Now the focus is on N-E monsoon

By T. Ramakrishnan

CHENNAI, OCT. 7. Chennai has cleared its biggest hurdle of the year, the long dry spell, without a crisis in water supply, and the focus now turns to its prospects during the wet season (October to December).

The pattern of rainfall in the next three months will greatly influence the coming year's level of drinking water supply to the city residents, despite the availability of Krishna water.

``The northeast monsoon is likely to be normal in Tamil Nadu this year'', the Meteorological Department says, adding that by the time, the monsoon sets in (which is expected a week before or after October 20), it will be able to give more data about the season's probable pattern of rainfall.

At present, Chennai's water supply system is basically dependent upon the storage position in three water sources - Poondi, Cholavaram and Red Hills. This year, to tide over the water scarcity, the State Government converted the Chembarampakkam lake into one more source and distributed a net quantum of around 500 mcft to the public.

As these reservoirs store surface run-off water, the intensity and behaviour of the rainy season, also called northeast monsoon, become crucial for sustaining the water supply to the city.

The three sources of Chennai receive, on an average, 60 per cent of rainfall only during this season. Their annual rainfall, going by the average for the decade 1990-99, came to around 140 cm, of which 85 cm was recorded between October and December.

The highlight of this seasonal rainfall is that in five out of 10 years, the sources received more than the average. But, in two years, the rainfall was marginally less than the anticipated amount. During three years, it was abysmally low.

In the last decade, the poor rainfall during the monsoon, on two occasions, led to water scarcity in Chennai the subsequent year. The years were 1992 and 1999 when the reservoirs received 52 cm and 50 cm respectively.

Though the season's performance was low in 1995 with 67 cm of rainfall, the city did not witness any problem in water supply as it experienced unprecedented heavy spells during May 1995 and June 1996.

The question that comes up is whether the city will have problems in water supply or not in 2001. ``To avert water scarcity, should there be a normal rainfall or a surplus rainfall'', many citizens ask.

Considering factors such as Krishna water and the availability of Chembarampakkam tank, even normal rainfall will take care of the city's requirements, experts say. One point stressed by experts is that the rain spells should be dispersed over this period, instead of being concentrated on a few days or a week.

``If the season's rainfall is well distributed, we can manage the supply position even with 65 cm-70 cm. Otherwise, it will accentuate the problem of flooding with the reservoirs not being able to optimally store water'', they observe.

The experts also point out that despite the water sources registering a normal rainfall during the 1998 northeast monsoon, it was the realisation of 2.8 tmc ft of Krishna water that year which helped maintain, on an average, the supply quantum at 450 million litres a day (MLD) throughout 1999 which was the highest for the city.

As for this year, about 700 mcft of Krishna water during September was realised. Chennai can continue to get water so long as it wants, PWD officials say.

A good northeast monsoon will remove any uncertainties about the coming year.

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