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Chennai’s storm water drain work has become a major disruption for normal life in a big city. But it could well have been minimised or avoided.
One striking feature of Chennai Metro Rail’s construction methods is the speed at which the concrete spans and pillars come up along the elevated alignment. A lot of the concrete fabrication work for CMRL takes place off-site, and at a steady pace. This fast-paced work along stretches that don’t need tunnelling has already made a limited rail service in parts of the network between Porur and Poonamallee feasible by the end of next year.
What if the storm water drain work practice in Chennai had been similar? Logically, it should have been possible to create the drains within a few weeks and close them up, restoring normalcy. The present situation is one of gridlock or severe traffic disruption, new residential areas facing higher traffic flows, and vast dust clouds released into thickly populated areas.
The massive SWD project is also questioned by experts on whether it is the best method to handle the flood similar to 2015, 2021 in the city and witnessed in Bengaluru recently. Should precious rainwater be treated as a burden rather than a resource and dumped into polluted canals and abandoned into the sea during a heavy spell? Could it instead have flowed into old and new reservoirs, ponds, temple tanks and larger wetlands?
The Greater Chennai Corporation (GCC) has presented the city with an irreversible decision, and the drain work began in the third week of April. With no end in sight to the work in many areas – on a mega project stretching along 1,033 km at an outlay of Rs.4,070 crore – GCC Commissioner Gagandeep Singh Bedi has set a deadline of September 30 for completion, that too as per mandated engineering norms.
The massive SWD project is also questioned by experts on whether it is the best method to handle the flood similar to 2015, 2021 in the city and witnessed in Bengaluru recently
This is unlikely to be met. Contractors have been adopting uneven practices, deploying too few workers, and officials have also been cutting them generous slack at Zonal and Divisional levels. Half complete drains with mounds of loose earth are a common sight along many Chennai roads, threatening to be filled with muddy water as it happened in August.
The GCC’s Deputy Commissioner, Works, M.S. Prashanth has blamed unseasonal rains in August for the delay.
The Central Public Health and Environmental Engineering Organisation (CPHEEO) manual on SWD, which has been adopted by the GCC this time, sets a clear goal: that urban facilities must be water-sensitive by design, prepare for climate change aberrations such as heavy rainfall in short periods, and ensure that rainwater is retained as close to the point of origin as possible through good harvesting structures. The Executive Engineer, Storm Water Drains department of the GCC was a member of the panel that wrote the manual of 2019.
To avoid building expensive and vast networks of SWD, the manual from the Union Ministry of Housing and Urban Affairs lays down a checklist of possibilities for cities. These are:
- In situ storage / percolation within or around premises
- Storage of runoff in nearby pond / water tank
- Percolation of storm water inside / outside the drain along the stretch
- Spreading water for recharge in low lying areas and parks / gardens
- Disposal to reservoir / water body
It is unclear if the Tiruppugazh Committee, which was set up by the Tamil Nadu government last year to go into the issue of flood mitigation, took these ideas on board while making its recommendations. The report of the panel is not in the public domain.
Pursuing its theme of storage and percolation of rainwater in a variety of ways, the Union Ministry’s manual lays down filtration methods for storm water drains, to reduce rain runoff percolating or stagnating along with pollutants including oil.
There is consensus now in Chennai that the ‘reclamation’ of urban wetlands for construction in almost all areas for half a century and more has dealt a sharp blow to efforts at trapping urban runoff. The AIADMK government in the 1991-96 tenure said it was working to channel such runoff into temple tanks in every neighbourhood, but that plan met with less than marginal success.
Ironically, the Union government’s 2019 manual said that Chennai is one of the few cities working to adopt Water Sensitive Urban Design, along with Bengaluru, Melbourne and Ottawa. Obviously, nothing happened until the floods of 2021.
One of the complications faced by Chennai, according to rainwater harvesting expert Sekar Raghavan, is the general rise in groundwater level due to repeated years of heavy rainfall, as recently as 2021. This makes it imperative to create more public harvesting structures such as wetlands and ponds within the core city, besides protecting suburban lakes from encroachment and retrieving lost water bodies.
It is unclear if the Tiruppugazh Committee, which was set up by the Tamil Nadu government last year to go into the issue of flood mitigation, took these ideas on board while making its recommendations. The report of the panel is not in the public domain
Precast concrete for speed
It is in technology that the GCC may have lost the most momentum, by allowing contractors to do drain-building at a relaxed pace. Some contracts in Kodambakkam were drawn up from March to November, ignoring the prospect of rainfall arriving much earlier.
With some foresight, the Tamil Nadu government could have considered putting up a prefabrication plant to produce concrete drains. These U-shaped drains have been made at factory scale in many countries such as Korea , and could remove severe disruptions in congested areas and speeded up the work process. Chennai’s own CMRL operations could have provided some insights.
Clearly, there is no turning back for the GCC, now that the excavators have dug pits and there are no prefab drains to fit into these. In Kodambakkam, for instance, the narrow space between a hospital and the Rangarajapuram flyover is just a long open pit even now, with no work progressing as of Monday night. The story is similar at many other places.
CM and ground reality
Chief Minister M.K. Stalin was in the thick of rain relief operations in end-2021, inspecting the damage and arranging for help. The administrative machinery may have convinced him that the drain work will be concluded soon, by end-September. But only a hands-on, on-the-ground assessment can tell Mr. Stalin whether the work is anywhere close to completion. He should be worried that one man was injured when a protruding rod from an unfinished drain pierced his thigh in Virugambakkam. Many more accidents could be waiting to happen, if business-as-usual is allowed to continue. A SWD pit looks like a level surface when it is filled up with rainwater, and could act as a death trap with protruding rods.
The drain contractors got an extraordinarily long lead time, but they have failed. Most have employed too few people to do the job, and counted on an indulgent government. Mr. Stalin should crack the whip at least now.
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