Corporation should draw up new contour maps: Experts

Experts are of the opinion that an updated map would go a long way in helping Chennai Corporation handle excess run-off of rain water or blockages in drains. Satyarupa Sekhar, Director, Government Outreach and Advocacy, Citizen Consumer and Civic Action Group (CAG) said the city’s stormwater drain network even in core areas, has been poorly planned. Sekhar, who worked with the Corporation in 2014-15, to create a GIS database for the SWDs, said that the civic body used an outdated map. “This map was built using Autocad and not updated or geo-referenced. It is linked to roads but cannot be seen in a satellite image. The data needs to be updated,” she pointed out.  

S Thirunavukkarasu, a retired engineer with the Public Works Department (PWD), said that standard stormwater drain designs are used, without considering the topography or hydrology. “The Corporation doesn’t have a close-level contour map (0.30m interval), which will give an accurate understanding of runoff and other factors. Other factors, such as the intensity of rainfall, should also be calculated. For example, earlier, the intensity of rain was 12-15mm per hour. Due to change in rainfall pattern, the current intensity goes up to 50mm an hour. We need to design SWD to handle this intensity. That is not done, as the Corporation uses a few standard designs, without taking these factors into consideration. In most drains, a proper slope is not given, due to which there are problems with carrying the run-off to the nearest major canal,” said the engineer, pointing out that many SWD’s are illegally connected to sewerage lines. He added that lack of supervision results in such shoddy execution of projects by the Corporation. 

Refuting the charges of lack of supervision, a senior Corporation official said, “We have a system of regular checks in place. Entities like the World Bank are very particular and joint inspection with the funding agency happens every six months. There is also a third-party quality control team.” 

The official said that 80 per cent of the work in Adyar-Cooum basin has been completed. “We are hopeful of finishing the work in Adyar-Cooum basin by early 2018. The major challenge, however, is the coordination between different departments. Since the extended areas are the focus, works are simultaneously going on from other departments like the Chennai Metro Water Supply and Sewerage Board (CMWSSB),” added the source. 

The tender process for Kovalam basin will start over the next couple of months. “We have given a clear picture to the German development bank, KfW, about how we will go about the project. The revised DPR has been completed for M3 basin, while M1 and M2 will soon follow. Revised DPR is under preparation for Kosasthalaiyar basin and is expected to be completed by September,” said the official.