Mark Voorendt Delft University of Technology, Department of Hydraulic Engineering

Transcription

1 Flood risk in the Netherlands Mark Voorendt Delft University of Technology, Department of Hydraulic Engineering Water minor 12 september 2013 Willem Schellinks The breach of the St. Antony Dike near Houtewael, 1651

2 Flood risk in the Netherlands - contents of the lecture flood risk management flood risk control flood risk analysis flood risk acceptability multifunctional flood defences

3 Flood risk in the Netherlands - contents of the lecture flood risk management flood risk control flood risk analysis flood risk acceptability multifunctional flood defences

4 Flood risk management

5 Flood risk management

6 Flood risk management Different conceptual levels of dicision making: Strategical level Policies to deal with climate and economic growth, development of deltamanagement plans, Stipulation of safety standards, Psycho-societal developments. Time horizon: from 50 to more than 100 years Tactic level Dutch 'Room for the River' policy, river discharge regulation systems, generation of dike types like the 'climate dike' and the 'unbreachable dike'. Time horizon: several decades Operational level Specific, working solutions, feasible in a technical and economical sense and fit in the urban or rural environment, acceptable for the local society. Implementation of adaptability and extendibility. Time horizon regards realisation is several years.

7 Flood risk management Dutch society has changed: Flood defence has moved to a higher level in the hierarchy of needs (Maslow):

8 Flood risk management Levels of problem solving: Spiral dynamics theory of Don Beck

9 Flood risk management More changes during the last decades: The acknowledgement of authority and expertise individuals are less likely to accept authority or expertise society strives for equality, so disqualification of knowledge by 'laymen' Management philosophy: process management without actual knowledge of the primary processes The dichotomy between sciences and humanities technocratic approach versus idealistic approach materialistic versus holistic view

10 Flood risk management So, decision making on flood protection is changing Design is becoming ever more multidisciplinary: design team exist of various experts relevant stakeholders are involved in the process Systematic and multidisciplinary design needed, integrated design method and also transparency required, otherwise: suboptimal solutions (not functioning or too expensive) lack of public support for the project (social failure)

11 Flood risk management - Laws and regulations

12 Flood risk management - Laws and regulations

13 Flood risk management Laws and regulations Guidelines of the Technical Advisory Committee for Flood Defences (TAW / ENW) The Dutch Water Act stipulates that the responsible minister takes care of the establishment and publication of technical guidelines for the design, management and maintenance of primary flood defences (article 2.6). Requirements regards retaining height, reliability of closure means and the strength and stability of hydraulic structures. The technical guidelines serve as recommendations for those responsible for the management and supervision.

14 Flood risk management How well are we protected? In 2011 still 1/3 of the Dutch primary flood defences did NOT comply with the required (outdated) safety level. This is 1225 km. Plus 335 hydraulic structures.

15 Flood risk management To meet the required safety level, the flood defences have to be improved. This costs money. Budget is limited and the flood protection level is regulated by law. So, if additional values cost money, they cannot be afforded, which causes loss of spatial quality.... or they are paid from the flood defence budget

16 Flood risk in the Netherlands - contents of the lecture flood risk management flood risk control flood risk analysis flood risk acceptability multifunctional flood defences

17 Flood risk control Flood risk = probability of flooding x consequences of a flood Risk control aims at risk reduction, which can be accomplished by: reducing the probability of flooding (= preventive measures) flood defences reducing the consequences (economic losses, fatalities): sustainable spatial planning disaster management insurance (actually does not reduce the damage, but only compensates losses)

18 Flood risk control Dutch policy: Multi-layered safety (Meerlaagsveiligheid) Flood risk reduction in three layers: 1. Prevention 2. Sustainable spatial planning 3. Disaster management

19 Flood risk control - prevention Definition of a flood defence A flood defence is a hydraulic structure intended to protect land from irregular covering by water "anything that can be used to divert, restrict, stop or otherwise manage the natural flow of water" - USACE

20 Flood risk control - prevention Note: the flood defence has to be part of a system: concrete system: a continuous protective line around the area that has to be protected (dike ring) abstract system: organisation of the operation and maintenance of the concrete part. Also the settling of safety levels and assessment methods.

21 Types of flood defence structures

22 Natural soil structures dunes

23 Artificial soil structures dikes Boven Merwededijk (Gorinchem, 2012)

24 Specific water-retaining structures sheet pile wall

25 Hydraulic structures in flood defences navigation lock (Zevenhuizer verlaat, 2005)

26 Hydraulic structures in flood defences storm surge barrier (Oosterschelde stormvloedkering)

27 Utilitarian objects non-water retaining object (Ammerstol Lekdijk 2012)

28 Layer 1: prevention: (urban integration) Kampen, 2011

29 Layer 1: prevention: (urban integration - temporary measures) Tiel, 2012

30 Layer 1: prevention: (urban integration - temporary measures) Kampen, 2012

31 Layer 1: prevention: (urban integration - temporary measures) Kampen, Kampen 2012

32 Layer 1: prevention: (urban integration - temporary measures) Kampen, 2011

33 Layer 1: prevention: (urban integration - temporary measures) Dordrecht, 2012

34 Layer 1: prevention: (urban integration - temporary measures) Dordrecht, 2012

35 Layer 2: spatial planning: (urban integration) This is not a flood defence! Hamburg, 2012

36 Layer 2: spatial planning: (urban integration) Hamburg, 2012

37 Layer 2: spatial planning (urban integration) Hamburg, 2012

38 Layer 2: spatial planning (urban integration) Hamburg

39 Layer 2: spatial planning (floating houses) IJburg, Amsterdam, 2012

40 Layer 2: spatial planning (houses on piles) Sliedrecht, 2012

41 Layer 2: spatial planning: (houses on mounds) Westervoort, 2012

42 Layer 3: disaster management (creating awareness) Hamburg, 2012

43 Layer 3: disaster management (precaution) Dordrecht, 2013

44 Layer 3: disaster management (evacuation, shelters) Pasig City, Philippines 2009

45 Philippines 2009

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47 'Layer 4': private insurance

48 Effectiveness of multi-layered flood safety Results of recent research "A flood defence system heavily based on dike rings does not lend itself to implement the multi-layered approach." (Hoss, 2011) Measures to reduce the probability of flooding (first layer) and non-expensive measures of risk management (third layer) can be cost-effective. Physical measures in spatial planning (second layer) are less or not at all cost-effective (Kolen, 2011) Conclusion: prevention of floods still is the best method of flood risk reduction in the Netherlands

49 Effectiveness of multi-layered flood safety Measures in the second layer, however, can be justified if other values than flood protection become prevalent (Kolen 2011). More drawbacks: For 2nd and 3rd layer only process requirements, no risk reduction requirement Each layer has a different responsible authority Changing response of people to flood risk Changing flood characteristics

50 What to do if the actual flood risk is higher than the acceptable risk level? decrease the probability of flooding decrease the consequences of flooding (change the acceptable risk level) (change calculation method reliability)

51 Possible improvements: change boundary conditions Room for the River project impression Deventer

52 Possible dike improvements: heightening Delftse wallen, Zoetermeer, 2012

53 Possible dike improvements: outer berm Ammerstol, 2012

54 Possible dike improvements: outer berm reduces wave impact (overtopping) Termunterzijl

55 Possible dike improvements: inner berm reduces piping and instability inner slope Ammerstol, 2012

56 Possible dike improvements: revetment reduces erosion by waves Ammerstol, 2012

57 Complicated dike improvements: built-on environment! Sliedrecht, 2012

58 Complicated dike improvements: one structure is built on or in the other Herwijnen, 2012

59 Complicated dike improvements Herwijnen, 2012

60 Complicated dike improvements: sheet piles reduces instability inner slope if there is no space for a berm Ammerstol, 2012

61 Construction can be complicated Ammerstol, 2012

62 Construction can be complicated Ammerstol, 2012

63 Complicated dike improvements: soil improvement reduces instability and impermeability also: bio-grout

64 Complicated dike improvements: expanding columns (dike dovels)

65 Complicated dike improvements: dike nailing

66 Flood risk in the Netherlands - contents of the lecture flood risk management flood risk control flood risk analysis flood risk acceptability multifunctional flood defences

67 Flood risk analysis Structural safety: sollicitation should be resisted by the structure: S < R Methods to determine the margin between S and R: deterministic semi-probabilistic full probabilistic

68 Flood risk analysis - deterministic design based upon experience, trial & error in general: R > S γ (γ = overall safety factor) dike height = highest observed flood level to 1.0 m

69 Flood risk analysis - semi-probabilistic design Sollicitation and resistance are considered to be stochasts (so not fixed values, but distributions)

70 Flood risk analysis - semi-probabilistic design design values for resistance and sollicitation and calculated (partial) safety factors: limit state function: failure if Z < 0

71 Flood risk analysis - semi-probabilistic design semi-probabilistic method in hydraulic engineering Approach of the Delta Committee: - Costs of protective measures should balance the obtained risk reduction - Calculate the economic loss per dike ring in case of a flood and the failure probability of the flood defence system - Relate this failure probability to water level exceedance frequency - Relate this design water level to a retaining height

72 Flood risk analysis - semi-probabilistic design semi-probabilistic method in hydraulic engineering economic optimum at probability of flood in a year of 1/ exceedance frequency of 1/ per year

73 Flood risk analysis - semi-probabilistic design semi-probabilistic method in hydraulic engineering estimation of the crest level of a dike

74 Flood risk analysis - probabilistic design distribution functions of loading and strength probability of failure:

75 Flood risk analysis - probabilistic design

76 Flood risk analysis - failure of flood defences Failure occurs: if flood defence structure has insufficient height if flood defence structure is not able to resist the acting loads - strength - stability - stiffness due to operational errors (human errors) (failure is 'acceptable' if it does not occur more often than stipulated by law)

77 Flood risk analysis - failure mechanisms

78 Dawlish, 2004

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81 Delftse wallen, Zoetermeer, 2012

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87 Wilnis, 2003

88 New Orleans, 2005

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90 earthquake Leeuwen, Limburg 1992

91 ship-worm

92 Almere, 2011

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94 Delfzijl, 2000

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97 construction failure

98 construction failure

99 construction failure

100 Flood risk in the Netherlands - contents of the lecture flood risk management flood risk control flood risk analysis flood risk acceptability multifunctional flood defences

101 Flood risk acceptability probability of failure of flood defences 0 so what is an acceptable failure probability? balance of advantages and unwanted disadvantages. depends on: age and personal attitude of the decision maker(s) the extent of voluntariness of exposure to the risk and possibilities for an individual to avoid the risk the extent in which the risk is recognizable the advantages for the individual to oppose the risk the societal advantages of opposing the risk the historical background of the risk (frequency of occurrence)

102 Flood risk acceptability Three criteria: Economic risk Individual risk Societal risk

103 Flood risk acceptability - economic risk balance of the amount of money needed for risk reduction and avoided damage economic risk dike ring

104 Flood risk acceptability - individual risk limitation of the probability that an individual will die due to flooding < 10-5 in a year

105 Flood risk acceptability - societal risk limitation of the probability that a certain number of people will die due to flooding < 10-4 in a year for fatalities

106 Flood risk acceptability In an ideal case, the flood safety standard is based upon the strictest of these three criteria. In practice, however, if the individual or societal risk criterion deviates too much from the economic optimum, flood protection will appear to be not affordable any more and the economic criterion will appear to be predominant

107 Flood risk in the Netherlands - contents of the lecture flood risk management flood risk control flood risk analysis flood risk acceptability multifunctional flood defences

108 Multifunctional flood defences Why combination of functions? necessary improvements of existing flood defences conflict with other functions (housing) improvements necessary because of increased flood risk: expected higher water levels / river discharges increased economic activity increased population decreased risk acceptance ongoing urbanisation requires additional space public funding under pressure (economic crisis) changing societal and political attitude also: in future possible shift in safety level approach (?)

109 Spatial integration of functions / structures (Peter van Veelen, 2012)

110 Shared use: a structure is (temporarily) used by another function Tiel, 2012

111 Optimisation: shape of flood defence is modified to save space Dordrecht, 2010

112 Overlay: one structure is built on or in the other Arnhem, 2012

113 Integration: both spatial elements are making use of the same structure Zwijndrecht, 2011

114 Integration: both spatial elements are making use of the same structure Rotterdam, 2012

115 Multifunctional flood defences = flood defences combined with other functions than floor protection assessment aspects:

116 Multifunctional flood defences = flood defences combined with other functions than flood protection Problem: present assessment method already assumes specific solutions (gates, soil embankments), which poses restrictions regards innovation and multifunctionality. Goal: find a generic assessment methodology. Proposed solution: relate assessment rules to the fulfilment of technical functions regards flood protection.

117 Multifunctional flood defences = multi-structrural flood defences composing structural element types in flood defences: 1. Water retaining elements 4. Subsoil 2. Erosion-proof elements 5. Non-water retaining objects 3. Supporting elements 6. Structural parts that change boundary conditions

118 Multifunctional flood defences composing structural elements

119 Multifunctional flood defences The distinguished structural elements have been derived from the technical requirements that together let the structure fulfil its functional water retaining requirement. The element types are described without specification of material or shape (therefore: generic).