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Better sewage management to tackle floods

Better sewage management to tackle floods
The city, much to its shame, has three dead and defiled rivers – the Cooum, Adyar, and Kosathalaiyar, which flow into the Bay of Bengal. But this is not all the water wealth of the city. Chennai is crisscrossed with canals and dotted with lakes and other water bodies. According to the City Development Plan, prepared for the centrally sponsored Jawaharlal Nehru National Urban Renewal Mission (JNNURM), there are as many as 320 tanks and lakes within the city’s boundary.

In addition, its “human-made” canal – the Buckingham (known locally as the B-Canal) – adds to the pollution. The canal, built for saltwater navigation, is over 420 km in length, connecting the Pulicut Lake in Andhra Pradesh to Tamil Nadu. In this journey, it crosses the city of Chennai and links its two natural rivers, previously with its water, and now with its wastewater. In the past, the canal used to be an important channel for transport; now, it is virtually non-navigable because of its silt and organic waste load. All pollution surveys have found that the canal is heavily polluted.

But this is not all. The city also has many other waterways – the Captain Cotton Canal, only 3 km long, draining into the Cooum; the Otteri Nullah, which flows into the B-Canal; and the Mambalam, which joins the Adyar River. The total length of these waterways within the city is over 23 km; in the Chennai Metropolitan Area, they extend over 158 km.

The Cooum almost divides the city into one-half. The most important waterway of northern Chennai, it journeys for 18 km in the city and another 22 km in the metropolitan area. According to environmental scientists from Anna University, given the hydraulics of the four waterways of that part of the city, all the pollution generated would theoretically pass into the Cooum. The river is described as a languid stream as it has no flow in most months.

Adyar, the river of south Chennai, flows for 15 km in the city and 9 km in the metropolitan area. It enters Chennai at Nandambakkam and in its journey to the sea; it gets transformed into a wide lagoon – the Adyar estuary, with many islands and large sludge-filled backwaters. The Kosathalaiyar is a river of the Chennai metropolitan area; it does not enter the city.

All these water bodies are in serious trouble. Explaining the problem of pollution, the City Development Plan says: “The waterways of Chennai are not perennial in nature and receive flood discharge only during the monsoon season; the rest of the year these act as carriers of wastewater from sewage treatment plants and others.” The study on sludge in Chennai, done in the mid- the 1990s, also shows most of these waterways were choked with sludge and wastes. In Adyar, for instance, the water width was only 15-200 m in the dry season, while sludge filled up 90-500 m.

Why are water bodies polluted?
Why do these rivers and canals remain so polluted when the city has a near-perfect track record in water and sewerage provisioning? Also important to note here is that Chennai has received the single biggest chunk of the money under the National River Conservation Programme – some 11 per cent of the sanctioned cost till 2005 – for cleaning of its rivers. The Adyar and Cooum together were sanctioned 15 per cent of the river cleaning budget of the entire country.

The key issue in Chennai is that the city is planning with the assumption that its near-perfect sewerage coverage, pumping, and piping plan will successfully intercept all its wastewater. Therefore, its entire programme for river cleaning is focused on investing in building and augmenting sewage treatment capacity; increasing the length of the underground sewage network; and adding to pumping and piping capacity.

In the late 1990s, the Union Ministry of Environment and forests sanctioned three major projects to the state under its river cleaning programme, among them the Chennai City River Conservation Project (CCRCP). This integrated project was sanctioned for Rs 1,200 crore, of which the Central government agreed to pay Rs 492 crore as a grant. The state government paid the rest, which amounted to about Rs 700 crore. The objective was to improve city waterways and disposal networks for increasing the capacity of the existing sewer system.

By the end of 2005, MetroWater had executed more than 95 per cent of its components under the project. Under CCRCP, another 80 km of sewerage lines was added at a cost of about Rs 12 crore to achieve 100 per cent coverage of Chennai city. MetroWater also put up five new pumping stations under the project.

The money spent has not helped. In 2006, the City Development Plan quoted a state pollution control board report, saying, “all waterbodies in the city are polluted and not suitable for any designated uses; the level of contamination is worse in B-Canal, followed by Otteri Nullah and Cooum River”. So what is going wrong in Chennai?

Why is the pollution not under control?
Chennai’s STPs are all situated at the far corners of the city. Wastewater is pumped across the city to these plants located on the outskirts. This would make eminent sense if the treated wastewater was reused in nearby areas, for irrigation or by industries. Instead, the bulk of the treated and clean wastewater is disposed of into rivers and canals, which traverse the entire length of the city (carrying this wastewater) before flowing into the sea. This may still have been sensible if the rivers and waterways did not have any outfalls of sewage and were themselves clean and clear. But they are not.

Despite Chennai’s much-vaunted sewage treatment infrastructure, its waterways continue to receive sewage from the colonies and industries along their way. In 2000, some 532 MLD of sewage was generated in the basins of Chennai’s waterbodies. Along the length of the B-Canal, which cuts across both the Adyar and Cooum rivers, as much as 158 MLD of sewage was generated. The Tamil Nadu Pollution Control Board (TNPCB) has identified some 116 outfalls into just the Cooum. Altogether, some 423 outfalls have been located in the city. An article in the daily newspaper, The Hindu, says that even though MetroWater officials insist that only treated wastewater flows into the waterways, this does not explain the huge amount of sludge and sewage which is evident in these drains and rivers.

In fact, the newspaper’s correspondent even photographed and reported instances of tankers emptying raw sewage into the Cooum. In this way, the treated effluent is mixed merrily with huge quantities of untreated effluents. And the job of pollution control, thus, becomes endless and pointless.

In fact, strangely enough, the government’s own studies accept that the waterways in Chennai convey treated and untreated sewage and garbage together. These waterways, which are also the city’s flood discharge channels, are encroached and built upon as well, thereby severely reducing their flow. A 1994 sludge disposal consultancy commissioned by the state government had revealed that huge amounts of untreated waste in the rivers had led to sludge formation, clogging the waterways.

 These waterways also traverse the growing outer city areas of this metropolis. The Chennai Metropolitan Area (CMA) covers some 1,189 square km, of which the city limits, are a mere 176 square km. The sewage generated by this gigantic extended area flows into the same waterways, which get heavily polluted before they even enter the city limits!

For instance, the seasonal graph for biochemical oxygen demand (BOD) concentration in the Cooum shows that the river is already polluted when it enters the city. It gets more polluted as it traverses the city, with the big jump coming after the B-Canal mixes its waste with the flow. DOWN TO EARTH
(The author is Director General of the Centre for Science and Environment and Editor, Down to Earth. Views expressed are strictly personal.)
Sunita Narain

Sunita Narain

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