Landslide Risk Management

Regulators Quiz

This module of the website is aimed at the Regulator who have the responsibility for setting risk criteria, administering planning controls and approving development proposals under the requirements of specific planning controls or a policy.

The format of the module is for a series of Questions relating to the understanding required by the Regulator in respect to a number of aspects relating to the implementation of a landslide-zoning scheme, policy requirements and the approvals process.

Question 4 of 10

4. How important are Definitions and Terminology and which ones do I need to understand?

  • Definitions are not really important.
  • Only need to know just a few.
  • Moderately important so I need to know some key ones.
  • Very important and I need to understand all the terms commonly used.

Landslide definitions and zoning terminology is very specific and it is only when regulators, practitioners and the general public speak the same language can each stakeholder fully understand what each other is saying.

4. How important are Definitions and Terminology and which ones do I need to understand?

Definitions for terms used in landslide zoning and risk management are given in Appendix A. These definitions are based on IUGS (1997), with some amendments in matters of detail based on internationally adopted definitions prepared by The International Society of Soil Mechanics and Geotechnical Engineering (ISSMGE) Technical Committee 32. These definitions should be used for all zoning, reports and land use planning documents. It is recommended that the definitions are attached to these documents so there is no misunderstanding of the terms.

Definitions of the main terms are:

  • Landslide. The movement of a mass of rock, debris, or earth (soil) down a slope.
  • Landslide Inventory. An inventory of the location, classification, volume, activity and date of occurrence of individual landslides in an area.
  • Landslide Susceptibility. A quantitative or qualitative assessment of the classification, volume (or area) and spatial distribution of landslides, which exist or potentially may occur in an area. Susceptibility may also include a description of the velocity and intensity of the existing or potential landsliding.
  • Hazard. A condition with the potential for causing an undesirable consequence. 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 probability of their occurrence within a given period of time. Landslide hazard includes landslides which have their source in the area or may have their source outside the area but may travel on to or regress into the area.
  • Risk. A measure of the probability and severity of an adverse effect to health, property or the environment. Risk is often estimated by the product of probability and consequences. However, a more general interpretation of risk involves a comparison of the probability and consequences in a non-product form.

For these guidelines risk is further defined as:

  1. For life loss, the annual probability that the person most at risk will lose his or her life taking account of the landslide hazard and the temporal spatial probability and vulnerability of the person.
  2. 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.
  • 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). For property, the loss will be the value of the damage relative to the value of the property; for persons, it will be the probability that a particular life (the element at risk) will be lost, given the person(s) is (are) affected by the landslide.
  • 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.

In this guideline use of the word ‘landslide’ implies both existing (or known landslides) and potential landslides which a practitioner might reasonably predict based on the relevant geology, geometry and slope forming processes. Such potential landslides may be of varying likelihood of occurrence.

The term landslip is sometimes used to describe landslides but is not the recommended term.

It is noted that the term ‘zoning’ has particular application by planners in Australia. This document uses the term as it best describes the process and is used internationally. To avoid confusion, those preparing landslide zoning using this document should always refer to: landslide susceptibility zoning, landslide hazard zoning and landslide risk zoning.

AGS 2007a (pages 14-15)

Australian Geomechanics Society Downloads