‘Concrete drains prevent groundwater recharge’

Thursday, 14 July 2016 07:39 administrator
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The Hindu     14.07.2016 

‘Concrete drains prevent groundwater recharge’

Mayor says groundwater recharge facility will be put in place across the city

Drawing flak:The box-type concrete drains being built by the Mangaluru City Corporation and the National Highways Authority of India would not allow rainwater to seep into the ground, say experts.— Photo: H.S. Manjunath
Drawing flak:The box-type concrete drains being built by the Mangaluru City Corporation and the National Highways Authority of India would not allow rainwater to seep into the ground, say experts.— Photo: H.S. Manjunath

Even as the Mangaluru City Corporation and the National Highways Authority of India (NHAI) are busy building concrete box-type drains along major roads in their jurisdiction, civil engineers and rainwater harvesting exponents have questioned the rationale behind the move.

At a time where every inch of urban space is covered with concrete, the rainwater has no space to percolate down to the soil and groundwater is not being recharged. In Mangaluru city, almost every major road is being topped with concrete and shoulder drains are built using concrete-box technology.

Kannada Sahitya Parishat’s Dakshina Kannada district president Pradeep Kumar Kalkura, who is an engineer, said that the concrete box-type drainage was not suitable for areas where water gets percolated down to the ground immediately. It might be suitable in regions with black soil where even a small shower results in water stagnation and creation of water puddles, he said.

Mr. Kalkura told The Hindu that the earlier model of placing granite slabs at the drainage base was most suited for places like Mangaluru. Under that system, the gaps in between granite slabs would have allowed percolation of water, he said. It had twin benefits. On the one hand, it would have recharged the groundwater and on the other, reduced the inflow to storm water drains. “Because of concrete drains, heavy rain will result in flash floods as the rainwater flows at once into major drains. It is unfortunate that the corporation and the NHAI have introduced a system alien to the region,” Mr. Kalkura said. Another view was expressed by rainwater harvesting exponent Shree Padre. According to him, even if concrete drains are built, the authorities should provide soak pits at regular intervals so that the rainwater gets absorbed by the soil.

Mangaluru Mayor Harinath, being aware of adverse effects of box-type drainage, has been insisting that every drain in his ward, Marakada, should have space for rainwater percolation. Mr. Harinath told The Hindu that for every metre of the drain base, he had got installed PVC pipes to facilitate water percolation.

Not only such a move would help vegetation in the surrounding area, but also would recharge the groundwater. Otherwise the excess water flows somewhere, gets stagnated and becomes breeding ground for many diseases, he said.

He has instructed the engineering department to follow the model across the city, the Mayor said.