Homes and gardens

Saving Bengaluru from a water crisis

Majority of the population in Arasikere depend on borewells for drinking water.   | Photo Credit: Prakash Hassan

What is the ground reality for Bengaluru with respect to the water scenario? The parched grounds are seeing a high percentage of borewells drying up even before the actual onset of summer. The alarmingly reduced Cauvery water supply adds to the scene where people are seen queuing up in front of BBMP lorries for filling water. The larger scene is one of indifference, according to experts, for maintaining our water bodies, just like the non-adherence to rainwater harvesting and its piece-meal implementation at newly constructed projects and layouts. What are the parameters required from water experts, builders & developers, and the local bodies to tackle this issue, especially with Bengaluru seeing the highest number of buildings cropping up year on year?

The Hindu-Property Plus spoke with K.C. Subhash Chandra, hydro-geologist and former member on the expert panel in the Karnataka Groundwater Authority. Delving deeper into the status of water scarcity of Bengaluru with a myriad suggestive measures that need be considered for implementation is the book, ‘Bengaluru Water Resource Management - Challenges and Remedies’ authored by hydro-geologists K.C. Subhash Chandra and G.V. Hegde.

The cumulative effects of urbanisation, unplanned and haphazard growth of lay-outs, encroachment of lake-beds, diversion and distortion of storm-water drains, and discharge of waste water / sewage water/ industrial effluents into the natural stormwater drains have all caused a disastrous effect, wasting nearly 170 Million Cubic Metre (Mm 3), according to Mr. Subhash Chandra, even as he targets the initial conservation of the rapid pre-monsoon rains of April-May.

Could you give us a background of the water resource availability of Bengaluru?

Bengaluru, with an approximate extent of 800 sq. km, located in the eastern dry agro-climatic zone of Karnataka, forms a basin divide and a catchment part of the Ponnaiyar River Basin in the east and Arkavathi river system of the Cauvery River Basin in the west. The city has no perennial water resource of its own, and is in fact benefited by both South-west and North-east monsoons and receives normal annual rainfall of 830 mm.

What is the physical boundary and the population that you must have done studies on?

The unprecedented expansion of the physical boundary of the city in 2007 from 540 sq. km to nearly 800 sq.km paved way for the city to grow in all dimensions, both vertically and horizontally, which resulted in the increase of population from 51 lakh (2001) to 85 lakh (2011). The present density of population may have crossed 11,500 per sq. km. By the year 2020, the population of Bengaluru is expected to cross 9.5 million. The water requirement to meet the domestic and non-domestic needs at 140 litre/ head /day is 485 Million Cubic Metre (Mm 3) per year. As against this demand, with the Hessaraghatta and Thippagondanahalli reservoirs having become defunct, the main dependency has been on the Cauvery. The BWSSB has a designed resource to tap 478Mm 3 / year from the Cauvery to meet the water requirement of 9.3 million people.

What about the Cauvery supply and its losses?

The supply from Cauvery is mainly dependent on the Southwest monsoon. But, there are strong reports of unaccounted loss of nearly 40 % of the water so tapped which includes leakage, transmission loss and illegal connections. Out of this 40 % loss, the reported leakage and transmission loss of nearly 30 % (nearly 159 Million Cubic metre (Mm 3) per year implies there has been an uncertainty and non-uniformity in the status of river water supply and only about 6.2 million people of Bengaluru may be getting water at 140 litre/ head / day (51M 3 / per year) or 8.5 million people of Bengaluru may be getting a reduced water supply at 37M 3 / year.

What are the reasons for this that your book says?

By preventing and plugging of the water loss so being caused, the water supply can be restored to about 9.3 million people. Given the uncertainty in water supply, people tried to be self-reliant and sank borewells in their residential premises which led to indiscriminate, excessive exploitation of groundwater resources.

Independent estimation by me and Hegde in 2012 revealed that as against normal annual groundwater recharge of nearly 33 Mm 3 / year, groundwater withdrawal was 124.51 Mm 3 / year i.e., nearly 358 % more than annual groundwater recharge from about 3,12,000 borewells then.

As of today, the number of borewells is said to be more than 4 lakh in Bengaluru. The continued excessive exploitation of groundwater resources over years and successive drought condition for 2 years now has brought in a condition of the city aquifers almost becoming dry.

The rocks in the city, below 280 metre depth, are in general non-aquifers and not water yielding as they are massive and without fractures. Most of the borewells of 240-260m depth have now gone dry or the yield has dropped considerably.

The groundwater as of now is not a sustainable resource.

What are the ways in which one can treat water and make up?

Out of 401 Mm 3 / year (1100 mld) of sewage / waste water generated in the city, if 70 % (281 Mm 3 / year or 770mld) is initially treated up to secondary level and further 60% of the secondary treated water (462 mld or 168 Mm 3 / year) is after tertiary treatment brought up to potable standard, it would meet the requirement of nearly 3.3 million people of the city. In case this quantity cannot be included in the regular water supply system, this can be used for sanitary services, gardening and other non-domestic services through a separate piped system.

And the roof-top RWH?

Since there are about 500,000 houses in Bengaluru having an average roof area of 100 sq. m with 800 mm of normal rainfall, about 40 Mm 3 of water per year through roof-top rainwater harvesting can be conserved. If 70 % of such a resource is properly protected and stored, it can meet the requirement of about 600,000 people.

With these measures, the water requirement of 15 million people at 140 litres per day can be met without any dependency on the groundwater resources or any other further distant resources. Non-dependency and non-exploitation of groundwater resources for a few years would automatically promote the city aquifers to get revived.

Mr. Subhash Chandra will deliver a talk on ‘Is there real dearth of water resources in Bengaluru ? - A Ground Analysis’ on the Geological Survey of India premises, Kumaraswamy Layout, on February 22, 4 p.m. (subcha@gmail.com)

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Printable version | Mar 4, 2021 10:37:08 PM | https://www.thehindu.com/life-and-style/homes-and-gardens/Saving-Bengaluru-from-a-water-crisis/article17318982.ece

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