Inundation in several parts of the city, some for over 120 hours, raised doubts on the effectiveness of the stormwater drains, that are being built and upgraded for the past two decades spending thousands of crores.
While a hashtag with what happened to Rs 4000 crore stormwater drains went viral on social media platforms, Municipal Administration, Urban and Water Supply Minister K.N Nehru had to clarify that it was not true and only half that amount had been spent by the DMK since it came to power in 2021 and the remaining funds would be utilised in the coming years.
Many also alleged of ‘missing links’ of stormwater drain that caused inundation. Now, the Corporation has shared details of the different projects and the percentage of completion.
In October 2023, Greater Chennai Corporation (GCC) Commissioner issued a document to officials at all levels and the stakeholders regarding monsoon preparedness which stated: “So far, approximately 3,331.19 km of SWD have been provided for the city limits, including 876.19 km constructed during the last two-and-a-half-years in addition to the existing 2,455 km existing storm water drains.
The focus of GCC should be to complete the balance missing links in the storm water drain network. Focus should thus be on the left over 3000 meters in about 30 locations, including those in the arterial roads maintained by the Highways Department and under construction by the Corporation.
Corporation officials at Head Office and Zones must follow up with the Highways Department to complete their portion of missing links of Storm Water Drain especially in EVR Periyar Salai, Anna Salai, Inner Ring Road and residual works of GCC, such as Rajaji Street, Barracks road, Medavakkam tank road etc, he had said.
The ₹5866.06 crore project
The inundation across several parts in Chennai city, raised questions if stormwater drain was effectively installed by the Greater Chennai Corporation. With 67.71% completion of the total 1408.83 km length, the civic body details the status of the infrastructure.
The total length of the stormwater drain under several schemes to be installed by the Storm Water Drain Department of the Greater Chennai Corporation is 1408.83 km for an estimated ₹5866.06 crore, as per data shared by the civic body. Of this, 953.96 km was completed with ₹2,891.30 crore under various schemes thus far, the data revealed. It means, so far - 67.71% of the total length has been completed.
In this, the work to install 220.34 km of SWD was completed using the Singara Chennai 2.0 funds, flood relief funds, Infrastructure and Amenities (I&A) Fund, Capital Grant Fund and World Bank fund - totally summing up to 699.71 crore.
As for the remaining drains that lead up to Kosasthalaiyar and Kovalam basins, so far 61.73% of the work is done and the remaining are mulled to be finished in 18 months, as per the civic body.
More ground to cover
According to Greater Chennai Corporation Commissioner J. Radhakrishnan: ”Existing drains can withstand normal and above average rains of roughly 10 cm spread over 48-72 hours and not the 50-cm rainfall that was recorded in Sholinganallur and Royapuram.”
“Chennai city stormwater drain improvement program has two components. The first is funded under various schemes of the State government funds, Chennai corporation’s own resources and World Bank funding. This was sanctioned first and consisted of inner city drains and many missing links, which have been completed.”
He said, “The second is through other externally aided projects, funded by the Asian Development Bank (ADB), KfW (a German Bank) and the State Disaster Management Fund. This is being implemented in the Kosasthalaiyar and Kovalam basins. It consists of longer and larger river basin drain works. Their execution period as per the project itself is up to the end of 2024 and in some cases 2025. It is ₹5,166 crore project and only 42% of works have been completed.”
“Both are two separate work permit packages and the degree of progress is different. One has been completed and the other is in progress, but both are as per timelines. But the issue is being twisted by mixing them up,” said the Corporation Commissioner.
Outlet issues
The Commissioner added: “Chennai has around 3,331 km of stormwater drains. There are 33 micro canals maintained by GCC, 14 drains with the Water Resources Department, and Buckingham Canal, Adayar, Cooum and Kosathalayar. Yet, the actual discharge to the sea is only via Ennore Creek in the north region, Adayar and Cooum in the Central and Kovalam Basin in the south - with Pallikaranai marsh also being a holding point.
Unrelenting rain along with high tidal waves increased water level in the three rivers and Buckingham Canal, leading to large-scale over-wash from the other micro and major canals, SWD. Once the rain stopped in most areas, the water drained rapidly.
“As soon as the relief work ends we would go for a detailed analysis with experts in the field and it would be too early to attribute it to any one cause,” he said.
The Pallikaranai question
The watershed of Pallikaranai marshland situated in South Chennai Metropolitan limits has a drainage area of about 225 sq. km. in which 60 or more number of medium and minor irrigation tanks are situated.
Due to the changes in land use patterns for residential and industrial needs, the channels draining the surplus water of these tanks were disrupted. Hence, to convey the surplus water of the tanks safely into Pallikaranai marshland a proposal for restoration / formation of the disrupted surplus channels with open channels, closed conduits under the roads or a combination of both depending on the present land use is under consideration at a cost of about ₹1000 crore.
The 200 feet road which connects OMR and Velachery through Pallikaranai marsh area was completely cut off from any form of vehicular traffic on December 6, 2023 due to storm water stagnation. | Photo Credit: S.R. Raghunathan
To avoid inundation in the low-lying areas of Tambaram, Mudichur, and Perungalathur areas in the Adyar Basin, construction of a stormwater drain for 4400 meters at an estimated cost of ₹14.5 crore is in progress under CRIDP 2016 – 2017 scheme through Highways and Minor Ports department.
Similarly, in other urban areas in Adyar and Kovalam Basin adjoining Chennai, a proposal for forming stormwater drains in areas under the jurisdiction of Highways, Rural Development, Municipal Administration and Town Panchayats are contemplated by the respective departments at an estimated ₹230 crore.
Moreover, the civic body had earlier clarified that the infrastructure can withstand normal rains and not torrential, incessant rains as seen on December 3 and 4.
