iahr 2015 - nature-based flood defenses: panacea or illusion, weesenbeeck, deltares, 20150629
TRANSCRIPT
Asian Tsunami (2004)
Hurricane Katrina (2005)
Japanese tsunami (2011)
Hurricane Sandy (2012)
Typhoon Haiyan (2013)
Disaster aftermath
Role of ecosystems in reduction of impact
and damage
Asian Tsunami (2004)
Hurricane Katrina (2005)
Japanese tsunami (2011)
Hurricane Sandy (2012)
Typhoon Haiyan (2013)
Transition in flood risk management
Use of natural processes and ecosystem services for
flood defence and flood risk mitigation
Type of ecosystems
Why?
• Call for sustainability and quality of life
• Hard infrastructure is expensive
• And does not apply everywhere
Risk reduction cascade
Spalding et al. 2014
Cumulative interventions
Initial
risk
Residual
risk
Wetlands
Levees/
Flood walls
Building codes/
zoning
Early warning/
Evacuation plans
Structural and non-structural combinations
Combinations of structural
More space needed
What about risk?
Space and risk
Van Wesenbeeck et al. In prep
Ready for implementation?
Design
Construction
Maintenance &
management
State of quantitative engineering knowledge:
• Design (effectiveness)
• Hydraulic
• Geotechnic
• Construct (uncertainty)
• Manage (adaptive)
State of knowledge: salt marshes
Model data
Flume data
Field data
Functioning under extreme conditions
Vegetation versus elevation
Elevation
Elevation clay platform with vegetation
Models without vegetation
Smale et al. 2013
Testing on realistic scales
With extreme conditions
With and without vegetation
Moller et al. 2014
Modelling extreme conditions woody vegetation
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-20 -10 0 10 20 30 40 50 60 70 80 90 100
x (m)
Wave H
eig
ht
(m)
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und level (m
) N
AP
VF000
HS1
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HS3
Van Wesenbeeck et
al. submitted
Modelling extreme conditions grassy vegetation
Dijkstra et al. in prep
Modelling extreme conditions
• Veg factor: density * diameter * height * Cd
(Mendez and Losada 2004)
• Cd as calibration factor
• However, Cd changes with water levels and wave
characteristics
Models: bulk drag
Remmers et al. In prep
Future research and developments
• Improve predictability (validated models and generic rules)
• Sensitivity analyses of model parameters
• More controlled tests on realistic scales
• Full parameterization versus quick assessment models
Take home
• Ecosystems contribute to reduction of flood risk
• Ecosystems are likely to be most effective in combination with
other measures
• Vegetation matters
• Design rules can be derived but need to be improved
• Long term trends, such as sea level rise, will ask for constant
management of soft protection strategies