As sea water intrudes into the groundwater of the heart of Chennai city, an ecological overhaul is on the cards
Blaring horns, hawking vendors and loud chatter characterise bustling Mylapore, the heart of Chennai city, a congested and raucous old settlement that was built around a temple.
Mylapore is cosmopolitan Chennai – cutting across class lines, with the rich mansions, middle income homes and the vulnerable lower income population living together in tight clusters.
In 2018, as the Chennai Corporation worked with the 100 Resilient Cities under the “Water As Leverage” programme initiated by the Netherlands Entreprise Agency and a host of organisations and experts from India and abroad, IIT Madras was commissioned to conduct groundwater samples in several locations across Mylapore.
Their findings were grim.
“There is enormous seawater intrusion due to the restaurants and businesses and residences that are pumping groundwater at huge levels,” said Eva Pfannes, Director of Ooze Architects, a Rotterdam based firm. “IIT Madras found that there was 4000 ppm (parts per million) of salt in the groundwater in Mylapore as against the acceptable standard of 500 ppm as recommended by the World Health Organisation. 500 ppm is the maximum limit that can be present in groundwater,” she told The Lede.
This means that thanks to the furious pumping of groundwater, the sea, which is not very far from Mylapore, has begun to seep inland and mixing with the water table.
“In most parts of Mylapore the groundwater is already salty,” said Pfannes. “If we don’t act now, it will be gone forever.”
The consequence of sea water intrusion is dire – there will be no drinking water available if this continues and it will also lead to the destruction of flora in the area.
The immediate mission for the team working on Mylapore is to push back the sea water and recharge ground water. This project, developed by the City of 1000 Tanks is called the Mylapore Trail.
Ironically, the 100 Resilient Cities organisation sped up work with the Chennai Corporation immediately after the devastating floods of 2015. Four years later, in a year of severe water scarcity, the solutions are exactly the same.
The idea of this program is to use water as leverage – to store flood waters and save it during drought. This means not only storing water in tanks, lakes, ponds, reservoirs or in rain water harvesting pits but storing water underground so that when the monsoon fails, there is no problem.
The plan is holistic and is what Eva Pfannes calls, a combination of green and blue – of plants and water.
The Mylapore Trail project has built around Chennai’s existing water body ecosystem – the temple tanks, the lakes and what are called ery (pond or lake) in Tamil. These water bodies are centuries old and are naturally interconnected. They serve as storage areas for rainwater during the monsoon and also replenish the groundwater table.
“The people of Chennai have been working for many centuries with nature based solutions which have now been forgotten or lost thanks to rapid urbanisation,” said Eva Pfannes.
Before rapid urbanisation and construction set in, local communities were involved in managing and maintaining these water bodies. Many water bodies, once thriving, are now built over, concretised or neglected.
Political short sightedness has only exacerbated the problem. Two-thirds of the city is paved with tar roads, meaning zero percolation into the ground here. 50% of the water used by the city’s residents can be recycled and reused but that is not being done.
Rainfall pattern over decades has not changed drastically – nine dry months are followed by three months of heavy bursts of rainfall. This rain water which used to be stored earlier in erys and tanks is now going through the storm water lines into the sea.
With an average of around 1600 mm of rainfall annually, Chennai is in prime position to manage the water demands of its one crore population.
But this needs sustainable long term plans.
The team of City of 1000 Tanks has identified two “lost tanks” in Mylapore which are completely dry. Their effort will be to reclaim, restore and rejuvenate them.
“The Chitrakulam tank for example has been empty for a long time and it is a constant struggle to keep the Kapaleeswarar temple tank filled,” she said. Smaller tanks around these would need restoring so that rainwater can be stored.
“Tanks like these filled with rainwater will recharge groundwater rapidly,” she explained.
But in a tropical climate like Chennai’s, standing water could breed dengue-carrying mosquitoes.
“We have a solution for that. We would install solar pumps that keep the water moving so that no mosquitoes can breed. This has been done in Singapore and we can look at a similar solution here too,” she said.
Along the circumference of the famous Kapaleeswarar temple in Mylapore the project envisages the construction of bioswales.
“Bioswales are storm water runoff conveyance systems that provide an alternative to storm sewers. They can absorb low flows or carry runoff from heavy rains to storm sewer inlets or directly to surface waters.
Bioswales improve water quality by infiltrating the first flush of storm water runoff and filtering the large storm flows they convey. The majority of annual precipitation comes from frequent, small rain events. Much of the value of bioswales comes from infiltrating and filtering nearly all of this water,” according to the US Department of Agriculture.
As the water runs along these bioswales, the rocks and stones in its course perform a filtering effect, removing debris and other waste and pollutants from the rainwater.
Bioswales are connected up to the storm water drain systems and ensure that only water flows in and not the debris which clogs the storm water drain, causing flooding during monsoon.
Bioswales are also effective groundwater recharge tools.
The other idea is to construct islands of plant filtration units next to roads and other available open spaces in Mylapore.
These constructed wetlands would consist of sand beds with a sub-surface water flow and a variety of plants.
“There are beautiful plants in the city that are native to wetlands,” said Eva Pfannes. “These will provide green cover to the city, bringing down the heat and will also look beautiful. These wetlands naturally treat and purify grey water. The wetlands will also slow down the rainwater from entering the storm water system, acting as a flood mitigation tool,” she said.
Phragmites australis also known as the common reed is an excellent plant that naturally treats sewage in wetland like conditions.
Another type of constructed wetland is also being planned for use in sewage treatment, thereby reducing the burden on the city’s civic bodies.
“A constructed wetland is essentially, a shallow basin filled with a substrate, usually sand and gravel, and planted with vegetation tolerant of saturated conditions. Constructed wetlands are efficient sanitation technologies and act as bio-filters that remove a range of pollutants from wastewater. They also increase the biodiversity in urban areas and present exciting opportunities for decentralised wastewater treatment in the city,” according to the City of 1000 Tanks.
Canals and rivers that flow through Mylapore will be cleaned and “renaturalised”. Riparian buffers are planned to be created along the length of canals and rivers.
Riparian buffers are plants and vegetation native to the area that will be grown along the sides of the water body so that when it rains heavily, the water will be absorbed, slowed down and carried downstream.
The riparian buffers act literally as buffers – protecting human habitations along the water by preventing flooding.
These are water holding areas and can be created in a number of spaces including in playgrounds and parks.
They are meant to hold rainwater during the monsoon and during heavy rainfall, they release water slowly to a waterway nearby, thus preventing flooding.
Detention parks are like small ponds and help in groundwater recharge as well.
Another key part of the project would be to dig recharge wells in parts of Mylapore where human movement is restricted. Recharge wells are basically concrete lined borewells that are dug right up to the deep acquifer.
During rainfall, the water directly reaches the acquifer, thereby speeding up recharge of the ground water table.
“No project can be successful without the involvement of the citizens,” said Eva Pfannes.
We need a paradigm shift in the way we think about water and rainwater. This project is likely to take about five years to complete. But the direct beneficiaries of the project would be 80,000 people while the indirect beneficiaries would be the entire population of Chennai,” she said.
The project is estimated to cost around USD 16 million of which the Chennai Corporation will contribute USD 6 million. The United Nations’ Green Climate Fund is expected to provide funding for the rest of the project.
Pfannes says four schools have already shown interest in running educational and awareness programs about the City of 1000 Tanks project.
She says that decentralisation is the way to go – whether it is grey water recycling, rain water harvesting or sewage treatment - individual buildings and establishments need to take up the cause.
“We start with something immediately and build up trust and then we can build up a good group of stakeholders. All of the solutions that are proposed are low maintenance but still need to be taken care of. We need to work with different groups of society and the government so we can experiment,” she said.
The team spoke to hundreds of residents, businesspersons, street vendors and members of vulnerable populations living in slums in Mylapore to understand what they wanted their city to be like and what their priorities were.
“The solutions that we finally have come up with helps improve their quality of life as they want it to along with increasing productivity,” said Pfannes. The team insists that there would be no displacement of the vulnerable population in Mylapore in their effort at conservation.
Mylapore Trail along with three other similar projects, if implemented as envisioned, is expected to bring as much as 200 million litres of water a day to these areas. This is equal or more than a desalination plant in Chennai.
“Desalination plants are bad for marine ecology and they also increase carbon footprint,” said Eva Pfannes. “They are not recommended solutions.”
The Mylapore Trail project alone is expected to provide 4 MLD of water to the area’s residents. The project is expected to have a benefit-cost ratio of 3.5, since residents would save on buying expensive tanker water and health and business interruption costs would be reduced.
“The Mylapore project can be replicated across 53 other temple tanks in Chennai for a total of more than 60 MLD of recharge. Beyond Chennai, there are 2359 temple tanks across the state of Tamil Nadu, many of which no longer function to their full potential for recharge,” according to the City of 1000 Tanks team.
The Chennai Metropolitan Water Supply and Sewerage Board (CMWSSB) also known as Metro Water would implement the key aspects of the project, including collection, distribution and treatment of the water retained as a result of this project.
The project has been split into a number of parts – this part is called the Mylapore Trail and is being carried out by a team called The City of 1000 Tanks – and the partners in the project are many.
Ooze Architects, Madras Terrace, IIT Madras, Care Earth Trust, Paperman Foundation, Biomatrix, Pitchandikulam Forest Consultants, The Rain Centre, IRCDUC, Urayugal Social Welfare Trust, The Goethe Institute, TU Delft, IHE Delft, HKV Consultants, Professor T Swaminathan and Ramakrishnan Venkatesh.
All of these are working with guidance from Henk Ovink, the Special Envoy for International Water Affairs of the Kingdom of The Netherlands and the Netherlands Enterprise Agency.
The Greater Chennai Corporation is leading the effort. The Asian Infrastructure Investment Bank, the Dutch Development Bank, the International Architecture Biennale Rotterdam, Architecture Workroom Brussels, the Global Centre on Adaptation and UN Habitat, supported by the UN/World Bank High Level Panel on Water are also involved in the Mylapore project.