FRAMEWORK FOR LANDSLIDE QUANTITATIVE RISK …...Hazard assessment Landslide hazard map Risk...

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FRAMEWORK FOR LANDSLIDE QUANTITATIVE RISK ASSESSMENT

- an overview-Jordi Corominas

Department of Geotechnical Engineering andGeosciences

Civil Engineering School of BarcelonaTechnical University of Catalonia - UPC

Enginyers de Camins, Canals i Ports

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Definitions and terminologyLandslide Risk Management frameworkComponents of the QRAQualitative vs. Quantitative assessmentPurpose of the assessment and scale of work

CONTENTS

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Landslide Susceptibility. The classification, volume (or area), and spatial distribution of landslides which exist or potentially may occur in an area.

DEFINITIONS AND TERMINOLOGY

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008 Hazard The description of landslide hazard should include the

location, volume (or area), classification and velocity of the potential landslides and any resultant detached material, and the likelihood of their occurrence within a given period of time.


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Risk – A measure of the probability and severity of an adverse effect to health, property or the environment. (a) For life loss, the annual probability that the person most at risk in the risk zone will lose his or her life taking account of the landslide hazard, and the temporal spatial probability and vulnerability of the person (b) For property loss, the annual probability of the consequence or the annualised loss taking account of the elements at risk, their temporal spatial probability and vulnerability


Rockfall at Upper Island Cove . Source:www.heritage.nf.ca/environment/car1.html

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Elements at Risk – The population, buildings and engineering works, economic activities, public services utilities, infrastructure and environmental features in the area potentially affected by the landslide hazard

Vulnerability – The degree of loss to a given element or set of elements within the area affected by the landslide hazard. It is expressed on a scale of 0 (no loss) to 1 (total loss).

Zoning: The division of land into homogeneous areas or domains and their ranking according to degrees of actual or potential landslide susceptibility, hazard or risk.

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THE RISK MANAGEMENT FRAMEWORK

Fell et al. 2005

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LANDSLIDE RISK ASSESSMENT AND ZONING

Location, volume and classification ofexisting landslides

Location, volume and classification ofpotential landslides

Areas with a potential to experiencelandsliding in the future (traveldistance – head retreat)

Estimated frequency (annualprobability)

Magnitude (Intensity )– frequencyrelationships

Landslide inventory map

Susceptibility assessmentLandslide susceptibility map

Elements at riskVulnerabillitySpatial and temporal probabilityPotential damage (scenarios)

Hazard assessmentLandslide hazard map

Risk assessmentLandslide risk map

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Qualitativeis the most common adopted approach by many agencies in

the worldGoal: (a) evaluate and rank relative risk; (b) identification of

hotspots and prioritisation of actions to be undertaken

QuantitativeQRA is more and more a requirement of the administrations

and professional societies. It allows

(a) the direct comparison of the risk levels between areas(b) the cost-benefit analysis(c) the consideration of risk tolerance and acceptability

LANDSLIDE RISK ASSESSMENT AND ZONING: QUALITATIVE VS. QUANTITATIVE

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QUALITATIVE VS. QUANTITATIVE. SUSCEPTIBILITY MAPPING DESCRIPTORS

Large Landslides on Natural Slopes

Small Landslides on Natural Slopes

Rock FallsSusceptibility Descriptors

(a) Quantitative susceptibility descriptors

Factor of safety values from stability models



Absolute

Scores of contributing factors obtained from data treatment techniques

Geomechanicalratings (SMR, RMS)

Relative

(b) Qualitative susceptibility descriptors

Overlapping of index maps with or without weighting

Overlapping of index maps with or without weighting

Index map or parameter map

Presence or absence of activity indicators

% of area covered by landslide deposits

Density of scars on a rock slope

Presence or absence of landslides and their degree of preservation

# of landslides per square kilometer

Presence of absence of potential instability factors (cracks, dipping joints)

Field geomorphological analysis

Fell et al, 2008

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Very lowVery lowVery lowNon-susceptible

LowLowVery lowLow

MediumMediumLowMedium

HighHighMediumHigh

MagnitudeHighMediumLow

Frequency

HAZARD MATRIX: MAGNITUDE - FREQUENCY RELATIONSHIP

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MAGNITUDE – FREQUENCY. SINGLE LANDSLIDES VERSUS LANDSLIDING EVENTS

Landslide magnitude. It isa measure of the landslidesize (i.e. volume, area)

The magnitude of a landsliding event can be expressed by the number(or density) of triggeredlandslides

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ASSESSMENT OF THE LANDSLIDE RISK

R = H x Σ (E x V) Varnes (1984)

R: Risk. Expected damage from the occurrence of a hazardous event of a given magnitude

H: Hazard (probability of occurrence of a damaging event –i.e. rockfall- in a given place and in a given time span)

E: Exposed elementV: Vulnerability

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Risk maps provide a global view of the expected annualdamage due to the potential landslide hazardBased on the information supplied by risk maps and cost-benefit analyses, either protective or reinforcement workscan be envisaged to minimize risk level whereas alertsystems can be set up in places to protect human livesRisk maps are documents that are not intended for directuse in urban planning and development because theyreflect the current situation of the potential damages but notthe spatial distribution of the hazardous zones.Non-urbanized areas are usually displayed as having lowrisk level regardless the level of the existing hazard which isnot appropriate


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What should be taken into account The elements at riskThe vulnerability of the elements at risk (different vulnerabilities)The expected damages for given scenarios :

- Triggering events of a given magnitude (i.e. rainfall, earthquake, etc)- Landslides with a given probability of occurrence- Cascading effects (i.e. valley damming) - Risk remaining after protection works have been completed- Risk transfer

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FUTURE SCENARIOS

(A) Landslide distribution similar to that of the last 50 yr; (B) Landslideincrease: linear trend; (C) Landslide increase: exponential trend (Remondo et al, 2005)

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DIFFERENT VULNERABILITIES TO LANDSLIDING

Uncertainty on the expected landslidemagnitude and frequency

Vulnerability depends on the landslidemechanisms

Damage depends on the location of the exposed element relative to the landslide

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Van Westen et al, 2005

DIFFERENT VULNERABILITIES TO LANDSLIDING

The resistance of a building may be high enough to resist the impact of a falling block but it may be insuficient toavoid the development of tensioncracks due to differential displacementsproduced by a translational slide

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ASSESSING VULNERABILITY TO LANDSLIDING

Dai et al, 2002

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QUANTITATIVE RISK ASSESSMENT

Risk to properties (i.e building)

R(P) = P(L) x P(T:L) x P(S:T) x P(T:P) x P(S:P) x V(D) X C

R(P): expected annual loss due to landsliding (€/yr)P(L): probability of occurrence of a landslide of a given

magnitudeP(T:L): probability of a landslide reaching the building levelP(S:T): probability of the building being on the landslide pathV(D): vulnerability of the building C: cost of the building

the analysis must consider all landslide magnitudes and all the potentially affected buildings

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Van Westen et al, 2005

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Map scale 1:25,000Map scale 1:25,0000 0.5 1.0 1.5 2.0 0 0.5 1.0 1.5 2.0 kmkm

Map scale 1:2,000Map scale 1:2,0000 20 40 60 800 20 40 60 80

ZONING LEVELS AND MAPPING SCALES

Cascini, 2006

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Ho, 2006 – LARAM


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AdvancedIntermediatePreliminaryRiskHazardSuscept-ibility

Inventory

Applicable Map

Scales

Zoning LevelType of ZoningPurpose

NOT RECOMMENDEDStatutory

(X)X(X)XXAdvisory

1:25,000to

1:250,000

XXXInformation

XX(X)X(X)Statutory

XXXXXX(X)Advisory

1:5,000to

1:25,000

(X)X(X)XXXInformation

X(X)X(X)Design

XXXX(X)Statutory

NOT COMMONLY USEDAdvisory

1:5,000to

1:1,000

NOT RECOMMENDEDInformation

Notes: X= applicable; (X) = may be applicable

Site Specific Zoning

Local Zoning

Regional Zoning

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SCALE OF MAPPING

Scale

Description Indicative Range

of Scales Examples of zoning application

Typical Area of

Zoning

Small < 1:100,000 Landslide inventory and susceptibility to inform policy makers and the general public

>10,000 square

kilometres

Medium 1:100,000

to 1:25,000

Landslide inventory and susceptibility zoning for regional and local development;

or very large scale engineering projects. Preliminary level hazard mapping for local

areas

1000 – 10,000 square kilometres

Large 1:25,000

to 1:5,000

Landslide inventory, susceptibility and hazard zoning for local areas

Preliminary level risk zoning for local areas and the advanced stages of planning for large

engineering structures, roads and railways

10-1000 square kilometres

Detailed > 5,000

Intermediate and advanced level hazard and risk zoning for local and site specific areas and for

the design phase of large engineering structures, roads and railways

Several hectares to tens of square

kilometres

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ZONING LEVELS & ACTIVITIES: ASSESSING LANDSLIDE FREQUENCY

For seismically-induced landslides, analyse displacements using ‘Newmark’ type analyses and for liquefiable soils, the likelihood of liquefaction and flow sliding.

Assess geotechnical parameters of the soils. Model slope factors of safety from geotechnical parameters and rainfall frequency or piezometric data.

Advanced

For seismically induced landsliding, relate sliding to seismic loading including the peak ground acceleration and magnitude of the earthquake using empirical methods.

Analysis of rainfall including the effects of antecedent rainfall. Search for critical rainfall and its return period

Prepare series of landslides using proxy data such as silent witnesses (e.g. damage to trees), dendrochronology and dating techniques

Assess the historic frequency from incident databases: develop and use frequency volume curves.

Intermediate

Identify and count the number of landslides from aerial photographs taken at known time intervals and from field work

relative freshness of the morphological features of the scars and landside depositstaking into account the presence of active geomorphic events

Basic

Activities

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Basic level

Geomorphological approach


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Basic level

Geomorphological approach

i.e.: Density of scars, # open cracks

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Assess geotechnical parameters of the soils. Model slope factors of safety from geotechnical parameters and rainfall frequency or piezometric data

Advanced





Intermediate

Identify and count the number of landslides from aerial photographs taken at known time intervals and from the field work

relative freshness of the morphological features of the scars and landside deposits taking into account the presence of active geomorphic events

Basic

Activities

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Intermediate level

Landslide incident records

Hungr et al. 1998

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Assess geotechnical parameters of the soils. Model slope factors of safety from geotechnical parameters and rainfall frequency or piezometric data

Advanced





Intermediate

Identify and count the number of landslides from aerial photographs taken at known time intervals and from the field work

relative freshness of the morphological features of the scars and landside deposits taking into account the presence of active geomorphic events

Basic

Activities

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Advanced levelProbabilistic models

Salciarini et al. 2007

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REFERENCES

Fell, R.; Corominas, J. ; Cascini, L.; Leroi, E. and Savage, W.Z. (2008, in press)“International Guidelines for Landslide Susceptibility, Hazard and Risk Zoning”. Engineering Geology

FRAMEWORK FOR LANDSLIDE QUANTITATIVE RISK …...Hazard assessment Landslide hazard map Risk...

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