CHENNAI: With the city roads becoming increasingly dangerous for motorists due to sudden cave-ins, the Chennai Metropolitan Water Supply and Sewerage Board (Metro Water) has decided to overhaul the entire underground drainage system. A senior Metro Water official said that the sewage system will be segregated into sewage catchment areas centering around four sewage treatment plants (STP). The city currently has STPs in Koyambedu, Perungudi, Nesapakkam and Sholinganallur.
“Most of the underground sewer lines in the city are 25-30 years old. Due to leakages and some external factors such as construction works on the road, cave-ins occur. Once the pipelines are replaced, such incidents will come down,” he said.
Meanwhile, officials are in the process of finalising a contractor to replace existing pipelines falling under Nesapakkam STP catchment area with cast iron (CI) and ductile iron (DI) pipes at an estimated cost of Rs 800 crore. The new pipelines will be laid in a way to leverage gravitational force rather than depending on pumps, the official added.
Metro Water has plans to complete the works in Nesapakkam catchment area in two years and start works in other catchment areas later. “The completion of the works will take much time since we need to obtain permissions from several departments such as Chennai Corporation and Police to carry out the works.”
When asked about a recent cave-in incident on Karukku Main Road in Ambattur, the official explained that sewer lines in the extended areas were laid while they were functioning as separate local bodies. “Pipes were mostly concrete that have a lesser lifespan than CI and DI. Under the new project, those concrete pipes will be replaced,” the official added.
Alagirisamy Salai in KK Nagar, Rajiv Gandhi IT Expressway near Madhya Kailash Junction, Karukku Main Road, and RK Mutt Road in Mylapore are the stretches that face frequent road cave-ins. It may be recalled that Metro Water replaced large sewage pipelines under Anna Main Road in KK Nagar a few years ago since the road suffered repeated subsidence.
Sewage leaks from defective pipelines cause significant soil erosion by washing away surrounding soil particles, creating underground voids, and leading to ground subsidence or cave-ins.