It is all in the books that landslides are among the major hydro-geological
hazards that affect large parts of India, especially the Himalayas, the
northeastern hill ranges, the Western Ghats, the Nilgiris, the Eastern Ghats
and the Vindhyas, in that order. In the Himalayas one could find landslides of
every name, fame and description. India’s northeastern region, the Darjeeling
district of West Bengal, Sikkim, Tripura, Meghalaya, Assam, Nagaland and Arunachal
Pradesh are all landslide-prone. In Uttarakhand also, it would therefore be
inappropriate to see the Kedarnath tragedy of 16–17 June 2013, as merely an
isolated event frozen in time and space.
Whenever landslide disasters strike, we rush to lean on fixed ideas in our
minds. From the school days we are tutored that events like landslides and
earthquakes are only to be regarded as nature’s safety valves because we live on
the surface of an unfinished planet. The fragile ecology, immature geology,
meandering rivers, snow bodies, climatic variations and cloudbursts of the
Himalayas are after all our inheritance without choice. For centuries, landslides
have come and gone, and these can be explained by recounting a long list of
causative factors. If and when our justification is not good enough, there is
climate change to buttress our argumentation. But, by ignoring human violence
against nature, we only speak the half truth. Let us always remember that ‘a
scientific truth does not triumph by convincing its opponents and making them
see the light, but rather because its opponents eventually die and a new
generation grows up that is familiar with it’ [Max Planck].
Those who make off-the-cuff conclusions must know that the science of
landslides has no contract with their way of thinking. It demands honest and
comprehensive scientific studies. We can understand landslides only by elucidation
of landslide boundary-shears, concurrent monitoring of time-dependent
piezometric pressures, surface and subslope displacements and mapping of ground
deformations and shear zones, plus behavioural studies of associated human
settlements form an integral part of the landslide investigation. Sadly,
success will continue to elude us so long as scientific landslide investigation
does not precede landslide remediation. We have not been able to fix the
landslides not because of lack of expertise or technology, but because we never
had the will or direction to do so.
It has almost become ritualistic to name cloudburst to explain away cataclysmic
floods and devastating landslide events, without even attempting to understand
the slope dynamics in the ecological theatre of nature. We did so to explain
the great Alaknanda tragedy of 20–21 July 1970 in Uttarakhand on the premise
that the previous maxima of 200 mm rainfall recorded at Joshimath on 28 September
1924 was crossed by a new high of 212.8 mm. Further probe removed a layer to
show that the tragedy was caused by the bursting of a landslide dam. The
formation of the landslide dam on Alaknanda was then traced to the enormous
sediment load brought by Patalganga. And this huge sediment load was in turn
traced to numerous landslides in the Patalganga valley. Further, it became evident
that these landslides themselves were the result of neglect, misuse and abuse
of our lands for decades on end. But for the ecological neglect, the Alaknanda
floods would not have hit the headlines.
We are yet again stumped by the ghastly Kedarnath tragedy and cajoled by the
very same reason – cloudburst, which is in fact no more than the most visible
trigger at the tipping point. Could we have anticipated the trouble? The answer
is no, because we had neither fail-safe instrumentation nor real-time vigil on
our glaciers, glacial lakes, moraine accumulations,
dormant and active landslides, rivers and their tributaries and unsafe housing stock.
We plead for zero tolerance against mindless urbanization, but suffer it
instead. We have mapped landslide hazards on the pilgrim routes many times
over, but never placed a single user-friendly validated map in the hands of
disaster managers. We should do it now.
We should not continue to ignore the gross disconnect between our scientific
discourse and our approach to hazard-mapping. In scientific discourse, we dread
factors such as climate change, exceptional rain, receding of glaciers, bursting
of glacial lakes, poor road alignments, non-engineered constructions,
earthquake-induced landslides, and overtopping of dams. However, in the case of
hazard-mapping, we disregard all these factors and only account for lithology,
structure, slope morphometry, relative relief, land use/land cover and
hydro-geological condition India needs large-scale, validated and user-friendly
hazard maps based on a scientific understanding of the multitude of factors,
both natural and human induced.
The main reason why the natural landslide hazards are turning into man-made
disasters is because people have not only moved in large numbers to the
remotest of the mountain slopes where no one ever lived before, but the violence
they have unleashed against nature is unprecedented. There is a Chinese saying
that ‘a man who removes a mountain begins by carrying away small stones’. We
have been removing, not small stones, but mountains of rocks for building
townships, roads, dams and reservoirs. Many of the landslides we know are the result
of these very actions, and they in turn remove from slopes incredibly large
amount of sediments, loading rivers, silting reservoirs and creating new land
masses in the sea. Little do we realize that when a slope gets robbed of one
inch of its soil cover, Nature may take nearly 1000 years to replenish it! It
is time therefore to revive the Chipko Movement and reverse the trend of slope
degradation.
One vexing question which often haunts us is whether a landslide can be
predicted and a landslide disaster averted? In Uttarakhand, some of the
landslides occur annually. We do not need any rocket science to predict them;
simple slope instrumentation and monitoring would do. Similarly, mountain
slopes supporting human habitat with visible signs of instability like tilting
of trees, bulging of retaining walls and widespread ground subsidence are
already on the verge of failure. What more early warning do we need to predict
a landslide in such situations? It is a scientifically proven fact that even
the first time landslides are predictable provided we probe deep enough to
arrive at the bottom of the truth, through studies, instrumentation and
monitoring. Like human beings, a slope also has a heart that beats! Let us
recall Terzaghi, who more than six decades ago said that ‘If a landslide comes
as a surprise to eye witnesses, it would be more accurate to say that the
observers failed to detect the phenomena which preceded the slide.’
Today, we have the knowledge, tools and experience we need to predict and avert
most, if not all, landslides. By tapping the phenomenal power of geotechnology,
instrumentation, remote sensing, integrated GPS and information communication
systems, we can monitor unstable areas in real time even during unfavourable weather
conditions. It is time therefore to launch selected mission-mode projects to
initially cover timely prediction of (a) possible reactivation of major old,
dormant and seasonal landslides, (b) landslides and floods due to bursting of
glacial lakes, (c) flash floods due to bursting of landslide dams, (d)
first-time landslides in urban and strategically important areas falling in the
zone of exceptional landslide hazard and (e) rockfalls. But, why is this not
happening?
The criteria for early warning against landslides we use must be credible. The
direct connection between ‘incidence’ of a landslide and ‘rainfall’ may look
both obvious and simple, and may even work in cases where ground conditions are
already bad enough and rainfall exceptional. There is a strong case to position
monitoring stations to advance on-line rainfall forecasting procedures using
digital radar data and an on-line run-off forecasting procedure based on space
techniques to enhance lead time. The early warning criteria we aim should be
rooted in holistic and concurrent interpretation of real-time rainfall records,
seismic records, spatial piezometric variations, slope surface and subsurface
movements and movement rates on discrete boundary shears, runout effects and other
collateral threats in the catchment and on the higher slopes. We should refrain
from over-simplifying the criteria for early warning to minimize bogus
forecasts and it must be continuously put to test. We must prepare ourselves to
effectively utilize every second of the available lead time.
We have all agreed time and again that landslide disaster management should be
integrated with development planning. The vast potential for hydro-power in
Uttarakhand is in a sense a big blessing, but the way it is being exploited is
a curse as hydro-power schemes are no longer environment-friendly and power
generation is no longer based on natural flows and sound engineering. Unless
safety issues appear continuously on RADAR, mega projects like the Tehri dam
will always keep us on tenterhooks.
Dozens of landslides in India, like the one at Kaliasaur on the
Srinagar–Rudraprayag highway, are quite old. We should fix them once for all. A
township on a landslide infested mountain slope can be best tackled by looking
at the stability of the mountain as a whole rather than frittering away the
resources in fixing landslides affecting individual buildings. We need breed
the culture of truth-seeking rather than data-seeking nature of landslide
investigations. Our reports and papers by hindsight reflect more of perceptions
inspired by loyalty to the accepted trends than science. In many cases, truth
eludes us because vital field evidences get erased even before landslide
investigations begin.
R. K. Bhandari
Forum on Engineering Interventions in Disaster
Mitigation,
Indian National Academy of Engineering,
New Delhi 110 016, India
e-mail: rajmee@yahoo.com
Comment by Praful Rao
Dr RK Bhandari, is long acknowledged to be one of the foremost authorities on landslides in the world. STH is proud to be associated with him from several years back.
