Floods :
Among all the disasters that occur in India, floods are the most commonly occurring
natural disasters due to the irregularities of the Indian monsoon. Flood is most prevalent and costliest
natural disaster in the world which devastates both life and economy at a large extent. Any flow which
is relatively high and which overflows the natural or artificial banks in any reach of the river is called
flood. About 75% of the annual rainfall in India is concentrated in 3 – 4 months of the monsoon season.
Flood, an excess of water, can be caused by heavy rainfall followed by inadequate capacity of rivers to
hold the water within their banks. According to National Flood Commission, about 40 million hectares
of land area is prone to flood in the country. On an average, the area affected by floods annually is
about 8 million hectares, out of which the cropped area affected is about 3.7 million hectares.
India witnesses flood due to excessive rain which then results in overflow of rivers,
lakes and dams, which adds to cause large amounts of damage to people's lives and property.
Fig. Kerala floods during the year 2018

Fig. Uttarakhand Floods during the year 2013
Causes of Floods :
Inadequate capacity of the rivers to contain within their banks the high flows brought
down from the upper catchment areas following heavy rainfall, leads to flooding. The tendency to
occupy the flood plains has been a serious concern over the years. Because of the varying rainfall
distribution, many times, areas which are not traditionally prone to floods also experience severe
inundation. Areas with poor drainage facilities get flooded by accumulation of water from heavy
rainfall. Excess irrigation water applied to command areas and increase in ground water levels due to
seepage from canals and irrigated fields also are factors that accumulate the problem of water logging.
The problem is exacerbated by factors such as silting of the riverbeds, reduction in the carrying
capacity of river channels, erosion of beds and banks leading to changes in river courses, obstructions
to flow due to landslides, synchronization of floods in the main and tributary rivers and retardation due
to tidal effects. Floods and landslides result not just from rainfall but also from other factors such as
land cover and topography. Indiscriminate development and encroachment of flood plain areas,
improper planning and construction of roads, railway lines, etc., are also responsible for increase in
flood damages.

Regions in the country prone to floods :
India can be broadly divided into the following four regions for a study of flood hazard.
In addition the Andaman and Nicobar Islands and Lakshadweep have peculiar characteristics, which
result in drainage congestion, flooding and erosion in coastal areas.
i. The Brahmaputra River Region :
This region consists of the rivers Brahmaputra and Barak and their tributaries, and
covers the states of Assam, Arunachal Pradesh, Meghalaya, Mizoram, Manipur, Tripura
Nagaland, Sikkim and the northern parts of West Bengal. The catchments of these rivers receive
very heavy rainfall which occurs mostly during the months of May – June to September. As a
result floods in this region are severe and quite frequent. Further the hills, where these rivers
originate, are fragile and susceptible to erosion and thereby cause exceptionally high silt
discharge in the rivers. In addition, the region is subjected to severe and frequent earthquakes,
which causes numerous landslides in the hills and upset the regime of the rivers.
The predominant problems in this region are cloud bursts followed by flash floods, soil
erosion in the watershed and bank erosion along the rivers, flooding caused by the spilling of
rivers over their banks, drainage congestion and the tendency of some of the rivers to change
their courses. The plain areas of the region suffer from the inundation caused by spilling of the
ii. The Ganga River Region :
The river Ganga has many tributaries, the important ones being Yamuna, Sone, Ghaghra,
Raphti, Gandak, Burhi Gandak, Bagmati, Kamla Balan, Adhwara group of rivers, Kosi and the
Mahananda. It covers states of Uttarakhand, Uttar Pradesh, Jharkand, Bihar, south and central
parts of West Bengal, Punjab, parts of Haryana, Himachal Pradesh, Rajasthan, Madhya Pradesh
and Delhi. The rainfall increases from west to east and from south to north. The flood problem is
mostly confined to the areas on the northern bank of the river Ganga. Most of the damage is
caused by the northern tributaries of the Ganga. In the north – western parts of the region and
southern parts of West Bengal, there is a problem of drainage congestion. The flooding and
erosion problem is serious in in the states of Uttar Pradesh, Bihar and West Bengal. The problem
of flooding and drainage congestion is getting accentuated due to large scale encroachment of
flood plains flood plains of the rivers for habitation and various development activities.

iii. The North – West River Region :
The main rivers in this region are the Indus, Sutlej, Beas, Ravi, Chenab and Jhulem.
These rivers are the tributaries of the Indus. They carry quite substantial discharges during the
monsoon and also large volumes of sediment. They change their courses frequently and leave
behind vast tracts of sandy waste. This region covers the states of Jammu and Kashmir, Punjab
and parts of Himachal Pradesh, Haryana and Rajasthan. Compared to the Ganga and
Brahmaputra regions, the flood problem is relatively less in this region. The major problem is
that of inadequate surface drainage which causes inundation and water logging over vast areas.
Indiscriminate use of water for irrigation and development of low lying areas and depressions
has created problem of drainage congestion and water logging.

iv. The Central India and Deccan Region :
Important rivers in this region are Narmada, Tapi, Mahanadi, Godavari, Krishna and
Cauvery. These rivers are mostly well defined and stable courses. They have adequate
capacities within the natural banks to carry the flood discharge except in delta area. The lower
reaches of the important rivers on the east coast have been embanked, thus largely eliminating
the flood problem. However the embankments need to be raised and strengthened to latest
standards to continue to provide protection against against floods and erosion. This region
covers the states of Andhra Pradesh, Telangana , Karnataka, Tamil Nadu, Kerala , Orissa,
Maharashtra, Gujarat and parts of Madhya Pradesh. The region does not have serious flood
problem except that some of the rivers in Orissa state namely Mahanadi, Brahmini, Baitarni
and Subarnarekha are prone to floods every year. The delta and coastal areas of the states on
the east coast periodically face flood and drainage problems in the wake of monsoon
depression and cyclonic storms. The problem is accentuated when the floods synchronize with
high tide. The rivers Tapi and Narmada, are occasionally in high floods affecting areas in the
lower reaches in Gujarat.

Damages caused by Floods :
The floods not only result in loss of precious human lives, cattle and damage to public
and private property but create a sense of insecurity and fear in the minds of people living in the flood
plains. Floods cause extremely large numbers of fatalities in every country, but due to India's extremely
high population density and often under enforced development standards, a large amount of damages
and many deaths could be happen. The after effects of floods such as the agony of survivors, spread of
epidemics, non availability of drinking water, essential commodities and medicines, loss of dwellings
etc. make floods the most feared among the natural disasters.
Floods can also bring many benefits, such as recharging ground water, making soil more
fertile and increasing nutrients in some soils. Flood waters provide much needed water resources in arid
and semi arid regions where precipitation can be very unevenly distributed throughout the year and
kills pests in the farming land. Fresh water floods particularly play an important role in maintaining
ecosystems in river corridors and are a key factor in maintaining floodplain biodiversity. Flooding can
spread nutrients to lakes and rivers, which can lead to increased biomass and improved fisheries for a
few years.
Floods in India over a Decade :
India has faced many floods during the past years. Here is the list of some worst floods
which were occurred in last decade.
i. Kerala floods in 2018
ii. Gujarat floods in 2017
iii. Chennai floods in 2015
iv. Jammu and Kashmir floods in 2014
v. Uttarakhand floods in 2013
vi. Bihar floods 2008

Kerala Floods 2018
Kerala state has an average annual precipitation of about 3000 mm. The rainfall in the
state is controlled by the South-West and North-East monsoons. About 90% of the rainfall occurs
during six monsoon months. The high intensity storms prevailing during the monsoon months result in
heavy discharges in all rivers and causes severe floods.
Kerala experienced an abnormally high rainfall from 1 st
June 2018 to 19 th
2018.This resulted in severe flooding in 13 out of 14 districts in Kerala state. As per Indian
Meteorological Department (IMD) data, Kerala received 2346.6 mm of rainfall from 1 st
June 2018 to
19 th
August 2018 and expected rainfall was 1649.5 mm. This rainfall was about 42 % above the normal.
The rainfall over Kerala during June , July and 1 st
to 19 th
August was 15% ,18% and 164% respectively,
above normal.
Water was released from several dams due to heavy rainfall in their catchments. The
water levels in several reservoirs were almost near their Full Reservoir Level (FSL) due to continuous
rainfall from 1 st
June. As per annual records of IMD, it has been found that the rainfall depths recorded
during 15 th
– 17 th
August 2018 were comparable to the severe storm that occurred in the year 1924.
The storm of 15 th
– 17 th
August 2018 was spread over the entire Kerala with eye centred
at Peermade , a place between Periyar and Pamba sub basins . The storm was so severe that the gates of
35 dams were opened to release the flood runoff. All 5 overflow gates of the Idukki dam were opened
for the first time in 26 years. Heavy rains in Wayanad and Idukki caused severe landslides and left the
hilly districts isolated. On August 15 th
, Kochi International Airport , India's fourth busiest in terms of
international traffic , and the busiest in state , suspended all operations until August 26 , following
flooding of its runway. As per the reports in media, the flooding has affected hundreds of villages,
destroyed several roads and thousands of homes have been damaged. The Kerala State Disaster
Management Authority placed the state on a red alert as a result of the intense flooding. A number of
water treatment plants were forced to cease pumping water, resulting in poor access to clean and
potable water, especially in northern districts of the state