EXPANSION OF URBAN AREAS INTO FLOOD PRONE ZONES

The study shows that urban areas in India are expanding into flood-prone zones at an alarming rate, doubling since 1985. This poses a significant risk due to increased instances of flooding, leading to life and livelihood losses.

Examples:

> Libya, which suffered from devastating flooding in September 2023, had an 83% increase in settlement extent in the worst flood zones.

> Pakistan, experiencing catastrophic flooding both in 2022 and 2023, witnessed an 89% increase in settlements in prone areas.

Middle-income countries, including India, have more urban settlements in flood-prone areas. The study underscores the urgency of considering flood-related risks in urban planning and making low-income housing more flood-resilient while implementing improved storm-water management.

Notable initiatives:

> Stormwater disposal system: The Brihanmumbai Storm Water Disposal System or BRIMSTOWAD, the project to overhaul Mumbai city’s old stormwater drainage system was started after the 2005 deluge.

> Water-sensitive urban design (WSUD in Australia): regards urban stormwater runoff, and wastewater as a resource rather than a nuisance or liability.

> Bioswales or ‘Rain Garden’ (New York): are landscape features that collect polluted stormwater runoff, soak it into the ground, and filter out pollution.

Conclusion:

Therefore, there is a need to include public open spaces within the urban fabric in the form of storm management infrastructure, which could help our cities transform into water- sensitive cities.

URBAN FLOODING AND HUMAN SETTLEMENT

Urban flooding is the term used to describe the flooding of land or property within a constructed environment, especially in locations that are more densely inhabited (like cities), as a result of excessive rainfall that exceeds the capacity of drainage systems. Urban flooding, in contrast to country floods (heavy rain over flat or low-lying terrain), is a result of both increased precipitation and unplanned urbanisation (catchments).

Causes Of Urban Flooding: 

Encroachment on drainage channels; unplanned tourism; climate change; Unplanned release of water from dams; Illegal mining

Impact Of Urban Flooding: 

Loss of life and property; Negative impact on Ecosystem; Negative impact on Human and Animal Health; Negative Psychological impact.

Climate Change Impact On Costal India Cities: 

Cropland turning unfit for production; Rise in sea level; Species Extinction; Chronic water scarcity; Increase in incidences of extreme events; Loss of biodiversity; Urban Heat Island.

Climate Smart Cities Assessment And Its Impact: 

 To inculcate a Climate-Sensitive Approach to Urban Planning and Development, the Climate Smart Cities Assessment framework, for 100 smart cities, was launched by the Ministry of Housing and Urban Affairs. 

 The framework has 28 diverse indicators, across 5 categories namely (i) Energy and Green Buildings, (ii) Urban Planning, Green Cover & Biodiversity, (iii) Mobility and Air Quality, (iv) Water Management and (v) Waste Management.

Sustainable Cities India Program: 

 The National Institute of Urban Affairs (NIUA) and the World Economic Forum have signed a Memorandum of Understanding (MoU) to work together on a jointly developed "Sustainable Cities India programme." 

 It aims to create an enabling environment for cities to generate decarbonization solutions across the energy, transport and built environment sectors.

Disaster Management - Flood Fued

✓ The devastating floods across North India have renewed attention on the dynamic between climate change, urbanisation, and the infrastructural lacunae that bedevil India’s large cities. 

✓ India is now right in the middle of the monsoon and it is only to be expected, given the topography of the hill States, that extended rains will cause landslips, landslides and pose extreme threats to life and property. 

✓ Himachal Pradesh, Punjab, Haryana and Delhi are among the States that have reported record rainfall and at least 60 deaths have been confirmed though the actual toll may be higher. However, it is the inundation of Delhi, a city that is not usually associated with rains, that has brought to national focus the disasters that lie in store. 

✓ In the terminology of the India Meteorological Department, Delhi received ‘excess’ and ‘large excess’ rain on five out of eight days, from July 3-10. On July 9, it recorded 221.4 mm of rain, more than the 209.7 mm that is the average for all of July. 

✓ While this contributed to the flooding, rainfall in the last few days has dramatically reduced. And yet, large parts of the city which include iconic landmarks such as the Red Fort and the Supreme Court, continue to be flooded. 

✓ Delhi’s officials have attributed this to the flooding of the Yamuna in upstream States, particularly at Yamunanagar in Haryana, with the barrages in Delhi unable to effectively regulate and redirect the river’s flow.

✓ While urban flooding is far more frequent in Bengaluru, Chennai and Mumbai, Delhi should no longer consider itself immune given that its population and infrastructural needs are only going to expand. 

✓ Much like the National Capital Territory evolved a joint management strategy to tackle air pollution, on realising that clean air is interdependent on action by all cities, these States must set aside their differences and evolve a joint strategy on countering future floods.

✓ This however elides the role of Delhi’s infrastructural development that through the years has given short shrift to restricting construction on the Yamuna’s floodplains, failed to prioritise the desilting of drains ahead of the monsoon, and scrimped on steps to avoid the large-scale concretisation of the city. Though there is the case that even upstream of Delhi, riverbed mining has meant that huge amounts of silt from Haryana block the natural flow of the river, blame games and pointing to “record rains” are unhelpful. 
✓ The increased probability of spells of extreme rain, given warming trends in the Arctic as well as the Arabian Sea, means that there will be several more instances of flooding in the future. 

Urban Flooding in Metropolitan Cities

 

Flash Floods in India

 

Flood Disaster in India

India is extremely susceptible to flooding. Over 40 million hectares (mha) of the 329 million hectares (mha) total geographic area are at risk of flooding. Floods are a frequent occurrence that result in significant human casualties as well as damage to property, infrastructure, and public services. The fact that flood-related damages are on the rise is cause for alarm.

In the past ten years, from 1996 to 2005, the average yearly flood damage was Rs. 4745 crore, compared to Rs. 1805 crore, the corresponding average for the prior 53 years. Numerous factors, such as a sharp rise in population, fast urbanization, an increase in economic and development activity in flood plains, and global warming, might be blamed for this.

Flood Zone Map:

Punjab, Haryana, the majority of the Gangetic plains, including Uttar Pradesh, North Bihar, and West Bengal, the Brahmaputra valley, coastal Andhra Pradesh and Orissa, and southern Gujarat are the primary flood zone in India. Kerala and Tamil Nadu are currently experiencing the full force of the floods. In September 2014, the Indian-administrated Jammu and Kashmir territory saw catastrophic flooding that affected the majority of its districts. Devastating floods and landslides were created in June 2013 by a multi-day cloudburst that was centered on the state of Uttarakhand in northern India. 

What is Flood:

Flood is a state of high-water level along a river channel or on the coast that leads to inundation of land. Floods are commonly associated with a stream or river. A stream floods when its discharge is greater than the capacity of its river channel. Excess water flows over the riverbanks and submerges the adjacent land which is usually dry. When it happens, the channel and the flood plain together allow passage of water.

Flood in India 2023:

Heavy rainfall during the 2023 monsoon season resulted in severe flooding and landslides across Northern India, primarily affecting residents in Himachal Pradesh, Punjab, Chandigarh, Uttarakhand, Jammu and Kashmir, Haryana, Rajasthan and Delhi. A monsoon surge, coupled with a western disturbance has led to the highest rainfall in decades in some parts of the region, causing nearby rivers to overflow, with flooding and landslides washing away vehicles, destroying bridges and roads, and disrupting power and electricity.

Over 100 individuals across Himachal Pradesh, Uttar Pradesh, and Delhi, have died over a two-week period of intense rain and flooding, with thousands of others evacuated to relief camps. The states of Rajasthan, Punjab, and Haryana experienced extensive waterlogging due to heavy rainfall.

Causes of Floods:

The causes of flood can be classified into two types first the Natural causes and second is the Anthropogenic Causes. The natural causes have been mentioned below:

Heavy rainfall:

Heavy rain in the catchment area of a river causes water to overflow its banks, which results in the flooding of nearby areas. The Assam floods are due to heavy rainfall in a short period of time.

Snow melt:

Snowmelt and glacial melt are gradual processes and usually does not cause major floods. But sometimes glaciers hold large quantity of bounded water, which may be suddenly released with melting of ice block resulting into Glacial Lake Outburst Floods (GLOFs). In June 2013, flashfloods in Uttarakhand that wiped out settlements and decimated lives are attributed to a GLOF in the Chorabari glacier.

Sediment deposition:

Riverbeds become shallow due to sedimentation. The water carrying capacity of such river is reduced. As a result, the heavy rainwater overflows the river banks. Frequent floods were observed in 2003, 2008, 2011, and 2013 near the deltaic region of the Mahanadi River due to the excessive sediment deposition.

Tropical cyclones and hurricanes:

These powerful weather systems often bring heavy rainfall and storm surges, resulting in widespread flooding in coastal and low-lying areas. In 2019, Cyclone Fani hit the eastern coast of India, resulting in heavy rainfall and storm surges.

Change in the course of the river:

Meanders, erosion of riverbeds and banks, and obstruction of flow due to landslides also lead to changes in river courses. The 2008 Kosi River flood resulted from heavy rainfall and a subsequent course change, leading to catastrophic flooding, displacement of thousands, and widespread damage in Bihar, India.

Tsunami:

Large coastal areas are flooded by rising sea water, when a tsunami strikes the coast.

Lack of Lakes:

Lakes can store the excess water and regulate the flow of water. When lakes become smaller, their ability to regulate the flow become less and, hence flooding.

The Anthropogenic Causes has been discussed below:

Deforestation:

The removal of trees and vegetation reduces the natural absorption of rainfall, leading to increased surface runoff and a higher likelihood of flooding. The devastating floods that hit the state of Kerala in 2018 were partially attributed to deforestation, as the loss of forest cover reduced the natural water-holding capacity of the region.

Urbanization:

Construction of buildings, roads, and other infrastructure reduces natural permeable surfaces, which can exacerbate surface runoff and overwhelm drainage systems. Chennai experienced severe flooding in 2015 due to heavy rainfall combined with unplanned urbanization. The city’s drainage systems were overwhelmed, resulting in widespread inundation and disruption.

Land use changes:

Alterations in land use, such as converting natural wetlands into agricultural or urban areas, can disrupt natural water retention and drainage patterns, increasing the risk of flooding.

Dam failures:

Structural failures or breaches in dams and reservoirs can release large volumes of water downstream, causing severe flooding. In 2019, the collapse of the Tiware Dam in Maharashtra caused flash floods in downstream villages.

Interference in drainage system:

Drainage congestion caused by badly planned construction of bridges, roads, railway tracks, canals etc. hampers the flow of water and results in floods.

Flood Vulnerability in India:

As per the Geological Survey of India (GSI), over 40 million hectares which is nearly 12 % of the total land area of India is prone to floods.

India receives an annual rainfall of 1200 mm, 85% of which is concentrated in 3-4 months i.e., June to September. Due to the intense and periodic rain, most of the rivers are fed with huge quantity of water, much beyond their carrying capacity leading to mild to severe flood situations in the region.

The major flood areas in India are in the Ganges – Brahmaputra – Meghna Basin which accounts for nearly 60% of the total river flow of the country.

Floods in India in Last 5 years:

This is a list of significant floods that have been documented in India. In India, floods are the most frequent natural calamity. The Brahmaputra, one of the heavier southwest rivers, as well as other rivers, often cause nearby communities to flood. Check the flood disaster from 2018 to 2023.

Kerala Flood in 2018 and 2019:

Kerala experienced a 23% overflow of the southwest monsoon in 2018, and August saw 96% above-average rainfall. Kerala, India, experienced significant rainfall on August 8 in the middle of the evening that was 116% over average, causing dams to overflow. The state received 310 mm (12 in) of rain over the last 48 hours. Since the water level had increased to almost overflow level as a result of severe rain, flooding nearby low-lying areas, nearly all dams had been opened. 35 of the state’s 54 dams have been opened for the first time ever. The leveling of wetlands is thought to be one cause. It has been said that the flood was a result of global warming.

Kerala was severely flooded on August 8, 2019, as a result of the monsoon season’s abundant rainfall. A low that tossed the Arabian Sea caused heavy convection over Kerala, which led to the severe rains. To safer locations and relief camps, thousands of people have been evacuated. As of August 19th, 2019, 121 persons had lost their lives as a result of rain-related incidents.

Assam Flood in 2020:

The state of Assam is susceptible to yearly flooding because of its tropical monsoon environment. The COVID-19 pandemic and the large flood of the Brahmaputra River in the Indian state of Assam are referred to as the “2020 Assam Floods.” Heavy rains in May 2020 caused the first floods, which affected 30,000 people and destroyed crops in five regions.

Uttarakhand Flood in 2021:

The Chamoli tragedy, also known as the 2021 Uttarakhand flood, started on February 7, 2021, near the Nanda Devi National Park, a UNESCO World Heritage Site in the outer Garhwal Himalayas of Uttarakhand state, India. It was brought on by a massive rock and ice avalanche that was triggered by debris that was displaced from Ronti mountain. The Rishiganga, Dhauliganga, and Alaknanda rivers—the main headstream of the Ganges—all experienced floods in the Chamoli area as a result. Over 200 people were murdered or missing as a result of the catastrophe. Most were laborers at the Tapovan dam construction site.

Assam Floods in 2022:

One of the worst floods Assam has ever experienced occurred in 2022, lasting over 7 months (from April to October 2022) in a series of waves. The Pre-Monsoon Rains, which began in the state on April 6, 2022, and the Monsoon Season that followed are the main contributors to the floods. A total of 5.6 million people were impacted, 4.7 million were displaced, 108,308 hectares of cropland were devastated, 3,660,173 animals were impacted, and 32 districts in the state were affected.

North India Flood in 2023:

In Northern India, the monsoon season of 2023 brought about severe flooding and landslides that predominantly affected the people living in Himachal Pradesh, Punjab, Chandigarh, Uttarakhand, Jammu and Kashmir, Haryana, Rajasthan, and Delhi. The heaviest rainfall in certain parts of the region in decades has been brought on by a monsoon surge and a western disturbance. This has caused local rivers to overflow, flooding and landslides to demolish bridges and roads, wash away cars, and impair power and electricity.

Consequences of Floods:

Loss of life and injuries: Floods can result in the loss of human lives and cause injuries, especially when people are caught unaware or unable to evacuate in time.

Damage to infrastructure: Floodwaters can cause severe damage to roads, bridges, buildings, and other infrastructure. This damage can disrupt transportation networks, communication systems, and essential services, making rescue and relief operations challenging.

Displacement and homelessness: Floods often force people to evacuate their homes and seek shelter in temporary accommodations or relief camps.

Impact on agriculture and food security: Floods can devastate agricultural lands and crops, destroy livestock leading to significant losses in the agricultural sector.

Water contamination and health risks: Spread of diseases like cholera, gastro-enteritis, hepatitis and other water-borne diseases spread in the flood-affected areas.

Environmental damage: Floods can cause erosion, sedimentation, and the destruction of natural habitats.

Soil fertility: Floods also make a few positive contributions. Every year, flood deposit fertile silt over agricultural fields which restores fertility of the soil.

Flood Prevention and Mitigation:

Structural Measures:

Dams and Reservoirs: Construction of dams and reservoirs to store excess water during heavy rainfall and release it in a controlled manner, reducing downstream flood risk.

Levees and Floodwalls: Building embankments, levees, and floodwalls along rivers and coastlines to contain floodwaters and protect adjacent areas from inundation.

Flood Diversion Channels: Creation of diversion channels or canals to redirect excess water away from vulnerable areas, reducing flood impact.

Flood Control Basins: Designing flood control basins or detention ponds to temporarily store and regulate floodwaters, preventing their rapid downstream flow.

Channelization: Modifying and straightening river channels to improve their flow capacity and efficiency, reducing the risk of overflow and flooding.

Floodplain Restoration: Restoring natural floodplains by removing obstructions, reconnecting floodplain habitats, and creating additional space for water storage during floods.

Non-Structural Measures:

Flood plain Zoning and Land Use Planning: Implementing zoning regulations that restrict construction in high-risk floodplain areas, ensuring that development is appropriately located and mitigating potential flood damage.

Early Warning Systems: Establishing robust early warning systems that use technology and community engagement to provide timely alerts and evacuation guidance to vulnerable populations.

Flood Insurance and Financial Mechanisms: Promoting the availability of flood insurance to incentivize risk reduction measures and provide financial protection to individuals and businesses affected by floods.

Public Awareness and Education: Conducting public awareness campaigns to educate communities about flood risks, safety measures, and preparedness strategies, fostering a culture of resilience.

Urban Drainage Systems: Developing and maintaining efficient stormwater drainage systems in urban areas to manage excess rainfall and prevent waterlogging and urban flooding.

Ecosystem-Based Approaches: Preserving and restoring natural ecosystems, such as wetlands and mangroves, which act as natural buffers and absorb floodwaters, reducing flood impacts.

Integrated Water Resources Management: Adopting an integrated approach to water resources management that considers the entire watershed, balancing water allocation, flood control, and environmental sustainability.

Urban Floods

What is Urban Flooding:

Urban flooding refers to the inundation of land or built-up areas, particularly in densely populated locations such as cities, due to excessive rainfall that surpasses the capabilities of drainage systems to handle the water.

Urban flooding is a major problem in many parts of the world and it is the leading cause of global flood losses.

How urban flooding is different from rural flooding:

Flood intensity: Urban flooding is significantly different from rural flooding as urbanization leads to developed catchments, which increases the flood peaks from 1.8 to 8 times and flood volumes by up to 6 times. Consequently, flooding occurs very quickly due to faster flow times.

Vulnerability: As urban areas are densely populated; people are more vulnerable to flooding and secondary effect of exposure to infection.

Economic impact: Urban areas being centers of economic activities have key infrastructure that has a bearing on national and global economy.

Causes of Urban Floods:

Meteorological factors:

Heavy rainfall: Intense and prolonged rainfall events can overwhelm the capacity of urban drainage systems to handle the volume of water, leading to floods.

Cyclonic storms and thunderstorms: They can bring heavy rainfall, strong winds, and intense downpours, resulting in rapid runoff leading to urban flooding.

Climate change: Climate change has resulted in extreme weather events, exacerbating the frequency of heavy rainfall episodes characterized by short durations.

Hydrological factors:

Overbank flow channel networks: The presence or absence of well-designed and maintained drainage systems, such as canals, rivers, and stormwater channels, affects the capacity of an area to handle excess water during heavy rainfall.

High tides in coastal cities: Coastal cities face additional challenges, as high tides can impede the drainage of rainfall water into the ocean or other bodies of water. This can cause water to back up and flood urban areas.

Anthropogenic Factors:

Land use changes and urbanization: Extensive urbanization and land use changes, such as replacing natural surfaces with impermeable materials like concrete and asphalt, reduce the land’s ability to absorb rainfall. This increases surface runoff and the risk of urban flooding.

Example: Chennai Floods 2015 – The rapid and unplanned urbanization in Chennai, particularly the conversion of wetlands and water bodies into built-up areas, played a significant role in exacerbating the flooding.

Occupation of floodplains and obstruction of flood flows: Building structures in flood-prone areas or obstructing natural watercourses can disrupt the natural flow of water during heavy rainfall events. This can cause water to accumulate and lead to flooding.

Example: Mumbai Floods 2005 – The flood event in Mumbai was partly attributed to the occupation of floodplains and the obstruction of flood flows due to encroachments and improper land use.

Urban heat island effect: Urban areas often experience higher temperatures than surrounding rural areas, creating what is known as the urban heat island effect. This can influence weather patterns and increase localized rainfall, which can contribute to urban flooding.

Dam operations: Sudden releases of water from upstream dams can result in a surge of water downstream, overwhelming urban areas. Conversely, failure to release water from dams during heavy rainfall can cause a backwater effect, where water cannot flow freely, leading to flooding.

Example: Uttarakhand Floods 2013 – The devastating flood event in Uttarakhand was exacerbated by the sudden release of water from dams located upstream. Heavy rainfall combined with the release of water from dams caused flash floods and landslides, resulting in significant loss of life and infrastructure damage in the region.

Improper waste disposal: Indiscriminate disposal of solid waste, such as garbage and debris, into urban water drains and channels can clog the drainage system. This obstruction impedes the flow of water during the monsoon season and increases the likelihood of urban flooding.

Example: Bengaluru Floods 2017 – The improper disposal of solid waste, particularly the clogging of stormwater drains with garbage and debris, contributed to urban flooding in Bengaluru.

Illegal Mining Activities: Illegal mining of river sand and quartzite for use in building construction deplete the natural bed of the rivers and lakes. It causes soil erosion and reduces the water retention capacity of the waterbody increasing the speed and scale of water flow.

Impacts of Urban Flooding:

Loss of Life and Property: Urban flooding poses a direct threat to human life and can result in casualties and injuries. It also leads to damage and destruction of buildings, infrastructure, and personal property.

Disruption of City Functions: Urban flooding can damage water supply systems, sewerage networks, power transmission lines, communication networks, transportation infrastructure (roads and railways), and other essential services.

Environmental Impact: The force of floodwaters can uproot trees, destroy vegetation, and lead to soil erosion. It also washes pollutants, debris, and waste into rivers and other water bodies, harming aquatic ecosystems and contributing to water pollution.

Health Impacts: Urban flooding increases the risk of waterborne diseases and the spread of infections. Contaminated floodwater can carry pathogens, chemicals, and pollutants that pose health hazards to humans and animals.

Psychological Impacts: loss of shelter, personal belongings, and the trauma of witnessing the destruction and potential loss of lives can lead to long-lasting emotional distress and post-traumatic stress disorder (PTSD).

Urban Flood Risk in India:

There has been an increasing trend of urban flood disasters in India over the past several years whereby major cities in India have been severely affected.

Recent events of urban floods include Chennai floods of 2015 Mumbai floods of 2017, Guwahati floods of 2010, Bengaluru floods 2017 and Hyderabad floods of 2020.

There will be a rise in the frequency of floods in India due to rise in temperatures between 2070 and 2100, according to Climate Change and India: A 4×4 Assessment, a report by the Union Ministry of Environment and Forest.

Regions susceptible to floods, according to the National Disaster Management Authority (NDMA), lie mostly along the Ganga-Brahmaputra river basin, from the northern states of Himachal Pradesh and Punjab, covering Uttar Pradesh and Bihar and stretching to Assam and Arunachal Pradesh in the northeast.

The coastal states of Odisha and Andhra Pradesh, parts of Telangana and Gujarat also witness yearly floods, NDMA observed.

National Disaster Management (NDMA) Guidelines on Urban Flood Management:

In 2010, NDMA had issued guidelines on Urban Flood Management in India:

✓ Create a National Hydro-meteorological Network.

✓ The guidelines say that for providing early warning, the Central Water Commission (CWC) should maximize the real-time hydro-meteorological network to cover all urban centres to effectively deal with the problem of urban flooding.

✓ Use of Doppler Weather Radars to be expanded to cover all urban areas in the country.

✓ An inventory of the existing stormwater drainage system to be prepared. The inventory will be both watershed-based and ward-based.

✓ Catchment to be the basis for planning and designing the stormwater drainage systems in all ULBs (Urban Local Bodies).

✓ All future road and rail bridges in cities crossing drain to be designed such that they do not block the flows resulting in backwater effect.

✓ Every building in an urban area must have rainwater harvesting as an integral component of the building utility.

✓ Low-lying areas in cities have to be reserved for parks and other low-impact human activities.

✓ Encroachments on the drain should attract penal action.

✓ Pre-monsoon desilting of all major drains to be completed by March 31 each year.

✓ Urban Flooding has to be dealt as a separate disaster, de-linking it from riverine floods which affect the rural areas.

✓ Suitable interventions in the drainage system like traps, trash racks can be provided to reduce the amount of solid waste going into the storm sewers.

✓ Inlets to be provided on the roads to drain water to the roadside drains and these have to be designed based on current national and international practices.

✓ Concept of Rain Gardens to be incorporated in planning for public parks and on-site stormwater management for larger colonies and sites that are to be developed.

✓ Flood hazard assessments should be done on the basis of projected future scenarios of intensities and duration of the rainfall and land-use changes.

Way Forward:

Climate-Resilient Infrastructure: Develop climate-resilient infrastructure that can withstand extreme weather events and effectively manage water runoff. This includes incorporating green infrastructure, such as bioswales, permeable pavements, and rooftop gardens, which can absorb and store rainwater.

Early Warning Systems and Communication: Establish robust early warning systems that utilize advanced technologies to disseminate flood warnings in real-time. This helps residents and authorities to take necessary precautions and evacuate if required.

Developing Sponge Cities: The idea of a sponge city is to make cities more permeable so as to hold and use the water which falls upon it. The approach aims to enhance the capacity of cities to absorb, store, and utilize rainwater to mitigate flood risks and improve water resource management.

Urban Drainage Systems: Implement proper watershed management and develop emergency drainage plans. Regular maintenance and cleaning of drains and stormwater channels are essential to ensure smooth water flow and prevent blockages caused by solid waste and debris.

Conservation of Water Bodies: Protect and restore urban water bodies like lakes, tanks, and ponds, as they play a crucial role in managing urban flooding. These water bodies can act as natural retention basins, reducing stormwater runoff and preventing flooding.

Role of Science and Technology: This includes the use of predictive precipitation modeling, geospatial frameworks for vulnerability assessments, and innovative tools for analyzing and planning effective flood management strategies.

Urban planning with nature-based solutions: urban flood management in India continues to focus only on improving grey infrastructure, rescue & relief, instead of building solutions to increase flood resilience. Therefore, urban planning should adopt a hybrid approach of integrated green and grey infrastructure solutions.

Urban Flooding

Recently, many parts of Chennai have been flooded by heavy rainfall and faced a wide range of urban flood related issues repeatedly over last few years.

✓ Urban flooding is the inundation of property in a built environment, particularly in densely populated urban areas, caused by intense rainfall (on impermeable surfaces) which overwhelms the capacity of drainage systems.

✓ Urban flooding is significantly different from rural flooding as urbanization leads to developed catchments, which increases the flood peaks from 1.8 to 8 times and flood volumes by up to 6 times. Consequently, flooding occurs very quickly due to faster flow times (in a matter of minutes).

Why in spite of Chennai being a well-developed city faces issue of Urban Flooding:

✓Geographical reasons: low-lying topography, relatively flat terrain and close to sea-level.

✓Man-made reasons: Encroachment of wetlands for settlement and agriculture; Concretization leading to reduced percolation of rainwater; Wetlands clogged with sewage impacting their buffer role.

✓Politico-Administrative reasons: Lack of funding and functions with urban local bodies; Poor design and construction and inadequate carrying capacity of the city’s streets and storm-water drains; Lack of scientific Disaster management plans and roadmaps etc.

Impacts of urban flooding:

Socio- Economic impact:

✓ Damage to urban infrastructure and temporary disruption of utility services;

✓ Economic losses due to disruption in industrial activity and supply chains;

✓ Risk of epidemics due to spread of waterborne diseases;

✓ Can trigger mass migration or population displacement, especially of people in low lying areas etc.

Environmental: 

✓Destruction of biodiversity and wildlife habitats by floodwater and contamination of rivers and habitats.

Measures required to control urban flooding:

✓ Water-Sensitive Urban Design and Planning and a green infrastructure approach for stormwater management.

✓ Prepare drainage master plans for cities to augment stormwater infrastructure in cities.

✓ Integrating Flood mitigation plans (floodplain, river basin, surface water, etc.) within the overall land use policy and master planning of a city.

✓Participatory approach for a risk-based early action coordination among stakeholders to mitigate flood risks.

National Disaster Management Authority (NDMA) guidelines on urban flood management:

✓ CWC (Central Water Commission) should maximize the real-time hydrometeorological network to cover all the urban centers in support of the emerging priorities in dealing with urban flooding.

✓ Doppler Weather Radars to be expanded to cover all urban areas in the country.

✓In situ flood management approaches should ensure community preparedness. This includes participatory urban flood planning and management involving both local government and the community.

✓ Stormwater drainage concerns will be made a part of all Environmental Impact Assessment (EIA) norms.

✓National Urban Information System (NUIS) to cover infrastructure facilities at community level integrated with socioeconomic data.

Related concept: 

Flood plain zoning (FPZ):

✓FPZ is aimed at demarcating zones or areas likely to be affected by floods, and specify types of permissible developments in these zones, to minimize damage caused by floods.

> Floodplains are crucial for regulating flow of water in a river.

✓However, in recent years, floodplains have become sites for urban development resulting in alterations like increase in impervious surfaces, development in-filling on and near floodplain, construction of embankments etc.

FPZ policies in India:

✓ FPZ is within state government’s ambit as it is deals with land along the riverbanks and land is a state subject.

✓ Union Government circulated a Model Bill for Flood Plain Zoning (MBFPZ) which provides for surveys of floodplain area, notification of limits of floodplains, prohibition or restriction of the use of the floodplains etc

✓ National Disaster Management Guidelines for floods includes regulation of floodplains and enforcement of FPZ.

Government initiatives to tackle urban flooding:

✓Sponge Cities mission: It aims to promote positive interactions between socio-economic systems within the cityscape and with the urban water cycle to enhance local urban resilience, particularly in the face of increasingly volatile water-related disasters.

✓Atal Mission for Rejuvenation and Urban Transformation (AMRUT)

✓Flood management programme: It provides financial assistance to the state governments for undertaking flood management works in critical areas.

✓ Integrated Flood Warning system like IFLOWS-Mumbai: It is a state of art Integrated Flood Warning system for Mumbai which makes it possible to have an estimate of the flood inundation three days in advance, along with immediate weather updates.