CHENNAI: A month back when Corporation officials began installing stormwater drains (SWD) in Kapaleeshwarar Nagar in Neelankarai, a strong community of 3,000-odd residents nipped the project in the bud. They repeatedly questioned the need to construct such drains barely 500 metres away from the sea, and finally stopped the project altogether. Similarly, since 1999, residents of Besant Nagar opposed the construction of SWDs in their locality. Even now, a handful of residents are trying their best to stall the linking of the drains between 1st Cross Street and 1st Avenue.
What is the need to drain rainwater into the sea along Chennai’s coast? Why can’t water be directed into the groundwater table instead? Why not build recharge wells instead of storm water drains? These are the broad questions raised by locals, environmentalists and activists, which kindle the need to question the functionality and purpose of these widely installed structures of SWDs.
What’s the alternative
With an average rainfall of 1,400 mm a year, every resident can be comfortably provided with 162 litres per day, if rainwater was harvested using recharge wells, said experts. Instead, SWD directly discharges rainwater into the sea, wasting it. Sekhar Raghavan, an expert in rainwater harvesting for over two decades, questioned the need for SWDs when 75 per cent of the city is made up of sandy alluvial soil which has a high absorption quality.
“The coastal aquifer from Besant Nagar to Muttukadu has extremely low water table levels combined with high absorption rates. The scope for recharge is very high right from Ennore in such a scenario. "Recharge wells can be sunk to a depth of 20ft so as to reach sandy soil later to have maximum percolation"
To collectively oppose the installation of storm water drains along ECR, residents from Neelankarai, Besant Nagar, Valmiki Nagar, and Kottivakkam have come together to form Save Water And Recharge Aquifers Network (SWARAN). This comes in the wake of Chennai Corporation, which will start work by June to construct integrated storm water drain structures along the Kovalam basin covering areas like Kottivakkam, Palavakkam, Injambakkam, Akkarai and Uthandi.
Experts said that overextraction from the water-rich shallow aquifer resulted mainly in saline intrusion. If a series of open wells and recharge wells were constructed along the coast, rainwater will not get discharged into the sea, thus helping the city to avoid a constant water crisis. “We used to get clean drinking water even at 15 ft due to our proximity to coastal aquifers. This is the case with all localities along ECR. Even during the 2015 floods we didn’t have even water stagnation anywhere. This is because the soil takes in even huge quantities of water,” said B Sivakumar, president of Kapalesshwarar Nagar Resident Welfare Association in Neelankarai.
Ironically, a few months back, Corporation officials had installed recharge wells in Besant Nagar and two streets in T Nagar to avoid flooding. “It is peculiar that the civic body, which promotes SWDs, set up a series of recharge wells almost in the same location. As SWD has thick concrete on three sides, water cannot percolate into the ground. Now with the new integrated system, they are leaving a small portion empty to facilitate recharge. Instead, a recharge well can be sunk in which rainwater is saved and at the same time it can be a flood mitigant,” said Ramshankar, a member of Rain Centre.
Recharge-friendly city
Due to rapid urbanisation, most open spaces have been used for construction or converted into roads. This includes dried-up water bodies which are covered with concrete. As a result, space for rainwater to penetrate into the ground has been compromised. Experts said that if either side of the road is left unpaved, water stagnation can be drastically reduced and at the same time ground water recharge will be at its maximum.
Also, rainwater must be harvested to the maximum extent right at individual houses and flats to minimise the amount of water that comes onto the road. For this, rainwater from the roof can be directed to the sump and run-off water from the driveway can be directed into a recharge well. Mini speed breakers can also be installed before the gate to push the rainwater into the recharge well and prevent them from stagnating on the road.
Next, storm water drains installed in areas where groundwater tables are high like MRC Nagar or in low lying areas like Madipakkam and Kilkatalai, should be diverted into temple tanks or small ponds after desilting them. “In Mylapore and Tiruvottiyur, two huge temple tanks have gone bone-dry. If water which stagnates in these localities is diverted into the tanks, residents will never face water shortage. A few recharge wells can be sunk in the tank’s bed, also,” said Sekhar.
Why recharge well is a sustainable option
● Directs rainwater straight to
the aquifer
● Can be used in both sandy alluvial and clayey areas
● Prevents saline intrusion and boosts water table levels
● Prevents water stagnation
● A well-like structure with 3 ft- 4 ft width and 10 ft-15 ft depth costs `17,000-`20,000 and can be installed in a day’s time
● Needs to be cleaned only once in six months or a year
● Can be installed along roads and inside houses too
Why SWDs failed
● Existing structures do not allow rainwater to percolate into the groundwater table
● Sewage, garbage let into SWDs due to poor design and planning
● Concrete slabs on three sides, no space for water to go into the ground
● Drains rainwater, the only source of freshwater for the city, directly into the sea
● High on cost and labour, time-consuming process to install
● Not needed in coastal areas and localities with a low water table