Reference Document - MCU25 0060 (As Published)

5.2           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 2 and the
Qualitative Terminology for Use in Assessing Risk to Property is also attached in Appendix B.

Table 2: Stability Risk Levels

 Risk Level             Example Implications(1)
 V      Very High       Unacceptable without treatment. Extensive detailed investigation and research,
 H      Risk            planning 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
        Risk            requires 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.

Given the geology, topography and particularly the relatively moderately sloping terrain across the
proposed development area, it is considered rare that a landslide could affect the proposed development.
Sand dune slopes are generally close to the ‘limit of equilibrium’ where the surface gradient is about 30°,
although possibly lower in the order of 26˚ to 28˚ for very loose sands. The limit of equilibrium is the
‘tipping point’ to instability, where the factor of safety (FOS) of the slope is approximately 1.0. The FOS of
a slope is the balance (ratio) between the forces driving instability (e.g. soil weight, groundwater pressure)
and the resisting forces (e.g. soil friction and cohesion). Natural slopes around this site are between 8°
and 14°, with a slightly steeper area parallel with the southern boundary extending to no more than 24°.
Considering the existing site conditions (Ref. Section 2), and subject to the implementation of
recommendations given below, it is assessed that there should be a Low (L) Risk of global slope
instability affecting the proposed development. Regulators (NC) normally require that a Very Low or Low
Risk of landslide affecting the property must be demonstrated to enable development approval.
Summarised in Table 3 overleaf is our qualitative assessment of landslide risk for the development site. A
summary of qualitative terminology for use in assessing risk to property is attached (taken from AGS
2007).




Proposed Residential Development
25 August 2025 | 25038-001-Rev0                                                                                                   10