This document discusses the causes of flooding in Chennai, India. It provides background on Chennai's climate and geography, noting that the city receives heavy rainfall during monsoon season and contains two rivers. Urbanization has decreased drainage capacity through encroachment on water bodies and increased impermeable surfaces. The city's flat terrain also hinders drainage. The 2015 floods were particularly severe due to strong northeast monsoon winds and an El Niño effect that increased rainfall. Releases from the Chembarambakkam reservoir overwhelmed existing drainage systems and flooded parts of the city. The document recommends delineating flood zones, improving drainage infrastructure, and increasing public awareness of flood risks.

1. A STUDY OF CHENNAI
FLOOD
BY
V.ABINAYA @ MEENA PRIYA
Ist year M.Sc. Geography

2. FLOOD
 A flood is an overflow of water that submerges land which is usually dry.
 Flooding may occur as an overflow of water from water bodies, such as a
river or lake, in which the water overtops or breaks levees(an embankment
built to prevent the overflow of a river), resulting in some of that water
escaping its usual boundaries, or it may occur due to an accumulation of
rainwater on saturated ground in an areal flood.

3. URBAN FLOOD
 Flooding in urban areas can be caused by flash floods, or coastal
floods, or river floods, but there is also a specific flood type that is
called urban flooding.
 Urban flooding is specific in the fact that the cause is a lack of
drainage in an urban area. As there is little open soil that can be
used for water storage nearly all the precipitation needs to be
transport to surface water or the sewage system.
 High intensity rainfall can cause flooding when the city sewage system
and draining canals do not have the necessary capacity to drain away
the amounts of rain that are precipitated. Water may even enter the
sewage system in one place and then get deposited somewhere else in
the city on the streets. Sometimes you see dancing drain covers.

4. CHENNAI
 Chennai is the capital city of the Indian state of Tamil Nadu. Located on the
Coromandel Coast off the Bay of Bengal.
 Chennai is situated on the north-east end of Tamil Nadu on the coast of Bay of
Bengal. It lies between 12°59' and 13°9' of the northern latitude and 80°12' and
80°19' of the eastern longitude at an average altitude of 6 metres above sea level on
a 'sandy shelving breaker swept' beach. It stretches nearly 25.60 kms
 Chennai is a low-lying area and the land surface is almost flat like a pancake. The
even topography of the land throughout the district renders sub-divisions into natural
regions rather difficult
(Google maps)

5. Cont….
 Chennai has a tropical wet and dry climate. The city lies on the thermal
equator and is also on the coast, which prevents extreme variation in seasonal
temperature.
 The city gets most of its seasonal rainfall from the north–east monsoon winds,
from mid–October to mid–December. Cyclones in the Bay of Bengal sometimes
hit the city. The previous highest annual rainfall recorded is 421mm in 2005 .
But now the highest rainfall in Chennai is recorded as 1218mm on December
01, 2015.
 The city is intersected by two languid streams, the Cooum and the Adyar.
Cooum runs through the heart of the city and enters the sea in-between the
university buildings and the Fort. St. George underneath the Napier Bridge,
while the latter wends its way through the southern part of the city and enters
the sea near Adyar. slow and relaxed.
 These two rivers are almost stagnant and do not carry enough water except
during rainy seasons.

6. REASONS BEHIND CHENNAI FLOOD
 Chennai receives more rainfall during the month of November and December
(North-East Monsoon).
 The northeast monsoon has been particularly vigorous over southern India in
the previous year and more so in Tamil Nadu state, of which Chennai is the
capital. According to Skymet data, during the month of November, Chennai
recorded a whopping 1218.6 mm of rain – three times its monthly rainfall. The
normal rainfall figures for November stand at 407.4 mm.
 According to Indian Meterological Department, due to El Nino effect several
low pressure zones created near the coastal area of Bay of Bengal which
influenced more rainfall in the coastal as well as interior parts of Tamil Nadu.
 As a city on the high-energy coast facing the Bay of Bengal, Chennai is no
stranger to heavy rains and cyclonic storms. Chennai has experienced
particularly heavy rains roughly once every 10 years—1969, 1976, 1985, 1996,
1998, 2005, and 2015.

8. EL NINO EFFECT
 El Niño means The Little Boy, or Christ Child in Spanish. El Niño was
originally recognized by fishermen off the coast of South America in the
1600s, with the appearance of unusually warm water in the Pacific Ocean. The
name was chosen based on the time of year (around December) during which
these warm waters events tended to occur.
 The term El Niño refers to the large-scale ocean-atmosphere climate
interaction linked to a periodic warming in sea surface temperatures
across the central and east-central Equatorial Pacific.
 Climate experts say El Nino responsible for heavy Chennai rains
 Also blame poor town planning as the canals are blocked and there is no way
the excess rain could be drained
 "As of now, El Nino continues to be strong. In an El Nino year, the South west
monsoon will have deficit rains and North East monsoon will see excess
rainfall," said G P Sharma, vice president, meteorology at Skymet, the private
met agency.

9. CHEMBARAMBAKKAM RESERVOIR
 All the reservoirs that cater to Chennai and its suburbs were empty before
Diwali. Consistent rains started on November 8, lasting a week, and were
followed by another spell on November 23, which was not forecast. By the end
of November, the level in the reservoir had reached its limit.
 Water in the Chembarambakkam reservoir — one of the city’s main water
sources — stood at 22 ft at this time, against its capacity of 24 ft. Official data
shows outflow from the reservoir, into the Adyar River, as 900 cubsec (1 cusec=
28.7 Litres of water)
 It started raining again on December 1, and continued into December 2. By
December 1 afternoon, the water in Chembarambakkam had swollen to 3,396
million cubic feet — almost its full capacity. Engineers started to increase the
outflow.

10.  On December 01, Chennai received 200 mm rainfall over 14 hours. Given the
advance warning, and another by the Met department on November 30.
Following an increased outflow from Chembarambakkam lake and from over 40
tanks in its catchment area, low-lying areas in the city were already swollen. In
few hours the discharge from the Chembarambakkam at 5pm, the outflow was
around 7500 cusec raised to 29400 cusec ,which caused an alarming effect on
the Chennai’s flood.
 By around 10 pm, the water was being released at 29,400 cubsec into the Adyar
River, which was already in spate, as engineers feared a breach of
Chembarambakkam’s boundary. It took three to four hours for the water to reach
the city from the reservoir 25 km away, but by midnight of December 2, land in
more than a 4-km radius around Adyar, which flows through the heart of
Chennai, had gone completely under water.

14. chennai wikipedia retrieved dec 17

15. Table 1. Causes of Chennai Floods
CAUSES TYPES OF FACTORS ELEMENTS
Direct Factors
Increase in rainfall Due to global climatic change
Urbanization
Encroachment of all water bodies, wetlands, etc.,
Construction of transportation networks all along the
major watercourses
Increase in concrete spaces which stops percolation of
water into the ground
Decrease in open areas/green spaces
Lack of Transportation facilities (esp. in slums)
Topography Plain terrain lacking natural gradient for freerun-off
Indirect Factors
Inadequate & poor drainage systems
Sewage systems were planned originally before 4 decades
and only few minor modifications made which is far
below the required capacity
Heavy siltation all along the drainage channels
Lack of coordination between the agencies
Disposal of solid waste & other
debris
Attitude of people
Lack of management measures by the agencies
Vehicle parking on roads
Increase in concrete spaces
Discrepancies between public & local authority

16. FINDINGS AND RECOMMENDATION
 Both humans and nature put together the ground for the perennial flood
tribulations. The immediate need is to create a scientific inventory of water
bodies and delineate flood zones within the city.
 The flood zone will have to be identified based on the location of the
water bodies, natural drains, water shed area and it has to be made as a
no building zone.
 More campaigns have to be conducted at the local level in order to create
awareness to the public about the causative factors for the flood disasters. In
addition to the above, the wide-ranging management measures will help
Chennai to be relieved from the recurrent flood menaces almost every
monsoon

18. Bibliography
 Chambers, C. (2002). Wild Weather Flood. Chicago.
 Chennai - Wikipedia, the free encyclopedia. (n.d.). Retrieved December 17,
2015, from Chennai - Wikipedia, the free encyclopedia:
https://en.wikipedia.org/wiki/Chennai
 District Administration, C. (n.d.). Chennai District Welcomes You. Retrieved
December 17, 2015, from Chennai District Welcomes You:
http://www.chennai.tn.nic.in
 Geography of Chennai. (n.d.). Retrieved December 17, 2015, from Geography
of Chennai - Wikipedia, the free encyclopedia:
https://en.wikipedia.org/wiki/Geography_of_Chennai
 Google maps. (n.d.). Retrieved December 17, 2015, from Google maps:
https://maps.google.com
 India Meteorological Department. (n.d.). Retrieved December 17, 2015, from
India Meteorological Department: www.imd.gov.in

19.  Janardhanan, A. (2015, December 14). Chennai floods: The day city went under, who did what
— and who did not . The Indian Express .
 Kanthimathinathan, T. (2011, December 30). Cooum Sub Basin Restoration & Management.
 Lavanya, A. (2012). Urban Flood Management – A Case Study of Chennai City. Architecture
Research , 2, 115-221.
 Maps of India. (n.d.). Retrieved December 17, 2015, from Maps of India:
http://www.mapsofindia.com
 (2007). Master Plan - II for Chennai Metropolitan Area - 2026. Tamil Nadu: Chennai
Metropolitan Development Authority.
 Metrowater Lake Level - Chennai Metro Water. (n.d.). Retrieved December 17, 2015, from
Metrowater Lake Level - Chennai Metro Water: www.chennaimetrowater.tn.nic.in/reserve.asp
 Regional Meterological Department. (n.d.). Retrieved December 17, 2015, from Regional
Meterological Department: www.rmg.nic.in
 The Indian Express. (n.d.). Retrieved December 17, 2015, from The Indian Express:
www.indianexpress.com
 6The mounting economic toll of the record rainfall in Chennai. (n.d.). Retrieved December 17,
2015, from QUARTZ: http://www.qz.com/
 Welcome to Chennai Metro Water. (n.d.). Retrieved from Welcome to Chennai Metro Water:
www.chennaimetrowater.tn.nic.in

20. THANK YOU