Tuesday, September 13, 2016

Urban Flooding Phenomenon in India - Background, Reasons and Solutions

Urban floods in the past few years have been on a rise with the problem affecting the length and breadth of the country right from Mumbai floods to Chennai floods and water-logging in Gurgaon. A report by Centre of Science and Environment has highlighted that the problem is only set to exacerbate in the years to come. 

The factors which have contributed to increased urban flooding are: 

1) Global warming and Climate Change which has altered the rainfall patterns across the world. India has also seen many incidents of copious rainfall in very short time resulting in breakdown of drainage infrastructure in cities. This along with melting glaciers and rising sea levels has increased risks of urban floods 

2) Bad urban planning – India is witnessing unprecedented level of unplanned urbanization. The CAGR of urbanization is 2.1% in India which means that by 2031, we will have approximately 60cr urban population and sizeable urban assets. In this scenario, unplanned urbanization and poor urban infrastructure management are exacerbating the problem of floods. 

The chief culprits in bad urban planning are 


a. Haphazard construction with little regard for natural drainage systems, storm-water drains: 

i. While storm water drainage is an important means of discharging floodwaters into the sea, as per a report in the Down to Earth, Chennai has only 855 km of storm water drains as against 2,847 km of urban roads; consequently, even a marginally heavy rain could cause floods. 

ii. Storm water drains are an essential part of urban infrastructure, which have not received adequate attention or investment. 

iii. The design of storm water drains is equally important. As witnessed in Mumbai, they simply did not have the right diameter to carry the heavy amount of rainfall 

iv. Important to increase the carrying capacity of storm water drains through regular desilting and cleaning before the rains. In most cities this exercise is fraught with corruption, with frequent allegations that contractors do not clean the storm water adequately. 

v. Cities need to develop separate systems for disposal of sewage and storm water. But in the absence of a proper sewerage system in many cities, urban residents discharge their sewage into the existing storm water drains 

vi. The use of storm water drains for discharge of sewage seriously reduces the capacity for draining the rainwater, besides polluting the outfall 

b. Illegal construction on wetlands 

c. Poor management of urban reservoirs which supply drinking water to the city. The release of water from the Chembarambakkam reservoir into Adyar River in Chennai worsened the flood situation and caught people by surprise. For most part these reservoirs do not have sufficient water and although there are guidelines for managing them, there is generally a tendency on the part of civic authorities to store as much as water as possible, releasing it only when the stored quantity poses a risk to the reservoir. As the water is released at the last minute, there isn’t enough time to evacuate people. The release of water has the impact of flash floods. 

d. Lack of soft grounds to act as aquifers due to excessive concretization 

e. Lack of an early warning system 

3) Problems in wetland management 


a. There exists no legal protection for city’s lakes, catchments and drainage systems. Water bodies and their catchment have been taken away for illegal construction 

b. In South India, the loss of lakes had been widespread. In 1960, Bengaluru had 262 lakes, but today not even 10 lakes are in a healthy state. Hyderabad, too, is losing its water bodies. 

c. Chennai’s flood sink–the Pallikaranai marsh–which was around 5,000 ha at the time of independence got reduced to almost 600 ha around 2010-11 due to urbanization and mismanagement. The government’s own studies accept that the waterways in Chennai convey treated and untreated sewage and garbage together. These waterways, which are also the city’s flood discharge channels, are encroached and built upon as well, severely reducing their flow 

d. The degradation of rivers across cities has also exacerbated the situation. In Chennai, the floodwaters are carried by Cooum and Adyar rivers, and the Buckingham Canal all of which do not have enough water flow in normal times. They are silted and choked and often encroached upon, which reduces their carrying capacities. 

Steps required for dealing with urban floods: 


● Must begin with planning process. Must do vulnerability assessment, demarcate no development area, build urban drainage infrastructure in sync with natural drainage patterns and allow for redundancies 

● Retrofitting porous pavements and large tanks to store rainwater 

● Current approach of connecting local drains to dump in rivers inefficient. Can consider short circuiting the drains to dump water in local parks having aquifers which will also enhance Ground Water percolation 

● There is a need of strong laws to protect urban lakes 

● Urban planning should be integrated with the study of the geology and the hydro-geology of the area so that new developments are not at the cost of the lakes and wetlands 

● There should be an umbrella authority to protect and conserve the water bodies.

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