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Environment
A Country Deluged
by VK Joshi
 Floods
have been there ever since the drainage system of the earth's surface
came in to being. There are myths almost in all religions about the
great floods. As per the
Wikipedia the
stories of Noah and the ark in Genesis, Matsya in the Hindu Puranas,
Deucalion in Greek mythology and Utnapishtim in the Epic of Gilgamesh
are among the most familiar versions of these myths. A large percentage
of the world's cultures past and present have stories of a "great flood"
that devastated earlier civilization.
In other words floods have been ravaging the human societies since times
immemorial. In India nearly eight million hectares of land (about 2.73%)
pf geographic area are annually flooded says K.S. Valdiya a renowned
Earth Scientist and a great teacher of Geology. Nearly 32 million
Indians experience the deluge year after year. The number of people
affected keeps swelling each year. A report of the Central Water
Commission (CWC) says nearly 37 million hectares (m ha) of fertile land
are prone to floods annually. Lush green fertile fields forming a prized
land constituting 3.8 m ha are ravaged by the floods making nearly 32
million people depend for their food on doles from the government, NGOs
or forced to search alternative source of living.
Rivers have been considered sacred by our ancestors. Even today the
rituals of bathing in rivers on particular occasions are religiously
followed. It is a different issue that the rivers have been converted to
refuge carriers.
The rivers in India have different dynamics in different parts of the
country. Rivers in the Himalayas for example, are most dynamic and
frequently affected by earthquakes and landslides. Co-seismic landslides
are frequent and the lose rock mass and mud slide down the slope to get
dumped in a rivulet/river. Sudden onslaught of material obstructs the
stream, creates a lake behind. When the pressure of water from behind
exceeds the limit of tolerance of such a blockade, it gives way and
leads to flash floods in the downstream. Climatic factors also cause
landslides. The rain soaked mountain slope decides to slides down.
Whether a blockade is created or not the total load of the stream down
below is increased many times. This changes the hydraulic gradient of
the river and upsets the natural balance of the channel.
Flash floods have been taking place in the Himalayan terrain since ages.
However, they have become exceptionally frightening because of the
settlements along the rivers and heavy investment by the government to
generate hydroelectric power.
Recently in mid 2005 Pareechu River a tributary of Sutlej in Tibet was
in the limelight. Flash floods due to possible bursting of a natural dam
formed across Pareechu River were expected. As per the newspaper reports
as a precaution more than 3000 persons were evacuated and taken to safer
places to escape the fury of Sutlej in the higher reaches of Himachal
Pradesh. Nathpa-Jhakri Project (NJPC) that generates 1500 Megawatts (MW)
power from the mighty Sutlej had to be shut down. Satellite imageries of
Pareechu River were studied by the Survey Of India (SOI). The study
indicated a 60 metres deep lake formed on the course off the Pareechu
River. The lake was spread over an area of 230 metres. It was estimated
that the lake contained 114 million cubic metres of water.
What if the lake bursts was the major cause of anxiety. RMSI, a global
company for Geographical Information System (GIS) solutions had
independently worked out that in case of a lake burst approximately five
lakh persons would be affected. Based on 2001 census and remote sensing
data they postulated that Rampur (230 km downstream from the lake) in
H.P. may be submerged under five meters of water. The situation was
indeed alarming. A similar flood in 2000 took away 70 lives, damaged
around 100 bridges and also damaged the power plant at NJPC.
Sutlej is a mighty river that originates in Tibet at an elevation of
4500 meters from Lake Mansarover and Rakas Tal. Prior to entering Indian
Territory near Shipki La in Kinnaur district in Himachal Pradesh it
travels some 320 km in Tibet. The catchments of Sutlej upstream of
Rampur are 51000 km2 of which 37000-km2 lies in Tibet and 14000 km2 in
India.
The hydropower of Sutlej River basin is estimated to be 9000 (MW), out
of which 1500 MW has only been tapped so far. Projects for tapping
another 1500 MW are being developed.
A river basin with such a high potential for power generation is
certainly an asset for the nation. However, the altitude, terrain
conditions and geomorphology of the area warrant specialized feasibility
studies for full utilization of the asset. The investigations carried
out by the Geological Survey of India (GSI) enumerate that the area
falls in the zone V of the Seismic Zoning Map of India. Kaurik fault an
active fault passes through the area. The Kinnaur earthquake of January
1975 and 1997 are attributed to this fault. An earthquake of intensity
M+8 rocked neighboring Kangra in 1905.
Huge debris fans at the mouths of most of the tributaries of the Sutlej
indicate freak and sudden erosion episodes, a consequence of past
cloudbursts. Accumulation of snow in the higher reaches of the mountains
and excessive rain during monsoon adds to the total water content of the
jointed and sheared slope forming material. Water acts as a lubricant
and the rock mass slides down as soon as the angle of rest is disturbed.
Upper Sutlej valley has such gravitational landslides and landslides
generated by the earthquakes as well. Scars of landslides generated by
Kinnaur earthquake of 1905 are still visible. Geologists have observed
that the upper reaches of Sutlej River were prone to cloudburst in the
pre-historic days as well. Apart from the risk to lives and property,
the cloudbursts cause great damage to the engineered structures. The
load of silt carried by a river during a flash flood is doubled than
during the tranquil periods. Therefore the problem is compounded.
Harnessing the river is essential for developing hydropower for the
Country. While the engineers have to keep in mind the advice of the
geologists about the high seismicity and possibilities of flash floods,
the residents need to be constantly enlightened about the natural
hazards that haunt the area. Habitation should never be permitted below
the highest flood level.
Despite the flash floods of 1997 and 2000 we were caught napping in
Sutlej valley in 2005. Suppose there was no warning from the other side
the consequences could have been beyond imagination. In the age of
Information Technology and Remote Sensing it is not difficult to foresee
such mishaps. Provided we have the will to 'see' them!
Not only Sutlej , there are many major rivers that transcend from across
the international borders. Brahmaputra is one such classic river. The
floods of Brahmaputra and its tributaries are a big annual hazard.
We will read about some more floods in the Indo-Gangetic Plains in the
coming issues.
December 3, 2006
Image under license with Gettyimages.com
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