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Monday, November 29, 2021

Explained: Why Bengaluru neighbourhoods were flooded during recent rain

Poor urban planning and the construction of buildings on valleys and lake beds have led to the flood mess in Bengaluru, say experts.

Written by Aksheev Thakur , Edited by Explained Desk | Bengaluru |
November 23, 2021 5:37:30 pm
Karnataka Chief Minister Basavaraja Bommai visits flood-hit Yelhanka Central Residential Complex, in Bengaluru, Tuesday, Nov. 23, 2021. (PTI Photo)

The unprecedented heavy rain and flooding in Bengaluru over the last few days have opened the Pandora’s box of unauthorised constructions on the city’s valleys and lake beds. Yelahanka lake, Singapura lake, Allasandra lake and Amanikere lake overflowed leading to flooding.

Residents were stuck inside waterlogged houses and had to be rescued on boats by various rescue troops.

Which areas in Bengaluru received the most rain?

On Sunday, Yelahanka zone received the highest rainfall of 153 mm followed by Horamavu in Mahadevapura zone (103 mm), Kannuru gram panchayat (143.5 mm).

On Monday, Yelahanka zone recorded 130 mm of rain and it led to massive flooding of residential complexes and academic institutions. National Disaster Response Force (NDRF) and State Disaster Response Force (SDRF) were deployed to carry out relief and rescue operations.

Kendriya Vihar in Yelahanka which houses central government employees had stagnant water up to 4 feet compelling the residents to stay indoors. The campus of Jawaharlal Nehru Centre for Advanced Scientific Research (JNCASR) was also flooded.

IMD recorded 1,480.2 mm of rainfall in Bengaluru this year. In 2017, the city received 1,696 mm rain.

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What is the major reason behind the flooding of Yelahanka?

The city’s topography is characterised by a series of well-defined valleys which radiate from a ridge and fall gradually in all directions. The four major valleys are Vrishabhavathi valley, Koramangala valley, Challaghatta valley and Hebbal valley. The lakes were built across these valleys and floodwater used to flow through these valleys. The lesser-known valleys are Marathalli in the east, Arkavathy and Kethamaranahalli in the northwest, Kathriguppe and Tavarekere in the south and they also play an important role in forming a natural drainage system where rainwater can flow through.

Map showing the extent of construction works on the Hebbal valley (Courtesy: Raj Bhagat)

However, due to rapid urbanisation, these natural canals have been blocked by construction layouts, residential apartments and academic institutions. Manyata tech Park and Kendriya Vihar, which were flooded in the last two days, are built on the Hebbal valley.

Senior programme manager (geo-analytics) at World Resources Institute (WRI) India, Raj Bhagat explained: “It is imperative to understand the importance of valleys if we want to reduce flood damages in the cities. Unfortunately, construction is happening right in the middle of the valleys. The settlements, in the past, had been above the valleys and agricultural lands acted as a buffer. Due to urbanisation, agricultural lands were sold for residential or commercial establishments. Canals were rerouted post urbanisation. The present drains do not have the capacity to carry excess rainwater. Therefore the entire valley gets flooded.”

How many illegal layouts are there in Yelahanka?

According to government officials, the estimated number of illegal layouts in Yelahanka is more than 3,200. There are more than 6,000 illegal layouts across the city.

A senior official told The Indian Express that Bangalore Development Authority (BDA) is the biggest encroacher. “The moment we go to demolish the property, there is a public outrage because BDA has permitted them to construct houses. They have formed more than 22 layouts over lake beds in Bengaluru urban district. Unfortunately, the government regularises such encroachments and our hands are tied. We face heavy resistance while evicting the encroachers,” he added.

Ram Prasad, co-founder of Friends of Lakes, an environment group, said that the government’s detailed project report (DPR) on lake rejuvenation is bereft of engineering and environmental standard procedures. “There is no way for the water to escape. Haphazard layouts were given permission. Lakes should be treated as flood mitigation centres and rainwater harvesting points. Urban planning has been the worst in the peripheral areas of Bengaluru. The construction of buildings on valleys and lake beds has resulted in the mess we are around today,” he added.

Which other areas in Bengaluru are vulnerable to flooding?

The researchers at Indian Institute of Science (IISC) have pointed out the vulnerability of Koramangala during heavy rains. In a study conducted by researchers at IISc Dr TV Ramachandra, along with Mr Vinay S and Mr Bharath H Aithal, it was highlighted that in the wetland of Agara-Bellandur lake, which had earlier aided in retaining rainwater, groundwater recharge and bioremediation, has been abused with construction activities in the SEZ by Karnataka Industrial Areas Development Board (KIADB). IISC scientists observed that the stormwater drain connecting Bellandur lake from the city market was narrowed to 28.5 metres against the original width of 60 metres thereby violating National Green Tribunal (NGT) guidelines of maintaining the physical integrity of stormwater drains and buffer zone.

Ramachandra said: “If the drains are concretized the velocity of water increases which further enhances the chance of flooding. The SEZ in Bellandur-Agara wetlands should be shifted to other regions in Karnataka and further industrialisation and construction of commercial establishments in the region should be stopped.”

Bruhat Bengaluru Mahanagara Palike (BBMP) has identified 209 areas prone to flooding out of which 153 were sensitive and 53 were extremely sensitive. Parts of Bengaluru like JP Nagar, Puttenahalli, BTM, Koramangala, Ejipura which fall in the low lying areas witness flooding were on the list.

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