Lack of proper drains and the encroachment of floodplains amid heavy urbanisation has put at least 49 locations of Bengaluru at high risk of flooding, a recent study has shown.
These areas include Adugodi, Horamavu, Mysore Road, Lakshman Rao Nagar (near Shanti Nagar bus stand), Ejipura and Silk Board Junction. Even some areas of residential hubs such as Indiranagar, Koramangala, Sarjapur Road and Shivajinagar are at risk. These areas may face intense flash floods, say researchers NN Rama Prasad and Priya Narayanan from the Central University of Karnataka.
A flash flood is a sudden local flood, typically due to heavy rain. Their research focused on creating a database of the city where the extent of vulnerability of each area could be outlined and categorised into zones, and the reasons behind the risk could be classified so that targeted action could be initiated.
The overlay analysis of floodplain and impervious surfaces shows that 5.4 square km of urban development has taken place in high-risk flood zones. The researchers warn that there should be no further developments in these areas and there must be preparedness for rescue operations during intense rain. The researchers have also created a geographical information system (GIS) map, which shows the areas which have been subjected to flash floods over the last several years.
“Large-scale land conversions, loss of lakes and occupation of floodplains have resulted in many problems like urban heat island, depletion of groundwater and, more importantly, flash floods in the city. The dumping of solid waste, laying of cables in the channels, under-potential culverts and allotment of the floodplain for housing purposes has developed vulnerability to frequent flooding,” said researchers in the study.
“Increased urbanisation with intensified vertical growth of the city has led to the liquid waste disposal along storm water drains, making the run-off models unpredictable. The breach of lake embankments and overflowing lakes at the initial monsoon rains is the widespread phenomenon as the lakes are silted and saturated with sewage. The recent flood on July 29 at Kodichikkanahalli is one such example,” said the researchers, whose findings have also been published in the journal ‘Annals of GIS’.
Mapping the threat
The researchers used Survey of India maps, Bhuvan web portal, open street maps, handheld GPS to identify flood locations and prepare the flood-affected zones. “The flood vulnerability map generated by us will help in the improved understanding of flash floods for local planning. It will aid in the design of remedial measures according to flood zones. It is high time for authorities to wake up and use the city’s rain by converting it as a resource and reducing surface run-off,” the researchers told Bangalore Mirror.
Their assessment further shows that 65.1 square km of urban development has been done in the moderate flood-risk area. A total 136 flood locations lie in moderate flood risk zone. Among them are Anand Rao Circle, Anepalya, Begur Road, Kaval Byrasandra and Ashwath Nagar. The moderate-risk zones arise due to dumping of solid waste in drains and alteration of stream morphology. Another 68 identified locations fall in the low-risk zone. These areas could see flash floods owing to drainage congestion by solid waste dumping or use of storm water drains for wastewater disposal, faulty construction of medians and under-capacity culverts and drains. Among them are Binny Mills, BTM Layout, Konena Agrahara and Gurappanapalya.
Flooding at 27 locations fall under the safe zone, said the findings. Flash floods in these areas could be attributed to engineering flaws like under-capacity bridges and culvert and improper maintenance of drains in subways. Among them are Akkipet, Mysore Bank Circle, Abbigere, Majestic and JP Nagar.
Credits Bangalore Mirror