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Context: Floods storms Chennai

Several parts in Chennai and its suburban areas reported waterlogging after heavy rains lashed the city.
The showers have now been marked as the heaviest downpour since 2015.
In fact, 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.

The increasing trend of urban flooding is a universal phenomenon and poses a great challenge to urban planners the world over.

What are Urban Floods?

Urban floods stem from a combination of various meteorological and hydrological extremes, such as extreme precipitation and flows in short spans of time.
Thus, flooding in urban areas is caused by intense and/or prolonged rainfall, which overwhelms the capacity of the drainage system.
It 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.

Features of Urban Floods

Faster Flow times: Consequently, flooding occurs very quickly due to faster flow times, sometimes in a matter of minutes.
Catchment destruction: Urban flooding is significantly different from rural flooding as urbanization leads to developed catchments which are the most vulnerable areas.

Various causes

[A] Natural

Meteorological Factors: Heavy rainfall, cyclonic storms and thunderstorms causes water to flow quickly through paved urban areas and impound in low lying areas.
Hydrological Factors: Overbank flow channel networks, occurrence of high tides impeding the drainage in coastal cities.
Climate Change: Climate change due to various anthropogenic events has led to extreme weather events.

[B] Anthropological

Population densities: Population density and proximity to urban centres significantly alter the dynamics and complexity when it comes to urban flooding.
Unplanned Urbanization: This is the key cause of urban flooding. A major concern is blocking of natural drainage pathways through construction activity and encroachment on catchment areas, riverbeds and lakebeds.
Encroachment: Ideally, the natural drains should have been widened to accommodate the higher flows of stormwater. But on the contrary, there have been large scale encroachments. Habitations started growing over them.
Drainage System: Stormwater drainage systems in the past were designed for rainfall intensity of 12 – 20 mm. These capacities have been getting very easily overwhelmed whenever rainfall of higher intensity has been experienced.
Destruction of lakes: Lakes can store the excess water and regulate the flow of water. However, pollution of natural urban water bodies and converting them for development purposes has increased risk of floods.
Unauthorised colonies and excess construction: Reduced infiltration due paving of surfaces which decreases ground absorption and increases the speed and amount of surface flow.
Poor Solid Waste Management System: Improper waste management system and clogging of storm-water drains because of silting, accumulation of non-biodegradable wastes and construction debris.
Irresponsible steps: Lack of attention to natural hydrological system and lack of flood control measures.

Impact of Urban floods

Problems associated with urban floods range from relatively localized incidents to major incidents, resulting in cities being inundated from hours to several days.

Loss of life: Urban areas are densely populated and people living in vulnerable areas suffer due to flooding, sometimes resulting in loss of life.
Loss of property: Major cities in India have witnessed loss of life and property, disruption in transport and power.
Infrastructure damage: In most of the cities, damage to vital infrastructure has a bearing not only for the state and the country but it could even have global implications.
Health hazards: The secondary effect of exposure to infection also has its toll in terms of human suffering, loss of livelihood and, in extreme cases, loss of life.
Others: The impact can also be widespread, including temporary relocation of people, damage to civic amenities, deterioration of water quality and risk of epidemics.

Losses caused

[a] Tangible losses: The losses that can be measured physically and can be assigned an economic value. These losses can be direct or indirect

Direct – Structural damage to buildings, property damage, damage to infrastructure
Indirect – Economic losses, Traffic disruption, and emergency costs

[b] Intangible losses: Intangible losses include loss of life, secondary health effects, and infections or damages to the environment which are difficult to assess in monetary terms since they are not traded.

Direct – Casualties, health effects, ecological losses
Indirect – Post-flood recovery process, mental damage to the people

Who owes the responsibility?

Human determinism: The fact is that our cities have been built with little to no regard to the natural topography and severely lacks holistic action.
Weaker laws: We have in place the provisions of rainwater harvesting, sustainable urban drainage systems, etc, in regulatory mechanisms like the EIA, notification 2006.
Weaker implementation: Public bodies’ focus is largely on de-silting of storm water drains before monsoon and expansion of the over-burdened infrastructure, but at a crawling pace.

Lacunae in Urban Planning

No mapping of water bodies: The preliminary work of mapping and documentation of the surface water bodies even though mentioned in NDMA under the National Database for Mapping Attributes has not been undertaken.
Failed early-warning system: During floods of Uttarakhand in 2013, there were questions about the role of NDMA, where it failed to implement the early warning systems to inform people about the floods and landslides.
Response rather than mitigation: The importance of preparedness for the disaster situation like urban floods was realized by the government agencies only after the devastations during Chennai Floods in 2015 and Kerala Floods in 2018.
Responsiveness of Local bodies: Sufficient training, equipment, and facilities for immediate response and to tackle the disaster situation efficiently is not being carried out by the local governments. More onus of mitigation lies with NDMA/SDMA.
Misutilization of Funds: NDRF/SDRF constituted by the government to deal with the disasters, were used for expenses that were not sanctioned for disaster management. There were cases of financial indiscipline in state management of funds.

Way forward

Climate variability assessment: As the incidence of climate variability and extreme weather events increases, it is inevitable that we look at the issue from a broad-based perspective.
Resilience building: Focus has to be on increasing the resilience of communities and adaptive capacity of our infrastructure.
Innovation: Water sensitive urban design and planning techniques — especially in the context of implementation — are of utmost importance. Ex. Sponge Cities.
Environmental determinism: Planning must take into consideration the topography, types of surfaces (pervious or impervious), natural drainage and leave very less impact on the environment.
Vulnerability Analysis: Vulnerability analyses and risk assessments should form part and parcel of city master plans.

Conclusion

Disabling spawning of squatter settlements in sensitive zones by providing adequate affordable housing will reduce number of persons vulnerable to changing climate.
All this means urban local bodies will continue to have a central role to play in cities’ battle with extreme weather events such as flooding and their overall resilience.