With wells instead of recharge pits, new RWH structures to help stave off future water scarcity

“For all these years, the natural recharge of aquifer was happening in the city given the dysfunctional model,” said Sekhar Raghavan of the Rain Center.

With an aim to replace the existing RWH structures, the new ‘Tamil Nadu Combined Development and Building Rules, 2019,’ has mandated recharge wells instead of pits to make sure the rainwater is indeed harvested.

“We submitted an audit report to the Chennai Metropolitan Development Authority highlighting the pitfalls in the existing RWH structure a couple of years ago. The new system will have recharge wells that have a life of 10 to 15 years, unlike the recharge pits which have only two years,” said Sekhar Raghavan.

According to him, the two models are like borewells and open wells. “It means that the wells can recharge efficiently given they are recharged once in a year. But the pits have to be abandoned after two years and replaced with a new one,” he added.

During heavy rains, water was overflowing from the RWH structures instead of percolating into the soil and recharging the aquifer, experts added.

As per the new rule, recharge wells can have a diameter of 3, 4 or 5 feet, with the depth remaining constant at 15 meters. The diameter of the wells would depend on the catchment areas. “The catchment area of 100 square meter is suitable for wells of 3 feet in diameter. Similarly, the area of over 100 square meter but less than 200 square meter can accommodate a 4 feet diameter well. A 5 feet diameter well is required for a catchment area of over 200 square meters,” he explained.

In the rules brought into force in 2001, there were three types of harvesting systems: recharge pit, trench or dug up wells, which can prevent the runoff water getting wasted. The Town Planning section of the Chennai Corporation or the Municipality is authorised to provide a no-objection certificate and an approval.

These models are adapted based on the road design, terrain and rainfall. The percolation pits or wells is only suitable for the urban areas. The Stormwater Drain department of the city Corporation is the nodal agency to take care of the RWH installation in public spaces. While the 2001 rules considered saving only the rooftop water, the new model will help conserve water from the driveways, too.

“The result will be evident after just one monsoon. A recharge well can be drilled up to 12 feet in the rocky terrain in places like Tirusulam and Pallavaram. This model will not work in the places like Perungudi and Kandanchavadi where there is clay soil. Also, this will not work out at a few places in Nungambakkam including the CBDT and MOP Vaishnav College due to presence of clay. For the rest of the city, this model is suitable.”