Appendix H - Slope Stability Assessment

Brett Hage                                                                                      22328-001-Rev0
                                                                                             14 September 2022



                                                                 Drill rig at borehole BH1




                                                  Historic terraces



                             Area of wet ground


Text Figure 7: View looking west over proposed Lot 2 building area, from downslope

2.3    Groundwater
No signs of groundwater seepage (‘springs’) were observed during our walk-over, and neither was any
seepage encountered during borehole drilling. Groundwater conditions may vary seasonally, and could
rise to shallow depths, particularly following periods of prolonged or heavy rainfall.

2.4    Surface Drainage
Broadly, the natural surface drainage follows the ground surface contours, which over the proposed building
area on Lot 2 fall towards the main drainage line to the east. Surface water flows affecting the proposed
building locations on Lot 2 may be sourced from surface water overtopping the unprotected edge of Black
Mountain Range Road directly west and above. The intermediate drainage line to the south is largely
contained in areas downslope of the proposed building area. Ground below the building area forms a gently
rounded spur, which may also aid in dispersing, rather than concentrating flows.
No significant erosion was noted during our walkover inspection, however rilling of about 100 mm depth was
noted over the face of the existing fill material.
Surface water is expected to drain well away from the level building pad, considering the moderately steep
natural gradients and low permeability of the soils in the immediate subsurface, and relatively shallow depth
to rockhead.
The drilling of borehole BH2 just upslope and west of the area of possible seepage noted in Text Figure 7
indicated no proliferation of ‘groundwater’ laterally. With the topography observed, it is more likely that
this is as a result of surface water being retained in soils upslope in the intermediate drainage line, and
fed out at the transition to the natural soils on the sloping ground below.

2.5    Vegetation
To the west of the site area was a mixture of periodically slashed grass and sporadic small to medium size
trees; which were observed to be relatively ‘plumb’.
Further downslope to the east and south-east, slightly larger mature trees were present in a forested area.
These were also noted to be quite straight at the time of our inspection, with no tilting or distorted growth
present, which can be an indicator of slope instability.

2.6    Buildings and Other Structures
The existing residence located on the main spur to the north of the site area comprised a lightweight
structure, formed of two shipping containers. A larger, sheetmetal shed was present along the crest of the
spur to the east. The driveway servicing the existing residence had a gravel surface. While these structures
appeared to be in relatively good condition, it is acknowledged that with the nature of their construction,
signs of structural distress as a result of global slope instability may not always be apparent based on an
external, visual assessment.




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