How a city can tackle floods

The heavy rains of August 14 and 15 will remain in the memory of the Bengalis for some time. Floods, bottlenecks, sewage in homes are not things that people will quickly forget. There are many criticisms of the unpleasant state of our city’s infrastructure, but there are also lessons to be learned.

Precipitation data generation has improved by leaps and bounds. The Karnataka State Natural Disaster Monitoring Center (www.ksndmc.org) has a complete set of meteorological monitoring stations, currently numbered 82, which provide increasingly granular city rains. Recent precipitations, for example, were concentrated in the south-central part of the city while the north had much less rainfall. The city is not homogeneous in case of rain by intensity, duration and total precipitation.

Is there a pattern for that? Are there areas that receive stronger precipitation? Are there areas more vulnerable to rain? All of these questions are interesting, which can be solved by flood modeling. This is underway by IISc and KSNDMC together, we understand. In the mean time, what citizens, communities, neighborhoods and the city can do to address the problem.

Citizens: Do not build on old tanks beds, buffer zones of lakes and rajakaluces, and generally weak areas that can flood. Understand that the built earth can increase runoff from rain drainage by factors of 6. A rain of 150 mm falling on a site of 150 square meters can send 22,500 liters of water outside the plot. Add all the sites in a neighborhood and it is a flood you expect.

Follow and exceed the regulations for harvesting rainwater. If the law requires 20 mm of rain falling on a site, design to keep in well tanks or perch in wells recharging at least 60 mm of rain, otherwise 100 mm. This means that a roof surface of 100 square meters should provide 6,000 liters or 10,000 liters of storage. In the case of a recharge well, the dimensions must be at least 3 feet in diameter and 20 to 30 feet deep with a grid at the top for safety. Allow the entire rainwater site to recharge aquifers and prevent flooding

Communities: Identify and manage flood prone areas in your development, apartment complex or neighborhood. Make sure that the sewers are cleaned regularly and that there are no landfills or sewers. Keep the emergency pumps ready with a plan to dump the water and place to put the water in. Have the contact numbers of the local civil defense authority and the BBMP.

Identify the nearest lake or body of water and make sure the dam is strong and retains full levels. Make sure the overflow and rajakaluves landfills are clean and ready to drain the rainwater. Safety level: with the help of the manufacturer, identify suitable areas for flooding and develop drainage plans. The regular disillusionment of storm drains and withdrawal should be underlined and pushed especially during the months of August, September and October, when heavy rains are expected.

The connections between roads and storm drains are weak points that tend to get stuck. Good design should be ensured here. As far as possible, recharge wells should be carried out in the drainage of rainwater to infiltrate the water into the aquifer. Regular removal of leaves and a good collection system of solid waste avoiding the discharge of waste into the sewers should be in place during the monsoon.

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