Slope Stability Assessment

Paul & Janelle DeSouza                                                                                  22198-001-Rev1
C/- Sarah Waller Architecture                                                                              25 July 2022

It should be noted that the NC map is a broad-scale indication of the potential landslide hazard only, is
largely based on ground slope; and is superseded by this site specific assessment. At the time of our
visit, the site did not exhibit any indicators of significant slope instability.

While the natural ground slope inclinations at the site were moderately steep, no landslide back scarps,
groundwater springs, or areas of naturally ‘hummocky’ ground were observed. Shallow rock was found
consistently in the test pit excavations.

3.2   Stability 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 1, and the
Qualitative Terminology for Use in Assessing Risk to Property is attached.
Table 1: Stability Risk Levels
 Risk Level            Example Implications(1)
                       Unacceptable without treatment. Extensive detailed investigation and research, planning
       Very High
 VH                    and implementation of treatment options essential to reduce risk to Low; may be too
       Risk
                       expensive and not practical. Work likely to cost more than value of property.
                       Unacceptable without treatment. Detailed investigation, planning and implementation of
 H     High Risk       treatment options required to reduce risk to Low. Work would cost a substantial sum in
                       relation to the value of the property.
                       May be tolerated in certain circumstances (subject to regulators’ approval) but requires
       Moderate
 M                     investigation, planning and implementation of treatment options to reduce risk to Low.
       Risk
                       Treatment options to reduce to Low risk should be implemented as soon as practicable.
                       Usually acceptable to regulators. Where treatment has been required to reduce the risk
 L     Low Risk        to this level, ongoing maintenance required.
       Very Low
 VL                    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 (Refer Section 2), and subject to the implementation of
recommendations given below, it is assessed that there would be a Low (L) Risk of global slope instability
affecting the proposed residence and shed. 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 2
below is our qualitative assessment of landslide risk for the site. A summary of qualitative terminology for
use in assessing risk to property is attached (taken from AGS 2007).




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