Karnataka - Bangalore

Land use changes in catchment area cause for floods

BANGALORE: When it rains heavily, the abysmal manner in which the city has been planned stands pitifully exposed. Storm water drains overflow, roads turn into rivers, people are stuck for hours and life comes to a standstill.

Particularly affected are the southern parts of the city which fall under the Koramangala-Challaghatta valley, also called the Bellandur catchment area.

Extending up to about 280 sq. km., the catchment area is one of the largest wetlands in the city. It comprises Puttenhalli, Varthur and Hulimavu chains of lakes and includes 22 tanks. What this also means is that any unplanned development activity in this ecologically sensitive area can affect adversely several parts of the city, which fall under the catchment area.

As many as 41 wards are part of the catchment area including Gandhinagar, J.P. Nagar, Jayanagar, Lakkasandra, BTM layout, Madivala, Koramangala, Airport, Shanthi Nagar, Richmond town, Sampangiramnagar, Shivajinagar, Ulsoor and Devarajeevanahalli.

But the city’s unplanned growth, significantly concentrated in the catchment area, has meant that every time it rains heavily, the much-neglected lakes in this area such as Arakere, Begur, Puttenahalli, Madivala and Agara overflow, causing flood-like situation in surrounding areas.

Tracing the implications of the haphazard development, a report prepared recently by the Centre for Ecological Sciences at the Indian Institute of Science says that land use changes have resulted in the alteration and even loss of natural drainage networks. “There are no mechanisms for the excessive storm water to drain and thus the water stagnates flooding the surroundings itself,” the report says.

Titled “Environment Impact of Development Activities in the Bellandur Catchment Areas,” the report says that the alteration of landscape topography has resulted in “the storm water runoff to take a new course that might get into the existing residential areas.”

Remote sensing data for the catchment area in 1972 showed that the network of tanks in the catchment area were well connected to each other as well as the vegetation along the drainage linking these tanks. In contrast, data from 2000 shows that the entire catchment area had succumbed to urban sprawl with water bodies, vegetation and drainage disappearing.

“The city has over the past twenty years received more than 110 mm of rainfall on a single day on at least four instances. This kind of rainfall is enough to fill up all the tanks in the city, even if they are totally dry. Earlier, excess water flowed from one lake into the nearby lake. Water has followed this course for hundreds of years and the development activities in the recent decade will not make it alter its course,” says H.S. Sudhira, land use researcher from IISc. He further adds: “If we want to prevent flooding, we must ensure that some low lying areas are evacuated and drain management taken seriously.”

Until then, rain woes will continue to plague the hapless citizens of the IT city.

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