In the wake of depleting groundwater level, most places in the State face a severe water crisis in recent years. With no dramatic change in rainfall yield, and a fall in the number of rainy days, a lot of focus is on harnessing rainwater and improving groundwater level.
As part of the initiative, Madurai Corporation has installed a new model of rainwater harvesting structure on a pilot basis along roadsides at two places in the city. This advanced model is an addition to the existing rainwater harvesting structures built recently by the civic body at 153 low-lying spots. According to Corporation officials, the new model with ‘eco bloc,’ made of plastic, will help in faster percolation of rainwater, compared to the existing model.
The new model has been installed near Raja Muthiah Mandram on Dr. Ambedkar Road and Nirmala Girls Higher Secondary School on Kamaraj Salai.
Corporation Commissioner S. Visakan says that the existing rainwater structures do prevent waterlogging on roads. “This is an additional move to conserve more rainwater. Greater Chennai Corporation has installed the new model at 40 places and they have proved to be successful. We are testing the model and once its efficacy is proved, we will erect them in many places,” he says.
Design
This structure is built by digging the ground to a depth of about 10 feet and creating multiple layers of filters, including one made of geo fabric (a polystyrene sheet). “The multiple layers of filters help remove sludge and dirt from stagnant rainwater so that pure water reaches the ground,” says a Corporation engineer.
Concrete blocks, which can withstand heavy weight, are placed on top of this structure along the road. The main component of the model is the ‘eco bloc,’ says Mr. Visakan. “Unlike the existing model, water seeps through it from all directions to the ground. This will ensure faster recharge of groundwater,” he says.
The structure can be erected at parks, on the roadside and at parking lots. “The main advantage of this model is that the size of the structure can be easily changed by either increasing or decreasing the number of eco blocs,” says the engineer.
At any given time, each structure can hold up to 3,000 litres of water and drain it into the ground. “During trial, 5,000 litres of water drained in an hour,” says the engineer.
A better alternative?
The existing rainwater harvesting structures, consisting of concrete rings and slotted pipes (pipes with holes), have been getting mixed reviews in draining rainwater. While the structure has been helpful in preventing waterlogging on Tamil Sangam Road and Palanganatham Bypass Road, a few other structures constructed elsewhere do not serve the purpose.
Poor maintenance makes them unfit for draining water in the long run, say residents. For instance, the earlier model installed near Nirmala Girls Higher Secondary School is in a shambles now. Slush, mud and other waste cover the holes of the rainwater harvesting structure, preventing water from entering it. “This place is prone to heavy waterlogging after rain. Though the structure was helpful in the first few days, it did not serve the purpose later,” says P. Subramanian, an autorickshaw driver operating in the area.
A similar problem plagues the structures present on Theni Main Road. “Unless regular maintenance work is undertaken, these structures will not serve the purpose,” says M. Singaravelu, a shopkeeper in the area.
A Corporation official says in the existing model, the entire structure has to be dismantled for removal of silt. “But the new structure requires minimal upkeep. We can just remove the top layer of pebbles and clean the geo fabric. Moreover, since the capacity of the new model is three times higher, the water will drain quickly,” he says.
