RFI - Att 1 - Slope Stablility Assessement

Table 1: Stability Risk Levels
 Risk Level                 Example Implications(1)

 VH        Very High Risk   Unacceptable without treatment. Extensive detailed investigation and research, 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 Risk    May be tolerated in certain circumstances (subject to regulators’ approval) but 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 Risk    Acceptable. Manage by normal slope maintenance procedures.

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 (Ref. Section 2), and subject to the implementation of
recommendations given below, it is assessed that there should be a Low Risk of global slope instability
affecting the existing and proposed dams. 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 2 is our qualitative assessment of landslide risk for the development. A summary of qualitative
terminology for use in assessing risk to property is attached (taken from AGS 2007).
Subject to following the recommendations given in Section 4, we conclude that:
      a.     the stability of the dam sites would be maintained and operational for the life of the
             development;
      b.     the dam sites are not subject to greater than a low risk of landslide activity originating from
             other land, including land above the site; and
      c.     development of the site will not increase the risk of landslide activity on other land greater than
             a low risk.

Table 2: Details of Qualitative Risk Assessment for Property (AGS 2007)
                                                                 Assessed
             Hazard              Likelihood    Consequence                    Comments
                                                                   Risk

                                                                              The likelihood of existing/proposed dam wall
                                                                              instability is considered Unlikely, given the low
                                                                              natural gradients, low to moderate
                                                                              existing/proposed cut/fill batters, stiff (or
                                                                              stiffer) natural soils and controlled fill, lack of
     Instability of dam walls     Unlikely        Medium            Low
                                                                              groundwater, and no signs of instability within
                                                                              the existing dam or on adjacent land. The
                                                                              consequence of such instability would be
                                                                              Medium, with the resultant risk being Low as
                                                                              per AGS 2007.




18 March 2026
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