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RISK ASSESSMENTMETHODOLOGIESFOR LANDSLIDES

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Jean-Philippe MALETOlivier MAQUAIRE

CNRS & CERG

Final Meeting, Brussels, 26 January 2009

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Rotational and translational slides

Diversity of landslide types

Soil spreading

Debris flow

Mudflow

Fall Toppling

Definition of a landslide – Movement of a slope (mass of rock, of soil or of debris) controlled by gravity. Three main mechanisms of movement are distinguished: fall, sliding and flow type processes.

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Some statistics on landslides

- A major threat to human life, property, infrastructure and natural environment

- On average, landslides are responsible for ca. 17% of all fatalities from natural hazards worldwide (CRED, 2005)

- The socio-economic impact of landslides is underestimated because landslides are usually not separated from other natural hazard triggers, such as extreme precipitation, earthquakes or floods.

- In the last century, Europe has experienced the second highest number of fatalities and the highest economic losses caused by landslides compared to other continents:

- at least 16,000 people have lost their lives because of landslides - the material losses amounted to over 1700 mill. in Europe

- The European countries the most affected are: Italy, Spain, Greece, Switzerland, Austria, UK, France, Norway, Sweden.

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(Fell et al., 2005)

The landslide risk assessment framework

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Landslide risk analysis and landslide risk assessment

Source: ISSMGE-ISRM-IAEG JTC-1 Joint Technical Committee on Landslides and Engineered Slopes, 2006

* International terminology available

Landslide RAM – A method based on the use of available information to estimate the risk to individuals, property or the environment, from landslide hazards.

A landslide RAMs generally contain the following steps:

1/ definition of threat (danger)

2/ estimation of probability of spatial occurrence (susceptibility)

3/ estimation of temporal probability of an event of a given magnitude (hazard)

4/ evaluation of the vulnerability of the element(s) at risk

5/ consequence identification

6/ risk estimation.

It includes also the process of making a decision recommendation based on criteria/thresholds (tolerable/acceptable risks).

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Review of current landslide RAMs for EU27

1. General information about risk assessment

2. Data: Landslide inventory, conditioning factors, triggering factors, damages

3. Description of the RAM

4. Output documents

27 questions, 4 themes

• Questionnaire and litterature review 71 questionnaires / 30 answers success rate: 43%

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- Official RAM: 5 countries(France, Italy, Sweden, Switzerland, Austria)

- RAM in development: 9 countries(Belgium, Cyprus, Czech Republic, Hungaria, Ireland, Slovakia, Slovenia, Spain, and United-Kingdom)

- RAM used by R&D institutes / private companies: 4 countries(Germany, Greece, Poland, and Portugal)

- No RAM: 6 countries(Denmark, Germany, Latvia, Lituania, Malta, Netherlands)

- Information missing: Luxembourg, Finland

• Landslide RAMs available for 18 EU Member States + Switzerland

Review of current landslide RAMs for EU27

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Countries with ‘local’ RAMs used by research institutes or private companies

• RAMSOIL Report: fact sheet describing the status of landslide RAMs per country

Countries with an official RAM in development

Countries with an official RAM used in practice

Review of current landslide RAMs for EU27

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- Location, volume and classification of existing landslides

- Location, volume and classification of potential landslides

- Areas with a potential to experience landsliding in the future (travel distance – head retreat)

Estimated temporal frequency (annual probability)

Intensity – frequency relationships

Landslide inventory map

Landslide susceptibility map

Elements at risk

Vulnerabillity

Spatial and temporal probability

Potential damage

Landslide hazard map

Landslide risk map

All RAMs: susceptibility zoning

Some RAMs: hazard zoning

All RAMs: risk zoning

Common characteristics of the landslide RAMs

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Input data: • Topography & derived slope classes• Soil map• Bedrock map (eg. lithology) • Landcover

• Occurrence density of landslides

Data processing: qual. approach • Field geomorphologic analysis • Combination of index maps

Output information (documents): • Geomorphological map• S / H / R maps (often, 3 classes of H / R)

Techniques: • Inventory (historical archives, field observations, aerial photo- interpretation, remote-sensing)• GIS-based models

Perception:• Criteria / Threshold / Value judgment

Common characteristics of each landslide RAMs

Common principles in landslide RAMs:

- Data collection - Use of available data- Scale for risk zoning (1:25,000 – 1:10,000)

- Data processing- Expert ‘heuristic’ method- Based on principle of causality - Use of cost efficient methods

FRANCE

ITALY SWEDEN

SWITZERLAND

Indicators & spider graphs approach

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• PPR: Plan de Prévention des Risques (1995)

Philosophy:• Qualitative approach

• Based on expert judgment of the scientist

• Use of available data & reports; no specific investigation

• Scale of work:1/10.000 (or 1/5000 in urban zones)

Procedure:• Inventory of processes (type, activity, age, magnitude)

• Inventory of exposed elements & major stakes

• Hazard map = analysis of the type of processes, their activity, magnitude and frequency

• Risk map = hazard map x inventory of major stakes

• Criteria: reference event of 100 years

Example of a landslide RAM: French ‘PPR methodology’

R2: Area with low restrictions

R3: Area with specific restrictions

R1: Area without specific restrictions

G2: moderate hazard / risk

G3: high hazard / risk

G: low hazard / risk

Hazard & risk maps Landuse planning regulation

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Towards harmonization of landslide RAM at International level

• Guidelines on Landslide Susceptibility, Hazard and Risk Zoning (2006) JTC-1 Working Group (Leader: J. Corominas, UPC, Barcelona)

Terms and procedures already harmonised:

• Definitions and common terminology

• Information on what should be included in landslide susceptibility and hazard zoning and risk zoning schemes

• Definition of levels of zoning and suggested scales of zoning maps taking into account the needs of the users

• General methodology for a landslide QRA

Terms and procedures to harmonize:

• Criteria & thresholds for H & R quantification for each landslide type

• Number of classes of H & R

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• Recommended types and levels of zoning and map scales

Towards harmonization of landslide RAM at International level

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. 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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Certainly possible to harmonize: - Criteria and thresholds for frequency estimation (return period, annual probability)

- Criteria and thresholds for intensity estimation

Switzerland (Lateltin et al., 2005)

Towards harmonization of landslide RAM at International level

Slovenia (Komac et al., 2006)

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Certainly possible to harmonize: - Number of classes in the outputs maps

- Legend of the maps (color choice)

Towards harmonization of landslide RAM at International level

Switzerland (Lateltin et al., 2005)

4 classes3 classes

Austria (Huebl, 2005)

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Impossible to harmonize - Tolerance criteria and value judgements (by definition different for each country)

- Tolerable vs. Acceptable risk

ALARP principle

• If possibility of loss of life is high, probability of phenomenon should be low

• Higher risk than acceptable will be tolerated if control or reduction of risk is not possible

• Higher risk is tolerated for existing slope than for planned projects

• Higher risk is tolerated for natural slope than for engineered slopes

• Tolerable risk may vary from country to country

Number of fatalities

Frequency of N

Towards harmonization of landslide RAM at International level

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• The way forward: creation of a Pan-European map of areas at risk of landslides

(Conclusions of the ‘Expert Meeting on Guidelines for Mapping Areas at Risk of Landslides in Europe ’ animated by JRC, October 2007, Ispra)

Towards harmonization of landslide RAM at International level

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• Tier 1 approach: Generic landslide susceptibility map using a heuristic weighting-rating model

- Slope angle (SRTM data, 90x90 m)- Land Cover (from Corine)- Soil Parent (rock?) material (from 1:1M EuSoil database) - Climate date (rainfall totals): 12 x 12 km daily values from PRUDENCE- European earthquake catalogue

Proposition of a ‘Tiered’ approach

Mapping unit: grid approach of 90mMapping scale: 1:1M

• Tier 2 approach: Landslide susceptibility map (by types) using a multivariate statistical model

* Predicted variable: landslide occurrence – landslide inventory needed! * Predicting conditionning variables: - Tier 1 data - Second order topographical attributes (from SRTM data, 90x90 m or better if available) - Bedrock / Engineering soil database (including hydraulic & geotechnical properties) - European major discontinuities (faults) - Soil moisture maps - Daily climate date (rainfall totals): 12 x 12 km values from PRUDENCE - PGA data (from ESPON GSHAP project) Mapping unit: municipality or catchment

Mapping scale: 1:250,000

• Possible Tier 3 approach: Landslide susceptibility/hazard map using a process-based model Focus only on the high-susceptible areas identified by Tier 2

Mapping unit: catchmentMapping scale: 1:10,000

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Proposition of a ‘Tiered’ approach

• Method for the Tier 1 assessment is being tested (ex. of France)

Input data – Conditionning factors

Output maps –Landslide susceptibilityfor some departments

(Malet et al., 2008)

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Conclusions

- Landslide RAMs are available in 18 European Member States (because of the impacts of landslides on lives, infrastructures and the environment)

- A framework for landslide risk analysis, assessment and management is available at International level

- Most of the items in the landslide RAMs are harmonized (eg. International guidelines are available)

Input data Data processing

Output

(maps)

Criteria

Threshold

Risk perception &

zoning

Harmonized Not harmonized

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THANKSFOR YOURATTENTION

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