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.