geohazard risk mitigation strategies - forsiden › studier › emner › matnat › geofag ›...

1

GEO4180Geohazard Mitigation

Strategies for Mitigation of Risk Associated with Geohazards

Classification of geohazard mitigationstrategies

(1) land use plans, (2) enforcement of building codes and good

construction practice, (3) early warning systems, (4) community preparedness and public

awareness campaigns,(5) measures to pool and transfer the risks,(6) construction of physical protection barriers, and(7) network of escape routes and "safe" places.

2

Danger (Threat): Natural phenomenon that could lead to damage. Described by geometry, mechanical and other characteristics. Can be an existing one, or a potential one, such as a rockfall. Characterisation of threat involves no forecasting.

Hazard: Probability that a particular danger (threat) occurs within agiven period of time.

Risk: Measure of the probability and severity of an adverse effect to life, health, property, or the environment.

Risk = Hazard × Potential Worth of Loss

DEFINITIONS (Based on Glossary of TC32 of the ISSMGE)

Definition of Risk (from an engineer’s viewpoint)

H = Hazard (temporal probability of a threat)

V = Vulnerability ofelement(s) at risk

U = Utility of theconsequence to theelement(s) at risk

R = H . V . U

Risk = Hazard x Consequence

3

Quantitative Risk Assessment (QRA) for natural threats

(1) What can cause harm? → threat identification(2) How often? → frequency of failure occurrence (hazard)(3) What can go wrong? → consequence of failure(4) How bad? → severity of failure consequence(5) So what? → acceptability of risk(6) What should be done? → risk management

QRA refers to the assessment of threat, hazard, risk and countermeasures in terms of numbers. It addresses the following questions:

QRA is a tool for decision making under uncertainty

CollectInformation

Deterministic(Model) Phase

Probabilistic(Model) Phase

Decision

Updating Information(Model) Phase

QRA

4

Risk management process is easy …


5



6



7



8



9



10


LANDSLIDE (DANGER)CHARACTERISATIONMechanics, Location

Volume,Travel Distanceand Velocity

PoliticalAspirations

Otherconstraints

Budget

Socialdemands

Regulation

Risk acceptance

criteria

Elements at risk

Vulnerability

Temporal Spatial

probability

Frequencyanalysis

Consequences

ValuesJudgement

R I S K M A N A G E M E N T

R I S K A S S E S S M E N T

H A Z A R D A N A L Y S I S

Monitor and Review

Risk mitigationControl options & Control plan

R I S K A N A L Y S I S




Otherconstraints

Budget

Socialdemands

Regulation

Risk acceptance

criteria

Elements at risk

Vulnerability

Temporal Spatial

probability

Frequencyanalysis

Consequences

ValuesJudgement




Monitor and Review



Landslide risk management framework(JTC1 experts)




Otherconstraints

Budget

Socialdemands

Regulation

Risk acceptance

criteria

Elements at risk

Vulnerability

Temporal Spatial

probability

Frequencyanalysis

Consequences

ValuesJudgement




Monitor and Review






Otherconstraints

Budget

Socialdemands

Regulation

Risk acceptance

criteria

Elements at risk

Vulnerability

Temporal Spatial

probability

Frequencyanalysis

Consequences

ValuesJudgement




Monitor and Review



11

Computation of Hazard

• Heuristic methods• Statistical methods• Probabilistic methods

– Reliability analyses– Monte Carlo Simulations

New York State Rockfall Hazard Rating ProcedureRelative Hazard = GF x SF x HEF

GF = Geologic Factor= Sum of Seven Subjectively Assessed Indicators:

Fractures, Bedding Planes, Block Size, Rock Friction,Water/Ice, Rock Fall History, Backslope

SF = Section FactorDitch and Slope Geometry (Largely Deterministic)

HEF = Human Exposure FactorProbability of Being Hit by Falling Rock or HittingRock Lying on Road (Objective or Subjective ProbabilisticAssessment)

Example of heuristic/statistical approach

12

X1

X2

UNSAFE REGION

SAFE REGION

σ1

FAILURE BOUNDARY

m2

m1

ρ=0 ρ=0.75 ρ=0.99

ρ=0 ρ=-0.75 ρ=-0.99

σ1

σ2

σ2

][][ *

XXXE

σβ −=

Single variable:

( ) ( )][][min1

XEXXEX XT

X−−=

−ΣΩ∈

βMultiple variables:

β = Reliability Index

Probabilistic methods: Reliability Analysis

z

zw

β

mz

Failure Surface

mzcos2β

zp

L

D

⎟⎟⎠

⎞⎜⎜⎝

⎛⎟⎟⎠

⎞⎜⎜⎝

⎛−+=

tanβ'tan1

coszsinc'F

s

w

s

φγγ

ββγm

Slope StabilitySlope Stability

Variable Mean St. Dev

c' 15 5

φ' 30 5

z 25 0

γw 1 0

γs 2.75 0

m 0.4 0.1

β 35 2.5

P[F<1] = P[T]=0.30

13

Computation of Hazard

Hazard = P[Threat] = P[Factor of safety < 1] = 0.30

0.00%

10.00%

20.00%

30.00%

40.00%

50.00%

60.00%

70.00%

80.00%

90.00%

100.00%

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0 0.5 1 1.5 2 2.5 3

Realative Frequency

Factor of Safety

Relative FrequencyCummulative Frequency

HazardInitial Hazard

Mitigation Cost

ExcessiveCountermeasures

InsufficientCountermeasures

OptimalCountermeasures

InsufficientCountermeasures

Relation Between Marginal Cost and Hazard Reduction

14

Probability of occurrence

Exte

nt o

f dam

age

Hazard →

Con

sequ

ence

→

How much risk is acceptable?

10-1

10-2

10-3

10-4

10-5

10-61 10 100 1000 10000Lives lost

1 m 10 m 100 m 1 b 10 bCost in1984 USD

ANNU

AL P

ROBA

BILI

TY O

F FA

ILUR

E, P

f

1

CONSEQUENCE OF FAILURE

FoundationsFixed Drill Rigs

Canvey Refineries

Canvey LNGstorage

MinePitSlopes

GeyserSlopes

"Marginally Accepted"

Merchant Shipping

Mobile Drill Rigs

"Accepted"

Dams

Other LNG Studies

Estimated U.S. DamsCommercial

Aviation

CanveyRecommended

15

How much risk are we willing to accept?

Depends on whether the situation is voluntary or imposed.

Acceptable / Tolerable Risk

Criteria of Hong Kong Geotechnical EngineeringOffice

Societal: F - N Charts(Ho et al., 2000)

ALARP = As Low As Reasonably Practical

1 10 100 1000 10000Number of fatalities (N)

1E-009

1E-008

1E-007

1E-006

1E-005

0.0001

0.001

0.01

Ann

ual f

requ

ency

of e

vent

cau

sing

fata

litie

s

Acceptable

Tolerable

Unacceptable

Detailed studyrequired

ALARP

16

Consideration of Life Losses

10-9

10-8

10-7

10-6

10-5

10-4

10-3

10-2

10-1

1 10 100 1000 10000

Number (N) of Fatalities

Option A

ALARP

Unacceptable

BroadlyAcceptable

IntenseSecurityRegion

10-9

10-8

10-7

10-6

10-5

10-4

10-3

10-2

10-1

1 10 100 1000 10000

Number (N) of Fatalities

Option B

ALARP

Unacceptable

IntenseSecurityRegion

(Preferred option)

What is an early warning system?

• In common usage, an EWS is a component of a risk management system for detecting and dealing with an anticipated natural or man-made hazard.

• Early warning systems are not restricted to natural hazards and disasters. They are applicable to any activity or situation that may create a problem that must be dealt with.

17

An Early warning System (EWS) is a system or procedure designed to warnof a potential or an impending problem

One landslide in Italy kills 27. Property damage and remedial works cost 400 mill. Euros (1986)

One boulder

wrecks a train(2003)

One bridge collapses in Minneapolis and 13 people die

(2007)

Elements of an EWS

• Knowledge of and means of forecasting the danger faced

• Information from technical monitoring and visual observations

• A response plan• Dissemination of meaningful warnings to

population at risk• Public awareness and preparedness to respond

to the warning.

An early warning system will normally have a minimum of 5 components:

18

How “early” is early?

• Remote sensing using orbiting satellites that pass over a point on the surface of the earth every 2 to 4 weeks are sometimes referred to in the literature as EWSs!

• For most earthquakes an early warning can only be issued after the first tremor has been detected. This is obviously not early enough for evacuation of population at risk.

EWSs mitigate risk by reducing the consequences. Thus, the systems must issue warnings early enough to give sufficient time to implement actions to protect persons and/or property. Not all EWSscan satisfy this requirement.

Available Technology for EWSs

• Sensors and sensing technology• Communication technology• Data collection systems as well as data

processing, reporting and analyzing software• Forecasting methods and modelling tools

EWS technology is readily available today, for the most part, as off-the-shelf components.

19

Principal activities in an EWS

EWSs – nothing new?

• Early warning systems are not new. However, since the December 2004 tsunami catastrophe in the Indian Ocean, early warning systems have received a lot of attention.

• Geotechnical engineers have always relied extensively in their work on the concept “early warning” but under another name, namely the “Observational Method”.

20

The key to a successful EWS

• The key to a successful EWS is to be able to identify and measure the relevant precursors to the event.

• For example, typical precursors for an impending landslide event are:– Intense rainfall– Earthquakes and ground vibrations– High rate of slope movement– Rapid increases in pore water pressure– Erosion at the toe of the slope

Two major problems with EWS

• The most difficult problem in designing an EWS is to be able to specify proper threshold valuesfor the alarms.

• Avoiding false alarms. The consequences of false alarms are often so serious that every possible action must be taken to avoid them.

21

Steps to avoid false alarms

• Use well-proven components in the monitoring system

• Provide redundancy in instrumentation

• Put emphasis on data quality control measures in data processing

• Make maximum use of human intelligence and “engineering judgment” in decision making.

Successful early warning?

Evacuation from Hurricane Rita, September 23, 2005

Some experts refer to this case as an example of what can happen when human intelligence and judgment are lacking in decision making, while others refer to this as an example of a successful early warning.

22

Usoi Dam is a 600m high landslide dam.

It is the largest dam in the world!

Example: Usoi Dam on Lake Sarez in Tajikistan

UsoiDam

Usoi dam and LakeLake Sarez

The volume of the landslide was 2.2 km3

Scarp of the landslide

23

Usoi dam

U s o i D a m

How big is Usoi dam?

• Eifel tower in Paris

Bennett dam, 183 mOne of the largest dams in North America

Horizontal scale of Usoi Dam is compressed

24

Lake Sarez

Length, ~ 60 kmMaximum depth: 500 mMaximum width: 3.3

kmAverage width: 1.3 kmVolume: ~ 17 km3

Elevation 3260 – 3265 m

The threat and consequences

• The 600 m high Usoi dam is the largest dam in the world.

• Lake Sarez behind the dam currently holds 17 cubic-kilometers of water.

• If the dam were to fail, the resulting flood would be a catastrophe of inconceivable dimensions!

• Flood waters would flow down the Bartangvalley to the Panj River valley and end up in the Aral Sea.

25

Valleys downstream

Bartang valley

Panj valley between Tajikistanand Afghanistan

Disaster scenarios at LakeLake Sarez

Probable disaster Probable disaster scenariosscenarios

Active landslideActive landslide

Dam failure riskDam failure riskSeismic activitySeismic activityRising water levelRising water levelLandslide into lakeLandslide into lake

26

Right bank active landslideRight bank active landslide

The Right Bank Landslide

~1.8 km

Current rate of movement is ~15 mm/year

Nomitigationmeasures

27

Mitigation withearly warning system(EWS)

Mitigation with EWS and lowering ofreservoir

28

Åknes Tsunamigenic Rockslide Threat

Loen, 1905

Tafjord, 1934

Western Norway 1900’s:

3 rockslides causing tsunami

Caused 175 fatalities

Loen, 1936

29

Åknes

Hegguraksla

Hellesylt

Sylte

Tafjord

Stranda

Geiranger

StordalSykkylven

ØrskogÅlesund

Skodje

Åknes, SunnylvsfjordenThe potential slide area is shown

Tafjord, 19343 million m3 rock mass dropped into the fjordThe tsunami reached 62m above sea levelMore than 40 people were killed

Åknes

30

Åknes

Large rockslide

35 mill. m3

8 mill. m3

Tsunami analysesTsunami analyses

31

Run-up height (m) 8 mill. m3 35 mill. m3

Oaldsbygda (Stokke) > 50 >100

Hellesylt 8-10 25 - 35

Geiranger 8 -15 20 - 40

Raudbergvika 2-4 10-15

Stranda 1-3 3-6

Gravaneset 1-2 4-6

Eidsdal 1-2 4-6

Sylte/Muri 1-3 6-9

Norddal 2-3 7-10

Fjøra 1-2 5-7

Linge 1-2 4-6

Tafjord 3-5 12-18

Dyrkorn 1-2 2-4

Stordal 2-3 5-8

Sjøholt 1-2 3-5

Artist’s depiction of a tsunami disaster

32

Hurricane Katrina was a category 5 hurricane on August 28, 2005,One day before it made landfall on the Gulf Coast

Hurricane Katrina

The Levees are Breached: Water pours into New Orleans

33

Aerial photograph of the 17th Street Canal Breach

About 1800 people lost their lives because of Hurricane Katrina.Here is a makeshift grave on a street in New Orleans.

34

Indian Ocean tsunami of 26 Dec. 2004 Generated by M = 9.3 earthquake

35

Patong City

geohazard risk mitigation strategies - forsiden › studier › emner › matnat › geofag ›...

Documents