Landslide Risk Management

Regulators Quiz

Introduction

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 8 of 10

8. When should a Landslide Risk Management (LRM) assessment be undertaken and what are the basic requirements of a LRM report?

  • Should only be undertaken when advised by a consultant who sets the requirements for content as they see fit.
  • An assessment is triggered by a zoning study and the requirements of a report are set by the consultant.
  • An assessment is triggered by a zoning study and the requirements must be in accordance with AGS guidelines.
  • An assessment is triggered by a zoning study and the requirements must always be in accordance with the regulators requirements but should ideally be in accordance with AGS guidelines.

The requirements for where and when assessment in done and what is needed in a report is always the responsibility of the regulator.

8. When should a Landslide Risk Management (LRM) assessment be undertaken and what are the basic requirements of a LRM report?

The need for a LRM assessment is usually related to a Susceptibility or Hazard Zoning Study or some other plan or criteria defining areas or types of development which are to be included or excluded for assessment.

AGS 2007c (page 67)

The basic requirements of LRM reports must always be in accordance with the regulators specific requirements but where possible should ideally be based on compliance with the requirements of the AGS2007 Practice Note (AGS2007c). The report on the risk assessment is to document the data gathered, the logic applied and conclusion reached in a defensible manner.

The practitioner will gather relevant data, will assess the relevance of the data and will reach conclusions as to the appropriate geotechnical model and basic assessment of the slope forming processes and rates. Full documentation of these results provides evidence of completion, provides transparency in the light of uncertainty, enables the assessment to be re-examined or extended at a later date and enables the assessment to be defended against critical review. The process often identifies uncertainties or limitations of the assessment, which also need to be documented and understood.

The data to be presented includes:

  1. List of data sources.
  2. Discussion of investigation methods used, and any limitations thereof.
  3. Site plan (to scale) with geomorphic mapping results.
  4. All factual data from investigations, such as borehole and test pit logs, laboratory test results, groundwater, level observations, record photographs.
  5. Location of all subsurface investigations and/or outcrops/cuttings.
  6. Location of cross section(s).
  7. Cross section(s) (to scale) with interpreted subsurface model showing investigation locations.
  8. Evidence of past performance.
  9. Local history of instability with assessed trigger events.
  10. Identification of landslides, on plan or section or both, and discussed in terms of the geomorphic model, relevant slope forming process and process rates. Landslides need to be considered above the site, below the site and adjacent to the site.
  11. Assessed likelihood of each landslide with basis thereof.
  12. Assessed consequence to property and life for each landslide with basis thereof.
  13. Resulting risk for each landslide.
  14. Risk assessment in relation to tolerable risk criteria (e.g. regulator?s published criteria where appropriate).
  15. Risk mitigation measures and options, including reassessed risk once these measures are implemented.

Where any of the above is not or cannot be completed, the report should document the missing elements, including an explanation as to why.

The report needs to clearly state whether the risk assessment is based on existing conditions or with risk treatment measures implemented. In some cases, the assessment for both existing and after treatment should be documented to demonstrate the effect of risk control measures on reducing risk.

It must however be noted that the regulator has the final call on report content which is described in their planning controls. The use of the AGS LRM guidelines is one way to standardise report content and avoid content and methodology differences between reports. As such, the standardising of report content has a potential benefit of simplifying the approvals process for the regulator.