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Environment
Urban Floods: Bane for the
People
by VK Joshi
 Come
monsoon and the media reports are full of floods in the metros of India.
Mumbai, the film city of India was literally drowned in the great floods
of 2005. The floods caused a direct loss of Rs. 450 crores or US $ 100
million. This was just an example to show the enormity of the problem.
Each year the state governments come out with the flood 'protection
measures' taken by them and also about the 'preparedness', yet with each
passing year the situation appears to worsen. Why?
We will try to seek answers to this question along with other similar
questions like why the nature's scourge has started to hit the urban
centers more and what is the way out?
The experience of floods in Mumbai and Chennai in 2005 has been one of
the worst in the recent years. Amongst the metros, Mumbai is one place
which is cosmopolitan. People from all over the country try to seek jobs
there and elk a living. Many of them succeed. A stage comes when they
want to settle down there. The last floods have shaken all such would be
settlers.
The ire of the Mithi 'nadi' in Mumbai was such that it caused
imponderable loss of life, property, public facilities, interrupted all
activities and above all worse were the daily wagers. The stoppage of
work left them high and dry. In such circumstances people curse the
government and vice versa. The government tries its best to provide
relief to people and assuage the feelings, but that does not help much.
Post flood rehabilitation, health safety and reconstruction is a big
burden on the exchequer that comes all of a sudden and unexpected.
Flooding is not a new phenomenon. The recent experience has however,
shown that sudden, incessant rains are the major factor behind deluges.
Well one can not control the rains, but it is possible to tame and
utilize the flood waters in urban areas.
Let us take example of Mumbai. The reasons which led to massive flooding
as per the wikipedia include, antiquated drainage system. The 20th
century drainage network of Mumbai is capable of carrying only 25
millimeter of rainwater per hour. With drains clogged at several places
it proved inadequate for the 944mm rain which lashed Mumbai in one day
alone. It seems that only three drains which drain into the sea have
gates whereas, other 102 outlets have no such gates. Problem with
coastal areas is lack of adequate gradient for water to flow into the
sea. During high tides, the sea water incursion takes place through
these drains. Drains without gates become vulnerable points and a salt
water deluge engulfs upcountry. It goes without saying that the drainage
system needs a thorough overhaul with gates to man the backflow of the
sea water. During the last floods of Mithi River the residents had to
live under the constant fear of a deluge even after rains, just because
high tide water was difficult to control. Mithi River drains the
Salsette Island on which the city of Mumbai is situated. Originating at
Powai the river flows through densely populated areas and industrial
complexes of Powai, Saki Naka, Kurla, Bandra-Kurla complex, Dharavi and
Mahim where it meets the Arabian Sea. Dense clusters of slums right on
the river bank, disposal of industrial waste, sludge and domestic waste
all along have converted this natural drain to an open sewer. This river
carries the excess water from Powai Lake. During the monsoon the river
naturally swells. The river used to act as a storm water drain for
Mumbai. Now choked to capacity this natural facility is of no help
during the rains. Yes it does add to the problem by flooding the banks.
Since the British days the floods and their remedies have been the forte
of the engineers. In the recent years some of the earth scientists have
studied the problem of flooding in detail and have suggested remedies
too. H.S. Saini of Geological Survey Of India (GSI) in one of the papers
published in the prestigious science Journal, Current Science says that
the mechanism of urban flooding is complex and site specific. Heavy
rains, river overflowing the banks, sudden release of water from dams
due to natural or anthropogenic reasons, coastal hurricanes and tsunamis
and a combination of any of the above can create havoc in the urban
areas. If we revert back to Mumbai we realize the gentle slope of the
ground is towards the sea. Water flows down the slope. During rains if
the path of water is obstructed by buildings and the drains have no
capacity, the outcome is what the people of Mumbai experienced in 2005.
Floods in the rivers are dependent on topography, drainage, rainfall and
the ground geology. For example, if the drainage is poor as in Mumbai
even less rainfall will cause floods. If the channel of the river is
made of clay at a particular site excess water will rather spillover as
it will not be able to go down to the depths. All these criteria have to
be considered before planning development of a particular area.
Unfortunately it is not so, and as a consequence most of the cities are
flood prone.
One of the most urbanized areas is the Indo-Gangetic plain. Initially
towns came up on the higher terraces along the rivers at these places.
Gradually the human activity including development of huge residential
complexes descended down to the river bank or river lowlands. These
areas are now vulnerable to floods. Yet another problem faced by these
urban centers is the tremendous water logging during monsoons.
Anthropogenically superimposed concrete topography influences the origin
and augmentation of flooding/water-logging. The concrete pavements,
buildings and road dividers produce a triple effect. They reduce the
efficiency of the ground to permit seepage of water to depths, obstruct
lateral or down slope movement of water to reach a sink, like a river or
a natural depression. Pavements and apartments can reduce percolation of
water up to 90% says Saini. The vertical structures become geographical
barriers and divide the city into several sub-basins, which are
dislodges and disconnected from the main natural outflow.
Lucknow, the Capital of Uttar Pradesh never had the problem of water
logging. A posh colony, Gomtinagar, a dream of politicians and builders
came up on the bank of Gomti River despite warnings by the earth
scientists. In order to save the residential area thus 'developed'
massive Bunds were constructed all along the route of the river
throughout the city. It is common sense that the natural slope of the
ground in a city on the banks of a river is towards the river. Rainwater
just moves down the slope to reach the river. The approaches of water
been closed by the Bunds the city becomes a huge pool every monsoon.
People blame the government for not cleaning the drains and the
government blames the people for choking them. Unfortunately no one
realizes that water-logging has been actually 'invited'.
The coastal areas have mangroves as buffers between the land and the
sea. In Mumbai more than 40% mangroves have been 'reclaimed' in-between
1995 to 2005 by the builders and slum dwellers and the land has been
constructed upon. Destruction of Mangroves along Mithi river near Mahim
creek is one of the root causes of sea water incursion during tides.
The urban areas have been constructed upon and now it is too late to
plan and tackle the problem of flooding for such centers. Yet if the
people want to save themselves from the wrath of the floods and the
government wants to avoid paying recurrent compensations to the people
one of the way out is to construct large tanks where rain water could be
stored and also to puncture the ground at several places like it is done
for rain water harvesting. This would augment the seepage capacity of
the ground. In addition a holistic drainage system for every urban
complex would save many a lives, economic losses and inconvenience due
to floods. Seepage holes will prevent water-logging and the menace of
the mosquitoes.
December 24, 2006
Image courtesy
Hindu.com
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