The fresh designs for rainwater harvesting structures that were recommended by an audit report have now been incorporated in the Tamil Nadu Combined Development and Building Rules, 2019. If implemented stringently, they could help raise groundwater levels in the city.
The recommendations were made in a report submitted by Rain Centre, a city-based voluntary organisation, in 2016.
Planning permission
The new building rules insist on RWH structures for different types of structures to be granted planning permission. They have also detailed instructions on greywater recycling to be done in new structures.
Rain Centre director Sekar Raghavan recalled that the city’s groundwater level rose by six metres during the torrential downpour in 2005, though only 40-50% of the RWH structures were effective. If the new rules are implemented, the city will be able to reap the benefits in two or three years, he added. At present, the city’s average groundwater level is at a depth of eight metres.
Last February, the level was at a depth of five-six metres. This indicated excess usage of groundwater resources and lack of rain to replenish them.
Fallback option
With effective RWH structures, residents would be able to fall back on groundwater, particularly during a drought.
There is a need to build RWH structures and maintain them despite failed monsoons or less rainfall, as percolation would be more effective. Nearly 85% of rain water could be harnessed, Mr. Raghavan said.
The new building rules insist that recharge wells should be dug instead of recharge pits. Moreover, driveway runoff should also be harnessed apart from the water from the rooftops, as per the recommendations of Rain Centre. Some of the other recommendations of the audit report were third party monitoring of the projects that were completed and implementation of a water tariff system.
