Project: The City of 1,000 Tanks Chennai

The City of 1,000 Tanks team brings together experts from the fields of urban design, water management, social and cultural engagement, policy and finance to create holistic, inclusive and robust solutions that mitigate and adapt to climate risks of floods and droughts. The team is led by OOZE Architects in collaboration with Madras Terrace, IIT Madras, Care Earth Trust, Paperman Foundation, Biomatrix Water, Pitchandikulam Forest Consultants, Rain Centre, IRCDUC, Urayugal Social Welfare Trust, Goethe Institute, TU Delft, IHE Delft and HKV Consultants.

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The City of 1,000 Tanks project proposes holistic solutions for the interrelated issues of flooding, water scarcity, and pollution in Chennai.

Recognizing that 20th century flood protection measures have deprived the city of its available water, the team proposed to collect and clean water by means of a blue-green infrastructure system of tanks and cleansing channels rather than conventional drains. Existing temple tanks, new tanks and ponds, bio-swales and constructed wetlands form the basis of a new decentralized water system that helps treat wastewater and prevent floods and droughts.

The city must transform into a dynamic seasonal landscape to recharge aquifers during the yearly monsoon and rely upon storage capacity to provide water supplies during the drier months. Building upon interconnected art and pilot projects, the team introduced an incremental approach to realize this strategy. The project creates an active relationship between water management and the community instead of the top-down management approach that is currently in place. Empowering local communities and reviving ward-level management power helps create water capacity and the possibility to manage flood events locally.

Ultimately, the proposal considers spatial, technical, organizational, cultural, and economic challenges. The team acheives this through a staged and adaptive reform of the current water management system to better utilize Chennai’s water resources. Four areas (Mylapore, Chitra Nagar, Mambalam, and Koyambedu) are addressed in context of their unique water challenges in this comprehensive proposal.

Mylapore was originally designed as a smart city with a resilient water infrastructure system.

This system was comprised of connected ponds and temple tanks that retained water during monsoons for use in the dry season each year. Modern development in the historic core of Chennai has erased the functionality and knowledge of its temple tanks. But with a brilliant existing water infrastructure and ideal soil conditions, there is no reason for Mylapore to remain vulnerable to floods and droughts as it has been in recent years. “Mylapore Trail” seeks to restore and enhance Chennai’s important water heritage, acting as a precedent for the rest of the city as well as a sustainable tourist attraction. Two historic temple tanks that no longer function as water infrastructure are restored by collective efforts in increasing ground water recharge which will eventually raise water levels in the tanks.

Public spaces are designed using the principles of Nature-based Solutions (NbS). New dynamic tanks treat and recharge rainwater runoff to the underground aquifer. Residential and commercial properties also contribute to water treatment and groundwater recharge through a decentralised network of NbS interventions. An integrated network of bioswales connects the new recharge tanks to form a resilient and highly-visible system. The goal of this design is to increase awareness about how water infrastructure funtions in the city and highlight culturally important historic zones. The aesthetic design also improves the overall attractiveness of the neighbourhood to the benefit of tourism, commerce and residents' experiences. The Mylapore project can be replicated across 53 other temple tanks in Chennai for a total of more than 60 MLD of water recharge.

The project has strong backing from the local MLA (Member of Legislative Assembly), residents’ groups and local institutions.

Chitra Nagar-Kotturpuram tenements is a low-income slum resettlement housing scheme set up by the Tamil Nadu Slum Clearance Board.

Situated on the inner banks of a horse-shoe bend of the Adyar river, it was one of the hardest-hit areas during the November-December 2015 flood season. The settlement houses approximately 10,000 people and routinely floods even under normal conditions. In addition to being located in naturally flood-prone area, limited access to potable water, poor solid waste management, and lack of access to sanitation facilities present challenges for the health and living conditions of the residents.

In this proposal, the water loop is closed in Chitra Nagar housing scheme by retrofitting systems for water collection, recycling and recharge, as well as solid waste management. The structural changes provide residents with a reliable and clean source of water and prevent chronic flooding and standing water. Nature-based solutions are proposed for in-situ sewage treatment and sanitation schemes designed to improve the overall health of the population. A community engagement program helps to ensure that the systems are understood, accepted and well-maintained by residents. The project has gained interest from the Tamil Nadu Slum Clearance Board (TNSCB) as an innovative alternative to the possible redevelopment of the area and relocation of residents.

The Chitra Nagar project can be replicated across at least 20 other sites managed by TNSCB for a total of 200,000 beneficiaries and more than 80 MLD recharge.

Koyambedu is Chennai’s primary infrastructural and logistics hub.

Situated in a low-lying area between the Coovum River and the Virugambakkam Arugambakkam channel, the neighborhood houses the city’s largest perishable goods market (with a yearly turnover of $200 million USD), the largest inter-city bus terminal and a sewage treatment plant.

The critical supply of these services within the city heightens the risk associated with any kind of flooding in the area. In particular, the severe flooding in 2015 interrupted the entire transit system in the area, prevented the distribution of food supplies throughout the city, and compromised assets worth $191.3 million in total. The absorption capacity of the ground surface has been steadily decreasing, and now over 85% of all surfaces are impervious. In response, groundwater levels have been declining in recent years. Unregulated dumping of solid waste is also a significant issue: the Koyambedu Wholesale Market Complex creates 200 tonnes of waste daily.

This proposal protects the Koyambedu region from future water impacts by installing stormwater absorbtion measures and creating a solid waste recycling program. The sewage treatment plant (STP) operated by Metrowater is enhanced with post-treatment processing using NbS methods. Metrowater has encouraged the City of 1000 Tanks Team to pursue this recycling effort to increase its water assets using existing infrastructure.

The stormwater absorbtion measures proposed in Koyambedu can be replicated across at least 40 other industrial sites in Chennai, with a potential of 450 MLD of recharge. In addition, STP post-treatment and water recharge measures can be replicated across four other STPs in the city with a potential of 500 MLD.

Built on top of a former reservoir in the modern heart of Chennai, Mambalam is a neighbourhood facing severe problems from water pollution, chronic flooding, and shrinking aquifer supplies.

The neighborhood is home to many exclusive hotels, offices and retail space that collectively comprise $2.7 billion in assets. Just next door, residential properties along the canal's edge are designated as EWS (Economically-Weaker Sections) made up of state housing boards and informal settlements. Chronic flooding and a shortage of water supplies for commercial use interrupt business activities, put many households at risk, and compromise the vitality of the area.

Mambalam is also the location of the Chennai Smart City initiative. This proposal capitalizes on the area's high visibility as a commercial center to demonstrate the efficacy of NbS tools in collecting, cleaning, storing and recharging water in a variety of public and private spaces.

“Mambalam Arms” connects different socioeconomic groups with infrastructure to create resilience against floods and droughts. The proposal revitalizes the canal itself by adding public space and constructed wetlands that naturally clean the water. A waste sorting center creates an economic opportunity for a local business to clear up the tons of garbage currently in and beside the canal. The project will also incentivize investment in NbS by private property owners. Property owners that keep 5% of their land free as per the Open Space Requirement (OSR) will receive “water credits” as a rebate against the property’s monthly water bill. Greywater from private properties will be treated and used to recharge the aquifer. As water levels in the aquifer recover, Metrowater can construct local borewells and a water treatment plant to increase its overall service capacity.

As Mambalam represents the modern, typical fabric of Chennai, the project can be replicated across a vast majority of the city.