Reference Document - OPW25 0085 (AS Published)

5.2           Slope Stability Assessment
5.2.1         Qualitative Assessment
The risk assessment for this project has been carried out following AGS 2007 Practice Note Guidelines for
Landslide Risk Management. Relative levels of risk and their implications are given in Table 3 and the
Qualitative Terminology for Use in Assessing Risk to Property is also attached in Appendix C.

Table 3: Stability Risk Levels

 Risk Level               Example Implications(1)
 VH      Very High        Unacceptable without treatment. Extensive detailed investigation and research, planning
         Risk             and implementation of treatment options essential to reduce risk to Low; may be too
                          expensive and not practical. Work likely to cost more than value of property.
 H       High Risk        Unacceptable without treatment. Detailed investigation, planning and implementation of
                          treatment options required to reduce risk to Low. Work would cost a substantial sum in
                          relation to the value of the property.
 M       Moderate         May be tolerated in certain circumstances (subject to regulators’ approval) but requires
         Risk             investigation, planning and implementation of treatment options to reduce risk to Low.
                          Treatment options to reduce to Low risk should be implemented as soon as practicable.
 L       Low Risk         Usually acceptable to regulators. Where treatment has been required to reduce the risk
                          to this level, ongoing maintenance required.

 VL      Very Low         Acceptable. Manage by normal slope maintenance procedures.
         Risk

Note: (1) The implications for a particular situation are to be determined by all parties to the risk assessment and
may depend on the nature of the property at risk; these are only given as a general guide.

Considering the existing site conditions, and subject to the implementation of recommendations given in
Section 6, it is assessed that there would be a Low (L) Risk of global slope instability affecting the
proposed subdivision. Regulators (NC) normally require that a Very Low or Low Risk of landslide
affecting property must be demonstrated to enable development approval. Summarised in Table 4
overleaf is our qualitative assessment of landslide risk for the site. A summary of qualitative terminology
for use in assessing risk to property is attached in Appendix C (taken from AGS 2007).
It should be noted that this risk assessment excludes geotechnical risk associated with the existing
structures and areas of the site outside of the proposed development areas (environmental covenant
area around the natural drainage line).




Geo-Environmental Investigation for Proposed Subdivision
7 February 2025 | 24386-001-Rev0                                                                                       13