International Levee Handbook (ILH) –
approach to levee failure mechanisms
Jonathan Simm
HR Wallingford, United Kingdom
Presentation summary
1. Motivation and
drivers for ILH
2. Understanding
‘Failure’
Structure of
International
Levee
Handbook (ILH)
3. ILH approach to
failure mechanisms
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© HR Wallingford 2012
Handbook motivation
> Recent international levee failures during
severe flooding events causing loss of life and
severe property damage:
 Katrina (2005)
 Xynthia (2010) - Atlantic coast of France
 Summer 2007 fluvial floods UK
> Address poor understanding and interface
between geotechnics and H&H communities of
practice in levee design and management
> Desire to produce best practice handbook for
owners, operators, designers & constructors.
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© HR Wallingford 2012
ILH structure
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Failures and
levee management life cycle
> Levee deterioration
and damage in routine
levee management
(O&M, assessments)
> Managing damage
and breach before,
during and after
severe events
> Allowing for external
change (loadings,
land-use) and effect
on probability or
consequence of failure
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Failure frequency/probability
> UK probabilistic flood
systems analysis uses a
frequency-based approach to
levee failure (fragility curves).
> This allows back-attribution of
the residual risk in the flood
plain to levee segments.
Standard of protection
provided by defence
Probability of
defence failure
Difference relates to
factor of safety in design
1.0
Typically
assumed fragility
curve
‘True’ fragility
0
0
Severity of load event
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© HR Wallingford 2012
Levee fragility and
deterioration of asset state
HLM+ Fragility curve - Condition Grades 1 to 5
(Central estimates)
1.0
P (breaching¦feeboard)
0.9
0.8
0.7
Condition grade1
Condition grade2
Condition grade 3
Condition grade4
Condition grade 5
0.6
0.5
Structure 0.4
Deterioration0.3
0.2
0.1
0.0
-1.5
-1.0
-0.5
0.0
0.5
1.5
1.0
Overflow head (Water level - crest level)
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© HR Wallingford 2012
Progressive vs sudden mechanisms
Physical
State of a
levee segment
Deterioration threshold
(SLS)
Progressive
State of a
levee segment
Deterioration
Sudden
Break
Damage
(ULS)
Damage
(ULS)
Load
Time (or Loading or other)
(For instance: external/internal erosion mechanism)
(For instance: sliding mechanism)
Functional
Function
performance
Progressive
Function
performance
Degradation
Degradation threshold
(SLS)
Failure
threshold
(ULS)
Sudden
Break
Failure threshold
(ULS)
Time or Loading or other
Load
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© HR Wallingford 2012
Physical vs functional failure
PHYSICAL
FUNCTIONAL
1, n
1, n
Component(s)
Function(s)
Deterioration
Degradation
Damage
Functional failure
Mechanism(s)
Functional analysis
Granularity
Level 1
System
failure
Granularity
Level 2
Hydraulic
failure
Granularity
Level 3
Structural
failure
Type of failure
Physical
Not applicable at granularity 1
Functional
Functional failure of protection
Inundation not prevented by levee
Segment technical inability/ruin
e.g. gate, breach cannot be
closed
Damage to a levee cross section.
e.g. loss of water-side clay cover
Hydraulic functional failure.
e.g. unexpected inundation occurs
over/through the levee segment
Structural functional failure
e.g. failure of the impermeability
function
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Definitions (and difficulties)
Types of structural mechanism scenarios
> Deterioration – Generally slow process by which resilience or
standard of protection is reduced. Deterioration is best managed
by good maintenance.
> Damage – Rapid deterioration such as scour and slippage
(commonly during a flood) that does not cause a breach but which
requires immediate repair or emergency action.
> Breach – Catastrophic collapse (often at high water level). Results
in significant loss of crest and causes substantial loss of water.
Time and causation chains are significant in distinguishing
between the above.
Hydraulic performance mechanisms
> Performance Failure – Overtopping or through-flow at an
hydraulic elevation or load below the design standard which does
not cause damage or breach
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© HR Wallingford 2012
Scenarios of mechanisms
Breach
Key
Loss of crest
Animal borrowing
Overtopping
Erosion
Event
AND Gate
OR Gate
Lack of
resistance to
surface erosion
Overtopping
Lack of scour
protection
Local
overtopping
Extreme high
water level
Local
Settlement
Consolidation of
foundation soils
Compaction of fill
materials
Internal erosion of
fill or foundation
soil
Desiccation
cracking
Loose noncohesive soils
Animal borrowing
Deterioration
Overtopping
Erosion
Damage
BREACH
Breach
Poor vegetation
control
High water level
Animal borrowing
Trafficking by
animals or
humans
High water level
External
Event
Overtopping
Local Event
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Explaining mechanisms
> Explanations of
individual physical
mechanisms (Chapter
3)
> Deterioration/damage
mechanism categories:
 Internal erosion
 External erosion
 Mass instability
> Descriptions of
mechanisms help the
levee assessment
process (Chapter 5)
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Failure modes:
transitions and embedments
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Overtopping
(may be functional failure)
> Chapter 2 describes
flood risk management
context of levees and
setting of functional
requirements
> Chapter 8 gives
methods for calculating
overflow/overtopping
> Chapter 6 describes
emergency management
of overflow/overtopping
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Deterioration
> Chapter 4 describes
inspections and routine
repairs required for
various deterioration and
damage mechanisms
> Chapter 5 Describes
assessment of levee
state.
> Chapter 9 describes
design of engineered
improvement or repair
measures
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Damage
> Chapter 3 describes
different damage
mechanisms
> Chapter 8 gives tools for
analysing different
mechanisms (limit state
equations)
> Chapters 9 and 10
describe potential
failures than can arise
during construction and
how to avoid them
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Breach
> Chapter 8 gives tools for
assessing breach
dimensions and
inundation hydrographs
> Chapter 6 discusses
managing breaches and
temporary repairs
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Summary
> The issue of failure mechanisms has been identified as
an important practical theme for the International Levee
Handbook (ILH).
> The ILH team differentiates between:




Performance failure (water passage below design standard).
Deterioration (slow reduction in condition of levee)
Damage (physical damage requiring immediate repair)
Breach (collapse followed by uncontrolled loss of water).
> These are associated with interacting hydraulic
processes (overflow, overtopping, seepage) and
geotechnical processes (internal erosion, external
erosion and mass instability)
> The ILH describes how to identify and manage and
design for these mechanisms and scenarios
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© HR Wallingford 2012
> Draft for review by September 2012
> Technical work complete March 2013
> Editing / printing complete September 2013
> Will be available as hard copy and pdf
Questions?
See also www.leveehandbook.net
HR Wallingford
Howbery Park, Wallingford, Oxfordshire OX10 8BA, United Kingdom
tel +44 (0)1491 835381
fax +44 (0)1491 832233
email info@hrwallingford.com