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Tackling urban flooding

Urbanisation is inevitable as is climate change — the need is for a multi-pronged approach; write Shivali Jainer, Suresh K Rohilla and Dhruv Pasricha

Tackling urban flooding
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As the monsoon hit cities, we were reminded of the mayhem that usually surrounds urban India this time, where roads become canals, even if there is moderate rain.

The novel coronavirus disease (COVID-19) increased the problem of waterlogging as pre-monsoon desilting of drains was not carried out in full capacity. Others were a consequence of high-intensity bursts of a downpour for three to six hours, suddenly overwhelming drainage systems. The trend of urban flooding and waterlogging has continued in urban India this year too. July was the wettest month for Mumbai, which received 819 millimetres of rainfall on an average.

Also, more than 10 instances of damage to buildings were reported. This included the collapse of over 10 houses in an informal settlement near Delhi's ITO area. Like Delhi, neighbouring Gurugram in Haryana was waterlogged with a 22-36 mm downpour recorded July 22 in some of the district's weather stations. Several parts of the city were waterlogged, with residents pointing this out on social media. While these incidents were covered in the mainstream media, they were not isolated incidents: Most urban areas grapple with waterlogging and urban flooding every monsoon.

Context of urbanisation and climate change

It is important to note urbanisation is an inevitable process and urban areas will continue to grow demographically and spatially. Cities — considered engines of growth — contribute more than 65 per cent of the national gross domestic product and provide employment to more than a third of the country.

The collateral damage emerging out of these expanding cities is the result of a breakdown in natural systems. Urban areas, however, generate high volumes of polluted run-off, often resulting in the breakdown of the urban drainage system. In such a case, even moderate rainfall events can lead to flash floods in low-lying areas and can overwhelm drainage systems of cities.

Our weather patterns are altered because of global warming. There is evidence of change in some climate extremes based on data gathered from 1950, according to the Inter-governmental Panel for Climate Change (IPCC). In terms of precipitation, there were likely statistically significant increases in the number of heavy precipitation events, according to the IPCC.

Issues related to urban stormwater management

Deficiencies need to be identified under several structural and non-structural dimensions related to urban stormwater management.

Cities were not planned concerning stormwater management. In most cases, development control regulations in master plans do not provide for run-off control measures. Also, open spaces and water bodies are victims of 'planned' encroachments. Urban streams and water bodies are compromised for urban land uses. A section of the Barapullah drain in Delhi, for example, is covered to construct a bus depot. While the current response to urban flooding is limited to the construction of roadside drains, design standards recommended by the Central Public Health and Environmental Engineering Organisation (CPHEEO) are outdated.

While CPHEEO standards recommend a design according to one or two-year flood levels, drains are not able to accommodate increased run-offs because of more frequent high-intensity rain. Stormwater drains in cities are generally in poor conditions, with operation and maintenance largely inadequate and ineffective.

Stormwater drains are often choked with municipal solid waste and construction and demolition waste. One such example is the choked drain in south Delhi's Taimoor Nagar area, where garbage has piled up over the years.

In terms of non-structural deficiencies, there are no national/state-level policy frameworks and/or guidelines for urban stormwater management in India. Urban infrastructure development missions — including the Smart Cities Mission, the Swachh Bharat Mission and Atal Mission for Rejuvenation and Urban Transformation — fail to provide a comprehensive vision and strategy to address issues of urban flooding.

Measures by cities

Several cities in India have attempted to address issues regarding urban stormwater management. Mumbai launched a state-of-the-art Integrated Flood Warning System (IFLOWS) in June. The warning system helps to identify imminent floods due to high rainfall or cyclones. The Chennai Flood Warning System — that provides spatial flood warnings for the city — was launched in October 2019. These systems help build resilience and can inform the public and authorities regarding risks. The India Meteorological Department launched the Mausam mobile application that provides rain forecasts including warnings. The Karnataka government launched the Meghasandesha mobile application, which provides real-time rainfall measurements, along with forecasts for rain, flooding and thunderstorms for Bengaluru. Delhi has prepared several multi-dimensional strategies to address the issues of urban flooding. The city was the first to have a drainage master plan, prepared by the Indian Institute of Technology, Delhi. The Delhi Jal Board also took up the revival of 159 water bodies in the city, along with floodwater harvesting projects in the floodplains of Yamuna. All these measures have multiple economic, environmental, social and urban benefits for the citizens of Delhi.

Both Chennai and Delhi also recommended for properties to implement rainwater harvesting structures as run-off control measures. The Odisha government's housing and urban development department issued an advisory for implementing rainwater harvesting in public parks and open spaces in urban areas across the state. While these measures look good on paper, they must be followed through by effective implementation, taking operation and maintenance and coordination with stakeholders including architects, planners, hydrologists, groundwater experts, etc, into account. These strategies must be prepared and implemented with the support and contribution of and the local community.

Recommendations

A systemic change — which comprehensively resolves structural and non-structural issues — is required to address issues of urban flooding. Some of these recommendations are summarised below:

Water-Sensitive Urban Design and Planning (WSUDP) and a green infrastructure approach for stormwater management: Identification, protection and use of open spaces and water bodies as critical green infrastructure to manage run-off and mitigate urban flooding. This must be done in addition to the identification of urban catchments and prioritisation based on the level of risk and vulnerability.

Prepare drainage master plans for cities with periodic strategies to augment stormwater infrastructure in cities. This must be aided by state-of-the-art urban watershed modelling.

Identify vulnerable and high-risk areas and prepare monsoon action plans for those areas, based on context. Informal areas are more vulnerable due to high built-up area density and lack of infrastructure. This needs to be aided by a state-of-the-art rain atlas for cities, providing spatial rainfall maps with 15-minute intervals. The rain atlas can also feed in as a flood-warning system.

Formulate a nodal authority for urban stormwater management which should be responsible for preparation of drainage master plan at the local level and coordinate strategies with city master plan preparations.

Modifications of design standards and detailed reports to accommodate run-off control measures based on spatially variable rainfall statistics. Municipalities and development authorities can take the lead in implementing high visibility-high impact pilot projects that showcase the potential of capturing rainfall and flood-control measures.

Prepare a national/state-level framework for urban drainage, with modified service-level benchmarking, like percentage of municipal area under water-harvesting features, etc.

Develop the capacity of practitioners at the academic level by upgrading the curriculum to include WSUDP and green infrastructure strategies for infrastructure provision and continuous professional development of municipal functionaries and consultants to update with latest tools and techniques for planning and designing rain/stormwater harvesting features.

Views expressed are personal

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