German tech, funds boost Corpn plans to create RWH structures

According to a senior Chennai Corporation official, contractors — who have taken up stormwater drain projects under Chennai Mega City Development Mission (CMCDM) — have been instructed to adopt new technology wherever they can.

KfW, a German-based funding agency, which had already agreed to sanction Rs 1,243.15 crore to construct stormwater drains in Kovalam Basin, has provided the new technology and suggested that the civic body create rainwater harvesting structures with the new method.

“The basin is segregated into M1, M2 and M3 components and tenders were invited for M3 component that comprises of Kottivakkam, Palavakkam, Neelankarai, Injambakkam, Uthandi and Sholinganallur. We will use their method in the M3 area extensively,” the official said.As per the German method, rainwater harvesting structures – named Eco Bloc infiltration well – do not need steel reinforcements or cement.

The conventional rainwater harvesting structures in stormwater drains are constructed using cement and have a diameter of 3-foot and depth of 10 feet. The entire well will be left empty, allowing the rainwater to flow in percolate. The active infiltration area of the conventional RWH structures is only 7 square feet at the bottom.

On the other hand, Eco Bloc infiltration wells will be filled and made compact with filtration media that comprises four layers of geotextile (sand filling), fine media, coarse media and geotextile. As against conventional RWH having 7 square feet infiltration area, Eco Bloc infiltration wells will have 120 square feet infiltration area and the water will percolate from all the sides.

“The current RWH wells need intensive and high-cost maintenance including desilting and replacing top slabs and their life span is only three to five years. On the other hand, Eco Bloc infiltration wells do not need high maintenance and pressure washing it by removing the top slab will be sufficient to keep it clean. Also, the German wells will last for more than 50 years,” the official said.

These Eco Bloc infiltration wells will cost Rs 59,000 to construct which is almost equal to the cost of conventional ring well RWH structures. Eco Bloc infiltration wells have been in use in Germany for more than 35 years and takes only five hours to install. The civic body, as on October 18 inspected around 2.96 lakh buildings in the city and identified 1.99 lakh existing rainwater harvesting structures.