2022-07-12 Planning & Environment Meeting Agenda

PLANNING & ENVIRONMENT COMMITTEE MEETING AGENDA                                      12 JULY 2022


Geotechnical/ Coastal Building Line
The site is located within an area that is subject to the Landslide Hazard Overlay, with a small area
to the front of the site identified as High Landslide Hazard Area and significant parts of the site
identified as Moderate Landslide Hazard Area. The state has also mapped the site as being within
the Coastal Management District and an erosion prone area. A coastal building line of 10.5m also
applies to the site.
Council’s coastal hazards mapping identifies the site as being within an erosion prone area. The
following image details the erosion extents that the site is expected to be subjected to by 2020,
2040, 2070 and 2100. The erosion extents show the potential area that may be subject to erosion
within the given time horizon as a result of a major storm event and sea level rise.




                            Figure 11 –CHAP mapping (erosion prone area)

To address the known risks of instability and erosion the application material included a
Geotechnical Report and Coastal Hazard Assessment. These documents were reviewed by
external consultants (Geotechnical Engineer and Hydraulic Engineer) involved in previous appeals
for Council for similarly located sites. The reports were amended after the initial review by the
external consultants. The amended reports were reviewed and determined to include methodology
and recommendations which appropriately address the landslide and erosion risks. The measures
proposed, have been designed on the basis of 500 year average recurrence internal storm event
and include:
• A piled wall along the eastern boundary and along the eastern edge of the residence at least
    6 metres long and at 1 metre spacings.
• The proposed residence and any ancillary structures (including retaining walls and pools) must
    be supported by footings founded at least 1m into natural medium dense to dense (or denser)
    sands.
• Cutting for the lower level along the western site boundary will necessitate the installation of
    temporary shoring prior to excavation, comprising sheet piles or contiguous piles.
• Ground vibrations during construction to be minimised and monitored.
• All collected roof water to be directed by pipes to the council stormwater system along Seaview
    Terrace.
The Coastal Hazard Assessment has found that the proposed house and pool are unlikely to be
subject to erosion from the sea during the expected asset lifespan (i.e., 60 years for a residential
house).

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