A product of WRI Ross Center for Sustainable Cities

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RAJ BHAGAT P

URBAN FLOODING

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WHY URBAN FLOODS?

• Urban floods have huge social, environmental, and economic

cost

• Normal rainfall events could easily trigger urban flooding

• Brings the city to a stand still

• Chennai floods of 2015 caused Indian Industrial Production to

contract

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NOT JUST STAGNATION OF WATER

Source: Google Maps

BEFORE RAINFALL

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IT’S ALSO STAGNATION OF ECONOMY

Source : Google Maps

DURING RAINFALL

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NEED FOR DYNAMIC FLOOD MODELS : MEASURE

BEFORE MANAGE

• Static flood risk maps usually give a generalized and coarse picture of the damage faced by the city

• Need for creating and using efficient dynamic flood model tools instead of static tools

• Dynamic flood models inform us of water stagnation levels spatially and temporally

• They can be designed for any precipitation and urban development scenario

• Solutions might vary from place to place, time to time. Dynamic flood models allow us to test the solutions before implementation

• WRI – India has been developing a dynamic water flow model for this purpose

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RAINFALL PATTERNS

• Classical flood models use either historical precipitation data or extreme variations from historical precipitation

• Dynamic flood model like the one designed in WRI would allow users to create different precipitation scenarios

• The user can change precipitation amount, spatial distribution of precipitation, and temporal distribution of precipitation

Image: Spatially varying precipitation event; Chart: Temporally varying precipitation event

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BENGALURU

GEOGRAPHY

• Bengaluru is situated between 700 and 940 m above sea level

• Bengaluru receives 86 cms of rainfall annually

• It receives rainfall during both summer and winter monsoon

• Using openly available meteorological data, digital elevation model, and soil information; the dynamic model was created

Source: WRI India and SRTM (USGS)

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IMPACT OF 6 CM

RAINFALL IN BENGALURU

Image: Stagnation after 3 hours of rainfall

• Commercial areas face more stagnation

• 24% of population faces stagnation of more than 0.1 metres

0

10

20

30

40

50

60

70

80

90

< 0.05 0.05 - 0.1 0.1 - 0.3 > 0.3

Per

cen

tage

Stagnation in metres

Residential Area Commercial Area Industrial Area

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NEIGHBOURHOOD LEVEL

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NEIGHBOURHOOD LEVEL (CONTD..)

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CAUSES FOR

STAGNATION

• Lower percolation because of

rapid urbanization

• Loss of natural drains and water bodies

• Clogging of drains due to garbage and

other materials

• Lack of space to store surface water

Source: WRI India using LandSat 5 and LandSat 8 (USGS/NASA)

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SOLUTIONS

The most commonly proposed solutions for urban flooding are,

• Rain water harvesting• Waste water reuse• Water sensitive urban designs during master planning process• Preservation of natural drains and flood plains

Dynamic flood model would allow us to test these solutions!

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EFFECT OF RAIN WATER

HARVESTING ON FLOOD

Note: Assuming all the buildings in Bengaluru practice rain water harvesting

0

20

40

60

80

100

< 0.05 0.05 - 0.1 0.1 - 0.3 > 0.3

Per

cen

tage

Stagnation in metres

Residential Area Residential Area w RWH

Commercial Area Commercial Area w RWH

Industrial Area Industrial Area w RWH

• 0.2 TMC water collected more (6cm precipitation)

• Stagnation decreases in most places

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APPLICATIONS

Tools such as dynamic flood models could be used for multiple purposes

• Early warning systems – Increase resilience and disaster response

• City planning – effectively managing areas facing stagnation

• Water resource and infrastructure management

• To understand the effects of proposed solutions / plans

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THANK YOU