Diapositive 1

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RISK ASSESSMENT METHODOLOGIES FOR LANDSLIDES
Jean-Philippe MALET Olivier MAQUAIRE CNRS CERG
. Welcome to Paris!
Final Meeting, Brussels, 26 January 2009
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Diversity of landslide types
Soil spreading
Fall
Toppling
Mudflow
Debris flow
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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The landslide risk assessment framework
(Fell et al., 2005)
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Landslide risk analysis and landslide risk
assessment
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).
Source ISSMGE-ISRM-IAEG JTC-1 Joint Technical
Committee on Landslides and Engineered Slopes,
2006
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Review of current landslide RAMs for EU27

• Questionnaire and litterature review

• ? 71 questionnaires / 30 answers
• success rate 43

? 27 questions, 4 themes

• General information about
• risk assessment

1. Description of the RAM

1. Data Landslide inventory, conditioning factors,
   triggering factors, damages

1. Output documents

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Review of current landslide RAMs for EU27

• Landslide RAMs available for 18 EU Member States
  Switzerland

• 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 RD institutes / private companies
  4 countries
• (Germany, Greece, Poland, and Portugal)
• No RAM 6 countries
• (Denmark, Germany, Latvia, Lituania, Malta,
  Netherlands)
• Information missing Luxembourg, Finland

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Review of current landslide RAMs for EU27

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

Countries with an official RAM used in practice
Countries with an official RAM in development
Countries with local RAMs used by research
institutes or private companies
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Common characteristics of the landslide RAMs
All RAMs susceptibility zoning
- 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)
Landslide inventory map
Landslide susceptibility map
Some RAMs hazard zoning
Estimated temporal frequency (annual
probability) Intensity frequency relationships
Landslide hazard map
All RAMs risk zoning
Elements at risk Vulnerabillity Spatial and
temporal probability Potential damage
Landslide risk map
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Common characteristics of each landslide RAMs

• 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-

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Example of a landslide RAM French PPR
methodology

• 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 work1/10.000 (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

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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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Towards harmonization of landslide RAM at
International level

• Recommended types and levels of zoning and map
  scales

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Towards harmonization of landslide RAM at
International level

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

Slovenia (Komac et al., 2006)
Switzerland (Lateltin et al., 2005)
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Towards harmonization of landslide RAM at
International level

• Certainly possible to harmonize
• - Number of classes in the outputs maps
• Legend of the maps (color choice)

Switzerland (Lateltin et al., 2005)
Austria (Huebl, 2005)
4 classes
3 classes
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Towards harmonization of landslide RAM at
International level

• 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
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Towards harmonization of landslide RAM at
International level

• 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)

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Proposition of a Tiered approach

• 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 11M EuSoil
  database)
• - Climate date (rainfall totals) 12 x 12 km
  daily values from PRUDENCE
• - European earthquake catalogue

Mapping unit grid approach of 90m Mapping scale
11M

• 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 1250,000

• 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 catchment Mapping scale 110,000
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Proposition of a Tiered approach

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

Output maps Landslide susceptibility for some
departments
Input data Conditionning factors
(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)
Harmonized
Not harmonized
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THANKS FOR YOUR ATTENTION
. Welcome to Paris!