hidden vulnerability of mega cities · 2018. 12. 10. · land subsidence in asia location, country...
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Hidden Vulnerability of Mega cities
Srikantha HerathEnvironment and Sustainable Development
United Nations University
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ContentSafety from floodsCities and Natural Disasters
Inherent risks due to geology and geographyIncreased vulnerability
Increased Resource consumption: ground water Urbanization and increasing risk
Changes to hydrological cycle Increase FloodsUrban infrastructure
Some features from reconnaissance surveysVenezuela, Sri Lanka, Viet Nam, Tokyo
Catastrophic Floods The hidden vulnerability : UNU Programme
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Cities and Floods
Cities have traditionally evolved along rivers because of stable water supplyIrrigation in alluvial planes, amenity have made rivers close to peoples daily livesThis increased productivity also has associated risks
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Source: UN DHA, 1997/07
Flood Damage 1987-96 in Million DollarsTotal Damage - 250658
0.14%
35.33%
54.06%
9.84%0.63%Africa 1576
Americas 24656
Asia 135509
Europe 88568
Oceania 349
Deaths from Floods 1987 - 96 by ContinentTotal Number of Deaths 245355
0.17%1.58%
92.77%
2.95%2.53%
Africa 6200Americas 7249Asia 227612Europe 3878Oceania 416
Number of Floods 1987-96Number of Floods 982
6%10%
44%
27%
13%Africa 124 Americas 270Asia 432Europe 100Oceania 56
Floods 1987-1996
• Casualties in Asia is highest among the world
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Populated Areas and Past floods
Tectonic zones
Flood events reported from 1990-2000
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Urbanization and flood risk
The risks increase with urbanization1. Increasing demand and over utilization of
resources (ex. Ground water extraction)2. Urbanization affect hydrology – increasing
flood potential3. Rapid development – risks are unknown for
rare events
Area below normal low tide
Area below normal high tide
Area below abnormal high tide
Increased flood vulnerability due to land subsidence in Tokyo
Present embankment to protect subsided areas
Ground water is easily over exploited to meet growing industrial demands
Land subsidence in AsiaLocation, country
Area, km2 Depth range of compaction, m
Time of occurrence
Maximum subsidence, m
Osaka, Japan
120 (1960) 10-500 1948-1965 3-4 (1965)
Tokyo, Japan
230 (1974) 10-500 1938-1975 4.6 (1975)
Taipei Basin, Taiwan
100 30-200 1961-1975 1.8
Bangkok, Thailand
285 (1980) 10-200 1950-1980 0.80 (1980)
Source: Das Gupta, Ashim (1997) Groundwater and the Environment, in Water Resources
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Insufficient Drainage
HANOI, Viet NamBeijing, China, July 10
Rapidly urbanizing cities experience urban floodsUrbanization outpaces drainage infrastructureHolistic approach is required in solving the problem
Urbanization and flood disasters
It is well established that urbanization increase bothflood magnitude and flood frequencyIn addition to infrastructure: taking care of water at the location through infiltration and detention are recognized to be effective in reducing urban floods.
These measures need to be incorporated in City Planning and disseminated Slow down:
Reduce:
+
The recent underground urban expansion creates new flood risks. Fukuoka flood: June 29th, 1999.
Experience of high intensity rainfall
more than 100mm/hr
75-100 mm/hr
Year
(River information center)
NumberTokyo has experienced frequent UG floods – 17 events only in 3 years.
Maximum hourly rainfall varies from 44mm/hr to 131m/hr . (average 60mm/hr)
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Urban Expansion and increasing risks
Risk = F (Hazard, Vulnerability) Urbanization increases both the hazard and vulnerabilityExtremely rapid urbanization processes have made it difficult to ‘experience’ the consequences of catastrophic eventsVaries according to concentration of people at different times and facilities
Utility: Transport facilities, Public hallsThe day of the week and time of the day
Dynamic Assessment is necessary
Salient features:•Grid size: 20m•With DEM and DSM•Period: June 29, 1999:01.00 –24:00 hrs.•Rainfall data: 10 min. interval•Number of entrances for water to go in – 25
Safety ofUnderground
space
1999Maximum hourly rainfall is 77 mm/hr, total rainfall is 164mm. Subway was suspended for about 3.5 hours. :Water into subway is estimated about 2,000m3
2003Heavy rain in upstream of Fukuoka.104mm/hr at Dazaifu, less than 20mm/hr in FukuokaSubway stopped at 19th, resumed completely at 20th.:Water into subway is estimated about 10,000m3
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The Hidden Vulnerability
Urbanization increases vulnerability to floods.The rapid pace of urbanization makes it difficult to adjust for extremes.Major urban expansions give rise to whole new satellite cities. They grow very rapidly and can be devastated by a severe rainfall event.
The greatest danger is if an extreme event strike an Urban Center
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Venezuela floods and debris flow 1999 December30,000 persons lost lives.Over 480,000 people were affected.Us$ 2 million65,000 houses were damaged and over 24,000 houses were destroyed.
DS/DS/DicDic. 99. 99
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Development in vulnerable areas
Nepal - 1993
Venezuela - 1999
Therefore it is important to focus on Catastrophic Flood impacts where rare and extreme floods cause huge economic and human losses.This would happen when the floods exceed the design standards of flood control infrastructure, or if the infrastructure fail due to unexpected reasons
• The Venuzuela floods is not an isolated case. The extreme damage was caused by a rare event
• The last major rainfall was 50 years ago (though less in magnitude) when urban expansion has not started.
• The rarity, more than the absolute intensity increase losses
Catastrophic Flood Impacts
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Some near misses !In 1992 there was a large flood in Colombo Sri LankaA record rainfall – 1/1000 Rainfall 493 mm -> Total discharge 29 million cubic m.Drainage capacity 2 mil. cu. m, and it took 10 days to discharge the floodThe rainfall was only limited to Colombo – No river overflow. If a river embankment breach occurs A catastrophic loss
Maradana Pumping Station andImprovement of GalleFace Outfall
Restoration of Existing Mutwal Tunnel
New Mutwal Tunnel
North Lock Pumping Station
Construction of Storm WaterRetention Facilities in UrbanArea
Improvement of WelawattaAnd Kirilapone Canals
Madiwela South Diversion
Gotatuwa Pumping Station
Kelani Ganga
Beira Lake
Indian Ocean
Scale
ParliamentLake
N
Marsh
Marsh
Storm Water Retention Areain Bolgoda Basin
PStorm Water Retention Areas
P
Marsh
P
Conceivable Structural Measures for Weras Ganga
2002 July Flooding in Kathmandu
2002 floods in Kathmandu, Nepal has created severe damage
The inundation was caused by flow capacity restriction downstream of Katmandu
The rainfall that produced the flood was not the largest expected
What is the ‘worst case’ rainfall? This is one of the biggest problems for Nepal and elsewhereFrom DHM Nepal
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Asia Pacific Initiative on Catastrophic Flood Risk ReductionBangkok Resolution:
The need for an Asia Pacific Initiative on Catastrophic Flood Risk Reduction, and pledged support for the mission and goals of this
initiative by representatives from:
Bangladesh, Cambodia, China, Fiji, India, Indonesia, Lao PDR, Malaysia, Nepal, Pakistan, Philippines, Singapore Sri Lanka, Thailand and Vietnam
at this Regional Workshop “Ensuring Flood Security for Sustainable Urbanization in the Asia Pacific Region”, 2003
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Asia Pacific Initiative on Catastrophic Flood Risk Reduction
Mission: GOALTo integrate
Prior risk assessment (catastrophic flood scenario)Basic framework for response (action plan)
into urban development and planning process for sustainable urban futures
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Asia Pacific Initiative on Catastrophic Flood Risk Reduction
Components:1. Clarifying Catastrophic Floods and relations to
physical and social conditions2. Estimating extreme Rainfall for the basin3. Inundation modeling and prediction4. Risk Assessment (socio-economic) : response5. Community participation
Focus on those who are subjected to hazardThe whole area of social vulnerability should receive strong attention
6. Capacity development: Institutional needs
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ChallengesAs urban centers grow and develop, there will always be new risks
Increased floods, underground space flooding, etc.Ensuring human security in urban areas for sustainable urban communities – from ‘fail-safe’ to ‘safe-fail’
Infrastructure development considering vulnerabilityGuide lines for ‘catastrophic flood’ resistant urban communities
Why catastrophic flood risk assessment?Methods to assess losses consensus
Cost benefit analysis to mobilize investmentMethods that would be useful not only in managing extreme floods but also ordinary floods.
Thank you
for your attention