plains, impact on agriculture on the chapories (riverine islands and tracts), disruption of intricate socio-cultural linkages of indigenous communities with the river systems, increased flood vulnerability due to massive boulder extraction from river beds for dam construction and sudden water releases from reservoirs in the monsoons, dam safety and associated risks in this geologically fragile and seismically-active region.
One of the key issues that has come up is the drastic daily variation in river flows, which will take place after these dams are commissioned, particularly in winter. For example, the average winter (lean season) flow in the Subansiri river in its natural state is about 400 cubic metres per second (cumecs). Both the ecology of the downstream areas and peoples’ use of the riverine tracts in winter is adapted to this ‘lean’ but relatively uniform flow of water through the day.
After the commissioning of the 2,000 MW Lower Subansiri project, flows in the river in winter will fluctuate drastically on a daily basis from 6 cumecs for around 20 hours (when water is being stored behind the dam) to 2,560 cumecs for around 4 hours when the water is released for power generation at the time of peak power demand in the evening hours. Thus, the river will be starved for 20 hours and then flooded for 4 hours with flows fluctuating between 2 per cent and 600 per cent of normal flows on a daily basis.
The flow during peak load water releases in the Subansiri river in winter will be equivalent to average monsoon flows and will cause a ‘winter flood’, drowning drier riverine tracts that are used by both people and wildlife on a daily basis in winter. The downstream livelihoods and activities likely to be impacted by this unnatural flow fluctuation in the Eastern Himalayan rivers include: fishing, flood-recession agriculture, river transportation and livestock rearing in grasslands for dairy-based livelihoods. But downstream communities are yet to be officially acknowledged as project-affected persons due to upstream dams.
Flow fluctuations in rivers like Lohit, Dibang, Siang and Subansiri will severely impact breeding grounds of critically endangered grassland birds like the Bengal Florican, foraging areas of the endangered wild water buffalo, habitat of the endangered Ganges river dolphin and important national parks like Dibru-Saikhowa and Kaziranga.
The natural flow pattern of a river is like its ‘heart beat’ and alternate starving and flooding of these major rivers on a daily basis is a threat to the ecological and social security of the Brahmaputra floodplains. Comprehensive downstream impact assessment and public consent must be a mandatory part of the process which decides whether to grant or reject clearances to these dams.
Neeraj Vagholikar is a Panos South Asia Media Fellow (2010-11) and a member of the environmental action group, Kalpavriksh
The views expressed by the author are personal