Urban floods in Bangalore and Chennai: risk management challenges and lessons for sustainable urban ecology

Abstract

A number of major cities and towns in India reported a series of devastating urban floods in the recent decade. Mumbai flood 2005 followed by other major cities of South Asia like Dhaka, Islamabad,
Rawalpindi also suffered with urban flooding. Census 2001 figured 285 million people in 35 metro cities of India, and is estimated to cross 600 million with 100 metro cities in 2021. Regional ecological challenges coupled with climatic variability are noted to aggravate flood risks and impact on affected communities. Urban flooding was primarily a concern of municipal and environmental governance, has now attained the status of ‘disaster’, which has drawn the attention of environmental scientists and disaster managers. Challenges of urban flooding in terms of drainage and flood mitigation including structural and non-structural measures and key issues of urban ecology in two major metropolitan cities of India – Bangalore and Chennai, have been studied. Risk management challenges in the context of land-use, city and population growth, wetland degeneration,
waste disposal have been discussed.

Full text

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The authors are at the National Institute of Disaster Management, IIPA
Campus, New Delhi 110 002, India.
*For correspondence. (e-mail: envirosafe2007@gmail.com)
Urban floods in Bangalore and Chennai: risk
management challenges and lessons for
sustainable urban ecology
Anil K. Gupta* and Sreeja S. Nair
A number of major cities and towns in India reported a series of devastating urban floods in the re-
cent decade. Mumbai flood 2005 followed by other major cities of South Asia like Dhaka, Islama-
bad, Rawalpindi also suffered with urban flooding. Census 2001 figured 285 million people in 35
metro cities of India, and is estimated to cross 600 million with 100 metro cities in 2021. Regional
ecological challenges coupled with climatic variability are noted to aggravate flood risks and im-
pact on affected communities. Urban flooding was primarily a concern of municipal and environ-
mental governance, has now attained the status of ‘disaster’, which has drawn the attention of
environmental scientists and disaster managers. Challenges of urban flooding in terms of drainage
and flood mitigation including structural and non-structural measures and key issues of urban eco-
logy in two major metropolitan cities of India – Bangalore and Chennai, have been studied. Risk
management challenges in the context of land-use, city and population growth, wetland degenera-
tion, waste disposal have been discussed.
Keywords: Bangalore, Chennai, cities, floods, urban ecology, wetlands.
Cities and floods
‘IF there could be such a thing as sustainable develop-
ment, disasters would represent a major threat to it, or a
sign of its failure.’1 In 2000, 37% of Asia’s population
lived in cities and the proportion is projected to reach
more than 50% by 2025. Unfortunately, the majority of
Asian mega-cities and other urban localities occupy
hazard-prone land. In the period 1994–2004 alone, Asia
accounted for one-third of 1562 flood disasters. Urbani-
zation in developing countries doubled from less than
25% in 1970 to more than 50% in 2006 (ref. 2). It is
estimated that at least 13 cities of the world that are prone
to natural hazards will have a population in the 10–25
million range, with nine of them in Asia. In 2001, there
were 285 million people in India residing in 35 metro
cities (cities having a population of above 1 million).
This is estimated to exceed 600 million by 2021 in over a
100 metro cities as the trend is on a rise.
Recent events highlighted the man-made causes respon-
sible for recurring and prolonged floods in South Asian
cities like Dhaka, Mumbai, Chennai, Bangalore, Ahmeda-
bad, Surat, Patna, Jamshedpur, Rawalpindi and Islama-
bad. Floods result from the overflow of land areas,
temporary backwater effects in sewers and local drainage
channels, creation of unsanitary conditions, deposition of
materials in stream channels during flood recession, rise
of groundwater coincident with increased stream flow,
and other problems3. Disaster management the worldover
is undergoing a paradigm shift from approach to ‘response
and relief’ to ‘prevention and mitigation’4. The call for a
mix of resistance and preparedness for resilience towards
flood risk in cities depends on management of urban eco-
logy5, including land use, water bodies, waste disposal,
etc. Major implications of urbanization are the following6,7.
Heat island effect
Surface and atmospheric temperatures are increased by
anthropogenic heat discharge due to energy consumption,
increased land-surface coverage by artificial materials
having high heat capacities and conductivities, and the
associated decreases in vegetation and water-pervious
surfaces, which reduce surface temperature through
evapotranspiration.
Loss of aquatic ecosystems
Urbanization has telling influences on the natural
resources such as decline in the number of water bodies
and/or depleting the groundwater.

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CURRENT SCIENCE, VOL. 100, NO. 11, 10 JUNE 2011 1639
Figure 1. Causes of urban floods in India32.
Figure 2. Map of India showing location of Bangalore and Chennai.
Loss of drainage capacity
Unplanned urbanization has drastically altered the drain-
age characteristics of natural catchments, or drainage
areas, by increasing the volume and rate of surface run-
off. Drainage systems are unable to cope with the in-
creased volume of water and are often encountered with
blockage due to indiscriminate disposal of solid wastes.
Disasters are events of environmental extremes which
are inevitable entities of this living world, and linked to
every component of the ecosystem. Urban flooding has
been recognized as a ‘disaster’ only after the Mumbai
flood in 2005. As revealed in Figure 1, the interaction of
flood causes in urban environment indicates significance
of urban ecology in disaster risk reduction8. The present
article discusses the flood challenges and mitigation
issues for two important metro cities of India, viz. Banga-
lore and Chennai (Figure 2). The aim of the study was to
understand the problems of increasing flooding inci-
dences in urban areas and related contexts of urban deve-
lopment and ecological issues. Data of secondary origin
have been collected and interpreted in the context of
flood risks and urban management. The article also
conveys wider issues and lessons for flood challenges in
Indian cities and towns.
Bangalore
Bangalore is located almost equidistant from both the
eastern and western coasts of the South Indian peninsula.
The mean annual rainfall is about 880 mm with about 60
rainy days a year. Bangalore is known as the ‘IT city’ or
‘silicon valley’ of India due to the presence of several
software companies. It is the fifth largest city of India
with population of about 7 million, located around
100 km from the Kaveri River. There has been a growth
of 632% in urban areas of Greater Bangalore across 37
years (1973–2009). Encroachment of wetlands, flood-
plains, etc. is causing floodway obstruction and loss of
natural flood storage in Bangalore4.
The gap in the installed capacity of the wastewater
treatment system (450 MLD) as against the estimated
generation of domestic water (700 MLD) is evident. Ban-
galore has 134 flood-prone areas (Table 1). The City
Corporation has identified these areas after a survey of
critical locations which are prone to recurrent flooding.
However, some areas in the city face the brunt of the
rains more than the others and are more prone to flooding.
In 2005, flooding had worsened by unauthorized deve-
lopments along three lakes. Choked drains led to residential

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areas being inundated, and traffic was severely affected.
Thousands of office-goers were stranded on the city’s
waterlogged roads. Schools in the city were closed
and several apartment complexes were flooded. Water
entered some office buildings, including one of the
offices of India’s third largest software exporter, WIPRO.
The flood left hundreds of people homeless and ailing
due to various health problems and environmental chal-
lenges.
Built-up area (16% in 2000) has now increased to 23–
24% in the metropolitan area of Bangalore. There are 542
slums located in the jurisdiction of Karnataka Slum
Clearance Board (218) and Greater Bangalore City
Corporation (324), out of which 310 are undeclared set-
tlements according to 2001 Census. Temporal analysis of
water bodies indicated a sharp decline of 58% in Greater
Bangalore attributed to intense urbanization process, evi-
dent from 466% increase in built-up area from 1973 to
2007. Analysis revealed (Figure 3; Table 2) decline of
wetlands from 51 in 1973 (321 ha) to merely 17 (87 ha)
in 2007. The number of water bodies reduced from 159 to
93.
The lakes of the city have been largely encroached for
urban infrastructure. As a result, in the heart of the city
only 17 good lakes exist as against 51 healthy lakes in
1985. According to a study6, the water bodies of the city
have reduced from 3.40% (2324 ha; 5742.7 acres) in
1973 to just about 1.47% (1005 ha; 2483.4 acres) in
2005, with built-up area during the corresponding period
increasing to 45.19% (30,476 ha; 75,307.8 acres) from
27.30% (18,650 ha; 46,085.2 acres).
Figure 4 shows unplanned settlements with very poor
drainage. Enforcement of land-use laws and guidelines/
plans has been observed to be poor. Field surveys (during
July–August 2007) showed that nearly 66% of lakes are
Table 1. Top five flood-prone areas identified in Bangalore city
Ejipura/Koramangala : National Games Village area
BTM Layout : I and II stage area
Shankarappa Garden : Magadi Road area
Brindavan Nagar : Mathikere area
Ambedkar College : Airport road area
Figure 3. Land-use changes, 1973–2007.
sewage-fed, 14% surrounded by slums and 72% showed
loss of catchment area6. Also, lake catchments were used
as dumping yards for either municipal solid waste, con-
struction residue or building debris.
Bangalore city has a 180 km long primary and secon-
dary storm-water drainage system, which often fails to
take the load of the rains due to silt and garbage causing
blockage. A provision of Rs 45 million has been made for
the flood-management fund with 12 squads on call, of
which six are rain and flood relief squads; 20 personnel
have been assigned in each squad. The Jawaharlal Nehru
Urban Renewal Mission (JNURM) project was launched
in December 2005 and Bangalore has been allocated a
budget for the next six years.
Chennai
Topographically plain terrain with few isolated hillocks
in the southwest, Chennai is bounded on the east by the
Bay of Bengal and on the remaining three sides by the
Kanchipuram and Tiruvallur districts. Chennai receives
on an average approximately 1300 mm of rainfall per
year – most of this (~800 mm) falls during the northeast
(NE) monsoon in the months of October through Decem-
ber. The city is situated at approximately 13°N lat. and
80°E long. Chennai city currently encompasses an area of
172 sq. km, and the metropolitan area adds almost
400 sq. km of urban agglomeration to this figure. Chennai
faces a number of risks, partly climate-related, but also
human-induced such as waste disposal, water contamina-
tion and lack of drinking water, suburban sprawl and
mismanagement in urban planning7.
Due to the plain terrain Chennai lacks natural gradient
for free run-off. This necessitates an effective storm-
water drainage system. The sewage system in Chennai
was originally designed for a population of 0.65 million
at 114 litres per capita per day of water supply; it was
further modified during 1989–1991, but is now much
below the required capacity. Cooum and Adyar rivers in
Figure 4. Slums and high-density poor settlements.

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Table 2. Loss of water bodies
Bangalore city Greater Bangalore
Year No. of water bodies Area (ha) No. of water bodies Area (ha)
SOI 58 406 207 2342
1973 51 321 159 2003
1992 38 207 147 1582
2002 25 135 107 1083
2007 17 87 93 918
SOI, Survey of India, topographic maps (published in 1973); Source: Ramachandra and Uttam Kumar6.
Figure 5. Growth of Chennai since 1923 (from Gupta and Nair8).
Chennai city are almost stagnant and do not carry enough
water, except during the rains. These rivers play a major
role during floods, collecting surplus water from about 75
and 450 tanks in their respective catchments. Chennai
municipal area has a network of canals and channels
within its boundary. Buckingham canal, originally a
navigation channel and waterway till 1954, now serves
only as a drainage channel.
The physical growth of Chennai from 1923 to 1971 is
shown in Figure 5. The population has grown by eight
times in the period 1901–2001 and per hectare population
density has increased from 80 to 247. Chennai has a large
migrant population from other parts of Tamil Nadu and
other parts of the country, accounting for 21.57% of the
Chennai population in 2001. There are three major water
courses (Cooum, Buckingham Canal and Adyar) in Chen-
nai city and the banks of all the areas encroached (Figure
6). Slums (number recorded to be 30,922) have developed
here without basic amenities and are subjected to flood
every year. They often pollute the water courses, thus
worsening the health situation.
Several catastrophic floods in Chennai in the past
(1943, 1976, 1985, 1996, 1998, 2005, 2010) were caused
by heavy rain associated with depression and cyclonic
storms, leading to floods in major rivers and failure of
drainage systems. Chennai was severely flooded due to
heavy rains (16–20 cm, attributed to a trough of low pres-
sure from the Gulf of Mannar to the Southwest Bay off
the Tamil Nadu coast) during 30 October–2 November
2002. Residential areas became ‘islands’ and were cut-off,
paralysing life, services and trade, including transport,
communication, etc. On 5 November 2004, heavy rainfall
(6 cm within 24 h or less) caused flooding and waterlog-
ging in many areas, inundating most of the slums9. A
deep depression over the Bay of Bengal brought 42 cm
rainfall in around 40 h during the NE monsoon of 2005.
Several floods were reported during 2006, 2007 and
2008. Closing of schools due to flooding every year is
common in many parts of Chennai. The Chennai Munici-
pal Corporation has identified 36 localities as flood risk
hotspots (Figure 7).
Since the beginning of the 20th century, Chennai has
witnessed a steady deterioration of and decease in water
bodies and open spaces (Figure 7). It is estimated that in
Chennai city more than half of the wetlands have been
converted for other uses. Chennai had about 150 small
and big water bodies in and around the city, but today the
number has been reduced to 27. The important water bodies
include Adyar Estuary, Adambakkam lake, Ambattur
lake, Chitlapakkam lake, Ennore creek, Korattur swamp,
Madhavaram and Manali Jheels, Pulicat lake, Vyasarpadi
lake, besides Buckingham Canal, Coovum and Otteri nul-
lah. Ownership of water bodies is scattered among various
government departments and is the root cause for lack of
proper management. The Protection of Tanks and Evic-
tion of Encroachment Act, came into effect on 1 October
2007. However, there has been lack of implementation of
this law.

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The green cover reduced rapidly across the city between
1997 and 2001. In some wards almost 99% of the green
cover has been replaced by non-vegetative development.
As a result, the water-holding capacity of the city’s surface
has gone down drastically. The reduced city’s surface water-
holding capacity combined with the augmented imperme-
able surface increased the peak flow up to 89% from
Figure 6. Degradation of Madhuravayal lake.
Figure 7. Flood risk hotspots in Chennai metropolitan area (Source:
Chennai Metropolitan Development Authority, www.cmdachennai.
gov.in)
1997 to 2001 in some of the wards. Increased surface run-
off and reduced retention capacity of the land cover
almost stopped the groundwater recharging processes in
the city. Slum impact and environmental degradation of
Cooum river is shown in Figure 8 a and b (ref. 10).
Meteorologically, there is no major upward or down-
ward trend of rainfall during 200 years, and a decrease in
the last 20 years with a contrast record of increasing
floods has been experienced in Chennai. Causes of in-
creased flooding identified are:
(a) Uncontrolled urban sprawl and loss of natural
drainage. Drainage channels have been blocked and urban
lakes filled and encroached, canals degraded and polluted,
heavily silted and narrowed. A 1994 survey revealed
waterways contamination and anaerobic digestion led to
sludge accumulation causing hydraulic hindrances.
(b) Inadequacy of storm-water drainage system and
lack of maintenance. The city has only 855 km of storm
drains against 2847 km of urban roads. Plastic and poly-
thene constituents to the storm-water stream along with
poor or no maintenance aggravates flood.
(c) Increase in impervious surfaces. Paving of road-
sides, parks and open areas causing flood severity and
conditions for drought to follow.
(d) Lack of coordination between agencies. Lack of a
unified flood control implementing agency that integrates
Figure 8. a, A residential area backing onto the Cooum river33.
b, Cooum river narrowed by encroachments10.

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the functions of the Corporation, Development Authority,
Public Works Department, Slum Clearance Board, Hous-
ing Board, etc.
All the waterways in Chennai are considered to be pol-
luted, but the Cooum river and Buckingham Canal are
widely recognized to be the worst. A Government-funded
Flood Alleviation Scheme was launched in 1998, with a
cost Rs 3000 million, focused mainly on structural meas-
ures. Adequacy of flow in the arterial drainage system,
removing impediments, safeguard, against tidal and flu-
vial flooding, relocation and rehabilitation of encroachers
were the main objectives. Cleaning of certain waterways
and lakes was also undertaken under packages 2 and 3 of
the scheme. Chennai City River Conservation Project was
launched in 2000 to improve the waterways, with an esti-
mated outlay of Rs 17,000 million. The Master Plan
1992–1993 incorporated Madras Metro Flood Relief/
Storm Water Drainage study outcomes in the form of
structural and non-structural measures. Funds under
JNURM project have been envisaged for implementation
of underground sewerage schemes and detailed project
reports are being developed. Thiru Vi Ka Industrial
Estate has been proposed for rehabilitation and upgrading
of sewerage system.
Discussion and lessons
Urban flooding is significantly different from flooding in
rural areas as urbanization results in impermeable catch-
ments causing flood peaks by up to three times5. Conse-
quently, flooding occurs quickly due to faster flow times
(in a matter of minutes). As a reference to discuss the
growing flood menace in other cities in India, including
Bangalore and Chennai, the lessons of the July 2005
floods in Mumbai are important to mention. The flood of
2005 was truly a disaster as it receded only after seven
weeks and affected 20 million people. The floods killed
1200 people and 26,000 cattle. It destroyed more than
14,000 homes, and damaged more than 350,000; about
200,000 people had to stay in relief camps. The agricul-
tural sector was heavily hit as 20,000 ha of farmland lost
the topsoil and 550,000 ha of crop was damaged11. Un-
precedented rainfall in one day was certainly one major
cause of the floods; with a 24 h rainfall figure that
exceeds the monthly average of 30 years. The rainfall
data show that within a period of 18 h, the precipitation
level rose to 944 mm in the suburban area, with maxi-
mum rain between 14.30 and 17.30 h on 26 July, a stag-
gering 380.8 mm in 3 h. Between 14.30 and 20.30 h
maximum rainfall of 647.5 mm was recorded, coinciding
with the time people were trying to reach their homes
from their work places.
The Mumbai flood of 2005 was followed by incidences
of urban flooding as a regular phenomenon in many
Indian cities, not only metros but in many towns as well.
Floods were reported recently in cities like Ahmedabad,
Bhopal, Bangalore, Calcutta, Chennai, Delhi, Gorakhpur,
Hyderabad, Surat, Rohtak and Kurukshetra due to a com-
bination of many factors like heavy or patchy rainfall,
dam-water release or failure, inadequate drainage sys-
tems, blockade, housing in floodplains and natural drain-
age or riverbed and loss of natural flood-storages sites. It
demonstrated on how unplanned, rapid urban develop-
ment has stretched the natural ecosystems in and around a
city to its limits, and made disaster from natural flood
hazards inevitable12. Lessons drawn from the studies are
summarized here on critical issues for future research and
planning interventions.
Urban drainage
Some of the major hydrological effects of urbanization13
are: (1) increased water demand, often exceeding the
available natural resources; (2) increased wastewater,
burdening rivers and lakes and endangering the ecology;
(3) increased peak flow; (4) reduced infiltration and (5)
reduced groundwater recharge, increased use of ground-
water, and diminishing base flow of streams. Vegetation
plays a vital role in evapotranspiration and soil-water
storage components of this balance. The driving force
behind the biodrainage concept is the consumptive water
use of plants14. The role of biodrainage in controlling
waterlogging and secondary salinization is important in
urban flood mitigation15.
Urbanization has marked effects on basin run-off in
terms of higher volume, higher peak discharge, and
shorter time of concentration3,16. As the risk of flooding
increases with climate change, so does the importance of
the major drainage systems. New design approaches,
which explicitly design roads to act as drains, can radi-
cally reduce the duration of flooding. Litter management
is critical to the management of urban drainage sys-
tems17,18. Often the best investment in drainage is better
handling of solid waste to prevent systems from becom-
ing rapidly blocked with debris16,19. Chennai witnesses
425 new vehicles on the road every day causing pressure
for motorable and parking space. A total of 42.6 million
people living in 8.2 million households have been living
in slums of 640 cities/towns spread across 26 states and
Union Territories, according to the 2001 Census. The
slum population constitutes 4% of the total population of
the country. Interestingly, the share of slums in urban
population has grown in major metro-cities compared to
smaller ones.
Flood impacts and risk assessment
Given the high spatial concentration of people and values
in the cities, even small-scale floods may lead to consid-
erable damage. In extreme cases urban floods can result

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1644
in disasters that set back urban development by years or
even decades. Velocity is also a major factor in determin-
ing per cent damage, with velocity floods capable of
causing building collapse even in relatively shallow
waters. Climate change is likely to amplify the challenge
of pest and disease control, as new ecological niches
appear that may sustain exotic pathogens and disease vec-
tors20. For example, flooding may become more frequent
in some geographic locations with climate change and
can affect health through the spread of water-borne dis-
eases17. Flood risk assessment is an essential part of flood
risk management. The ‘urban’ approach includes a specific
urban-type set of economic, social and ecological flood
risk criteria, which focus on urban issues: population and
vulnerable groups, differentiated residential land-use
classes, areas with social and health care, but also eco-
logical indicators such as recreational urban green spaces.
Vulnerability assessment21 represents, an important con-
tribution to decrease and control of land damage caused
by natural hazards, as it helps in strategies that limit
weakness by integrating flood risk into urban develop-
ment22.
Ecological aspects
‘All ecological projects (and arguments) are simultane-
ously political–economic projects (and arguments) and
vice-versa. Ecological arguments are never socially neu-
tral …23’. As work on disasters since the nineties increas-
ingly focused on issues of human vulnerability and
resilience, a more integrative approach has gained
favour24. Hazards are now defined as ‘human ecological
interaction that can generate disaster’25. Urban ecosys-
tems are the consequence of the intrinsic nature of humans
as social beings to live together6,26. Ecosystem function-
ing is guided by abiotic steering variables related to
hydrology, water quality and sediment load. These can be
used as primary indicators of ecosystem condition
and changes to them are first-order impacts. Floods and
storms are an integral part of the ecosystem dynamics and
have both positive and negative effects on human well-
being27.
Urban meteorology has come to require much more than
observing and forecasting the weather of our cities and
metropolitan areas17. Risks must be considered through
continuing assessments of science, technology and appli-
cation uncertainties, as well as in the costs and benefits
associated with each of the urban issues and the proposed
actions to mitigate adverse hazards or impacts17. Abrupt
variability and increased uncertainties about rainfall
pattern, periods, days and amount, and risk of weather
extremes as an impact of global climate change28 aggra-
vated by ecological and anthropogenic factors as local
climate actors8 pose ever-increasing risk of flood disaster
or waterlogging-led epidemics in urban areas.
Many of the water bodies, including man-made wet-
lands/lakes and natural depressions have disappeared due
to human-induced succession filled with waste, and
development or slum encroachments5. Urban wetlands in
India have reduced to approximately 30% during the last
50 years. Wetlands hold the run-off generated from heavy
rainfall, water discharge from reservoirs or channels or
snow-melt events. They reduce the possibility of flooding
in downstream or moderate flooding to some extent, de-
pending on the magnitude of run-off. Wetland vegetation
slows down the flow of flood water29. Wetlands reduce
the need for expensive engineering structures29. Under-
standing by many of the professional engineers working
on urban issues is not up to date with environmental
aspects and they generally look for structural solutions
which degrade the environment creating too many imper-
vious areas and thereby increasing the temperature, flood-
ing, pollution, etc.30. An integrated approach, therefore,
needs to combine watershed and land-use management
with development planning, engineering measures, flood
preparedness, and emergency management in the affected
lowlands, while taking into account the social and eco-
nomic needs of communities in both the highland source
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ACKNOWLEDGEMENTS. We thank the Executive Director of
National Institute of Disaster Management (NIDM), New Delhi for re-
search grant and inputs on aspects of urban governance and planning.
Inputs from Dr T. V. Ramachandra, IISc, Bangalore, and Drs T. Sunda-
ramurthy and L. Ramadurai, CPREEC, Chennai, as part of city teams
of the NIDM project are acknowledged.
Received 12 January 2010; revised accepted 30 March 2011