Urban News

Hindustan Times 03.02.2010

If the silt accumulated in the Tansa and Modak Sagar lakes is removed, it will increase water stocks by 18,000 million litres (ML) in both the lakes, an additional 12 days of supply without the current 15 per cent cut.

This is part of the findings of a report by Nashik-based Maharashtra Engineering Research Institute (MERI), which surveyed silt levels in these lakes for a year.

The report says 10 per cent of the total capacity of each of the two lakes is silt — by volume, that amounts to 32 days of water drawn every day from Tansa, or 550 million litres daily (MLD), and 30 days of water drawn every day from Modak Sagar, which is 610 MLD.

The survey was carried out over a year, with a budget of Rs 5 crore.

“This is the first survey to estimate the amount of silt that has deposited over time,” said V. Deshpande, chief hydraulic engineer.

Considering the existing water crisis, the Brihanmumbai Municipal Corporation is taking steps to increase the capacity of these two lakes.

“Siltation is a common phenomenon that any dam or reservoir goes through. Because of the continuous accumulation of sediment in the dams, its capacity has shrunk,” said Additional Municipal Commissioner Anil Diggikar.

“We will take all possible steps to restore the capacity of the lakes and tap more water from them,” he added.

Tansa dam is over 100 years old, Modak Sagar dam is 54.

“The BMC should take immediately steps to desilt the lakes — if done in time, it will help increase their water accommodation capacity,” said a MERI source.

Deshpande added that the BMC will have another meeting with MERI, to find out the exact locations where the silt has accumulated, and learn how it can remove the silt without disturbing the water.

“If the silt is heavily disturbed while removing it, the turbidity of the water could increase — it will then become very difficult to purify the water, which is why we need to complete the desilting without disturbing the water too much,” Deshpande said.

A separate survey of the Vihar and Tulsi lakes is also underway. Their reports are expected soon.

The Hindu 03.02.2010

“Improvement in quality of groundwater along coast”

Priti Narayan

PUDUCHERRY: A recent study suggests that quality of groundwater in areas along the coast in Puducherry may have improved to a certain extent over the last 15 years.

The study, conducted by an official of the Puducherry Pollution Control Committee (PPCC) and a student of Mysore University, said that total dissolved salts in groundwater (in milligrams per litre) and chloride-alkalinity ratio were less in many areas located near the sea in 2008 when compared to the levels in 1993.

The official involved in the study said that the chloride-alkalinity ratio, which is an indicator of saltwater intrusion, has gone down considerably. A ratio of over one indicates considerable saltwater intrusion, but the ratio has fallen below one in many areas, the official said.

According to the study, the change has been most pronounced at Kirumampakkam, where the ratio has come down from 7.83 to 0.37, and at Pillayarkuppam, from 5.99 to 1.69 from 1993 to 2008. Levels have also fallen at Pannithittu, Eachankadu, Manapet and Pudukuppam.

The level of total dissolved salts in most areas has also gone down. Apart from Kirumampakkam and Pillayarkuppam, Manapet has witnessed a significant drop from 2558.5 mg per litre to 920.4 mg per litre, according to the study. But, in some areas such as Veerampattinam, Pannithittu and Kirumampakkam, the total dissolved salts level stand below the permitted level of 500 mg per litre. The level has, in fact, increased at Andiarpalayam, from 617.17 to 1,069.2 mg per litre from 1993 to 2008.

The official said that samples collected and analysed in 2008 were from the same borewells selected in 1993. Samples were taken from 21 locations along the coast, in three seasons of the year, he said.

The overall decrease in salinity of groundwater has resulted in a change in biodiversity in the areas, the official said. Species such as aloe have been restored, and coconut and palmyra are flourishing, he added.

The positive change in quality of groundwater may be due to the government prohibiting establishment of water- based industries (those consuming 10,000 litres of water or more for everyday production and processing) over the years. Since 2004, the monsoons have also been favourable, said an official of the State groundwater unit. The setting up of check-dams may have also helped, he added.