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Flood security strategiesFlood security strategies
An assessment of the strategies of An assessment of the strategies of compartmentalization and flood shelterscompartmentalization and flood shelters
Lansink J., A.Y. Hoekstra, M.W.J. van Reedt Dortland, C.M. SteinwegLansink J., A.Y. Hoekstra, M.W.J. van Reedt Dortland, C.M. Steinweg
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Overview
• Introduction– Context– Objective– Case study area
• Scenarios
• Strategies– Compartmentalization– Flood shelters in self prepared cells
• Results
• Conclusions and recommendations
ConclusionsOverview Introduction Scenarios Strategies Results
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Context
• The development towards actual flooding probability
not only overtopping can result in dike failure
• Consider dike ring area as a whole
• Focus shift from probability to consequences
• Is it wise to invest in a lower probability by investing in dike heightening or do we need to invest in reduction of consequences?
ConclusionsOverview Introduction Scenarios Strategies Results
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Objective
Research objective:
To design, analyze and compare flood security strategies that aim to decrease the consequences of a flood.
I do not discuss:
- Probability of failure
- Cost benefit analysis of the strategies
ConclusionsOverview Introduction Scenarios Strategies Results
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The case study location
Dike ring area 6, the Northern Provinces of the Netherlands
(i.e. Fryslân and Groningen)
ConclusionsOverview Introduction Scenarios Strategies Results
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ConclusionsOverview Introduction Scenarios Strategies Results
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ConclusionsOverview Introduction Scenarios Strategies Results
Old (secondary) dikes are subject of discussion
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ConclusionsOverview Introduction Scenarios Strategies Results
Artificial hills, ‘terpen’, are part of this landscape
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Scenarios
ConclusionsOverview Introduction Scenarios Strategies Results
• Hydraulic boundary conditions (lake and sea differentiation)• Breach locations are defined (15 breaches)• Future scenario, by adding up sea level rise increased
storm surges and bottom inclination • These scenarios are used as input for 1D2D hydraulic
modelling
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Strategies: compartmentalization
ConclusionsOverview Introduction Scenarios Strategies Results
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Strategies: Flood shelters
• Support self-preparedness• Safe havens
– High grounds
– Water resistant buildings
– Artificial hills ‘Terpen’
• Division in hazard zones– Determining distance
Short < 5h
Time to respond
Sufficient >5h
Flo
od h
azar
d (u
*d)
Lo
w <
7H
igh
>7
Zone 1
Zone 3
Zone 2
Zone 4
ConclusionsOverview Introduction Scenarios Strategies Results
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Planning of flood shelters
ConclusionsOverview Introduction Scenarios Strategies Results
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Neighbourhood scale implementation
Van Reedt Dortland, M. De Fijter, W. and Hoekstra, A. 2008. Vluchtplaatsen in zelfredzame cellen als oplossing bij overstromingen (Dutch), H2O 41(7):35-38.
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ConclusionsOverview Introduction Scenarios Strategies Results
• Detailed 1D2D hydraulic modeling (Sobek)• Damage estimation (HISSSM) containing damage functions:
– Land use types
– Maximum waterdepth
– Rise rate
• Extensive database of GIS maps of results for publication on our website:– www.vluchtplaats.nl
Assessment of strategies: Hydraulic, damage and casualty modelling
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Flood pattern maps
ConclusionsOverview Introduction Scenarios Strategies Results
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Damage density maps
Damage intensity
ConclusionsOverview Introduction Scenarios Strategies Results
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Casualty density maps
Casualties
ConclusionsOverview Introduction Scenarios Strategies Results
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Summary of damage, affected inhabitants and casualties
ConclusionsOverview Introduction Scenarios Strategies Results
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Damage estimation for compartmentalization
0.0
1.0
2.0
3.0
4.0
5.0
6.0
7.0
No Comp. Secondary Dike Partitioning Value Protection
Sca
led
Dam
age
present sealevel sealevel rise
ConclusionsOverview Introduction Scenarios Strategies Results
Scaling 1.0 = 4.5 billion euros
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Casualty estimation for compartmentalization
0.0
10.0
20.0
30.0
40.0
50.0
No Comp. Secondary Dike Partitioning Value Protection
Sc
ale
d C
as
ua
ltie
s
present sealevel sealevel rise
Scaling 1.0 = 289 persons
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Preliminary conclusions
Given future scenarios the estimated damage for this region increases approximately with a factor 4 and the estimated casualties with a factor 10
The secondary dike strategy is promising, given the assumption that the secondary dike fails independent of the primary dike.
Partitioning can be very dangerous, depending on the flood scenario and can lead to an increased hazard
Self prepared cells using flood shelters are very promising, but need administrative arrangements and a proactive attitude of the inhabitants, which will be the greatest challenge
ConclusionsOverview Introduction Scenarios Strategies Results
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Recommendations
The probability of the scenarios has to be calculated in order to compare the risk to conventional strategies such as dike strengthening and dike heightening
Cost benefit analysis has to be performed to give insight in the feasibility of these strategies
Combination of strategies has not yet been assessed and would be interesting for areas close to the sea.
Do not (yet) destroy the old existing secondary dikes as they might turn out to be life saving by slowing down the flood
Further development of the administrative arrangements for self preparedness and awareness
ConclusionsOverview Introduction Scenarios Strategies Results
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Questions
? ??
?
??
?
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Additional slides
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Dike failure mechanisms
(Vrijling 2001)
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Dependent vs independent failure
Dikes fail when overtopping occurs
Pfail|(H>Hdike) = 1All other mechanisms depend on the water
level:
Pfail|(H<Hdike) << 1
independent
dependent
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Method
1
Water level (H) [m]
Probability of failure P(H) [-]
Hdike
P = F(H)
Pfail |H=Hdike
x
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Water levels at two breach locations