Dam Safety ManagementObjective Element of
Dam Safety
ANCOLD vs Malaysia
Responsibility Owner Responsibility
Why Dam Safety
A dam can fail
Failure Statistics
Dam Safety Legislation
St Francis Dam Vaiont Dam Malpasset Dam
Why Dam Safety?
Major consequence
St Francis Dam Vaiont Dam Mt. Polley Why Dam Safety?Early Warning
Baldwin Dam
Fontenelle
Zeyzoun
What Should Dam Safety Program Do?
Who should be involved?
Who have interest?
What is knowledge required?
Dam Safety Objectives
• To protect life, property (e.g., community infrastructure, dam) and the environment from the failure of any dam.
• These objectives can be achieved by implementing and maintaining an appropriate dam safety program
Element of Dam Safety Program (ANCOLD)• Plan• Design• Investigate• Construct• Commission
• Public Awareness• Role of Owner• Role of Government• Regulator
Operation & Maintenance
SurveillanceSafety Review
Risk Assessment
ReportingEducation & Training
Emergency Preparedness
Information Management
Deficiency
Is Dam Still Required?
Remedial Action
Continue Dam Safety Program
Decommission
Yes
YesNo
No
Operation Maintenance
Operation and Maintenance
Guidelines for Operation, Maintenance and
Surveillance of Dams (1989)
Monitoring Inspection
Surveillance
Safety Review
Data Collection
Responsibility and Accountability
Owner
• Safe Operation & Maintenance
• Dam Hazard Categories
• Surveillance Program
• Dam Safety Emergency Plan
• Qualified & Experienced Personnel
• Dam Safety Reviews
• Dam Risk Profiles
Regulatory Authorities
• Maintain register of dams
• Ensure that dams are designed, operated and maintained to current standard
• Owners of “significant” or higher Hazard Category Dams and other dam with Population at Risk (PAR)
Dams Operators
• Damage Potential
• Able to recognize deficiencies /adverse trends
ABSTRACT FROM UNICIV REPORT ON ANALYSIS OF
EMBANKMENT DAM FAILURE INCIDENTS
Overall statistics of failure occurring before and after 1950, large embankment dams
Mode of Failure % Total
Failures (where
mode of failure
known)
% Failures
pre 1950
% Failures
post
1950
Overtopping 34.2 % 36.2 % 32.2 %
Spillway/gate (appurtenant works) 12.8 % 17.2 % 8.5 %
Piping through embankment 32.5 % 29.3 % 35.5 %
Piping from embankment into
foundation 1.7 % 0 % 3.4 %
Piping through foundation 15.4 % 15.5 % 15.3 %
Downstream slide 3.4 % 6.9 % 0 %
Upstream slide 0.9 % 0 % 1.7 %
Earthquake 1.7 % 0 % 3.4 %
Totals (3) 102.6 % 105.1 % 100 %
Total overtopping and appurtenant
works
48.4 %
53.4 %
40.7 %
Total piping 46.9 % 43.1 % 54.2 %
Total slides 5.5 % 6.9 % 1.6 %
Total no. of embankment dam
failures (exc. During construction) 124 61 63
Total embankment dam years
operation (up to 1986) 300,400 71,000 229,400
Annual probability of failure 4.1 x 10-4 8.6 x 10-4 2.7 x 10-4
Notes: 1. Percentages based on the % of cases where the mode of failure is known.
2. Percentages are for failures of embankment dams in operation only, i.e. excluding failures during construction.
3. Percentages do not necessarily sum to 100% as some dams were classified as
multiple modes of failure.
Failure Incidents
ST FRANCIS DAM
• Failed on March 1928
• “Sole judgement of one man”
• State of California enacted legislation in 1929
VAIONT DAM (ITALY)
• 2,600 fatalities, economic & major infrastructure damages
• Animals move out 3 days prior to failure
MOUNT POLLEY MINE (BC CANADA)
• Breached August 2014
• Copper & Gold Mine Tailings
• No fatalities, environmental damage, business impacts
• Failed in 1963.
• 11.15am: Caretaker noticed high seepage flows
• 3.38pm: Dam failed, 1,600 people evacuated
• 5 fatalities
BALDWIN HILLS DAM(USA)
• H = 71 m, 198m long
• Homogenous Earthfill
• 0.95 m3 x 106 cap.
FONTENELLE DAM (USA)
• Nearly failed in May 1965 due to excessive seepage
• Operation personnel draw reservoir down
• Rockfill placement over seepage area
TSF DAM CONSTRUCTION STANDARD
REQUIREMENTS
1.) If seepage points are observed to have increased in flow by >50%, the following pre-emptiveaction is to be taken to prevent any further increase in flow which could lead to piping
Step 1: excavate a 2mx2m trench connecting the seepage point to the chimney drain.
Step 2: line the excavation with non-woven geo-fabric.
Step 3: backfill with TSF 150 coarse filter material. Place in 300mm lifts and bucket tamp.
2m
2m
TSF 150 CF
Cross-section Longitudinal Section
Seepage point
2m
Chimney drain
Dam Batter
Geo-fabric
Emergency Remediation of Excess
Dam Seepage
ZEYZOUN DAM(SYRIA)
• Embankment dam.
• Failed on June 2002
• Cracked appear several days before it collapse
• Thousand homeless and damage to cultivated land
What Should Safety Program Do?
Assurance that dams are safe
• Resources
• Prevailing Technology
• Sound Management
Who should be involved?
• Owner
• PAR
• Property’s Owner
• Those maintaining infrastructure facilities
• Those with interest in the environment
Who have interest in Dam Safety Management?
• Private owner
• Dam operators
• Dam safety professionals
• Emergency management agencies
• Governments
• Professional bodies (ANCOLD)
What is the knowledge required?Regulator
• Dam engineering & risk management
• Legislation & community expectation
Owner’s Manager• Significance of Hazard & Risk
• Risk Profile
What is the knowledge required?O&M Engineer
• O&M Procedure & Practice
• M&E Design Principle
• Dam Failure Modes
• Operating Risk
• Environmental & Water Quality Issue
What is the knowledge required?Inspector/Field Personnel
• Dam Failure Modes
• O&M Procedures
• ERP
• Surveillance i.e., Principles, Visual Sign
What is the knowledge required?Dams Engineer
• Design Principles (Structure, Geotechnical, Hydrology, Hydraulic)
• Construction
• O&M Procedures
• Dam Failure Modes, Consequence Assessment
• Surveillance process
• Audit, Review & Risk Management
• Emergency Planning
SurveillanceActivities
Monitoring, visual inspection, reporting
Monitoring
What do we monitor?
Loads parameter Response parameter
Available Instrument Example
Surveillance Activities
• Monitoring
• Visual field inspection
• Examination and reporting of the data and results of monitoring field inspections and routine or special reports on operation and maintenance
ICOLD Definition (Bulletin 118)
Objects of
Surveillance
• Dam
• Foundation
• Reservoir
• Appurtenant Structures (outlets, spillway)
• Structural Monitoring system
• Security Monitoring system
• Alert System
Surveillance
Monitoring VisualInspection
Checking &Testing
ReportsReportsData
Manual
Acquisition
Transmission
Processing
PreliminaryAnalysis
PreliminaryAnalysis
Automated
Acquisition
Transmission
Processing
PreliminaryAnalysis
Overall Assessment of Dam Safety
PreliminaryAnalysis
Monitoring Features (what do we monitor)1. Loads
• External and Internal
2. Structural Response/Performance/Behaviour
• Dam- wall, foundations & Appurtenant Structures
3. Structural Integrity/Condition/State
• Deterioration/ageing
EXTERNAL LOAD PARAMETERS▪ What are the loads being applied to the dam and associated structures
and what are their parameters?
▪ Reservoir and tailwater - metres depth & uplift (PWP)
▪ Sediment – Depth, Density grading & permeability
▪ Temperature (During and After Construction)
▪ Ice
▪ Climate (Sun - solar radiation; wind – speed & direction, rain – depth & duration )
▪ Earthquakes – acceleration
▪ Other dynamic loads (Blasting Ambient Vibration) – acceleration and Peak Particle Velocity
RESPONSE PARAMETERS• 1, 2, & 3D Deformation and Displacements
• Foundation• Concrete dam • Embankment dam • Reservoir Rim
• Seepage and Leakage quantity and quality
• Pore-water (interstitial) pressures and piezometric level
• Erosion
• Cavitation
• Sedimentation
• Unusual Animal Behaviour (Vaiont)
AVAILABLE INSTRUMENTS EXAMPLES Parameter Instrument
Foundation deformation Inclinometer, Trivec or Pendulum, Extensometer
Concrete Dam deformation Trivec or pendulum, Geodetic surveys, crack meters
Embankment Dam
deformation
Inclinometer, settlement gauges/plates, Geodetic
surveys
Seepage Pipes, or V notch weirs
Interstitial pressures and
piezometric level
Standpipes or piezometers (vibrating wire, pneumatic,
hydraulic)
Pore water pressure Piezometers (vibrating wire, pneumatic, hydraulic)
Stress and Strain Strain rosettes, Stress cells
Temperature Thermometer, Thermistor, Thermocouples
Pressure Barometer, Pressure Plate/Cell
Level Analogue/Digital - Gauge Plate, piezometer, Drum,
Sonar, bubbler
Dam Safety InspectionsANCOLD 2003
Type of
Inspection Personnel Purpose
Comprehensive Dams Engineer
and Specialists1
(where relevant)
The identification of deficiencies by a thorough onsite
inspection; by evaluating surveillance data; and by applying
current criteria and prevailing knowledge.
Equipment should be test operated to identify deficiencies.
For a Safety Review consider:
• Draining of outlet works for internal inspection.
• Diver inspection of submerged structures.
Intermediate Dams Engineer The identification of deficiencies by visual examination of
the dam and review of surveillance data against prevailing
knowledge with recommendations for corrective actions.
Equipment is inspected but not necessarily operated.
Routine Dam
Safety
Inspector The identification and reporting of deficiencies, by structured
observation of the dam and surrounds, by an inspector, other
than the operator, with recommendations for corrective
actions.
Routine Visual Operations
Personnel
The identification and reporting of deficiencies by visual
observation of the dam by operating personnel as part of their
duties at the dam.
Special /
Emergency
Dams Engineer
and Specialists1
The examination of a particular feature of a dam for some
special reason (eg. after earthquakes, heavy floods, rapid
drawdown, emergency situation) to determine the need for
pre-emptive or corrective actions.
Inspection Frequencies (ANCOLD)Inspection Type
Hazard
Category Comprehensive Intermediate Routine Dam
Safety Routine Visual Special
Extreme On first filling
then 5 yearly Annual Monthly Daily
1 As required
High A,B,C On first filling
then 5 yearly Annual Monthly
Daily to1
Tri-Weekly As required
Significant On first filling
then 5 yearly
Annual to
2-Yearly 3-Monthly
Twice Weekly
to Weekly 1
As required
Low On first filling,
then 5 yearly Monthly As required
Very Low Dam Owner’s
Responsibility2
Dam Owner’s
Responsibility2
As required
Arrangements before the inspection
• Determine the type of inspection – This defines• Who is required for the inspection – Operator, specialists,
owner representative;• Equipment needed and access requirements;• Testing requirements for operational and monitoring
equipment
• Job Safety Analysis• Risk identification
• Hazards
• Likelihood
• Mitigation
• Travel arrangements and contacts
A PHILOSOPHICAL POINT OF VIEW
In Dam Monitoring we work with x,y,z and t- coordinates.
In Dam Surveillance we have to add:• Common sense• Sound engineering judgement• Due Diligence
– Interest– Commitment– Dedication
(Some of these are forgotten human attributes)• Attending to detail• Putting things into perspective
Safety Condition
• Satisfactory – No deficiencies
• Fair – Maintenance, minor deficiencies
• Poor – Major repairs
• Unsatisfactory – Failure possible
Safety Review Requirements• Existing Dams not subject to routine and surveillance
inspection Safety Review ASAP
• From the outcome of Surveillance Inspection Report
• Following unusual events – earthquakes, major floods etc
• ANCOLD = 10 to 20 years depending on hazard, condition of dam etc
Safety Review Reporting• Reporting on original design criteria.
• Evaluation of the dam against current criteria including investigation where required
• Statement on the safety of the dam, indicating whether or not the dam is in a satisfactory condition, and what and when remedial or emergency action should be carried out to rectify the deficiencies
• Review of older dams may be more extensive
Safety Review Scope (Indicative)• Geology
• Seismicity (where applicable)
• Hydrology and Design Flood
• Dam Structure, Spillway and Outlet
– Materials
– Foundation
– Analytical data
– Operation and Maintenance
Safety Review Outcome• Dam Satisfactory
• Repair or Remedial Work
• Removal or abandonment
• Emergency Action
• Change in O&M Procedures
• Routine Maintenance Work
Hazard Classification What is Hazard?
Assessment Process
Data and Level of assessment
Hazard categories
Application Example
What is Hazard?ANCOLD 2003
The threat or condition which may result from external cause (e.g., flood, earthquake) with potential to create adverse consequence
Hazard (Consequence) Categories ANCOLD 2003
Population at
Severity of Damage and Loss
Risk
Negligible
Minor
Medium
Major
0
Very Low
Very Low
Low
Significant
1 to 10
Low Notes 1 and 4
Low Notes 4 and 5
Significant Note 5
High C Note 6
11 to 100
Note 1
Significant Notes 2 and 5
High C Note 6
High B
Note 6
101 to 1000
Note 2
High A Note 6
High A Notes 6
>1000
Note 3
Extreme Note 6
Note 1: With a PAR of 5 or more people, it is unlikely that the severity of damage and loss
will be “Negligible”.
Note 2: “Minor” damage and loss would be unlikely when the PAR exceeds 10.
Note 3 “Medium” damage and loss would be unlikely when the PAR exceeds 1000.
Note 4: Change to Significant where the potential for one life being lost is recognised.
Note 5 Change to High where there is the potential for one or more lives being lost
Note 6 See Section 2.7 and 1.6 for explanation of the range of High Hazard Categories
Inspection Frequencies ANCOLDInspection Type
Hazard
Category Comprehensive Intermediate Routine Dam
Safety Routine Visual Special
Extreme On first filling
then 5 yearly Annual Monthly Daily
1 As required
High A,B,C On first filling
then 5 yearly Annual Monthly
Daily to1
Tri-Weekly As required
Significant On first filling
then 5 yearly
Annual to
2-Yearly 3-Monthly
Twice Weekly
to Weekly 1
As required
Low On first filling,
then 5 yearly Monthly As required
Very Low Dam Owner’s
Responsibility2
Dam Owner’s
Responsibility2
As required
Hazard Category in dam safety
• Cost of ownership and potential liability
• Resource and management efforts allocated according to risk of business
• Consequence of Failure vs Likelihood of Failure
LAWN LAKE DAM (USA)
• About 8m high, 0.8 x 106m3
• 3 fatalities, Estes Park
• Remote location
• Damage to residential, commercial and infrastructure
Failure Mode Analysis (FMA)What is Failure Mode
What you need to know
What to do after you identified potential failure mode?
Component Definition Example
Identify PFM
Example PFM Description
Identify PFM FMA for monitoring program
What is a Failure Mode?
ANCOLD 2003A way that failure can occur, described by the
means by which element or component failures must occur to cause loss of the sub-system or system function.
What do you need to know?
• To understand and identify the potential failure of or weakness in a dam, inspecting personnel must have extensive knowledge of the causes of failure
• Failure modes analysis✓ Identify the components of the dam✓ What can go wrong with them (failure mode)✓ How will this happen (loads, weaknesses, operating errors etc)✓ What will the result be (consequences)✓ What can be done about it (mitigating action)
What to do after you identified potential failure mode?
• Fix (Remedial Works)
• Reduce Risk (Surveillance)
• Ignore
Component Definition Example
Reservoir Spillway
Foundation Rip Rap Shell Core Chimney Filter Blanket Drain Toe Drain
Main Dam Saddle Dam
Embankments Downstream Areas OUtlet Works
A Dam
Identify PFM
• 4- Dessication
• 5- Embankment to Foundation
• 6 - Foundation
• 7 - Embankment (e.g., poorly compacted layer)
Identify PFM
• Different Probability of Internal Erosion!
• Upper Berm and Lower Berm
3 1B 1A 1B 2
Flow path 1A
Flow path 1B
Photo 1: Freshly placed fill unsealed and
saturated by heavy rainfall
Photo 2: Fill placement over saturated,
unsealed fill
UNSEALED FILL = WRONG
Sealing fill prior to rainfall
PLACING FILL OVER WET
FILL = WRONG
Photo 3: Main Dam southern flank upstream -
Fill placed over waterlogged ground
Photo 4: Main Dam southern flank downstream
- Fill placed over waterlogged ground
PLACING DRY OVER WET FILL = WRONG
Placing fill over wet ground
Failure Modes and Instrumentation Central Core DamFailure Mode Cause/Loading Indicator Instrument to monitor
CCE1 Foundation piping
Erodible material
Joints open during seismic event
No blanket filter/incompatible gradings
Hydraulic gradient
Seepage increasing, non-linear with reservoir level or turbid
Increase in groundwater pressure
V-notch weirs
Rain gauge
Piezometer
CCE2 Embankment piping
Erodible material
Inadequate filter
Transverse cracking of core (drying shrinkage, differential settlement or seismic loading)
Hydraulic gradient
Seepage increasing, non-linear with reservoir level or turbid
Increase in pore water pressure if piezometer in area of piping
V-notch weirs
Piezometer
Rain gauge
CCE3 Upstream slope failure
Rapid drawdown – inadequate pore pressure dissipation
Inadequate material strength under seismic or normal loading
Movement of wall survey points
Visual observation of wall alignment, shape
Increased seepage (indicates failure may have occurred)
Increase in pore water pressure (indicates failure may have occurred)
Survey monuments
V-notch weirs
Piezometers
Accelerograph
CCE4 Downstream slope failure
As for CCE4 except no rapid drawdown
CCE5 Overtopping
Extreme flood
Inadequate spillway capacity
Spillway gate failure (if present)
Gate operational alarms
Water over crest
Spillway gate alarms
Water level gauge
Visual observations
Element of Dam Safety Program• Plan• Design• Investigate• Construct• Commission
• Public Awareness• Role of Owner• Role of Government• Regulator
Operation & Maintenance
SurveillanceSafety Review
Risk Assessment
ReportingEducation & Training
Emergency Preparedness
Information Management
Deficiency
Is Dam Still Required?
Remedial Action
Continue Dam Safety Program
Decommission
Yes
YesNo
No
References
• ANCOLD Guidelines on Dam Safety Management, 2003
• ANCOLD Guidelines on Assessment of the Consequences of Dam Failure, 2000
• Malaysia Dam Safety Training Seminar, 2008
• Guidelines for Operation, Maintenance and Surveillance of Dams, 1989
• USBR Dam Safety Risk Analysis and Best Practice
• Geotechnical Engineering of Dams, Fell et al, 2014