The menace of Urban Flooding

The menace of Urban Flooding

News: There was unprecedented flooding in India’s tech capital Bengaluru. Cities such as Kochi, Hyderabad,
Mumbai and Chennai have already faced the havoc caused by Urban flooding in the recent past.

What is Urban Flooding?
 Urban Flooding is an inundation of land in a constructed setting, particularly in densely populated areas.

What are the causes of Urban Flooding?

Natural causes
High Rainfall
Storm surges (coastal cities)
Rising Groundwater levels

Anthropoge nic causes
Unplanned Urbanization
Encroachment
Destruction of Mangroves
Illegal Mining Activities
Lack of Data and poor coordination
 

 High Rainfall – According to IMD, monsoon pattern is observing changes. It has become frequent and
unpredictable.
 Rising Groundwater levels – For example in Chennai, the replenished groundwater table across the city
after rains becomes a challenge for several buildings with basements.
 Encroachment – A large number of wetlands that soaked up the rainwater have been encroached upon.
Bengaluru had around 262 lakes in the early 1960’s but now only 10 hold water.
 Lack of Data and poor coordination – The CAG had highlighted that the Bengaluru municipality didn’t
maintain proper records of funds provided to it to manage stormwater management. It also noted poor
coordination between municipality and the Bengaluru development authority on drainage related matters.
 Destruction of Mangroves – One of the prime reasons why Mumbai floods almost every year. Mumbai has
lost around 40% of its mangroves between 1995 and 2005.
 Climate Change - The climate change has caused an increase in the frequency of short duration heavy
rainfall leading to higher water run-off.
 Urban Heat Island - NASA studies indicate that the urban heat island effect also results in increased
rainfall over urban areas that in turn leads to flooding. Whenever the rain bearing clouds pass over the
urban heat island, the hot air pushes the clouds up, resulting in highly localised rainfall which may
sometimes be of high intensity.
 Uninformed release of water from Dams - Unplanned and sudden release of water from dams and lakes
lead to floods in an urban area, without giving the public enough time to respond. For example, Chennai
Floods in 2015 due to release of water from Chembarambakkam Lake.

What are the steps to mitigate Urban flooding?
 Flood Vulnerability mapping - Identification of the vulnerable areas can be done by analysing topography
and historical data of inundations at city level.
 Effective water-shed management - Construction of flood walls, raised platforms along flood prone
river basins, timely cleaning and deepening of drainage channels should be taken up along the whole
river basin instead of just the urban areas.

 Bioswales – Also referred as ‘rain garden’ in New York are landscape features that collect polluted
stormwater runoff, soak it into the ground, and filter out pollution.
 Sponge Cities - The term “sponge cities” is used to describe urban areas with abundant natural areas such
as trees, lakes and parks or other good design intended to absorb rain and prevent flooding. Interest in
harnessing nature – or using “nature-based solutions” – to tackle climate shocks has grown in popularity in
recent years. Cities as diverse as Shanghai, New York and Cardiff are embracing their “sponginess” through
inner-city gardens, improved river drainage and plant-edged sidewalks.
 Public facilities like hospitals and schools and basic services such as food, water, health and sanitation
should be made disaster resilient. They should be located or relocated such that they are able to function
without hindrance during inundations.