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12 februari 2010
Comparing structural& non-structural measures
Kees Bons
Flood Risk Management and Urban Resilience Workshop II
May 28-29, 2013
Venue COEX, Seoul, Republic of Korea
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Urban Flooding Issues
o Unplanned Urban expansion and growth into river
valleys and coastal areas
o Water supply, Drainage, Waste water and Floodprotection did not develop as fast as the growing needs
o Subsidence (due to overexploitation of GW)
o Ineffective Operation and Maintenance of flood defences,pumping stations and drains.
o Loss of natural defences (for example, mangroves)
o Climate Change? (more extremes, sea level change)
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No solutions, just responses
Structural adaptation measures
(SAMs):Constructed permanent facilities to
reduce the damage risk
Non-structural adaptation measures(NSAMs):
Responses to urban water problems
that may not involve fixed or permanent
facilities. Their positive contribution to
risk reduction is most likely through aprocess of influencing behavior, usually
through building capacity in all
stakeholders through active learning
and appropriate and effective
engagement between stakeholders(Taylor and Wong, 2002).
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12 guiding policy principles
1. Every flood risk scenario is different: there is no flood management blueprint.2. Designs for flood management must be able to cope with a changing and uncertain
future.
3. Rapid urbanization requires the integration of flood risk management into regularurban planning and governance.
4. An integrated strategy requires the use of both structural and non-structural measuresand good metrics for getting the balance right.
5. Heavily engineered structural measures can transfer risk upstream anddownstream.
6. It is impossible to entirely eliminate the risk from flooding.7. Many flood management measures have multiple co-benefits over and above their
flood management role.
8. It is important to consider the wider social and ecological consequences of floodmanagement spending.
9. Clarity of responsibility for constructing and running flood risk programs iscritical.
10.Implementing flood risk management measures requires multi-stakeholder cooperation.11.Continuous communication to raise awareness and reinforce preparedness is
necessary.
12.Plan to recover quickly after flooding and use the recovery to build capacity.
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probability
of failure
risk
vulnerability
protection
measures
hazard map
damage
sensitivityo
risk
map
(changes in)
pressures
adaptability
hot spot map
osometimes called vulnerability or susceptibility
(changing)th
reshold
strength
protection
strategy
Flood protection measures: Result of extensive
vulnerability analysis
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Measures we could take to reduce flood risk
> 200 adaptation measures identified..
SAMs: Structural (hard) measures (# >100)
Collective: e.g. dikes, drainage systems
Individual: e.g. wet or dry proofing
NSAMs: Non-structural (soft) measures (# > 100)
Collective: e.g. contingency plans, legislation
Individual: e.g. risk consciousness, insurance
and counting
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Adaptation measures
Objective:Reduce vulnerabilityof urban areas by
avoiding damage
damage reduction
creating redundancy and adaptabilityfor long term, unexpected change
But what is their effect and effectivity ? (e.g. retention pond)
In everyday situation Under design conditions (T = 10-100 years)
Under very extreme conditions (T = 500>1000 years)
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What if we rely only on structural measures
- When they fail they often fail dramatically (a chain is as strong asits weakest link)
- Structural measures cannot evolve with development
- Structural measures generally require high investments
- Structural measures often have major side-effects
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Threshold capacity
Coping capacity
Recovery capacity
Adaptive capacity
recurrence time
Strategy to reduce/manage vulnerability
* Graaf, R. de, N. van de Giesen and F. van de Ven, 2007, Alternative water management
options to reduce vulnerability for climate change in the Netherlands, Natural Hazards nov.
Strengthen four capacities* to reduce vulnerability
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Traditional Vulnerability reduction approach
First priority:SAMs to strengthen threshold capacity for fluvial andcoastal flooding
e.g. World Bank (2010) Climate risk and Adaptation in Asian Coastal Megacities
Consequences:
Other capacities and NSAMs get neglected
Increased vulnerability for other riskse.g. pluvial flooding, drought, land subsidence, heat
Lock-in
Effectivity in very extreme conditions (T>100 yr) is poor
Adaptability is limited
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Vulnerability reduction approach
Conclusion:
Strengthen all four capacities
SAMs show limited adaptability
Most SAMs strengthen threshold &
coping capacity
SAMs require high federalor
regionalinvestments
NSAMs require less, localor
individualinvestments
NSAMs require study (learning) and
regular training
SAMs cant do without NSAMs
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SAMs cant do without NSAMs
What would have happened
in Holland without effective flood early warning system in Indonesia with an effective tsunami warning system
in New Orleans without an effective evacuation plan
in Brisbane if their zoning plan had been water resilient
SAMS are only effective if people are aware, prepared, trained
and space use and construction are regulated
(and preparedness, rules and
regulations are maintained)
Considering all the uncertainties
the buzz word now is:
ADAPTIVE Management
NSAMS prove to be much more
adaptive than SAMS
Raise level +1.1 m in spring
Scenarios
Steam 2050
Change to drougth/salt
tolerant crops
2100
Lower navigation sluices. Increasing
pumping capacity. Strenthen dikes.
Lower inlet structures.
Raise IJsselLake level
within current infra+0.1
Decrease level within
current infra (-0.6?)
Accept navigation abstructionduring extreme drougths
Decrease level and adapt
infrastructure (-0.8?)
More water through
IJssel in summer. Afh. NWW
Adapt regional water system
infrastructure. Raise dikes.
More water to Ijssel in spring
Raise level +0.6 mRaise dikes. More water to Ijssel.
Adapt regional watersystem
infrastructure
Change land use
Current policy
More efficient water use
-0.20 - -0.4 m NAP
e.g. increase regional storage, flushing
optimalisation, flex level control. After
2050 pumping capacity needs to be
increased.
After 2050 pumping capacity needs to
be increased
Optimising current policyFlexible water levels
Watervraagbeleidsopties
Waterbeschikb
aarheidbeleidsopties
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How to select an appropriate set of AMs?
Three-step approach
1: Complete vulnerability-analysis
2: Select a strategy to reduce vulnerability
3: Select appropriate set of measures
many stakeholders / many stakes
many SAMs and NSAMs
design and negotiation approach
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Every situation is unique and dynamic
Type of flood (fluvial, pluvial,coastal, ground water)
Development and (spatial)
planning stage
Economic and social values
Culture and government style
Individual vs Community
Environment
0,0000
0,0002
0,0004
0,0006
0,0008
0,0010
0,0012
2000 2020 2040 2060 2080 2100 2120 2140 2160
year
probability
(1/year)
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Resulting portfolio of AMs
1. Threshold capacity
Waterrobust infrastructure
Enlarged seasonal storage
High floor level vs street level
Floating housing
2. Coping capacity
Major drainage system; adapted street
profile
Wet proofing vulnerable buildings
Warm grass instead cold grasses
4. Adaptive capacity
Temporary houses & buildings
Adaptive management
Water-based spatial planningUpdates water & space policies
3. Recovery capacity
Redundant pumping capacity
Cleaning & drying capacity
Water supply capacity in extremely dryperiods
Measures to strengthen
With the varying time and adaptation horizons
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Resulting designNew Orleans
Dutch Dialogues III, April 2010, www.dutchdialogues.com
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Closing
Thank you for your attention!
mailto:[email protected]:[email protected]