It may be a part of Chennai’s heritage, conceived as a lifeline that would save Chennai during cyclones. But the city’s labyrinthine underground stormwater network, laid during the British era to drain away large quantities of rainwater, is crumbling. The old arch drains are used to carry huge amounts of stormwater to major disposal points, including canals, during heavy spells of rain.
The magnificent structures run nearly 800 km underneath several neighbourhoods in the core city. But they are collapsing, say Chennai Corporation engineers.
Civic authorities are in a scramble to restore it. It was while monitoring flooding this year that the authorities found that many of the drains built a century ago were failing. “At least 22 drains constructed using brick and mortar have collapsed. The government has sought estimates for the restoration of the drains,” says an official of the Chennai Corporation.
The location of these drains is only anecdotally known, passed on from one generation of Corporation employees to the next. “Believe it or not, there is no inventory of the old drains,” says a senior Corporation engineer. No accurate maps are there to serve as ready reference.
For example, the old arch drain along Sardar Patel Road near Raj Bhavan plays a key role in reducing flooding in neighbourhoods there. However, Corporation officials are not able to properly maintain the huge drain because of the lack of information on such facilities. The drains are located several feet beneath the road surface without any apparent manhole. The officials do not know what the actual condition of the drain is.
Digging out the reasons
Civic officials are unable to pinpoint the reasons for the poor condition of some of these drains. They, however, do cite the damage caused by major infrastructure projects, such as telecom, power and water supply that require the digging of the earth.
A stormwater drain built under T.T.K. Road before Independence, which is still in use.
Vikas Bhurat Jain, a resident of Sowcarpet, says flooding was not reported in his neighbourhood during the 2015 floods primarily because of the old drain constructed by British engineers some 100 years ago. “The design of the old drain is faultless. The slopes are perfect. Even during the peak flood season, most parts of Sowcarpet, including NSC Bose Road and Mint Street, were not flooded,” says Mr. Jain.
“As the old drains functioned well, the business community was able to carry out relief operations from Sowcarpet. Former Chief Minister Jayalalithaa lauded the efforts of the residents of Sowcarpet during the disaster,” says Mr. Jain.
Disaster management expert N. Mathavan, who developed a disaster resilience index for Chennai, says the dimensions of the rettai kannu kaalvai developed several feet below Broadway during the British era were so huge that a lorry could pass inside. “The workers, who clean the drain, used to marvel at the magnificence of the structure every time they entered it to desilt. The drain has a double arch. It was in good condition, maintained properly even ten years ago. Something has gone wrong in the last decade or so,” says Mr. Mathavan.
Some point fingers at Metro Rail. Corporation engineers say that the civic body gave permission to the Metro Rail consultant for carrying out soil investigation as part of the preparation of the detailed project report in 2003. “Metro Rail might have failed to study the impact of the project on old arch stormwater drains that are crucial for disaster preparedness,” says a corporation engineer.
Even as former councillors have claimed that MetroRail “might have probably damaged many drains developed by the British engineers,” Corporation engineers and Metro Rail engineers have not submitted any report on such damage to the Corporation Council in the past few years of Metro Rail work.
Inscrutable maze
Tracing the history of stormwater drains, historian V. Sriram says the first stormwater drain was constructed under Parish Venkatachala Iyer Street in George Town in 1875. “Such old stormwater drains may be part of our heritage. But this is a public utility. There will be wear and tear. Only engineers know how to make the right decision when such damage is reported. Corporation engineers should check the old administrative reports of the Corporation before restoring the structures. They are not maintaining old documents, so it will be a challenge,” says Mr. Sriram.
A few Corporation engineers who joined recently say that the flow of stormwater in the old drains “confuses them.” For example, the flow of stormwater in the old drain in Broadway is in both directions. “There are two slopes. I am yet to understand the design plan of the British engineers. The water flow toward Park station, towards beach in one direction, and the flow in the opposite direction, towards Old Jail Road and Royapuram, has us puzzled,” says an engineer.
“There were two different slopes. I was confused. In one ward, the water flow is in one direction. The flow is in the opposite direction in the neighbouring ward,” says the engineer. This runs contrary to what they have learned as engineers, they say.
Nevertheless, the old arch drains continue to be crucial for the city’s flooding preparedness. But they are often dealt with in a haphazard manner. “We even drill holes on such huge drains to ensure flow of water rapidly. Traffic police personnel also damage such drains using heavy equipment during heavy downpour to reduce traffic congestion on VIP routes,” says a Corporation engineer.
Former councillors stress the need for maintaining the old arch drains without demolishing them and reconstructing them. “The Corporation is not maintaining the old arch drains well. Following senior citizens’ requests, an old arch drain under P.V. Koil Street was desilted a few years ago. The drain runs beneath a temple and joins Buckingham Canal near Ambedkar Bridge. This has reduced flooding in Srinivasa Road in Mylapore,” says Mangala Raj, former Congress councillor.
According to Corporation engineers, the networks of telecommunication and electricity service-providers have criss-crossed the drains, causing hindrance to their maintenance. “The civic body engineers are unable to regulate these projects,” says Mr. Mangala Raj.
Old vs. new
A few Chennai Corporation engineers bat for the British-era design of arch drains. They say the drains were designed as per sound engineering principles and withstand heavy loads.“The arch helps ensure that the resultant force acting downwards is zero on the drain. The bricks used 100 years ago were very strong. There has been no corrosion. So such drains are strong. But the new RCC structures are flat and do not withstand heavy load. They may last for just 50 years,” says a Corporation engineer.
A few engineers point to the fact that old brick and mortar drains that were restored by Chennai Corporation a few years ago have failed. “Some of the contractors had been issued work order to demolish and reconstruct new drains using RCC structure. But they just plastered the drain without demolishing the old brick drain and only placed a RCC slab on top. They knew that the brick and mortar drains were very strong. The Corporation was unable to check the allegations on such corrupt practices by contractors who swindled money as the structures were located underground,” an engineer said.
The city’s stormwater drain network has grown significantly to 1,894 km because of the rapid expansion of new stormwater drains constructed using reinforced cement concrete. CMDA former member-Chief Urban Planner S.Santhanam argues for a scientific approach to revamping the old network in keeping with technology changes. He says the structural condition of old arch drains could have deteriorated if the maintenance was poor for many years.
“RCC technology is superior to the old technology of arch drains if the design is proper and work is good. We have to study the condition of the old arch drains and find a solution using modern technology,” says Mr. Santhanam.
Funding the repair
Following reports of water stagnation this year in locations hitherto unaffected by inundation, the Chennai Corporation is studying the reasons for the problem. However, work on restoration may not start next year in all areas.
Senior officials say the work will be restricted to 22 locations that have been damaged and reported by flood monitoring officers. “Funding from multilateral agencies for new stromwater drains in added areas has been delayed.
We need at least ₹3,000 crore for new stormwater drains. JICA has rejected the request for funding of stormwater drains. Other multilateral agencies are delaying the release of funds for Kosasthalaiyar and Kovalam basins. Work on 22 damaged locations has to be done using government funding,” says an official.
The unexpected flooding of roads near Madras High Court adjacent to Broadway opened a Pandora’s Box this Northeast monsoon. Severe flooding in roads such as Chamiers Road was a cause of concern for the civic officials.
Officials are keeping their fingers crossed as civic issues reported by residents in old areas including Royapuram, Teynampet, Purasawalkam, Triplicane, Nungambakkam and Mylapore have not been resolved during the monsoon. “This was not the case a few years ago. This is news. Areas with old arch drains did not have severe inundation. Now they seem to be failing,” says an official.
