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SCG 0599 - Landslide Risk Assesment
Dayne Lawrie Constructions Project Number: SCG 0599 2/2 Project Ave Project Name:: 5 Martin St Peregian Beach Noosaville, QLD SCG Consulting Engineers Email: [email protected] Landslide Risk Assessment 5 Marin St, Peregian Beach At the request of Lawrie Constructions the attached report is to provide a landslide risk assessment for the above-mentioned site in accordance with Noosa Shire Council guidelines. The site is located at 5 Martin Street, Peregian Beach and is identified as Lot 267 on RP93113. The site has an area of 744 m2 and is bordered by Martin Street to the north, Avocet Parade the east, residential dwelling to the south and vacant vegetated land to the west. Figure 1 shows an aerial view of the site and its surroundings, with the approximate site boundary shown in red. Figure 1: Site Locality Plan (Site boundaries depicted in red) Review of provided survey data completed by Max Watterson + Associates contour plans provided indicates that the that the site currently slopes from the South-western corner towards the north east from approximately RL 11.25 m to RL 8.18m AHD. Figure 2 below depicts an extract of the site contours. SCG Consulting Engineers Page 1 of 5 SCG 0599 24 September 2025
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Figure 2: Survey Plan (client provided) SCG Consulting Engineers Page 2 of 5 SCG 0599 24 September 2025
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Based on the provided plans, it is understood that the existing residence will be demolished, and a new 2- storey residence with a partial inground garage basement and a semi-inground pool will be constructed. A previous geotechnical report has been provided for the eastern neighbouring property located at 66 Peregian Esplanade by Pacific Geotech. The geotechnical investigation comprised the drilling and sampling of five (5) boreholes extending to depths ranging between 0.5 m and 7.4 m (drill rig refusal). The investigation summarised the site as comprising very loose grading to very dense sand grading with depth. Ground water was noted ranging between 2.6 m and 3.3 m below ground level. It is typical for groundwater to fluctuate regularly throughout the area. The provided report, in conjunction with local experience, is consistent with available mapping as shown in Figure 3 below. Figure 3: Local site geology (Queensland Geoscientific database) Noosa Shire Council mapping indicates that the proposed site is mapped ‘moderate hazards area’, as shown in Figure 4. SCG Consulting Engineers Page 3 of 5 SCG 0599 24 September 2025
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Figure 4: Landslide hazard overly map showing lot boundary in red (from Noosa Shire Council)
Based on a desktop review of the provided data and understanding of the area, there are two potential failure
mechanisms can be considered, these include:
» Hazard 1 – Small rotational failure through the natural loose sands – volume of failure less than 20m3
(failure will required an unusual sever triggering event)
» Hazard 2 – Large rotational failure through the natural loose sands – volume of failure less than 2000m3
(failure will required an extreme triggering event)
A qualitative landslip risk assessment was completed for these potential failure mechanisms in general
accordance with Australian Geomechanics (2007) Guideline for Landslip Susceptibility, Hazard and Risk
Zoning for Land Use Planning). The slope risk assessment is summarised in Table 1.
Table 1: Summary of the qualitative slope risk assessment
Hazard 1 – small rotational failure Hazard 2 - Large rotational failure
Hazards though the natural loose sands up to though the natural loose sands up to
20m3 2,000 m3
Property People, who Property People, who
either live, or may either live, or may
that spend some that spend some
Risk Element
time in the area time in the area
affected by the affected by the
landslip landslip
Likelihood POSSIBLE POSSIBLE BARLEY CREDIBLE BARLEY CREDIBLE
Frequency C C F F
estimate,
expressed as an
annualised
probability and
taking into account
the probability of
spatial impact
SCG Consulting Engineers Page 4 of 5 SCG 0599 24 September 2025
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Measure of INSIGNIFICANT INSIGNIFICANT MAJOR CATASTROPHIC
consequence 5 5 2 1
RISK LEVEL VERY LOW VERY LOW VERY LOW LOW
VL VL VL L
The small and large rotational failures through the loose sands of very low and low risk, respectively and are
unlikely to impact the property and people who live or spend time in the area, provided the following
recommendation are adhered too:
» All temporary and permanent retaining walls and excavations shall be design in accordance with AS4678,
and stability analysis be carried out by a geotechnical engineering ensuring minimum Factors of Safety
(FOS) for temporary and permanent conditions of 1.3 and 1.5, respectively are achieved.
» All foundations of the house to be extended to the medium dense sand, as a minimum.
» The development shall adhere to good hill side practice. Examples of good and poor hill side practice for
the construction of residential dwelling on slopes is presented in Appendix D, Practice Note Guidelines for
landslide risk management 2007, from Australian Geomechanics Journal Vo 42, No. 1 dated March 2007.
Excavations up to 3.0 m depth could generally be designed with a safe 1.5H:1V temporary batter slope or
2H:1V for permanent batter slopes. This assumes that soils are not wet/saturated and groundwater is not
present, and is subject to the below recommendations:
» All temporary batters should not have construction loads (i.e. plant, equipment or soil stockpiles) or
people at the crest of the batters at a distance equal to the height of the slope,
» Batters should be assessed to not effect neighbouring properties/dwellings,
» Permanent batters (at a minimum) should be protected from erosion. Topsoiling and planting, or erosion
matting should be applied to the batter as soon as possible,
» Suitable drainage and stormwater provisions must be installed for the batters. Surface and stormwater
runover must be directed away from batters and prevented from pooling at the base and crest. At a
minimum, spoon drained should be installed at the crest and base of permanent batters,
» Temporary batters should not remain open for extended periods of time.
» Any batters or excavations exceeding this should be inspected by a suitably qualified geotechnical
engineer to assess to the stability of the batter, and
» Batters exceeding the heights or slopes stated above, or batters that contain buildings or surcharge loads
within a distance equal to one batter height from the crest, should undergo detailed stability analysis to
determine risk levels.
If temporary batters steeper than 1.5H:1V are proposed for the site these will require the design of a suitable
retention system.
We trust this information is satisfactory for your current needs. Should you have any questions, please feel
free to contact the undersigned.
Regards,
PTG Consulting Reviewed By
Luke Goodluck Justin Taing
Branch Lead – Sunshine Coast Geotechnical Regional Director – Geotechnical (RPEQ 30087)
p | 07 5647 0457 p | 07 5647 0411
e | [email protected] e | [email protected]
SCG Consulting Engineers Page 5 of 5 SCG 0599 24 September 2025