iahr 2015 - nature-based flood defenses: panacea or illusion, weesenbeeck, deltares, 20150629
TRANSCRIPT
Transition in flood risk management
Use of natural processes and ecosystem services for
flood defence and flood risk mitigation
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
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
Modelling extreme conditions woody vegetation
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1.10
-20 -10 0 10 20 30 40 50 60 70 80 90 100
x (m)
Wave H
eig
ht
(m)
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Gro
und level (m
) N
AP
VF000
HS1
HS2
HS3
Van Wesenbeeck et
al. submitted
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
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