Landslides and GIS - ADPC - Asian Disaster Preparedness Modules/Landslide hazard...

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Transcript of Landslides and GIS - ADPC - Asian Disaster Preparedness Modules/Landslide hazard...

  • Landslide types and causes1

    Introduction to landslidesPart 4: Use of GIS for landslide mapping

    Cees van Westen

    International Institute for Aerospace Survey and Earth

    Sciences (ITC), Enschede, The Netherlands.

    E-mail: [email protected]

  • Landslide types and causes2

  • Landslide types and causes3

    First define the objective of the study. Danger exists that the data that will be collected will not be in

    accordance with the scale of analysis, or the method of analysis. This might lead to a waste of time and money if too detailed

    data is collected, or an oversimplification if too general data is collected.

    The following things should be considered: The objective of the study The scale of the study The type of analysis that will be followed The types of input data that will be collected.

  • Landslide types and causes4

    Defining objective

    Landslide hazard studies can be made for any different purposes. Some of these might be:

    For an environmental impact study for engineering works; For the disaster management of a town or city; For the modelling of sediment yield in a catchment ; For a watershed management project; For a community participation project in disaster management; For a the generation of awareness among decision makers; For scientific purposes.

    Each of these objectives will lead to specific requirements withrespect to the scale of work, the method of analysis and the type and detail of input data to be collected.

  • Landslide types and causes5

    Scales of analysis

    National scaleSmaller than 1:1.000.000, covering an entire country, mainly intended to generate awareness among decision makers and the general public. Maps on this scale are often intended to be included in national atlases.

  • Landslide types and causes6

    Scales of analysis

    Regional scaleBetween 1:100.000 and 1:1.000.000, covering a large catchment area, or a political entity of the country. The maps at this scale are mostly intended for reconnaissance phases for planning projects for the construction ofinfrastructural works, or agricultural development projects.

  • Landslide types and causes7

    Scales of analysis

    Medium scaleBetween 1:25.000 and 1:100.000, covering a municipality or smallercatchment area. Intended for the detailed planning phases of projects for the construction ofinfrastructural works, environmental impact assessment and municipal

    planning.

  • Landslide types and causes8

    Scales of analysis

    Large scaleBetween 1:2.000 and 1:25.000, covering a town or (part of) a city. They are used for disaster prevention and generation of risk maps, as well as for the design phase of engineering works.

  • Landslide types and causes9

    Scales of analysis

    Site investigation scaleBetween 1:200 to 1:2.000, covering the area where engineering works will be carried out, or covering a single landslide. They are used for the detailed design of engineering works, such as roads, bridges, tunnels, dams, and for the construction of slope stabilisation works.

  • Landslide types and causes10

    Data layers for slopeinstability hazard zonation

    Scale of analysis

    Regional Medium Large

    GEOMOR 1. Terrain Mapping Units 3 3 3

    PHOLOGY 2. Geomorphological (sub)units 2 3 3

    3. Landslides (recent) 1 3 3

    4. Landslides (older period) 1 3 3

    TOPOGRAPHY 5. Digital Terrain Model 2 3 3

    6. Slope map 2 3 3

    7. Slope direction map 2 3 3

    8. Slope length 2 3 3

    9. Concavities/convexities 1 1 3

    ENGINEERING 10. Lithologies 2 3 3

    GEOLOGY 11. Material sequences 1 2 3

    12. Structural geological map 3 3 3

    13. Seismic accelerations 3 3 3

    LANDUSE 14. Infrastructure (recent) 3 3 3

    15. Infrastructure (older) 3 3 3

    16. Landuse map (recent) 2 3 3

    17. Landuse map (older) 2 3 3

    HYDROLOGY 18. Drainage 3 3 3

    19. Catchment areas 2 3 3

    20. Rainfall 2 3 3

    21. Temperature 2 3 3

    22. Evapotranspiration 2 3 3

    23. Watertable maps 1 1 2

  • Landslide types and causes11

    General trends in landslide hazard assessment

    Type ofanalysis

    Techniques Required datafrom table 1

    Regional1:100,000

    Medium25.000

    Large10.000

    Inventory Landslidedistribution analysis

    3 Yes,but... (*)

    Yes Yes

    Landslide activityanalysis

    4,5,14,15,16,17 No Yes Yes

    Landslide densityanalysis

    1,2,3 Yes,but... (*)

    No No

    Heuristicanalysis

    Geomorphologicalanalysis

    2,3,4 Yes Yes,but.. .(**)

    Yes,but.. .(**)

    Qualitative mapcombination

    2,3,5,6,7,8,9,1012,14,16,18

    Yes,but...(***)

    Yes,but.. .(**)

    No

    Statisticalanalysis

    Bivariate statisticalanalysis

    2,3,5,6,7,8,9,1012,14,16,18

    No Yes No

    Multivariatestatistical analysis

    2,3,5,6,7,8,9,1012,14,16,18

    No Yes No

    Deterministicanalysis

    Safety factoranalysis

    6,11,12,13,16,20,21,22,23

    NO No Yes,but.. .(****)

  • Landslide types and causes12

    Landslide distribution analysis

  • Landslide types and causes13

    Activity analysis

  • Landslide types and causes14

    Density analysis

  • Landslide types and causes15

    Geomorphological hazard analysis

  • Landslide types and causes16

    Qualitative

  • Landslide types and causes17

  • Landslide types and causes18

  • Landslide types and causes19

    Hazard zonation

    Slope instability hazard zonation is defined as:

    The mapping of areas with an equal probability of occurrence of landslides within a specified period of time (Varnes, 1984).

    A landslide hazard zonation consists of two different aspects:

    the assessment of the susceptibility of the terrain for a slope failure, in which the susceptibility of the terrain for a hazardous process expresses the likelihood that such a phenomenon occurs under the given terrain conditions or parameters.

    the determination of the probability that a triggering event occurs.

  • Landslide types and causes20

    Hazard zonation

    Often slope instability hazard assessment uses the assumption:

    conditions which led in the past to slope failures, will also result in potential unstable conditions in the presentorThe past is the key to the present

  • Landslide types and causes21

    Direct / Indirect hazard mapping

    Division of hazard mapping methods: (1) Direct hazard mapping

    experience driven applied geomorphological approach, where the earth scientist evaluates the direct relationship between the landslides and the geomorphological and geological setting during the survey at the site of the failure.

    (2) Indirect hazard mapping the mapping of a large amount of parameters and the

    (statistical or deterministic) analysis of all these possible contributing factors in relation to the occurrence of slope instability phenomena, determining in this way the relation between the terrain conditions and the occurrence of landslides. Based on the results of this analysis statements are made regarding the conditions under which slope failures occur.

  • Landslide types and causes22

    Relative / absolute hazard

    Another useful division in techniques for assessment of slope instability hazard is given by Hartlen and Viberg(1988) :

    (1) relative hazard The relative hazard assessment techniques differentiate the

    likelihood of occurrence of mass movements for different areas on the map, without giving exact values.

    (2) Absolute hazard Absolute hazard maps display an absolute value for the

    hazard, such as a factor of safety or a probability of occurrence.

  • Landslide types and causes23

    Landslide hazard analysis methods

    Another division (Carrara, 1983; Hartlen and Viberg, 1988):

    (1) White box models,based on physical models (slope stability and hydrological models), also referred to as deterministic models;

    (2) Black box models, not based on physical models but on statistical analysis;

    (3) Grey box models, based partly on physical models and partly on statistics.