URBAN
FLOODING – GEOGRAPHY
News: What is China’s ‘sponge cities’ and
why aren’t they stopping the floods?
What's
in the news?
● China
has been hit by devastating floods in recent weeks, inundating cities and
causing deaths and infrastructural damage, as well as raising questions about
the effectiveness of its 2015 “sponge city” initiative aimed at reducing urban
flood risks.
Key
takeaways:
● The
initiative was launched to boost flood resilience in major cities and make
better use of rainwater through architectural, engineering and infrastructural
tweaks.
Urban
flooding:
● Urban
flooding is the inundation of property in a built environment,
particularly in densely populated urban areas, caused by intense rainfall (on
impermeable surfaces) which overwhelms the capacity of drainage systems.
● Urban
flooding is significantly different from rural flooding as urbanization leads
to developed catchments, which increases the flood peaks from 1.8 to 8 times
and flood volumes by up to 6 times.
Consequently, flooding occurs very quickly due to faster flow times (in
a matter of minutes).
● Overburdened
drainage, frenzied and unregulated construction, no regard to the natural
topography and hydro-geomorphology all make urban floods a man-made disaster.
Cause
of urban floods:
Natural
factors:
1.
Meteorological Factors:
● Heavy
rainfall, cyclonic storms, and thunderstorms cause water to flow quickly
through paved urban areas and impound in low-lying areas.
2.
Hydrological Factors:
● Overbank
flow channel networks, the occurrence of high tides impeding the drainage in
coastal cities are major hydrological factors responsible for urban flooding.
3.
Changes in the rainfall pattern driven by Climate Change:
● The
rainfall intensity, duration, and frequency are going to increase in the
future, suggests the International Panel for Climate Change.
● Urban
heat island effect also has increased the trend of sudden rain in urban areas.
● The frequency
of cyclonic circulations and cloud bursts is a major contributor to flash
floods.
Man
made factors:
● Unplanned
urbanization causes overstressed city infrastructure.
● Lack
of drainage infrastructure and less seepage.
● Encroachment
by builders and contractors.
● Density
of population.
● Uncontrolled
encroachments on wetlands.
● Neglect
of pre-disaster planning - In India, the focus is mainly on post-disaster
relief efforts rather than pre-planning to counter urban floods.
Impacts
of urban flooding:
1.
Damage to vital infrastructure: Urban flooding damage
the essential public infrastructure and it leads to the disruption of normal
life.
2.
Loss of life and livelihoods: This year, the heavy
rainfall has caused devastating floods in several States, resulting in more
than 1,439 lives being lost, 365,770 houses being damaged, and crop damage in
307 districts, per data from the Disaster Management Division, Ministry of Home
Affairs.
3.
Risk of epidemics: Due to water logging in the flood times,
exposure to water borne and viral vector diseases is very high.
Management
of Urban flooding:
Three phases of managing urban flooding:
Government
initiatives for managing urban flooding problem:
● Atal
mission for rejuvenation and urban transformation
● Smart
cities mission
● Sponge
cities mission
● It
flows: 72hour early warning system has been installed in Mumbai.
NDMA
guidelines:
● It
designates Ministry of Urban Development as the Nodal Ministry for Urban
Flooding.
● Among
key provisions of the Guideline are Early Warning System and Communication.
● Create
a National Hydro-meteorological Network - for providing early warning in all
urban centres.
● Developing
local networks for real-time rainfall data collection with a ‘Local Network
Cell’ in the IMD headquarters.
● Sub
divide Cities/ towns on the basis of watersheds and develop a protocol for
forecasting rainfall for urban areas on the basis of watershed.
● Design
and Management of Urban Drainage System.
● A
watershed based and ward-based inventory of the existing storm water drainage
system to be prepared.
● Pre-monsoon
desilting of all major drains to be completed by March 31 each year.
● Every
building in an urban area must have rainwater harvesting as an integral
component.
● Concept
of Rain Gardens to be incorporated in planning for public parks.
● Integrated
Planning and interactions between Water and Solid Waste Management.
WAY
FORWARD:
1.
Disaster resilience improvement - Focus has to be on
increasing the resilience of communities and adaptive capacity of our
infrastructure.
2.
Water sensitive urban design and planning techniques
- especially in the context of implementation - are of utmost importance. These
methods take into consideration the topography, types of surfaces (pervious or
impervious), natural drainage.
3.
Strong land use control - EIAs and enforcement will remain
vital to ensure that fragile wetlands and floodplains are not concretised.
4.
Utilise the power of digital technologies - To
digitise informal settlements, identify levels of vulnerability for flood
protection strategies and ensure timely actionable information including
financial supports.
5.
Framework and Contacts for Early Warning - It is necessary to
distribute flood alerts utilizing a variety of modern technologies. Whereas
traditional systems struggle, this will help transmit information in real-time.
6.
Coordination between various institutions - The
coordination between water resources and disaster management authorities needs
combined coordination and responsibility for disaster risk management.
7.
Disabling encroachment in sensitive zones.