Civic body’s mega plan to check flooding in city

Chennai: Admitting that the present storm water drain network in the city, most of which is unmapped and haphhazardly laid, is inadequate to weather even a day’s torrential downpour, the Corporation has drawn up plans to extend the existing 1660.31 km drainage system, including constructing new drains and restructuring existing ones. In a 60 page document, the civic body has detailed how it hopes to tackle the recurring issue of flooding in the city and the social and environmental impact of the proposed project, which will cost them an estimated Rs 9400 crore to implement.

The corporation has finally mapped out a detailed action plan to deal with the annual monsoon-related flooding woes of the city. Admitting that the present stormwater drain network, most of which is unmapped and haphazardly laid, is inadequate to deal with the expanding limits of the city or even a day’s torrential rains, the corporation has drawn up plans to extend the existing 1,660.31 km drainage system.

In a 60-page document, the civic body has detailed how it hopes to tackle the recurring issue of flooding in the city and the social and environmental impact of the proposed project, which will cost them an estimated Rs 9,400 crore. The civic body will now have to keep the report in the public domain, and also submit it to the World Bank for a loan. The integrated stormwater drain (ISWD) project will be carried out under the Tamil Nadu Sustainable Urban Development Project (TNSUDP) and concentrate only on the extended parts of the city.

The project will include construction of new drains and reconstruction of existing drains up to 1,002.8 km at an estimated cost of about Rs9,400 crore. The project areas for the ISWD in the extended areas are dived into four drainage basins – Kosasthalaiyar, Cooum, Adyar and Kovalam. Each drainage basin is further divided into 16 watersheds, based on the natural barriers like river, drains, channels, railway lines, road and highways and topography of the area. The entire expanded area will drain the stormwater into Bay of Bengal mainly through Cooum, Adyar and Kosasthalaiyar rivers.

The corporation will also carry out an overall stormwater drain modelling with the help of Anna University and provide flap gates to avoid back flow from rivers into the drains. Sediment control measures will also be incorporated in the new drains. The sediment that collects at the trap will be removed periodically.“This report will be submitted to the World Bank for the approval of the fund and also before the public. Public can also send their response to seswd@chennaicorporation.gov.in to register their opinion,” said a corporation official.

“The corporation must make sure that it has the right plan to construct stormwater drains before seeking huge loans,” said Mr Mark Selvaraj, a road construction expert and advisor to City Connect, an NGO that works with the civic body in designing roads.

According to Mr Selvaraj, creating retention points in the city is the only way to achieve a good stormwater drain system. “Like the city’s natural drains - ponds and lakes - retention points must be made in every area to which the drains from streets will connect. This will finally be connected to a major drain to the sea,” said Selvaraj. If there are no intermediary retention points, it will still lead to inundation, he explained.