The overflow of the river on its banks and the submerging of vast areas of its floodplain. Floods are an important component of the hydrological cycle of the drainage basin, here in this article we will learn Floods in India in detail.
Flood is a natural hazard that occurs in direct response to heavy rains and becomes a disaster when they cause great loss of life and property can be expected.
Causes of Floods in India
1. Metrological Factors
a) Heavy rainfall
In India, from mid-July to the end of Sep is the rainy season, the rainwater flows and collected in dams if the water collected exceeds the storage capacity it causes floods in those areas.
Usually, we can see these types of floods in the West Coast Region of West Ghat, Assam and the sub-Himalayan plains of West Bengal and Indo-Gangetic.
A cyclone is caused by atmospheric disturbances around a low-pressure zone and is usually accompanied by severe storms and extreme weather conditions.
Cyclone flooding is a very common phenomenon on the eastern coasts of Tamil Nadu, Andhra Pradesh, Odisha, and West Bengal. Nowadays we can see at least 1 Cyclone in a year.
c) Cloud Burst
Cloud Burst is the extreme precipitation in a short period, sometimes accompanied by hail and thunder, which can create flood conditions.
These conditions are particularly noticeable on the slopes of the mountains, as falling water rushes to the ground and the inhabitants have to suffer from destructive floods.
d) Global warming
Global Warming is a gradual increase in the global temperature of the Earth’s atmosphere which causes greater damage.
From Global Warming the glaciers of the Himalayas and other big mountains of the world start melting and the sea level rises, which eventually leads to floods.
2. Physical Factors
a) Large catchment area
The area from which rainfall flows into a river, lake or reservoir is known as a catchment area.
If the catchment area capacity of holding water exceeds then it results in flooding on the land, Many times it destroys the crops by entering agricultural land.
Afforestation in the catchment area prevents floods.
b) Inadequate drainage arrangement
Drainage is the natural or artificial removal of surface water from an area with excess water.
If the drainage arrangement is not properly planned the water gets stuck at the time of heavy rains, mainly you can see this in cities because of the congested area.
3. Human Factors
Deforestation is the removal of trees from the forest that is then converted to non-forest are which is utilized for commercial and other purposes.
Trees prevent sediment runoff and forests hold more water than farms. If a river cannot hold a lot of water then, it will rise above its banks. This is when floods happen.
Siltation is the contamination of water by small particles of silt or clay which reduces the carrying capacity of rivers and dams, hence that leads to flooding.
Proper periodical plan to take out of silt from the Dams and rivers can prevent flooding by increasing the capacity of water to store.
c) Faulty Agricultural and irrigational practices
Some upland farmers will leave soil and water in the rivers, the accumulation of waste particles into the river causes floods. Most of the traditional farmers do the same mistake.
Some experts want maize to be completely forbidden on steep slopes because its bare rows contribute a lot to floods.
e) Collapse of dams
Many dams are built along the rivers of India to store water and provide it to people for their daily necessities.
But the problem is, everything human-made on this planet has the age limit. Likewise, one or another day even dams should get weaker and may explode. The sudden flow of water to the surface will cause flooding.
f) Accelerated urbanization
Urbanization refers to the movement of people from rural areas to urban areas for various purposes.
As cities are overcrowded, the drainage system is not maintained properly and water will remain on roads, heavy rains will cause floods which creates greater damage to life and property.
Flood-prone areas (the geographical account of flood-prone areas in India)
The Rashtriya Barh Ayog (RBA), or the National Flood Commission established by the government in 1976, provided statistical evidence of the flood problem in the country.
The commission took the maximum area affected by floods in the state in any one year as its flood-prone area and added up the flood-prone areas of all the states to get the flood-prone area of the country.
Out of a total area of 329 million hectares in India, around 45 million hectares are exposed to floods.
Flood-Prone Areas in India Map
The geographical distributions of flood-prone areas in India are:
1. The Ganga River Region
Uttar Pradesh and Bihar are the most affected states and represent more than 1/3rd of the country’s flood-prone area.
In Uttar Pradesh, Ganga receives a large amount of water and sediment from the Himalayan territories such as Gomti, Gandak, Ghaghra, Kose and Rapti, Ramganga, etc.
It also receives abundant water and sediments from peninsular rivers such as Chambal, Betwa, Ken (tributaries of Yamuna), etc.
Ganga Delta is often flooded (leads to the erosion of banks near Farakka Dam). In June 2013, a multi-day cloud burst centered in Uttarakhand in northern India caused devastating floods and landslides remained as the worst disaster in the country.
While spilling of rivers like Rapti, Ghaghara, Sharda, and Gandak are responsible for floods in Eastern U.P.
The congestion of the drainage causes floods in the west of Uttar Pradesh, in areas such as Agra, Mathura, and Meerut. Erosion occurs in some places on the left banks of Ganga, and on the right banks of Ghaghra and Gandak.
In Bihar, floods are largely confined to the Northern part of the state. Rivers such as Burhi Gandak, Bagmati, Kamala, and other smaller rivers of the Adhwara group, the Kosi in lower reaches and Mahananda spill over their banks causing considerable damage to crops, and dislocation of traffic.
In West Bengal, the southern and central regions of the state are flooded with Mahananda, Bhagmati, Ajoy, Damodar, etc. Due to the insufficient capacity of the river channels and the effect of the tides.
There are occasional floods caused by Damodar River even after the construction of 4 dams and a Barrage under Damodar Valley Project.
2. Brahmaputra River Region
In the Brahmaputra regions, floods are an annual feature. The main causes of flooding in the Brahmaputra river system are summarized below:
a) The Brahmaputra has 34 major rivers, which bring huge amounts of water and silt that cause flooding.
b) Very intense rains that exceed 250 cm per year.
c) The narrowness of the Brahmaputra valley with a maximum width of about 81 km surrounded by hills.
d) A large amount of Silt deposited by the Brahmaputra and its tributaries in the river bed (made it shallow) considerably and has reduced the carrying capacity of the river.
e) Occasional earthquakes, such as the earthquakes of 1897, 1930, 1950 and 1984, caused changes in the course of rivers.
f) The very high population pressure, mainly to the migration of Bangladesh and some other states of India has forced people to live in flood-prone areas.
The valley of Assam is considered one of the most affected areas of the country. Although most of the areas affected by the floods in Assam are rural, some urban areas are also frequently flooded and about 45% are flood-prone.
3. North – West Region
The problem of floods is less serious than in other regions. The main problem is inadequate drainage of the surface that causes flooding in large areas.
In the plains of Punjab and Haryana, much of the rainwater flows into a flooded and poorly drained area.
The main and secondary rivers, such as Sutlej, Beas, Ghagghar, and Markanda, are the flooded areas during the rainy season.
In Punjab, floods are mainly due to the obstruction of natural drainage by deficient artificial structures. Some of the main channels of the Bhakra system do not follow the natural flow and create obstacles.
Secondly, the NH1 and the main railway line are almost perpendicular to the natural flow. The cultivation of areas near riverbanks and construction activities in low-lying areas, particularly in cities such as Ludhiana and Patiala, have jointly created obstacles to the natural flow of water and have caused serious damage to road and Rail traffic in Punjab due to floods.
Floods in Haryana are less frequent and occur once a decade. The Saucer shaped the topography of the state does not allow free flow of surface runoff and even moderate rainfall can cause flooding. Ambala and Rohtak have been severely affected by floods in the last 2 decades.
The Ghagghar River frequently floods Punjab, Haryana, and Rajasthan during the rainy season, submerging a huge area.
In the northwest basin covering Jharkhand and Himachal Pradesh, Sutlej, Beas, Ravi, and Chenab are causing floods in a large area.
Floods occur periodically in Jhelum and its tributaries, causing an increase in water level in the lake, which sometimes threatens Srinagar.
Similarly, Chenab and its tributaries, such as the Tandi River, often flood the densely populated areas of Jammu and Akhnoor.
In 2004, large parts of Himachal Pradesh were threatened by severe flooding in the Sutlej due to a large amount of water released by the Rakas Lake in Tibet.
4. Central India and Deccan Region
Floods are not a serious problem in this region since most rivers have well-defined and stable courses.
However, the deltas of the Mahanadi, Godavari, Krishna and Kaveri rivers suffer occasional flooding due to large-scale silting and the subsequent change in river flow.
The indiscriminate felling of trees in the basins of large rivers has complicated the problem of flooding. The high tide at the time of the flood adds the problem of flooding. The lower course in Narmada and Tapi are also subject to flooding.
In Andhra Pradesh, the problem of floods is limited to the overflowing of small rivers and the submergence of marginal seas and Kolleru Lake.
The Godavari and Krishna rivers have a serious drainage problem and face flooding, especially as a result of cyclonic storms. The Godavari Basin is known for its recurrent floods.
In Orissa, the floods are caused by the intermingling of floodwater of Mahanadi, Brahmani, and Baitarni in their common delta, causing considerable devastation.
The problem is noticeable when the flood synchronizes with high tides. The silt deposited by these rivers in its delta region raises the river bed, resulting in frequent overflows or the breaking through new channels that cause great damage.
The small rivers of Kerala, originating in the Western Ghats and flowing into the Arabian Sea, cause considerable damage when a sudden flood occurs.
Recently, on August 8, 2018, severe floods hit the state of Kerala, in southern India, due to the unusual rains during the monsoon season. It was the worst flood in Kerala in almost a century. More than 483 people have died and 14 are missing.
The above description of flood-prone areas indicates that one or other part of the country is affected by floods and flooding is almost an annual phenomenon.
Also, read about Facts About India
Factors Responsible for Floods in Himalayan and Peninsular Regions
Factors responsible for floods are different in Northern Plains of India, Peninsular India, and the Himalayas.
Factors responsible for floods in Northern Plains of India
a) The rivers of the Himalayas usually change course due to sedimentation and overflow. As the Himalayan rivers are in the youth stage, they are actively eroding and generating large amounts of sediments.
These sediments are deposited in their courses in the Indo-Gangetic-Brahmaputra plains. This leads to an overflow and a change in the course of the river, flooding large areas in the alluvial plains.
b) The monsoon rain combined with the rapid melting of the glaciers during the southwest monsoon season is causing severe flooding in the Himalayan and Indo-Ganga-Brahmaputra plains.
c) The Indo-Ganga-Brahmaputra plains are normally rich in groundwater due to the alluvial nature of the soil. There is a much lower possibility of percolation of floodwaters into sub-surface areas causing a significant overflow.
d) Impact of Development Activities
i) The development of canal irrigation on a large scale in the northern plains has raised the water tables. This has prevented the downward infiltration of excess water during monsoon season.
ii) Deforestation in the upper watersheds of Shivalik, Assam Himalayas, and the Chotanagpur plateau has caused widespread flooding in the region.
iii)) Jhumming cultivation in the North-east has led to deforestation and subsequent flooding in the region.
iv) Obstruction of free drainage due to developmental projects such as Dams and Hydel projects. Drainage congestion caused by faulty location and design of Bridges, Railways, and roads.
The construction of embankments, industrial and urban developments has led to reducing infiltration.
v) The intense development activity in the densely populated floodplains significantly disrupted the natural flow patterns of the rivers/streams, as well as reducing runoff. This leads to floods in an unpredictable manner in new areas.
The factors responsible for floods in Peninsular India
a) Shallow Courses in Hard Rock strata
The floods by the peninsular rivers are caused by heavy monsoon rains. The peninsular rivers cannot absorb this excess water because they flow in rocky terrain and avoid the infiltration of water in the subsoil.
b) Exposure to Cyclones and Storms
Cyclones and depressions in the Bay of Bengal led to strong winds and heavy rainfall. The damage is caused by strong winds and floods. These are typical to the coastal areas of Andhra Pradesh, Orrisa, West Bengal, and Tamil Nadu.
c) Human-made faults
The intense development activity in the Western Ghats has led to deforestation and the generation of huge amounts of solid waste.
This resulted in an increase in sediment deposits carried by rivers that originate in the Western Ghats. Rivers deposit silt in their own shallow water, which will eventually cause flooding.
The construction of dams and Hydel projects by interfering with the natural hydrology of the rivers has also resulted in flooding.
Criteria to Identify Flood-Prone Areas in India
a) Demarcate Floodplain Zones of Rivers
The flood areas of the river are areas naturally exposed to flooding. The river requires a careful study of its route for a reasonable period of time to determine the area of the floodplain zone.
The observation includes flood levels in different stretches especially in the middle course, due to the shallow course and densely populated regions that should be studied.
Changes caused by anthropogenic and natural factors in the flood cycle over a prolonged period.
b) Studying and Monitoring Hydro Characteristics of the River
The monitoring of river flows regimes at different stretches along with the assessment of groundwater levels in different locations allows knowing the level of infiltration and the capacity of the river to absorb excess water.
c) Monitor and Develop Maps of Cyclones and Storm Tracks
The deltaic areas are prone to flood by peninsular rivers and accentuated by tropical cyclones and storms. So by monitoring and developing cyclone and storm trajectory maps, we can take precautions to mitigate disasters.
d) Study of Siltation rates, Sediment loads and Flow Dynamics
Data collection and subjecting to computer modeling to understand the implications through simulating the situation can project future happenings and find possible solutions.
e) Survey / Studying coastal Morphology in detail helps to locate flood-prone areas as well.
Also read: Rivers in Karnataka