2021 DEC 2
Disaster Management > Disasters > Floods
- As rains continue to batter Tamil Nadu, several areas in Chennai city have been inundated.
- Urban floods in India have become a regular phenomenon.
- Recent events of urban floods include Hyderabad floods of 2020, Chennai floods of 2021 and 2015, Mumbai floods of 2017, Guwahati floods of 2010 and Bengaluru floods 2017.
- Floods in India are an outcome of both natural and anthropocentric changes. However, the latter has been more responsible for floods in the current age of Anthropocene.
CAUSES OF URBAN FLOODING:
- Meteorological phenomenon:
- Low pressure centres leading to cyclonic activities in Arabian sea and Bay of Bengal induce heavy rainfall resulting in floods.
- Eg: The 2020 Hyderabad flood was associated with Deep Depression BOB 02 that developed in the Bay of Bengal.
- Intense rainfall:
- Climate change has increased the intensity of rain falling over a small duration of time. Also, some areas can receive excessive rainfall due to weather anomalies like cloudburst, resulting in floods.
- Eg: The massive flooding Chennai had witnessed in 2015 was sparked by the more than 120 cm of rainfall the city received in November 2015
- Change in course of river:
- Young rivers can frequently change their course, resulting in floods.
- Eg: Kosi river causes flood in cities and towns of northern Bihar
- Inadequate drainage infrastructure:
- In the last 20 years, the Indian cities have grown manifold with its original built-up area. However, most cities rely on a century-old drainage system, covering only a small part of the core city.
- Eg: Delhi’s last drainage master plan was prepared in 1976, when the population was 6 million. By 2011, it has gone up more than three times and stood at 16.7 million. It is now estimated to be around 20 million. However, the drainage capacity remains stagnant.
- Increase in the urban population without corresponding expansion of civic facilities such as lack of adequate infrastructure for the disposal of waste results in waste clogging the natural channels and storm water drains.
- Cultural or religious festivals lead to dumping in water bodies, resulting in clogging.
- Encroachment and terrain alteration:
- Lasting irreversible damage has been done to the real estate sector and public agencies by flattening terrain and altering natural drainage routes.
- Eg: Of the total 1,547 lakes in Bengaluru, which is spread across 57,932 acres, 10,785 acres have been encroached upon by both government and private agencies.
- Reducing seepage due to concretisation:
- Indian cities are becoming increasingly impervious to water, not just because of increasing built up but also because of the nature of materials used (hard, non-porous construction material that makes the soil impervious).
- Destruction of wetlands:
- Marshes and flood plains play a very important role in draining out overflowing rivers. However, they are increasingly destroyed to meet the urban demands.
- Eg: The Pallikarni marshland, also known as the flood sink area of Chennai city was around 5,000 hectares during independence. But it got reduced to almost 600 ha around 2010-11. This destruction is identified as a key reason for the 2015 flood.
- Poor water management:
- Due to poor management and lack of interdepartmental coordination, reservoirs created for flood control have often become the reason for floods.
- Eg: In Kerala in 2018, intense rainfall from August 1 filled up the dams and led to the simultaneous opening of all major dams on August 15. This led to the flooding of coastal areas of Cochin.
- Illegal mining activities:
- Illegal mining for sand and quartzite both on the catchment and on the bed of rivers and lake have reduced the carrying capacity of rivers and alterations in their courses, thereby aggravating floods.
- Lax regulations:
- Implementation of provisions of rainwater harvesting, sustainable urban drainage systems and adoption of Environment regulatory mechanisms like the Environmental Impact Assessment (EIA) remains weak.
INDIA’S VULNERABILITY TO URBAN FLOOD:
- Tropical monsoon climate:
- During the short span of June-September (summer monsoon), the country receives an average of 88 cm rainfall. This accounts for about 70 percent of India's annual precipitation.
- Increasing urban population:
- 52% of Indians are predicted to live in cities by 2050 and, as per IPCC reports, the area and intensity of flooding events are expected to increase in the country.
- ‘Messy and Hidden’ urbanization:
- According to a report by the World Bank, India’s urbanisation is “messy and hidden”, citing the country’s inability to deal with pressures on infrastructure, basic civic services, land and housing, due to increase in urban population.
- Large vulnerable population:
- According to 2011 census, nearly 6.55 crore Indians live in urban slums, while 13.7% of the urban population lives below the poverty line. This aggravates the impact of any disaster.
CASE STUDY: Chennai’s urban floods:
- The coastal city of Chennai is affected by frequent floods.
- Chennai receives an annual rainfall of 1400 mm of which 800 mm is during the northeast monsoon season.
- The Adyar river basin acts as a permanent water retention structure to the city. However, siltation, pollution and encroachment has significantly reduced the carrying capacity of the river.
- Chennai also has a long history of vanishing lakes and water bodies. A study by Chennai-based Care Earth Trust shows that Chennai’s built-up area grew from 47 sq. km in 1980 to 402 sq. km in 2012, while wetlands declined from 186 sq. km to 71 sq. km.
- These factors, coupled with the low elevation terrain, inadequate storm drains and torrential rain results in severe floods.
- The Chennai Metropolitan Area was victim to a moderate ‘one in 50-year’ flood in 2005 and an extreme ‘one in 100-year flood in 2015’. These numbers are predicted to worsen as the city’s population is expected to touch 10 million by 2025.
NDMA GUIDELINES ON URBAN FLOOD MANAGEMENT:
- Creation of a National Hydro-meteorological Network:
- In 2010, NDMA had issued guidelines on Urban Flood Management in India to 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 technology:
- Use of Doppler Weather Radars to be expanded to cover all urban areas in the country.
- Data collection:
- An inventory of the existing storm water drainage system to be prepared. The inventory will be both watershed based and ward based
- Flood resilient infrastructure:
- All future road and rail bridges in cities crossing drains 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.
- Land management:
- Low-lying areas in cities have to be reserved for parks and other low-impact human activities.
- Delinking of urban flood and rural flood:
- Urban Flooding has to be dealt as a separate disaster, de-linking it from riverine floods which affect the rural areas.
- Integrated Flood Warning System for Mumbai (I-FLOWS Mumbai):
- It is a monitoring and flood warning system that will be able to relay alerts of possible flood-prone areas in advance.
- Similar systems are being developed for Chennai, Bengaluru and Kolkata.
- China’s sponge city initiative:
- Sponge City is a city that has the capacity to mainstream urban water management into the urban planning policies and designs. It should have the appropriate planning and legal frameworks and tools in place to implement, maintain and adapt the infrastructure systems to collect, store and treat (excess) rainwater.
- China has set an ambitious goal - by 2020, 80 percent of urban areas should absorb and re-use at least 70 percent of rainwater.
- Proper planning framework:
- Detailed survey of the wetlands and Inclusion of water bodies and their catchment in the city development rules.
- Comprehensive urban planning with proper study of topography, drainage, rainfall, soil lithology with improved flood water disposal system
- In a changing climate, the water sensitive urban design and drainage infrastructure (especially storm water drainage) has to be built considering the new ‘normal’.
- Each city should have their flood mitigation plans strongly embedded within the master plan of the city.
- Improve predictions:
- Detailed vulnerability mapping of each city should be carries out. Tools such as predictive precipitation modelling can help in this regard.
- Land use control:
- A well-defined land use policy for urban landscapes must be developed. EIAs and building codes should be effectively enforced to ensure that fragile wetlands and floodplains are not concretised.
- Develop affordable housing:
- Disabling spawning of squatter settlements in sensitive zones by providing adequate affordable housing will reduce number of persons vulnerable to changing climate.
- Proper solid waste management system:
- Control of solid waste entering the drainage systems through proper collection, segregation and recycling of wastes.
- Need For holistic engagement:
- Floods cannot be managed without concerted and focused investments from all levels of government and sufficient resources.
- The Metropolitan Development Authorities, NDMA, State revenue and irrigation departments along with municipal corporations should coordinate to develop and implement flood preparedness and mitigation strategies.
- Such efforts should also take into consideration the active participation of civil society organisations at the metropolitan scale.
- 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.
Q. Discuss the causes of urban floods in India and suggest measures to address it?