Bengaluru let 3.76 tmcft of rainwater go down the drain in 21 days

Bengaluru let 3.76 tmcft of rainwater go down the drain in 21 days
Bengaluru let 3.76 tmcft of rainwater and sewage water flow into drains in Tamil Nadu and eventually to the Bay of Bengal, from August 18 to September 7. 

The finding of the ongoing ‘Bengaluru Urbanisation and Sustainable Water Management Study’ comes at a time when the state government is preparing the data on diverting west-flowing rivers to meet the city’s water needs. The study by the Indian Institute of Science (IISc) focuses on assessing how much water is lost every year and how much can the city hold.

“The 3.76-tmcft loss is only from Kommaghatta and Chellaghatta (KC) valleys. This loss is because of silt accumulation in lakes and stormwater drains. The lakes and stormwater drains have lost their water-holding capacity due to the accumulation of silt, which has led to water wastage. The government is unable to withhold even part of the rainwater which the city gets through proper rainwater harvesting (RWH) mechanisms. Instead, it’s thinking of diverting west-flowing rivers and getting water from Yettinahole, Sharavathi and Netravathi,” said Prof T V Ramachandra, of the Centre for Ecological Sciences, IISc, who is conducting the study.

Both KC and Hebbal valleys join at Nagondanahalli village (Ward 94, Hagadur) before flowing to the Dakshina Pinakini River. The capacity of the KC Valley is 5.37 tmcft (measuring 271 sq km) while that of Vrushabhavathi Valley 5.6 tmcft (165 sq km) and Hebbal valley 4.4 tmcft (207 sq km).

Bengaluru gets rainfall of 15.3 tmcft per year. But during the study period, according to the India Meteorological Department (IMD), the city received 321 mm rainfall. This apart, 500 mld of sewage flows through sewerage lines every day, of which 470 mld flows through KC Valley.

As per the Bangalore Water Supply and Sewerage Board (BWSSB) records, only 74,000 out of 9.4 lakh connections have the RWH. The BWSSB has collected Rs 12 crore as penalty from 12,000 connections since last September for not implementing the RWH.

A R Shivakumar, an RWH expert and senior scientist at the Karnataka State Council for Science and Technology (KSCST), said though not all water can be tapped, a lot can be through the RWH. Apart from those in BWSSB limits, around 30,000 households have installed the RWH.

Seema Garg, CEO, Karnataka Lake Conservation and Development Authority, said desilting was an essential part of the detailed project reports that come for approval. But sometimes, the work may not happen for lack of funds. There is, however, a need to desilt drains to improve their water-holding capacity.

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