Why better sewage management in Chennai will help fight floods

Down To Earth Editor Sunita Narain explains how the city's three rivers and 320 tanks and lakes that worked as flood barriers are used mostly for dumping sewage

By Sunita Narain
Published: Friday 04 December 2015

Chennai’s waterways: its shame

This article is an extract from "Excreta Matters", India's first comprehensive survey on the state of its water and its management.

Chennai gets enormous amounts of money to clean its rivers and waterways, which continue to look like this (Photo: R K Srinivasan)

The city, much to its shame, has three dead and defiled rivers – the Cooum, Adyar and Kosathalaiyar, which traverse it to 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 waterbodies. 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 half. The most important waterway of northern Chennai, it journeys for 18 km in the city and another 22 km in the metropolitan area. What is clear, say environmental scientists from the city-based Anna University, is that 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 waterbodies are in serious trouble. Explaining the problem of pollution, the City Development Plan says: “The waterways of Chennai (see Map: Waterways in Chennai metropolitan region) 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- 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.

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