OPW052025 Report - Part 2

Table 3: Details of Qualitative Risk Assessment for Property (AGS 2007)
                                                          Assessed
 Hazard                     Likelihood     Consequence               Comments
                                                          Risk

                                                                     Taking into account the relatively wide and
                                                                     gently sloping crest of the basalt ‘cap’ to the
                                                                     north-western corner of the site, allowing for
 1: Proposed House
                                                                     the offset to the steeper flanking slopes (>10
 Site: Shallow or deep
                                                                     m) and shallow depth to ‘rockhead’ (<1 m
 landslide above or         Rare           Major          Low
                                                                     BGL) it is considered Rare that such
 below foundation
                                                                     movements would occur. The consequence of
 levels for building
                                                                     a deep-seated slide could range to Major, and
                                                                     therefore the residual risk is Low according to
                                                                     AGS 2007.

                                                                     Instability near the crest of the ridgeline over
                                                                     which the driveway will be constructed would
                                                                     be considered Unlikely where taking into
                                                                     account the relatively wide crest over most of
 2: Driveway: Shallow                                                the alignment, and negligible earthworks. The
 or deep instability in                                              geomorphological shape would limit the
 soils/rock on upper        Unlikely       Medium         Low        proliferation of chanelised surface water, and
 flanks of ridgeline                                                 the effects of such instability would be over a
 affecting driveway                                                  relatively small area where considering the
                                                                     overall length of the driveway. Therefore, the
                                                                     consequence would be Medium and the
                                                                     resultant risk according to AGS 2007 would be
                                                                     Low.

                                                                     With access and potential to create favourable
 2: Driveway: Through                                                engineered conditions for drainage above the
 sidelong section to                                                 cut batter, and diversion drainage above, and
 west (Ref. Section 4.1),                                            roadside drainage local to the driveway, and
 retrogressive slide                                                 shallow depth to ‘rockhead’ it is assessed as
                            Unlikely       Minor          Low
 from steeply sloping                                                Unlikely that such a slide would retrogress
 drainage line head                                                  and affect the driveway. The limited extent of
 within 3 m of road                                                  such movement would result in a Minor
 edge                                                                consequence, and as such the residual risk is
                                                                     Low as per AGS 2007.




Geotechnical Investigation & Slope Stability Assessment
9 April 2025 | 25050-001-Rev0                                                                                           15