While the Northeast monsoon has brought temporary relief to Chennai residents, the city will continue to face yearly water shortages unless we act now.

Blessed by rivers yet perennially short Why Chennai sees an annual water crisisPTI File photo
news Environment Wednesday, November 20, 2019 - 13:54

Fifty-five years ago, as a young college student in Madras of the 1960s (now known as Chennai), I attended a Corporation election meeting addressed by Navalar Nedunchezian, then the Leader of Opposition in the Tamil Nadu Assembly.

At the meeting he lamented over the poor shape the Cooum river was in, evoking memories of a bygone area in which great men such as the 18th Century philanthropist Pachaiyappa Mudaliar used to bathe in the pristine river. He also promised that if his party (then the DMK) was voted to power, they would accomplish wonders and see that both the Adyar and Cooum rivers were cleaned, rejuvenated and available for use as drinking water sources.

Much sewage water has flown in these two rivers since then as they have served only as sewage disposal channels. Half-hearted measures of cleaning the rivers as and when it suits the rulers, without taking meaningful measures of arresting large-scale pollution, have not led us anywhere. Things have only turned from bad to worse as both rivers have polluted the groundwater as well as the potential sandy aquifer covering the vast expanse of land to their side.

Despite the fact that Chennai is endowed with these two rivers and many lakes and tanks, there is a perennial water crisis in Chennai every year between the months of March and July. The Chennai Metro Water Supply and Sewerage Board (CMWSSB) is unable to supply even 80 litres per capita, even for those who have metro water connection, though the norm is 135 litres per capita.

Most middle and higher income families living in individual houses and apartments get their water requirement from open wells and borewells, created within the premises or through private tankers. Drinking water needs are met either by sourcing bottled water or by using Reverse Osmosis (RO) units, where a significant quantity is wasted.

During years with near normal rainfall, the four existing storage reservoirs cannot hold the entire water and invariably, the excess water is discharged into the Kosasthalaiyar, Adyar and Cooum rivers. A fifth reservoir conceived in Thervoy Kandigai in Tiruvallur district in the year 2013, is yet to be completed.

Where does our water go?

It has been a regular phenomenon every summer that the government tries to find some short-term solutions like hiring private irrigation wells in the neighborhood of the metropolitan area or pumping the stored water from abandoned quarries etc., to meet the city’s water needs.

The 42-km long Adyar river originates within the Chennai Metropolitan area (to the west of Tambaram in Aadhanur tank) and forms an estuary before it joins the sea. The river has meager flow throughout the year, but it is flooded during the Northeast monsoon season, when there are heavy spells of rainfall. It is estimated that 10% of the untreated sewage generated in the city is let into this river.

The Cooum originates to the west of the city from the surplus waters of the Cooum tank in Tiruvallur district, and discharges into the sea to the north of the Marina Beach. The Cooum, which isn’t very polluted until it enters Chennai, becomes highly polluted within the city due to the discharge of sewage water from hospitals, factories and commercial complexes.

Around 30% of the untreated sewage is let into this river. The rest of the city’s sewage goes into the unfortunate Buckingham canal, a manmade channel originating in the north in Nellore district of Andhra Pradesh, which drains through the city.

Besides these, there are many small drains that join the rivers or the canal and are used as only sewage carriers. I was a personal witness to the sewage water tankers regularly discharging sewage into the Pallikaranai swamp, notwithstanding the solid garbage being dumped. How this vast marshland has been encroached with the connivance of the rulers, in the environs of Velachery, Pallikaranai, Perungudi and Thoraipakkam and degraded to the present pathetic status in the last three decades merits for discussion in itself.

Pallikaranai marsh (Image courtesy: KM Vedapuri)                          

Chennai is among the large metros blessed with excellent reservoirs of water such as the Redhills lake, the Cholavaram tank, Chembarambakkam tank and Porur tank. These tanks that have been traditionally the city’s water sources are now at risk - the Velachery and Ambattur tanks for instance are being encroached upon by legal and illegal constructions and the limited water left is being polluted due to the disposal of sewage from both residential clusters and industries in the area. Even the temple tanks have not been spared.

If these tanks and lakes are properly maintained and desilted during summer, sewage disposal and garbage dumping prevented, they could not only store quality water to meet the needs of the nearby localities, but also serve as huge sources of recharging the groundwater. A regularly desilted lake of an area of 100 hectares can provide recharge of around 20,000 cubic metres per day. On a conservative estimate this can take care of the water needs of 20 to 30,000 families. You can imagine how we are losing this much-needed clean water!

Kapaleeshwarar Temple tank (Image courtesy: J Saravanan)

Now the sad story is that we are unable to use the river water either by storing water through check dams or by constructing collector wells. The extent of damage does not end here. Actually, these rivers have built up fairly good thickness of water bearing sand along their courses and these form good aquifers for retaining water. Had these rivers not been polluted, this sandy area would be a rich resource for our water needs, with long-term recharge from these water bodies. As there are many structurally weak zones along both the rivers and the sea coast, there is a rich possibility of there being a store house of ground water in both the top sand and the underlying highly weathered and jointed rock. But the level of pollution in these rivers is so high that even the deeper aquifers in the underlying hard rocks have brackish water. It is essential to stop polluting these water bodies further and repair the damage already done. Thus, Chennai is a blessed city in being endowed with these surface and groundwater bodies, but one wonders whether we deserve the blessing.

Sewage cess pool at Adyar (Image courtesy: KM Vedapuri)

Is it possible to undo the damage?

It may not happen overnight. But if there is cooperation between the government and the general public, redemption is possible over a period of time. As a first step, both legal as well as administrative measures should be taken to stop the artificial discharge of sewage and dumping of garbage in the rivers, canals and other water bodies. This is possible only if the rulers of the day and the officials take proper action, without the lure of any extra consideration. One thing that is certain is, all the sewage generated is not connected to the limited number of Sewage Treatment Plants (STP) that are in operation. As of now, there are 12 STPs with a total treatment capacity of about 720 MLD are woefully inadequate to treat the present volume of sewage. Hence more STPs should be created and properly maintained.

In many areas, the storm-water drains are used as sewage carriers and are also choked with plastic material. This will again directly pollute the rivers. This should be avoided. In future, no building permission should be issued for apartments, hospitals, educational institutions and other commercial buildings, if proper STPs are not in place. Grey water usage in these buildings should not only be made mandatory, proper monitoring mechanisms should be in place to ensure it is implemented in letter and spirit. This will help in reducing the consumption of fresh water and quantity of sewage generation will be considerably less.

A beginning has to be made on reducing the discharge of sewage into the water bodies immediately. This should be followed by cleaning the rivers, canals and tanks of thorny bushes and deepening these water bodies. Only this can render them usable. This in turn will prevent the pollution of the alluvial ground water aquifer and also the deeper ground water body in the underlying rock.

While other metros like Bengaluru and Hyderabad are covered with hard rocks with limited ground water potential and one has to drill deep borewells of more than 300m (1000 ft) depth to get water for domestic purposes, the residents of Chennai should thank their stars for having these water bodies and ground water still comparatively at shallow depth. Is it not the responsibility of the government and the public at large to stop the damage before it is irredeemable?

KM Vedapuri is a hydrogeologist who practiced in both the public and private sector in India for over three decades. He is a retired Ground Water Consultant with a keen interest in water and ecology.


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