Urban flooding has significant social, environmental, and economic costs for cities. Static flood maps do not provide accurate or dynamic information about flood risks over time and with changing conditions. The document discusses the development of a dynamic water flow model for Bengaluru, India by WRI India to better understand flood risks. The model can simulate different rainfall patterns and scenarios to inform solutions. Modeling results show that urbanization and loss of natural drainage systems contribute to flooding in Bengaluru. Solutions like rainwater harvesting can help reduce flooding when tested using the dynamic model. Such models can support early warning systems, urban planning, and infrastructure management.

1. 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
Percentage
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
Percentage
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