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Bengaluru's water story: Can the paradise be regained?

Shape of water: The lakes of Bengaluru have never been part of a formal water supply system but have informally benefited the city by groundwater recharge.

Shape of water: The lakes of Bengaluru have never been part of a formal water supply system but have informally benefited the city by groundwater recharge.   | Photo Credit: Bhagya Prakash K

We need a multi-pronged approach to make water use sustainable in the city which once had its tanks providing drinking water

Doomsday prophets have been around for a while. In 2010, a former Additional Chief Secretary to the State government argued that half of Bengaluru will have to be evacuated owing to water shortage by 2023. The BBC reported in 2018 that Bengaluru was one of the cities likely to reach ‘ground zero’ conditions by 2020 and the NITI Ayog, in 2018 also, suggested that Bengaluru would run out of groundwater by 2020.

The year of collapse has arrived, and the city continues to be one of the fastest growing urban economies in India. The water utility suggests that 1,450 million litres per day are being pumped into the city from the Cauvery and a project is on to bring in another 775 million litres daily from here by 2023.

The government has asked for the preparation of a Detailed Project Report to consider transferring water from the Linganamakki reservoir on the Sharavati to Bengaluru.

A pre-historic story

The city’s water story goes back 3,400 million years or so when the peninsular gneiss, which forms the city’s bedrock, came out and cooled from volcanic activity. The city settled at the fag end of the Deccan plateau at 900 metres above sea level. This gave it the salubrious climate that it became famous for, but the rock itself weathered and stored water in shallow aquifers.

Key part: Lakes need to be protected for the ecological and cultural role they have in the city.

Key part: Lakes need to be protected for the ecological and cultural role they have in the city.   | Photo Credit: Bhagya Prakash K

 

Another event took place about 88 million years ago. The sub-continent that is now India started drifting north to meet the Asian continent.

The Himalayas are the creation of this slow movement of India into Asia. As the author Pranay Lal mentions, a piece of the Sahyadri remained in Madagascar, from which India separated in its northward journey.

This piece is the Palghat gap, where the Western Ghats dips to about 300 metres above sea level. From this gap, humid winds rush in from the Arabian Sea, swing northwards and in April and May bring the ‘office showers’, around 5 p.m, to the city.

Bengaluru has a bi-modal rainfall with one peak in May and the other in September-October with a total of 970 mm, much higher than the surrounding areas.

Tanks are created

The people who occupied the land 1,000 years ago, as the inscription stones tell us, harvested rainwater by throwing an earthen wall across a valley, creating the famous ‘tanks’ ecosystem of the city. These waterbodies provided irrigation and recharged groundwater. It was drawn from wells for drinking purposes, and provided silt to enrich farm soil in the command area. Between 1875 and 1878, the drought was so severe that the tanks went dry and caused a famine in South India and Bengaluru claiming millions of lives.

This famine had a profound effect on the city and its water supply. A decision was taken to go in for piped water supply to every house at 55 litres per capita per day. After careful examination, the most reliable water supply was seen as the Hesaraghatta reservoir on the Arkavathy.

Since then, the lakes of Bengaluru have never been part of a formal water supply system but have informally benefited the city by groundwater recharge.

Lakes need to be protected for the ecological and cultural role they have in the city but are unlikely to be direct sources of drinking water.

From the reservoirs

Engineers then rigged up a technologically advanced scheme in 1894, using brick aqueducts and steam engines to bring water from the reservoir to the city. This piped water supply also led to a growth in the population of the city, and pretty soon by 1910 there were complaints of water shortage. By 1934, another reservoir was built on the Arkavathy at Thippagondanahalli. The population grew and by the 1960s there were once again complaints of water shortage and therefore the Cauvery was brought in by pumping water over 95 km and 300 metres high, a technical marvel of its kind.

In the meantime, the Arkavathy dried up and the first two sources are no longer used. The first, second, third, fourth, and finally the 5th stage of the Cauvery project is now on. About 1,450 million litres per day (MLD) are now being brought in and another 775 MLD will come through the fifth phase. But the population has now touched 13 million and it is expected to be 20 million by 2031. A city of 20 million will need 4,000 MLD.

What is to be done about this unbridled thirst?

Future thirst

One is to reduce the standards and say 100 litres per capita per day is enough.

The second is to reduce leakages in the system more aggressively. Already, it has been brought down to 37% or so, and it should be reduced to 20%.

The third is to harvest rainwater more systematically, both through individual buildings and also through lakes. The rainfall incident over a city of 1,250 sq.km. is equivalent of 3,000 million litres per day. All buildings must collect or recharge rainwater on their plots. This will also mitigate urban flooding.

The fourth is to manage groundwater better, to ensure more recharge and to control unbridled exploitation through better governance. The normal rate of recharge is estimated at between 3 to 10 % of rainfall. We must identify recharge zones and make sure that this number goes up to at least 50%.

This increased recharge will prevent the groundwater table from collapsing and keep alive over 4,00,000 borewells drilled in the city. Over 1,400 million litres should then become the annual replenishment of groundwater to be drawn sustainably. Groundwater rules and regulations must be implemented vigorously.

The fifth is to reuse treated waste water systematically to meet a large portion of the non-potable demand. The city will set up waste-water treatment plants to be capable of treating 1,440 million litres per day. Nearly 900 million litres daily will be transferred to the neighbouring dry districts, yet over 500 million litres per day can be directly or indirectly reused for non-potable purpose, industrial purpose or to fill our lakes, thus enhancing ecological diversity and refilling groundwater for use. Investment will also be needed to improve the collection of sewage and to prevent their flow in storm-water drains.

The best model to follow is that of the ‘four taps’ approach. Piped water from external sources, harvested rainwater and water from local catchments, treated waste water, and groundwater must be the four taps.

Finally, the most important thing to do is to build our institution of water supply, the Bangalore Water Supply and Sewerage Board, to be a strong, professional, capable, and financially independent organisation.

It should be capable of delivering universal connection to all people in the city and manage all water in the city, including groundwater. Then only can we come close to being water sustainable and resilient.

(S. Vishwanath is urban planner and water conservation expert. He is secretary-general, International Rainwater Rainwater Catchment Systems Association.)

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Printable version | Jul 13, 2020 9:22:44 AM | https://www.thehindu.com/news/cities/bangalore/our-water-story-can-the-paradise-be-regained/article31881200.ece

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