estimating urban flood exposure: application to extreme events in surat… · 2020-02-07 ·...
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Estimating urban flood exposure:Application to extreme events in Surat, India
Jorge A. Ramirez, Umamaheshwaran Rajasekar, Tom J. Coulthard, Margreth Keiler
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Surat Tapi river
Ukai dam
Tapi river reach• Northwest India• From the Ukai dam to the Arabian Sea• 120 km of the Tapi river
Study site
India
20 km
Source: Bing maps
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Surat Tapi river
Ukai dam
Ukai dam • Irrigation• Power generation • Flood control• Year completion: 1972• Max discharge: 46,000 m3 s-1
Study site
600 m
sources: youtube.com, Bing maps
20 km
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Surat Tapi river
Ukai dam
Surat• 7th largest city in India• Major industrial and commercial
center and port• Area: 325,000 km2
• Population: 3 million• Bisected by Tapi river
Study site
sources: wikipedia.org, Bing maps
20 km
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• Increase in urban area, construction in the floodplains, construction of embankments
• 170% increase in urban land cover in 25 yrs
1990 2001 2014
Study site: SuratSurat land cover
sources: Misra and Balaji [2015]Time (year)
Urban land coverAr
ea (h
ecta
res)
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Upstream from Ukai dam• Catchment area: 62,000 km2
• Tapi river is fed by monsoonal rains• 90% of the annual rainfall is received during the monsoon months (June to October)• Average annual rainfall: 830 mm
• Difficult to prevent flooding in Surat and also manage dam for irrigation and hydropower• 5 major floods since the construction of the dam (1972)
150 km
Source: TARU
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Surat flood 2006
time (hr)di
scha
rge
(m3
s-1)
Ukai dam release 2006 flood
Flood warning discharge
sources: Patel and Srivastava [2013], http://citiscope.org
• Intense rainfall in the Tapi catchment • Max. reservoir capacity during monsoon• Dam release near 25,000 m3 s-1
• Release lasted 15 days• Release exceeded flood warning discharge
for Surat (11,000 m3 s-1)
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Surat flood 2006
tidal flood
0-0.0750.075-0.10.1-0.25>0.25
water depth (m)
90% of city flooded40% of people received no warning300 deathsProperty damage: 3.3 billion USD
Source: TARU
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Surat flood 2006
source: TARU
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A first step towards strengthening resilience in Surat requires:• Mapping critical infrastructure exposed to flooding• Raising awareness of flood exposure to the public
Objectives
source: TARU
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MethodUse CAESAR-Lisflood two dimensional flow model to simulate flooding in Surat
Two distinct stages:• Stage 1: Model the flow of water from the Ukai dam to the city of Surat• Stage 2: Model flood inundation in Surat
discharge
tides
Stage 1Stage 2
SuratTapi river
Ukai dam
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CAESAR-Lisflood
• CAESAR-Lisflood is a storage cell model, where a Digital Elevation Model (DEM) represents the landscape and water is stored at the raster cell locations
• Water is routed over the landscape in the X and Y directions (2D) from raster cell to cell using a simplification of the shallow water equations
• Open source• Low computational demands• Low data requirements
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Stage 1: Modelling Ukai dam to Surat• Digital elevation model (DEM): SRTM 30 m• 9 synthetic dam releases, with different peak discharge• Flooding reduces amount of water arriving at Surat
Ukai damwater depth
low
high
flow
Time (days)
Dam release
Disc
harg
e (m
3s-1
)
Surat
10 km
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Stage 1: Modelling Ukai dam to Surat• Digital elevation model (DEM): SRTM 30 m• 9 synthetic dam releases, with different peak discharge• Flooding reduces amount of water arriving at Surat
Ukai damwater depth
low
high
flow
Time (days)
Dam release
Disc
harg
e (m
3s-1
)
Surat
Time (days)
Disc
harg
e (m
3s-1
)
Water arriving at Surat
10 km
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Stage 2: Modelling flooding in Surat• Ground survey to acquire 6,200 point elevations • 172 river bed cross-sections collected to represent the river bed elevations• Ground survey interpolated to represent bare Earth at 30 m spatial resolution• Outside of the city limits elevation information was obtained from a 30 m SRTM DEM
Bare earth city DEM
elevation
low
high
survey data
Surat
10 km
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Stage 2: Modelling flooding in SuratTidal input for Surat
Wat
er le
vel (
m)
Time (days)
River input for Surat
Time (days)
Disc
harg
e (m
3s-1
)
water depthhigh
low
Surat
10 km
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Stage 2: Modelling flooding in Surat
water depthhigh
low
Flood scenario with peak dam release of 23,000 m3 s-1
Time (hr):
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City flooding
Water depths (m)0-1
1-2
2-4
4-6
>6
Peak discharge 11,000 m3 s-1 Peak discharge 17,000 m3 s-1
Peak discharge 23,000 m3 s-1 Peak discharge 34,000 m3 s-1
• Flood maps represent maximum water depth at each DEM location
• Simulated flood map quality verified by Surat city engineers
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Critical infrastructureTransport Rescue, intervention, and other
roadsrailroadairport
hospitals (n=292)police station (n=21)fire station (n=10)water tanks (n=19)
source: TARU
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Critical infrastructure exposure
transport
rescue and intervention
other
Infra
stru
ctur
e flo
oded
≥ .5
m w
ater
dep
th (%
)
Flood scenario peak discharge (m3 s-1)
Dam releases 17,000 – 20,000 m3 s-1 exposure beginsDam release of 25,000 m3 s-1 (2006 flood), majority critical infrastructure exposure is > 50 %
2006
floo
d
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Population
source: www.asiapop.org
2015 population estimates
229
0
Population (people/100m2)
Total population: 3 million
10 km
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Population exposure
Flood scenario peak discharge (m3 s-1)
Flood of 25,000 m3 s-1 (2006 flood), exposure is near 50 % (1.5 million)
Popu
latio
n flo
oded
≥ .5
m w
ater
dep
th (%
)
2006
floo
d
Total population: 3 million
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Income group
Income groupvery low (slum)
low
middle
high
source: TARU, ESRI
5 km
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Income group exposureAr
ea fl
oode
d≥
.5 m
wat
er d
epth
(%)
Flood scenario peak discharge (m3 s-1)20
06 fl
ood
More exposure: High to middle income groups live proximate to the riverLess exposure: Low to very low income groups live in the periphery of the city, further from the river
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Lamp Post Number: GDR55(Kala Mandir Ghdo Road)
0-17,000
17,000-30,000
> 30,000
• Modelled flood maps have been used to demarcate possible flood heights within the city
• City is developing a smartphone app that displays flood animations derived from modelled floods
Communicating flood exposure
Modelled flood scenarios (m3 s-1)
source: TARU
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• Large, but possible floods in Surat will expose:• more than 50% of the critical infrastructure to deep water • 1.5 million people to deep water • more middle to high income groups to deep water
Conclusions
source: TARU