Onslow Townsite Planning Coastal Setbacks and Development Levels
The urban form of Onslow over many years has significantly modified the extent of the dunal system to the point where it is difficult to define. Accordingly, there is some conjecture as to where the “frontal dune areas of the townsite” as referred to in Sub Clause 7.3.1 actually exists. In June 2003, the Western Australian State Government released Statement of Planning Policy No. 2.6 - The State Coastal Planning Policy (SCPP). The SCPP provides guidance for new development, including subdivision and strata subdivision, on the Western Australian coastline. The SCPP outlines the recommended criteria for use in determining the appropriate Physical Processes Setback (PPS). The PPS should provide a low level of risk to the development from coastal erosion over a 100 year planning horizon.
The PPS is measured from the horizontal setback datum (HSD). For a sandy shoreline the HSD is identified as the seaward extent of ephemeral vegetation on an accreting coast, or the toe of the erosion scarp on an eroding coast. As the only rock observed onsite at Onslow was located in the intertidal terrace, the shoreline for Onslow will be taken as sandy. In 2010 a Position Statement (WAPC 2010) was released to update the requirements of the SCPP. This position statement related solely to the required allowances for climate change. Because Onslow is located within an area that experiences cyclonic activity the SCPP specifies that development should be set back from the coast to afford development protection from the impact of cyclonic storms. This requires a further variation to the general case of development on an undeveloped sandy shoreline.
At the Ordinary Meeting of Council 14 December 2011, Council was advised that some modification to the minimum AHD was likely due to a review undertaken by LandCorp and other State Agencies. This review was still to be finalised and a draft Local Planning Policy was adopted by Council requiring any applicant within the Onslow Coastal Hazard Area Special Control Areaâ€Ÿ to undertake an assessment in accordance with Clause 6.20.4. The draft Policy is subject of a further Report to the February 2012 Council meeting.
LandCorp, as part of its investigations for the release land for residential, commercial and industrial development within and around the existing Onslow Townsite, commissioned specialist coastal and ports engineers M P Rogers & Associates Pty Ltd (MRA) to assess the appropriate setback to account for the action of physical coastal processes in line with the State Government’s SCPP as well as to investigate potential coastal inundation in order to determine the appropriate development levels. MRA are a very well known and respected coastal and ports engineering company, particularly in Western Australia.
The MRA report has been completed and is titled: “Onslow Townsite Planning Coastal Setbacks & Development Levels”. In January 2012, LandCorp provided the Shire with a copy of the MRA Report and its findings have significant implications for existing and future development of Onslow. A copy of the MRA Report is attached.
Essentially, within the ‘Onslow Coastal Hazard Area Special Control Area’, the Scheme currently identifies that a floor level of either 4AHD or 5AHD (Australian Height Datum) is required, although the Scheme provisions don’t clearly identify where the required AHD level applies. The Scheme provision associated with the ‘Onslow Coastal Hazard Area Special Control Area’ also has numerous typographic errors that need rectified.
The MRA recommendation that development at Onslow be at 6.4mAHD has significant implications for the development of the town with respect to design, building impact and land use. One way on gauging the development impact of a 6.4mAHD finished floor level is to compare the finished floor level of the Ashburton Motel which is set at (approximately) 5.0mAHD. The MRA recommendation of 7.4mAHD associated with ‘Critical or Emergency Response Infrastructure’ will have implications for Shire infrastructure and presumably, the State. However, much of the State ‘Critical or Emergency Response Infrastructure’ is covered under the Public Works Act and it is not clear whether State Agencies would be obliged to consider higher finished floor levels.
Importantly, implementation the MRA recommendations could result in a larger expanse of the ‘Onslow Coastal Hazard Area Special Control Area’.
The findings and recommendations of the “Onslow Townsite Planning Coastal Setbacks & Development Levels” cannot be ignored by the Shire or any other agency or developer. It is considered vital that the Shire undertakes lead role in addressing the MRA Report and seeking a dialogue with State agencies and the community on the matter.
For any further queries, please contact the Shire’s Principal Planner on 9188 4444.
Last updated: 25 February 2020