The Greater Chennai Corporation has started executing one of the biggest civic infrastructure projects — construction of stormwater drains in northern part of the city to prevent flooding. The civic body is executing the integrated stormwater drain network running to 770 km under the Kosasthalaiyar Basin project at a cost of ₹3,220 crore. The Asian Development Bank (ADB) is funding the project. The work has been awarded in 46 packages.
L. Nandakumar, Chief Engineer (SWD) of the Corporation, said the added areas of the city in north Chennai were severely affected by the December 2015 deluge because of the absence of stormwater drains.
A detailed project report (DPR) has been prepared after studying the rainfall data of 46 years (1971-2016) and by including a combination of macro and micro drain designs by using rainfall of 70 mm an hour. Consisting of several factories and thousands of houses, the loss of property at the Kosasthalaiyar Basin had been estimated at a staggering ₹13,000 crore due to floods, he added.
The DPR spells out construction of integrated storm drains running to 600 km comprising primary, secondary and tertiary drains along with the renovation of 170 km of the existing dilapidated drains, to prevent water stagnation in Tiruvottiyur, Manali, Madhavaram and Ambattur zones. The Kosasthalaiyar Basin covers 3,757 square km area.
Mr. Nandakumar said since the Kosasthalaiyar Basin had hundreds of waterbodies, the civic body went for bathymetric study (a survey to measure the depth of waterbody) to find out the maximum water holding capacity and digital elevation model (DEM) of the project area, thereby creating 11 watershed zones and 7,300 micro catchment points.
The DPR has identified eight major canals (belonging to the Water Resources department) and 71 small waterbodies of the civic body which are part of the project area and serves the Kosasthalaiyar.
The project has identified Ambattur, Korattur, and Retteri lakes of the Water Resources Department and Sadayankulam and Kadapakkam lakes of the Corporation and 65 minor water bodies, for renovation and deepening. The rejuvenation of the six lakes and 65 waterbodies would increase the storage capacity to 23 million cubic metres against the present 10 million cubic metres.
Pumping stations
For the two flood-prone localities of Ernavur and Kargil Nagar, which are on a lower terrain and where evacuating the water through natural gravity is not feasible, the civic body has proposed to build pumping stations, fix shutters at the tail end of the drains and pump out water into the Buckingham Canal.
Mr. Nandakumar said the construction work, which was stalled due to the second wave of COVID-19 and delayed by the contractors citing high construction material cost, had resumed after the civic body cracked the whip by issuing notices to the contractors. He said more than 5% of the work had been completed and the project was proposed to be completed within 36 months.
