Vimal Khawas
Trans-boundary Tista Basin forms a part of the larger Brahmaputra
Basin in the Eastern Himalaya. The river drains a total geographical area of
about 12159 km².
Around 2004 km2 of the basin (about 17 percent) area lies in Bangladesh with the rest
being in India. In recent times,
traditional symbiotic and intimate human-environment relationship in the Tista
Basin has been increasingly put to danger by diverse undercurrents of development. This has resulted in
imbalances in the environment and various ecological systems there in. Besides
other forms of development including improper expansion of agriculture and
irrigation, unscientific construction of roads and buildings and unplanned urbanization, Central and
Provincial Governments of India are vehemently underway with series of
hydropower projects particularly within Sikkim-Darjeeling catchment of the
basin.
Drivers
The mega hydropower
projects proposed in the area are part of the Government of India’s
program of dam construction to create another 200 billion cubic metres of storage through the 50000 MW hydroelectric
initiatives launched in 2003. Considering huge untapped hydro potential of the
Tista and its numerous perennial tributaries, Central and Provincial
governments see huge opportunity
to mobilize flow of capital investment through public, private or joint sector.
Therefore, apart from
development of various small, mini and micro-hydel projects, several
mega projects have been awarded to NHPC, NTPC and private developers in the last one and half
decades. From these projects, the State governments of Sikkim and West Bengal
will get 12 percent of free power. Reportedly, Sikkim hopes to yield
approximately INR 2000 crores per annum by tapping into ‘the enormous
hydroelectric potential’
of the basin within the State. Besides contributing to the growth and
development of the country, Sikkim visualizes of a prosperous Sikkim with the
revenue earned.
However, the number of mega
projects in Sikkim allotted to public
and private sectors has been lowered radically from around 27 in 2007 to 16 in 2015. Important reasons cited by the government
include critical social, ecological, geological and financial considerations. Reportedly, the
Sikkim-Nepal earthquake of September 2011 played significant role in bringing down sizeable numbers of
hydro-projects in the Sikkim Himalaya. The data recorded in the official documents indicate that
number of ongoing mega projects came down from around 25 in 2010 to about 18 by
2012. Accordingly, the identified hydro capacity of the Sikkim Himalaya has been lowered from over 5200 MW to around 4200 MW
as per the recent reassessment study of the Central Electricity Authority (CEA,
2014). In the Darjeeling region, out of three mega projects one
(TDLP III) is already
commissioned. Others are in various stages of construction. Further, the
Chief Minister of West Bengal has recently announced four more projects in Darjeeling region of the
Tista basin. Consequently, the Sikkim-Darjeeling catchment is now expected to produce over 6000 MW of
electricity within the next few decades.
The biggest concerns at the
moment are the varied impacts of
such gigantic development
ventures on the regional environmental security in this fragile region and
its neighbourhood. The recent tectonic events in Sikkim (2011) and Nepal (2015) and the consequent disasters have further
challenged the very idea and future of mega hydropower dams in the region. These
seem to have either been overlooked or their impacts underplayed by
respective EIA
reports.
Earthquake
There are concerns that
building hydro-dams may lead to
river-induced seismicity in this
geologically young and seismically active region. The Darjeeling-Sikkim
catchment of the basin is located in the high-risk seismic zone IV
of the Indian seismic
zoning map and therefore had been active seismic region in historical times. Recent major
earthquakes in Nepal (April 2015) and Sikkim (September 2011) measuring 7.8
and 6.8 in magnitudes have clearly exposed the region’s wherewithal with regard to earthquake
disaster. The Nepal earthquake of April 25, 2015 and series of aftershocks thereafter have reportedly damaged about 14 hydropower plants across Nepal
resulting in a loss of 150 megawatt (MW) of electricity. In this regard, Sunkoshi Hydropower plant has apparently suffered serious damage with its 3-km canal suffering from multiple leakages. Environmentalists, activists and researchers in the region have long been warning
against too many constructions of mega dam projects in the upper Tista catchment.
The fragile geology coupled
with mega hydro-dams could induce earthquakes and the resultant landslides and flash
floods could result into a disaster. The central government, provincial governments and hydropower
companies may, however, dismiss the earthquake related concerns as fear mongering.
Yet, a contingency plan for disaster management in the event of
earthquake is a far cry for almost all the hydro-projects in the area!
Scholars across the world have reported the performance of various types of dams under
earthquake shaking. Their studies show that concrete dams may be subject to severe cracking, movement and opening of joints that may render the dam unserviceable
or may require major repairs.
Landslides
It may further be noted that Sikkim-Darjeeling segment of the Tista basin is featured by a number of active and
dormant landslides. A cursory glance at landslide statistics gives us a fearful idea of the enormity of
damage done and the ever-present threat to life and property in the region. In the last
one-century more than 10000 slides have been registered in Darjeeling region alone.
Thousands of lives have been lost and the overall economic development of basin negatively
impacted. Mention should be made that heavy and spontaneous rain on June 30 and July 01, 2015 triggered a
string of landslides across Darjeeling Himalaya killing over 40 people.
According to Praful Rao, President, Save the Hills, ‘Kalimpong was pummeled by torrents of rain
starting from approximately 20:00 hrs. I watched the clouding as it formed over us and remained
almost stationery much like the clouding over Uttarakhand in 2013. Kalimpong
received almost half (226 mm) the entire July month's average rainfall
(548.7mm) in the 06 hours’. Darjeeling Together, an initiative of the people of Darjeeling to help the
people affected by the recent landslides, has placed the following preliminary
figures on the immediate impacts of landslides: villages affected: 165, people affected:
94797, houses damaged: 1907, people in relief camps: 2360. Initial report of the district
administration has calculated property loss to the tune of INR 12 crores in the Darjeeling region.
According to a recent study
of Wadia Institute of Himalayan Geology (Dehradun), the Sikkim Earthquake (2011) triggered several hundred landslides
in Sikkim, Darjeeling, Nepal, Tibet and Bhutan Himalaya. In the Indian
Territory, the earthquake-triggered landslides were reported as far as 100
km away from the earthquake rupture
zone. Within Sikkim, the study
reported over 350 new
landslides in the post earthquake period.
Notably, after water
impoundment and pondage by the dam,
water level in the area rises considerably. As
a consequence, the strength parameters of the slope mass weakens and
it may become susceptible to destabilization thus triggering new landslides and further destabilisation
of already active slides. A live example of such a situation is seen along the
National Highway between Tista Bazar and 27 Mile near Rambi in
Darjeeling region where TDLP-III
regularly impounds water for several
weeks, although NHPC claims to be a run-of-river project (RoR),
threating livelihood security of the riparian settlements.
River Erosion
Of all the Himalayan Rivers, Tista reportedly has the highest
sediment yield. The effects of erosion and sedimentation provide favorable
conditions to river shifting. River Kosi has shifted by about 150 km to the west
during the last two centuries. According to Hunter’s statistical
account of Bengal, Tista originally was a river of Ganga basin. In 1787, due to
incessant rain followed by heavy flood and devastating earthquake Tista shifted its
course to Brahmaputra basin. If such sudden river capture occurs today, thousands of
villages will be swept away in a gigantic flash flood inflicting incalculable human and
environmental disasters.
This is no great news for
a region already facing the cost of shortsighted mountain development.
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