Over the past few years, Chennai has continued to receive unprecedented rainfall during the annual northeast monsoon. Sudden bursts of increased rainfall, with large volumes of water in very short spans, often result in urban floods, revealing the city’s vulnerability. Confronting the challenges of climate change, Chennai needs to find a solution that primarily enables its water reservoirs to absorb, store or recharge groundwater. The focus shifts to the imperatives of organised urban planning and the need to protect and rejuvenate Chennai’s water reservoirs — Pallikaranai marsh, Ennore creek and other large reservoirs such as Chembarambakkam lake and Red Hills lake.
Water stagnation in Pallikaranai, in spite of the lake there. | Photo Credit: R. Ravindran
The organic and rapid growth of the city has disrupted the natural hydrological cycle with the expansion of concrete and tar-paved surfaces, indiscriminate constructions and felling of trees and vegetation. Environmentalists suggest that this could be some of the many reasons behind urban floods, besides augmenting the capacity of the three rivers and their reservoirs — Adyar, Cooum and Kosasthalaiyar. The city requires a new imagination of its relationship to the unpredictable monsoons, the sea, and its water reservoirs.
A view of the Red Hills Reservoir in Chennai. | Photo Credit: B. Jothi Ramalingam
1. Public awareness
Over the last three decades, Chennai has been at the forefront of rainwater harvesting. The Chennai Metropolitan Water Supply and Sewerage Board (CMWSSB) provides detailed information about water harvesting and its relationship to floods. These are open-source documents that can be accessed online. (www.cmwssb.tn.gov.in/rain-water-harvesting) Chennai’s history indicates that well-designed rainwater harvesting systems, following safety standards, can substantially absorb excess rainwater and minimise the adverse impact of floods. Public awareness on waste disposal, preparedness and water conservation practices are essential to address climate-induced calamities and build resilience.
Image for representation purpose only. | Photo Credit: Getty Images/istock
2. Rainwater harvesting systems
In the face of heavy rains, residential complexes and institutions have begun to construct rainwater harvesting wells, as well as renew existing ones that have been defunct. The initiative, however, needs to be more widespread recognising its intrinsic benefits. It is a pragmatic indication to new apartment complexes, to be more diligent and provide for well-designed rainwater harvesting pits that collect excess rains to permeate the soil. The CMWSSB guidelines suggest that water collected from the terraces can be directed through a filtration process into storage tanks. While it can considerably reduce the floodwaters, it assures a long-term water security to Chennai.
Integrating these aspects into the Third Masterplan, presently under preparation by the Chennai Metropolitan Development Authority, could strengthen the city’s capacity to address urban floods. It has several other ancillary benefits such as reducing urban heat, recharging groundwater, and minimising the ingress of brackish seawater. Apartment complexes that have recharged groundwater, through rainwater harvesting, have discovered an improvement in water quality. Over the past decades, innumerable studies by CMWSSB have indicated the effectiveness of rainwater harvesting in reducing flood water volume and stopping water logging of roads. Large education campuses can contribute to augmenting and recharge of groundwaters. However, it’s a greater challenge to address and mitigate the impacts of such cataclysmic rains.
A view of Chembarambakkam reservoir in Chennai. | Photo Credit: B. Velankanni Raj
3. Permeable pavements and surfaces
Public awareness about designing permeable, porous pavements and surfaces can encourage and allow rainwater to infiltrate the soil and recharge groundwater naturally — urban parks and gardens, porous pavements, retention wells, and green roofs. Permeable pavements and surfaces have had a significant impact on reducing urban heat as well. While much of these details are known, their dissemination could ensure effective adoption.
Another view of the Chembarambakkam reservoir. | Photo Credit: B. Velankanni Raj
4. Integrated database system
Drawing from urban lessons of medieval Madras, these elements of rainwater harvesting can be combined with Chennai’s road network and its stormwater drain system — to assist in the natural flow of water into rivers and rejuvenate the lakes and other water reservoirs, through a natural process. Stormwater channels have also been equipped with filtration and recharge wells in the city today. A pragmatic neighbourhood approach, scientifically undertaken, ensuring surface and drain slopes and levels, requires a monitoring committee, including neighbourhood citizen groups, to coordinate the efforts. Digital technologies and apps, documenting citizen data of inundation, flooding, and other issues can empower a citizen-based participation and aid the planning process, providing local data. Low-lying areas would undoubtedly require more concerted efforts in infrastructure investments and planning.
A flooded road. Image for representation purpose only. | Photo Credit: Getty Images/istock
5. Protecting natural ecosystems
The impetus to creating urban green spaces, accessible to all, is imperative, for several reasons. During earlier natural calamities, the Greater Chennai Corporation had invited environmentalists and citizen groups to draw up ecological guidelines for tree-planting. Protecting natural ecosystems and biodiversity, regions like the Guindy deer-park and Vandalur area, and other local parks act as natural flood regulators as well. Rejuvenating untended parks, Open Space Reservation lands and other derelict zones would consolidate these nature-based solutions considerably. The flood mitigation process would require a constant monitoring and maintenance of stormwater drains.
In the present scenario of Chennai’s growth, nature-based solutions (through the creation of new green spaces and rejuvenation of natural water reservoirs) can support a natural “stormwater management”. Several studies have demonstrated the contribution of such nature-based solutions (if appropriately designed) in complementing the urban drainage system. The need for an integrated database system with early-warning systems has to be implemented to coordinate efforts.
Information on rescue, evacuation, helplines, relief measures, hospital support, and other relevant information have augmented such extreme predicaments. Areas with incomplete canals, or roads under construction have been the most affected. However, on a positive note, the early warning updates received by citizens provided adequate time to evacuate to safety. Several parts of Chennai continue to battle the receding floods, inundating low-lying areas. Prioritising vulnerable communities and neighbourhoods for infrastructural remedies is imperative.
In the long-term, flood mitigation measures have often influenced the microclimate, and have the potential to make the city cooler and more liveable.
Citizen groups can participate in urban neighbourhood discussions to suggest local observations. Community groups monitoring stormwater canals adjacent to their homes have informally emerged in Chennai since the last decade. If these volunteer efforts by citizen groups can be supported in the planning process, the city can chart a resilient road map to cope with natural calamities.
The writer is the founding Principal Architect of Artes Roots Collaborative, involved in the intersections of climate change, social landscapes, environment and habitat.
Published - October 18, 2024 03:28 pm IST
