Technical Workshop TW1 Survey of International Dam … The Dutch situation ... (Flood protection...
Transcript of Technical Workshop TW1 Survey of International Dam … The Dutch situation ... (Flood protection...
Technical Workshop TW1Survey of International Dam Safety
Risk Approaches and Practices:NETHERLANDS
Hans Janssen & Niels RoodeRijkswaterstaat (RWS)
A logo ofyour
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Context: The Dutch situation
Elevation < 5m MSL Flood prone
• 17 million people, 9 million are flood prone• Delta of Rhine/Meuse rivers, bordering North Sea• GDP 875 billion USD, spent on FRM 0,5 - 1 billion USD/yr• Levee systems protect 60% of Dutch territory
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The 1953 flood
• Lives lost: 1836• Homes lost: 100,000• Storm surge + high tide• Flood alerts were not
understood and telegrams came too late
• Levee maintenance had been insufficient (due to 1930’s depression & WWII)
• Too many organizations with overlapping tasks (public water boards, provinces, state and private water boards)
• Too few funds, insufficient tax base
11/7/17
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Response after 1953
1) Delta WorksShortened coastline and levee restoration, dams, surge barriers, overtopping under control
2) Better organizationDecrease # water boards, better oversight, maintenance and flood alerts, formal inspections
3) Better legislation and fundingStatutory flood risk standards and periodic assessments, structural national funding
4) Better informationRisk and science informed since 1960, monitoring, mapping, continuous improvement of models, statistics, consistency
11/7/17
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Purpose: inform decisions• Safety standard / ‘Tolerable Risk’ (national government)
(risk + cost/benefit political decision on tolerable risk)• Levee assessment ‘verdict’ (regional authorities + RWS)
(flood probability + ‘distance to safety standard’ + funding eligibility)• Prioritising + programming projects (Flood protection
programme)(‘distance to the standard’ or urgency)
• Design / upgrade (project level)(levee dimensions that comply with standard at end of life cycle)
• Operation and maintenance (regional authorities + RWS)(prioritisation of O&M measures)
Purpose and approachof risk assessment
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Approach: Levee safety risk management portfolio process
Riskstolerable when
standards are met?
Update statutorysafety standards
No
Statutory safety assessment
(standard testing)
Flooddefence meets
standard?
National Flood Protection
Programme
Restorationmeasures
Routine inspection and maintenance
Yes
No
Monitor risk Yes
• 2.300 km of primary levees
• Statutory safety standards (tolerable risk, 25-50yr cycle)
• Statutory safety assessment (test standard, 12yr cycle)
• Levees not meeting standard feed Flood Protection Programme
Purpose and approachof risk assessment
25-50 y
12 y
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Failure mode at location x
Overall ‘verdict’
Simple technicalassessment
Detailed technicalassessment
Adv. technicalassessment
Criteria met?
Criteria met?
Criteria met?
Subjectiveassessment
Positivejudgment?
Section failstechn. assessment
Section passestechn. assessment
Section failssubj. assessment
Section passessubj. assessment
Approach: Levee safety assessment process
• safety assessment: standard testing
• From coarse to fine• rules and expert
judgement: tell the story• Semi-probabilistic (safety
factors & design values)• Probabilistic techniques
from 2019 (both loads and strength)
• Sources (mandatory): standards, manuals, instruments
y
y
y
y
n
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n
n
Purpose and approachof risk assessment
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• 50 primary levee systems (dike rings); 2300 km
• Dams, barriers, levees, dunes, hydraulic structures
• Statutory safety standards ranging from 1/250-1/10.000 per year
• Derived from CBA (1959)
• Exceedance probabilities (i.e. design loading conditions)
Use of RA in decision making:
Flood Defence Act prior to 2017
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New flood risk insights (VNK)
Domino effect influences risk
Coastline: low risk due to wide dunesand nourishments
Risk varies within and between dike ring areas
Rivers: piping underestimatedfailure mode
Source: VNK national risk analysis
high risk of fatalities
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Translating policy goals to safety standardTolerable fatality risk
10-5per yr
Tolerable economic risk
Economical risk
investment
€Total cost
Policy choice: choose the strictest per levee system
‘Economic optimization’
‘Compared to other risk domains and natural character of floods’
From risk to tolerable risk
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A new standard type
Risk standard (e.g. 10‐5 for a certain area)
Flood probability standard(e.g. 1/x for part of levee
system)
Probability of hydraulic exceedance standard
(‘old practice’)
Tolerable risk considerations
Target tolerable risk (combination of probability and consequences), through prevention, spatial planning and/or disaster planning.(multilayer safety: find case by case optimal mix of measures to reach tolerable risk)
Target tolerable flood probability (specific requirement to levee performance: flood probability) where uncertainties in both hydraulic loads as geotech are incorporated.
Target tolerable hydraulic load (specific requirement to levee performance given a probability of hydraulic exceedance. Geotech as safety factors. (indirect and less efficient assessment of flood probability)
Direct derivation
From risk to tolerable risk
Indirect derivationJP
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JPFM3 wat wordt met deze laatste stap bedoeld?Janssen, Hans (GPO), 6/15/2017
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• New safety standards for specific levee stretches (no dike rings)
• Expressed as ‘flood probability’• Standards = ambition 2050• Total cost estimate: € 11-15 Billion• 60-70% in riverine area• Requires levee designs 20m-200m
extra width and, hence:• ‘Innovative’ piping measures
needed• In development:
1. new design guides; 2. new assessment tools 3. new programming/prioritisation tools; 4. the expertise to use them
New Water Act (from 1/1/2017)
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Stretches
Upgrade in %
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ResearchVNK / CBA
RiskInsights
Policy: new safety standards
Formal decision
Legal embedding
WBI2017
Under construction
Delivery of tools
Results
Programming and prioritisation
HWBP on basis of:
WTI2006 + Hybrid risk
tool
WTI2011 + VNK results
WTI 2017 results
3rd HWBPDesign & Execution
‘Old’ projectsHWBP2
1st
programmeOI2014
2nd
programmeOI2018
3rd
programmeOI2018?
2014
2017
2023
2029
Towards risk-informed decision making
Future
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Pro’s and Con’sNL: “rule based” decision makingStandardized decision making procedures (statutory standards, assessments, guidelines)
PRO’s+ Quality and consistency through
standardized rules and instruments
+ Legally arranged “Standard-driven” budgets (budget waiting for projects).
CON’s- Over-reliance on models/
automation- Loss of knowledge for
organisation (“tell the story”)
Advice for startersStart simple: expert based approach, case by case analysis, prioritize with risk, build capacity.
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Fundamentals of flood protection
Link between NL policy/legislation and guidelines/technical reports.