Urban floods in Bangalore and Chennai – Risk management challenges and lessons for sustainable urban ecology – A paper in Current Science

Unplanned urbanization has drastically altered the drainage characteristics of natural catchments, or drainage areas, by increasing the volume and rate of surface runoff. Drainage systems are unable to cope with the increased volume of water and are often encountered with blockage due to indiscriminate disposal of solid wastes. 

A number of major cities and towns in India reported a series of devastating urban floods in the recent decade. Mumbai flood 2005 followed by other major cities of South Asia like Dhaka, Islamabad, Rawalpindi also suffered from urban flooding. Census 2001 figured 285 million people in 35 metro cities of India, and is estimated to cross 600 million with 100 metro cities in 2021. Regional ecological challenges coupled with climatic variability are noted to aggravate flood risks and impact on affected communities.

Urban flooding, which was primarily a concern of municipal and environmental governance, has now attained the status of ‘disaster’, which has drawn the attention of environmental scientists and disaster managers. Challenges of urban flooding in terms of drainage and flood mitigation including structural and non-structural measures and key issues of urban  ecology in two major metropolitan cities of India – Bangalore and Chennai, have been studied. Risk management challenges in the context of land-use, city and population growth, wetland degeneration, waste disposal have been discussed.

Urban flooding is significantly different from flooding in rural areas as urbanization results in impermeable catchments causing flood peaks by up to three times. Consequently, flooding occurs quickly due to faster flow times (in a matter of minutes).

These are often caused due to a combination of many factors like heavy or patchy rainfall, dam-water release or failure, inadequate drainage systems, blockade, housing in floodplains and natural drainage or riverbed and loss of natural flood-storages sites. 

An integrated approach, therefore, needs to combine watershed and land-use management with development planning, engineering measures, flood preparedness, and emergency management in the affected lowlands, while taking into account the social and economic needs of communities in both the highland source areas, and also the lowland flood-prone areas.  

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