2019-12-16 General Committee Agenda

GENERAL COMMITTEE MEETING AGENDA                                            16 DECEMBER 2019


3.   Recent modelling carried out by the Council indicates significant erosion is likely to
     occur in the future which may threaten life and property should the proposed
     development proceed.
     Coastal erosion and subsequent slope failure and reprofiling analysis described in this
     report demonstrates that significant erosion that would fail the original proposed pool can
     occur under a severe storm tide and wave event. However the proposed geotechnical
     design ensures that, irrespective of coastal erosion and subsequent slope failure and
     reprofiling, the pool structure will remain in place following a 100 year storm tide and wave
     erosion event.
4.   The proposal does not comply with the Planning Scheme in force at the time of the
     original approval, given the extent of excavation and vegetation removal in a sand
     dune area.
5.   The proposal does not comply with the Natural Resources Overlay Code for Coastal
     Protection as it has the potential to adversely impact on natural coastal processes.
     With the proposed geotechnical design with mircro-pile support for the pool, coastal
     processes will not be impacted by the proposed development on all coastal events up to
     the 100 year storm tide and wave event, accounting for climate change to 2050. Under
     more severe events, further erosion could occur; however coastal structures of this nature
     are normally required to be designed to withstand events up to the 100 year event (noting
     that the minimum requirement for seawalls is a 50 year ARI event at stipulated in the
     Prescribed Tidal Works Code in the Coastal Protection and Management Regulation 2017).
6.   Given the site is affected by the Coastal Building Line and is located in a highly
     vulnerable erosion prone area, the proposed 6m setback is not sufficient to minimise
     the risk of erosion.
     It is acknowledged that further set-back beyond 6m would further reduce the risk of erosion
     affecting the proposed development; however, the proposed geotechnical design ensures
     that, irrespective of coastal erosion and subsequent slope failure and reprofiling, the pool
     structure will remain in place following a 100 year storm tide and wave erosion event and
     recession due to sea level rise of 0.3m by 2050.
7.   The proposal does not comply with the Biodiversity Overlay Code as vegetation is
     proposed to be removed within the Environmental Protection Overlay placing the
     integrity and resilience of the foreshore at risk.
8.   The proposal is contrary to the Overall Outcomes for the Eastern Beaches Locality
     as it does not protect the dunal area and natural environment nor maintain the safety
     of people and works.
     The proposed development of a swimming pool can be accommodated within the Coastal
     Building Line by incorporation of the modified geotechnical design with a number of micro-
     piles without compromising the future coastal management options for this section of coast.
     The design of the piled foundations prepared by Core Engineering dated 24 September
     2019 will provide protection of the swimming pool and subsequently the house by
     adequately managing erosion from impacting on the pool structure for all storm tide and
     wave events up to the 100 year climate change 2050 event.
     The Coastal Building Line is an arbitrary line set by the former Beach Protection Authority
     to allow for natural shoreline movements (i.e. erosion and accretion) associated with storm
     events.
     In terms of coastal engineering issues, we conclude that the inclusion of the modified piled
     foundation design by Core Engineering should ensure that the pool will withstand erosion
     associated with a 100 year ARI storm and recession due to sea level rise of 0.3m by 2050
     (i.e. the adopted design life of the swimming pool).



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