Even if the Bruhat Bengaluru Mahanagara Palike (BBMP) cleared all encroachments on storm-water drains (SWDs), the city would still not be safe from similar flood-like situations.
It is not just illegal, unauthorised construction that is choking SWDs; the underlying faulty design and the immense concretising of Bengaluru will continue to lead to such situations, says V.V. Srinivas, associate professor, Department of Civil Engineering, IISc.
Last year in May, Mr. Srinivas, along with research scholar R.L. Gouri, had authored a research paper on the susceptibility of North Bengaluru to flooding. The results had then forecast a grim situation: while internationally, drains are designed to fail only in rare storm events; in North Bengaluru, drains are liable to fail in weather conditions seen every two years.
Lower capacityThe study is currently being extended to the entire city, and worrying signs are emerging. “The capacity of the drains in many places is very low owing to accumulated silt or chokepoints. The capacity of lakes to accommodate excess flood water has also reduced over the years as many lakes (in the natural flood network) have disappeared,” he said.
While climate change has resulted in an increase in extreme rain events, the amount of water running off into drains and lakes has drastically increased too.
Changes in land coverAs reported often before, the city’s land cover has also changed drastically. Research in IISc has shown that built-up area has increased by 184 per cent over 15 years. This has led to the imperviousness – the reduction in the capacity of the landscape to absorb water, and instead let the water run-off. More water runs into SWDs now.
Mr. Srinivas believes the system’s design needs an overhaul. It must be made able to withstand extreme rain that is becoming more common owing to climate change; to consider rain data at a local level that can lead to better calculations of drain width and depth; to dredge lakes such that they become effective in flood protection; and to ensure regular dredging of drains to maintain their capacity.
BBMP banking on clearing encroachments
Staff Reporter
The Bruhat Bengaluru Mahanagara Palike (BBMP) is banking on the speedy clearance of encroachments on drains to solve the recurring problem of flood in the city.
During an inspection on Saturday, Mayor B.N. Manjunath Reddy said that nearly Rs. 6 crore-worth storm-water drain works were in the pipeline. “We have called in tenders worth Rs. 32 crores for around 224 SWDs that were assessed recently in the city,” he said.
