A Geodynamic Perspective of Arunachal Pradesh
and its bearing on environmental security and developmental planning
By Dr. K.S. Valdiya
Of the seven northeastern states, Arunachal Pradesh is slated to be the location of a large number of
hydel projects. The state has an extraordinary geological set-up, with the entire Himalayan mountain system
bending acutely around a mountain knot. The knot, the 7,756 m. high Namcha Barwa is growing fast in
height, with the Tsangpo river circumambulating it before entering Arunachal Pradesh as the Siang. Three
different geological domains occur in juxtaposition in eastern Arunachal Pradesh – the E-W Arunachal
NW-SE Mishmi mountains and the NNE-SSW Patkai-Naga ranges. The faults that divide these domains are
extremely active. Up-down and sideways movements of the mountain blocks are continuously taking place
along these and many other faults with which Arunachal is riddled. These movements are also manifested in
the frequent earthquakes that shake the province, sometimes devastatingly.
This high seismicity is understandable as the northeastward-moving Indian landmass is pushing and
pressing the Himalaya very hard. Since India continues to move at the rate of 54-62 mm. per year, the
Himalayan ranges are bound to experience the force of the squeeze against the Asian continent.
Consequently, the land of Assam is sliding northward under the Arunachal Himalaya and eastward beneath
Indo-Myanmarese ranges. Therefore, very severe deformation and attendant rupturing of the crust or
faulting and land displacement is taking place in the geological province of Arunachal Pradesh.
There is thus a continual build-up of strains within the framework of the Arunachal geological province.
Recurrent seismicity is the expression of relaxation of the accumulated strain. In this process, the mountain
quivers in some segments and ruptures and twitches spasmodically in other parts. Violent movements
trigger landslides in the belts cut by active faults, particularly where the rocks are in crushed, shattered and
sheared conditions, due to repeated movements in the past several million years. As there are hundreds of
faults along which movements have been taking place repeatedly and strongly, quite a large part of eastern
Arunachal has been affected or ravaged by mass movements of bewildering proportions. Consequently, the
natural environment is in a fragile state. These realities need to be taken into consideration while planning
the state’s development.
Natural hazards and environment security
Owing to the extremely active geodynamic condition of the terrain, even the slightest tampering with the
ecological-geological balance can initiate environmental changes, likely to assume alarming proportions.
There is an imperative need for extraordinary care when it comes to modifying topography by excavation,
placing loads of water and sediments in river impoundments, changing groundwater circulation through
road-cutting, removing protective forest cover, etc. Only those programmes of development should be
embarked on which cause minimum adverse impact to the stability of hill slopes and the integrity of ecology.
Alternatively, programmes of environmental security must be undertaken simultaneous with the
implementation of development projects. The environmental security and hazard management programmes
must form an essential part of the development paradigm of this mountain state.
Public policy for natural hazard management
Such a policy would entail formulating and enforcing laws and regulations for preventing or restricting
development and the use of lands prone to hazards as indicated in hazard-zoning maps. Since preventive
and restrictive measures have proved a failure, the most effective way of curbing the tendency to occupy
hazardous tracts would be to impose a series of disincentives. Codes for building and civil structures will
need to be formulated. A distinction must be made between a critical structure and an ordinary structure. A
critical structure, such as a power plant or a high dam, is one whose destruction or severe damage by a
natural disaster would cause such extensive damage that it should not be built even if the chance of hazard
is relatively small. An ordinary structure, such as a building or bridge, might fail or cause property damage or
loss of life but the destruction would not be catastrophic.
Problems of excessive sediment influx
The Namcha Barwa mountain is presently rising up at the rate of 3 to 5 mm. per year. The mountains
curving around this knot are likewise rising at rates no less than that of the pivotal point. The result of the
faster uplift is denudation at an unrelenting pace. Escalated erosion combined with the occurrence of
widespread and severe landslides is generating a large volume of sediment. The eroded materials find their
way through mountain torrents to river valleys in the foothills, choking the river channels. The carrying
capacity of these rivers consequently diminishes drastically, leading to frequent and uncontrollable flooding.
Yet another serious outcome is the waywardness of these rivers – they change their courses unpredictably
with destructive consequences. Roads cannot be laid and bridges cannot be built. Since the process of
choking channels with excessive debris cannot be reversed at this moment in geological history, it would be
allow these foothill rivers to flow freely in their undefinable floodways, without the interference of artificial
structures or settlement or cultivation.
Protecting forest assets
Arunachal Pradesh is covered with forests of exceptionally high biodiversity. There are 4,000 to 5,000
species of vascular plants per 10,000 sq. km. – the second richest biodiversity zone in the global context.
However, a look at a recent satellite image shows the appearance of many expanding patches deprived of
vegetal cover. If the people and the government look at this asset with greed in their eyes – and the powerful
who matter look away with indifference – Arunachal will be overtaken by the fate that has befallen Nepal,
Uttaranchal and Jammu, where the forest cover has gone down to far less than 30% of the geographic area
against the minimum of 60% required for the integrity of a mountain environment. In Kumaon in Uttaranchal,
where the forests are reasonably well-managed, the forest cover by 1983 had dwindled to less than 29% of
the surface – and only 4% of the geographic area was left with forests having more than 60% foliage.
Among the many consequences of forest degradation in Kumaon is the alarming decrease in spring
discharges. The Gaula river in south-central Kumaon, for example, showed 25% to 75% decline in the
discharge of springs and 38% decline in river discharge in the period from 1971 to 1981. While I do not
foresee this scenario in Arunachal just yet, the acceleration of erosion and loss of soil is bound to be very
Water resources planning
Nearly 455 billion cubic metres of water flows down the Brahmaputra (at Barak) every year, most of it
coming from the rivers of Arunachal. Long-term engineered taming of rivers is not possible in the Himalayan
terrain. Since high dams are known to generate environmental imbalances and cause enormous socio-
cultural problems, it would be imprudent to go in for high dams in Arunachal’s highly earthquake-prone
region of active faults. Smaller dams would better serve the purpose of harnessing energy and storing water.
Smaller dams cost less, start giving benefits quite early, bring greater profits and cause less damage to the
environment and distress to human habitations. While the cost of production of electricity is high for small
hydel projects, if one were to consider the real (total) cost of the water resource development project that
includes the loss of natural resources due to submergence, the expenditure on restoring or repairing
damaged land and the enormous financial implications for relocation of uprooted people,
as well as the higher costs of electricity generated by
small hydel projects is more than compensated. A network of small hydel power projects could meet the
needs of Arunachal Pradesh.
The task of locating appropriate sites for such dams as would cause minimum damage must be assigned
to environmental geologists. This calls for an organisation of environmental and engineering geologists,
working in conjunction with ecologists and hydrologists.
Arunachal is in the somewhat unique position of being able to forge its own path to development and
avoid the mistakes that other states have committed. I am sure that the people and the government of
Arunachal will not countenance selling their future to finance the present.
Dr. K.S. Valdiya is a Bhatnagar Research Professor at Jawaharlal Nehru Centre for Advanced Scientific Research,
Jakkur, Bangalore – 560 064. This article is an excerpt of his keynote address at a workshop in December 1999,
organised by the Arunachal Unit of G.B. Pant Institute of Himalayan Environment and Development.