Floods

When Surface run-off exceeds the carrying capacity of the river channels, streams, lakes and other inland water in which they flow bodies or the infiltration rate of the ground we call it a Flood. It flows into the neighbouring low-lying areas which generally do not experience natural water flow.

Types of Floods:

1. River Floods: These are caused when consistent rain or snow melt forces a river to exceed capacity.  Generally, River floods inundate the flood pains of a catchment.
   • Flood plain: An area of flat land adjacent to a stream/river that experiences flooding during periods of high discharge. It stretches from the banks of the channel to the base of the enclosing valley wall.
2. Coastal Floods: These are caused by storm surges associated with tropical cyclones and tsunamis.
3. Urban Floods: When urban areas are flooded due to excessive rainfall or overflowing water bodies, leading to the submergence of streets, homes, and public spaces.It is flooding in urban areas.
4. Flash Floods: These are caused by rapid and excessive rainfall that raises water heights quickly, and rivers, streams, channels or roads may be overtaken.
5. GLOF: When natural or artificial walls that contain the Glacial lakes burst, it creates a Glacial lake outburst flood. We have covered this in greater detail in the later part of this chapter.

Cloudbursts

A cloudburst is an extreme weather event where a sudden, intense rainfall of more than 100 mm per hour occurs within a localized area, often leading to flash floods and landslides. It typically happens in mountainous regions due to the rapid orographic lifting of moist air, causing intense precipitation in a short duration. Reasons for Occurrence: Orographic Effect: When moist air rises quickly over mountains, it cools rapidly, leading to heavy rainfall. Convectional Rainfall: Excessive heating causes warm air to rise sharply, condensing rapidly to form heavy rain. Wind Pattern Disturbances: Unstable monsoon winds and interactions with western disturbances increase the chances of cloudbursts. Climate Change: Rising global temperatures increase moisture retention in the atmosphere, making cloudbursts more frequent and intense. Recent Examples Uttarakhand (2023): Cloudburst triggered flash floods and landslides in Chamoli, leading to casualties and destruction. Leh (2010): A massive cloudburst in Ladakh caused severe flash floods, killing 200+ people and damaging infrastructure. Amarnath (2022): Cloudburst near the Amarnath cave led to a sudden flood, causing multiple casualties. Kedarnath Floods (2013): Cloudbursts remain highly unpredictable, requiring early warning systems and disaster preparedness to mitigate risks.

Causes of Floods

Natural causes:

• Meteorological causes: High-intensity rainfall for a considerably longer period. Cloud Burst, i.e. High-intensity rainfall in a short time, often causes flash floods.
• Storm surge (in the coastal areas) is the surging of ocean water into the land areas from the seas.
• Melting of ice and snow – such as in GLOF.
• The presence of eroded material in the stream is due to a higher rate of soil erosion. This is one of the main causes of floods in the Koshi River.

Human Causes:

The natural causes are further complimented by the human causes:

• Reduction in the infiltration rate due to pavement of the surface.
• Colonisation of flood plains.
• Disturbances along natural drainage channels or their blocking.
• Unscientific agricultural practices – causing infiltration rate to drop (creating runoff) and increasing soil erosion.
• Indiscriminate deforestation,
• Poor water and dam management practices.

Consequence & Control of Floods:

Negative consequences of Flood:

• Economic Damage: Total disaster-related damages amount to 62% of losses by all disasters combined. Due to the loss of standing crops and cattle.
• Cost to life: 2nd most lethal disaster in India after earthquakes (42%). Floods take 33% of all lives taken by disasters.
• Millions of people are rendered homeless.
• Spread of diseases like cholera, gastro-enteritis, hepatitis and other water-borne diseases spread in the flood-affected areas.
• Creates food shortages: Destroy valuable crops every year and often cattle are washed away.
• Damages physical infrastructure such as roads, rails, bridges, human settlements and communication infrastructure.
• Cattle and livestock loss:

Positive contributions of flood

• Every year, floods deposit fertile silt over agricultural fields which is good for the crops. Majuli (Assam), the largest riverine island in the world, is the best example of good paddy crops after the annual floods in Brahmaputra.
• Groundwater recharge is possible due to standing floods.

Areas affected by Flood:

Around the world, South, Southeast and East Asian countries, particularly China, India and Bangladesh, are frequent and equally disastrous.

Rashtriya Barh Ayog (National Flood Commission) identified 40 million hectares of land as flood-prone in India. [shown in map]:

• Assam, West Bengal, Bihar, East UP (flooding rivers), coastal areas of Orissa, Andhra Pradesh, Tamil Nadu and Gujarat (cyclone) and Punjab, Rajasthan, Northern Gujarat and Haryana (flash floods).
• Rajasthan, Gujarat, Haryana and Punjab are also been inundated(flooded) in recent decades due to flash floods – partly because of the pattern of the monsoon and partly because of the blocking of most of the streams and river channels by human activities.
• Sometimes, Tamil Nadu experiences flooding during November- January due to the retreating monsoon.

Kerala Floods

Western Ghats Floods: The Monsoon in 2018 led to floods in Kerala & Parts of Karnataka ringing alarm bells for the administrations in the State of Goa, Gujarat, Karnataka, Kerala, Maharashtra and Tamil Nadu. The Idukki Dam on the Periyar River contributed to the 2018 Kerala floods due to excessive rainfall, forcing authorities to open all five spillway gates after the reservoir reached full capacity, worsening downstream flooding. The government told to the Committee on Government Assurances in Rajya Sabha that Over 56,000km of Ecologically sensitive areas (ESA) in western Ghats could not be earmarked as ‘no-go’ zones due to state governments” insensitivity’.

Steps to be taken:

Mitigation of flood risk:

• Check-bunds: to control the flow of the water.
• Construction of Levees: To control the breach of water from the water banks of the rivers.
• Regular De-silting of water channels: So that the channels can accommodate more water flow.
• Reducing the risk from seas: construction of break-waters and sea-walls to prevent storm surge and some safeguard against slowing Tsunami waves.
• Removal of Human population from river channels and depopulation of the flood plains- particularly in western and northern parts of the country which experience flash-floods.
• Interlinking of rivers and creation of canal.
• Robust Water management and Dam management with best available practices and technology.
• Warning and Information sharing system between national, state and local bodies.
• Cyclone centres may provide relief in coastal areas which are hit by a storm surge.
• [rest urban Flooding]

Preparedness and Response:

• Flood Risk maps
• Flood forecasting and early warning system (FFEWS) launched by Kolkata Municipal Corporation.

Steps taken by the Government:

Policy Measures

• Rashtriya Barh Ayog (National Flood Commission), 1976 created under M/o Agriculture for Flood Management.
• Task force on Flood management and erosion, 2004: To suggest ways to minimize the damage & recurrence of floods. It had suggested immediate short-term & long-term measures.
• The frequency and intensity of extreme flood events in Uttarakhand have increased four-fold since 1970. More than 85% of districts in Uttarakhand are hotspots of extreme floods and its associated events – Council on Energy, Environment and Water (CEEW)
• Madhav Gadgil Report & Kasturi Rangan committee: Have recommended categorising Western Ghats as ESA (56,000sqkm area) which would mark them as no-go zones for polluting activities and deforestation, and large-scale deforestation, mining, and construction are continuing unabated, hurting the ecology of the Western Ghats. “Insensitivity towards an ecology of the Western Ghats is making the six states vulnerable to floods and landslides.”
• The government has put a draft notification regarding this, but the six states couldn’t be brought on the board for action.

Western Ghats Ecology Expert Panel (WGEEP) (2011)

Western Ghats Ecology Expert Panel (WGEEP), also known as the Madhav Gadgil Report (2011) was formed to study and recommend conservation measures for the Western Ghats. The report highlighted that unregulated development, deforestation, quarrying, and encroachment had made the region highly vulnerable to floods and landslides. It recommended classifying the Western Ghats into Ecologically Sensitive Zones (ESZs) and proposed strict land-use regulations to prevent environmental degradation. However, the report faced resistance from state governments and industries, leading to its partial rejection. It recommended the following: Three-tier Ecological Sensitivity Zones (ESZ 1, 2, and 3) with strict environmental regulations in ESZ 1. It called for a ban on large-scale development, mining, and deforestation in ecologically sensitive areas. Warned that uncontrolled urbanization and illegal activities would lead to increased floods, landslides, and biodiversity loss. Proposed community-based conservation with strong local governance and participation. Faced strong opposition from state governments and commercial sectors, leading to non-implementation of several recommendations.

Kasturirangan Committee (2013)

The Kasturirangan Committee (2013) was formed to review the Madhav Gadgil Report and propose a more balanced approach between conservation and development in the Western Ghats. It recommended the following: The committee reduced the ecologically sensitive area from 75% (as proposed by Gadgil) to 37%, focusing mainly on forested regions. It allowed regulated development in non-ESA areas, making it more industry-friendly. Excluded plantations and agricultural lands from conservation regulations. Recommended satellite-based monitoring and better land-use planning to mitigate disasters. However, experts criticized it for being less strict on mining, construction, and industrial activities, which were major causes of floods and landslides in the region. The 2018 Kerala floods and landslides validated the warnings of both reports, proving that unregulated development, deforestation, and quarrying contributed significantly to disasters.

Executive measures

• WRIS (water resource information system) (Under the Ministry of Jal Shakti) was created by a notification in 2018 as a single window source of updated data on water resources, including the water level data of the reservoirs in real-time. Now, Warning and Information sharing can be possible through WRIS.
• National Hydrology Project: A central scheme under which the Hydro-meteorological data will be stored and analyzed on real real-time basis and can be seamlessly accessed by any user at the State, District & Village levels.
• IFLOWS: developed by M/o ES to provide early warning for urban flooding, especially during high rainfall events and cyclones. It will be possible to have an estimate of the flood inundation three days in advance, along with immediate weather updates. It is functional currently in Chennai & Mumbai.
• Dam rehabilitation and Improvement Project (DRIP) to improve safety andoperational performance.
• MAUSAM app– created by IMD for Weather forecast and warning to citizens
• National Monsoon commissionfor dynamic monsoon forecasts
• Flood forecasting and early warning system (FFEWS) launched by Kolkata Municipal Corporation. It is the 1^st Comprehensive city-level flood forecasting system in the country.

Mitigation Measures

• South Asian Flash Flood Guidance System (FFGS) launched by IMD, is aimed at helping disaster management teams and governments make timely evacuation plans ahead of the actual event of flooding.
  A dedicated FFGS centre will be established in New Delhi, where weather modelling and analysis of rainfall data observations from member countries will be done.
• “Atmosphere & Climate Research-Modelling Observing Systems & Services (ACROSS)” during 2017-2020 and establishment of National Facility Airborne Research during 2020-21 and beyond.
  1. It is an atmospheric science program of M/oES.
  2. Aim: It addresses different aspects of weather and climate services, which includes warnings for cyclones, storm surges, heat waves, thunderstorms etc. Each of these aspects is incorporated as nine sub-schemes under the umbrella scheme.
  3. Atmospheric, Climate Science and Services.
  4. Numerical Modeling of Weather & Climate.
  5. Physics and Dynamics of Tropical Clouds.
  6. Agro Meteorology.
  7. Aviation Services.
  8. Centre for Atmospheric Technology.
  9. High Impact Severe Weather Warning System.
  10. Metropolitan Air Quality and Weather Service.
  11. Monsoon Mission of India.
  12. It is implemented in an integrated manner through the four institutes: IMD, IITM, National Centre for Medium-Range Weather Forecasting (NCMRWF) and NCOIS.
• National Facility for Airborne Research (NFAR): It comes under the Indian Institute of Tropical Management (IITM), Pune. Developed by MoES under the 12^th FY Plan.
  1. Under this, a state-of-the-art research aircraft equipped with instruments will be used for atmospheric research.
  2. It will take simultaneous measurements of aerosols, trace gases, cloud microphysics and large-scale meteorological parameters at high temporal resolution and at different altitudes in different seasons over the Indian subcontinent.

Urban Flooding

Urban Flooding: When urban areas are flooded due to excessive rainfall or overflowing water bodies, leading to the submergence of streets, homes, and public spaces. It is flooding in urban areas.

Urban waterlogging: When heavy or continuous rainfall in a short period of time exceeds the urban flood discharge capacity. This may lead to Urban flooding.

Reasons behind Urban Flooding:

• Old Drainage system: which is unsuited for the unplanned overgrown city.
• Poor Maintenance of Drainage: frequently gets clogged, like in the old cities of Hyderabad, and Mumbai & rapidly growing urban centres of Gurugram & Delhi.
• Disappearing Natural wetlands: In cities like Delhi, Hyderabad, Bengaluru, Chennai etc. thousands of ponds and lakes have been encroached. In tier 2 and 3 towns too, a similar trend is seen.
• Sedimentation of streams and canals: For example, in the 2014 Srinagar floods it was found that the emergency flood channel had disappeared due to sedimentation and encroachment over several decades.
• Rigid pavement and water permeability: Our cities are becoming increasingly impervious to water, not just because of increasing build-up but also because of the nature of the materials used.
• Increased intensity of rainfall due to Climate Change: It has increased the extreme weather events and incidence of flash floods all around the world.
• Bad Reservoir Management: During heavy rainfall, dams have to release water for example in the 2014 Srinagar floods, in the 2018 Chennai flood Chembarambakkam Tank released water, and in the 2020 Hyderabad floods Himayatsagar reservoir on the Musi River released water. Only 7% of Indian dams have emergency action plans.
• Data and Flood Prediction Systems: There is a lack of data sharing between reservoirs and the meteorological department.

Risks associated with Coastal cities

• Rising Sea Level: It has affected the flow of underground drains in coastal cities during high tides, especially in Mumbai where a lot of city is built on reclaimed land.
• Frequent flooding due to high tides and Storm surge.

Risks associated with landlocked cities

• Colonisation of the floodplains reduces the capacity of the waterbody to absorb additional runoff, intensifying the flooding.
• Poor slope and poorly designed drainage.

Solutions:

Legislative, policy and administrative measures

• Preventing Terrain alteration: this needs to be strictly regulated and a ban on any further alteration of terrain needs to be introduced. Often it is seen that urban lakes are
• Re-Planning Drainage system: which is easier to clean and de-silt, recognizes the importance of natural wetlands and artificial lakes; It should work on the principle of water security.
• Leveraging existing Schemes: such as Smart Cities Mission, Atal Mission for Rejuvenation & Urban Transformation (AMRUT) and National Heritage City Development & Augmentation Yojana (HRIDAY).
• Strict implementation of Environment Impact Assessment (EIA).

Technical intervention

• The idea of a sponge city: making cities more permeable to absorb the rainwater, which is then naturally filtered by the soil and allowed to reach urban aquifers. Use of Permeable material for roads and pavement construction to allow stormwater to trickle into the ground, and the idea of green roof.
• Rainwater Harvesting: Directing rainwater underground through specially designed recharge wells or storing in over-the-ground storages integrated with buildings.
• Reviving old water storage structures: There are hundreds of traditional structures, temple tanks, baolis etc. which can be revived to store excess water.
• Drainage Information system: this can help establish a systematic procedure for pre-monsoon de-silting, wastewater management, and flow data analysis for better design and is available to all stakeholders.
• Inter-river linkage: This can help in diverting excess water from one catchment to another.

What is a Glacial Lake?

A lake formed due to glacial activity is known as a Glacial lake. These lakes are often surrounded by drumlins, along with other evidence of glaciers such as moraines and eskers etc. Glacial Lake Outburst Flood (GLOF): When natural or artificial walls that contain the Glacial lakes burst, it creates a Glacial lake outburst flood. For example, a terminal moraine can act as a wall, behind which the meltwater from the glacier can collect. If this burst, it will create a GLOF.

GLOF

When natural or artificial walls that contain the Glacial lakes burst, it creates a Glacial Lake Outburst flood (GLOFs).

When glaciers melt, the water in glacial lakes accumulates behind loose, natural “glacial/moraine dams” made of ice, sand, pebbles and ice residue. A GLOF refers to flooding that occurs when the water is dammed by a glacier or a moraine is released suddenly.

Causes:

1. According to NDMA, glacial retreat due to climate change occurring in most parts of the Hindu Kush Himalaya has given rise to the formation of numerous new glacial lakes, which are the major cause of GLOFs.
2. Dislodging of Glacier: A significant slice of the glacier, dislodged by a landslide, according to some satellite images, produced roaring torrents in the Rishiganga and Dhauliganga rivers in Chamoli district, near Tapovan Hydroproject.
3. Landslip into the glacial lake: another potential reason for the disaster
4. Concern for earthquake risk in the region
5. Dam and other infrastructure construction: By one estimate, if the national plan to construct dams in 28 river valleys in the hills is realised in a few decades, the Indian Himalayas will have one dam for every 32 km, among the world’s highest densities. For example, a moderate quake in 1991 in the region where the Tehri dam was built and the 2013 floods that devastated Kedarnath, pointed to the threat from seismicity, dam-induced microseismicity, landslides and floods from a variety of causes, including unstable glacial lakes and climate change.

Potential risks:

Since glaciers in the Himalayas are in a retreating phase, glacial lakes are growing and pose a potentially large risk to downstream infrastructure and life.

An “Inventory and Monitoring of Glacial Lakes / Water Bodies in the Himalayan Region of Indian River Basins”, sponsored by the Climate Change Directorate, Central Water Commission, and done by the National Remote Sensing Centre during 2011-15, found that there are 352, 283 and 1,393 glacial lakes and water bodies in the Indus, Ganga and Brahmaputra basins respectively.

Reducing the Risk of GLOFs:

1. Identification and mapping: Potentially dangerous lakes can be identified based on field observations, records of past events, geomorphologic and geotechnical characteristics of the lake/dam and surroundings, and other physical conditions. For example: Synthetic-perture radar imagery can automatically detect changes in water bodies, including new lake formations.
2. Taking structural measures to prevent sudden breaches.
3. Establishing a response mechanism to save lives and property in times of breach.
4. Warning system: Since GLOFs are small occurrences globally and are mostly found in the Himalayan region, there are very little number of warning systems. GLOF early warning system is created by Sikkim recently.

 Government steps to reduce the risk of GLOFs

Subsequent to the Teesta-III Hydroelectric dam collapse in October 2023, the Central Water Commission (CWC) has decided to review the design flood of all the existing and under-construction dams vulnerable to Glacial Lake Outburst Floods (GLOFs) to ensure their adequate spillway capacity for a combination of Probable Maximum Flood/Standard Probable Flood and GLOF. Further, GLOF Studies have been made mandatory for all new dams planned to have Glacial Lakes in their catchments.

CWC monitors 902 Glacial Lakes and Water Bodies (including 477 Glacial Lakes & Water Bodies, having a water spread area greater than 50 ha and 425 Glacial Lakes having a size of 10 ha to 50 ha) during the period from June to October every year. This enables the detection of relative change in the water spread area of Glacial Lakes & Water Bodies, as well as identifying the ones which have expanded substantially during the monitoring month, from a disaster perspective.

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