SUPERSEDED Compiled Reference Document - MCU24 0153 & OPW24 0202 (As Published)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). Inferred natural slopes around this site are
        between 3° and 15°.
        Considering the existing site conditions (Ref. 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 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 Unit Development
        30 September 2024 | 24265-001-Rev0                                                                                                9
Document Set ID: 23376055
Version: 1, Version Date: 28/11/2024