20220109 - Geotech · OPW23/0182

                              PROPOSED RESIDENCE
                              21 MAHER TERRACE, SUNSHINE BEACH

4.6       Surface Drainage
Surface drainage would be expected to follow natural surface contours to the north-east towards
Maher Terrace, thus draining into the roadside drainage system. It is noted that the site has relatively large
catchment; however, most runoff from upslope of the property is anticipated to be intercepted by the existing
stormwater infrastructure from the neighbouring structures and streets.

No significant surface run-off features were noted during our assessment (e.g. deep rilling or scour/wash out
scars). This indicates that significant overland flow is generally absent during rainfall events.
Recommendations to improve surface drainage as part of the development works are provided in
Section 6.5.

5.0      SLOPE STABILITY ASSESSMENT
5.1      Existing Conditions
The Noosa Planning Scheme 2020 includes a landslide hazard overlay map (Ref. extract in Text Figure 9).
Mapping indicates that the site is within a Moderate (pale yellow shading) to High (orange-brown shading)
Landslide Hazard Area.



                                              Approx. Site Location




Text Figure 9: Extract from NSC landslide hazard overlay mapping

It should be noted that the Noosa landslide hazard map is a broad-scale indication of the potential
landslide susceptibility and is superseded by this site-specific assessment. Our observations of surface
features relevant to this slope stability assessment are summarised as follows:

       The existing residential building was noted to be in good structural condition based on an external
        assessment and showed no signs of instability (e.g. no significant cracks in rigid walls etc.).
       A downslope timber sleeper wall was distressed, likely a result of age and poor construction rather
        than global slope instability.
       No indicators of recent global slope instability were observed, i.e., no landslide scarps or ‘hummocky’
        ground was evident across the proposed building area.
       No signs of groundwater seepage ‘springs’ were observed across the proposed development area.
       Longitudinal cracking was observed in Maher Terrace. This cracking is consistent with creep
        movement in the road embankment and/or upper natural soils; however, it was well away from the
        proposed development area.




16 July 2021
Report No. 21236-001-Rev0                                7