2022-04-19 General Committee Meeting Agenda

GENERAL COMMITTEE MEETING AGENDA                                                    19 APRIL 2022


•    The building envelope for proposed Lot 1 which is currently subject to flood inundation in the
     39%AEP event and therefore must be filled to achieve flood immunity. The maximum existing
     depth of flooding in the 1%AEP event in this building envelope location appears to be
     ~250mm
All of the proposed building envelopes apart from Lot 1 and a very small part of the building
envelope of Lot 2, are outside the existing 1% AEP (2100). Filling is therefore not required to
achieve flood immunity of the building envelopes for the 1% AEP (2100) apart from Lot 1 (and a
small portion of Lot 2).
Although there are substantial impacts to flood levels associated with the new internal road, these
impacts are all contained fully within the development site.
The flood investigation proposes that all building envelopes (apart from Lot 8) are filled above the
PMF so safe refuge is achieved in each lot. This is an acceptable outcome as it meets the AOs of
the Flood Hazard Overlay Code. For Lot 8, the applicant argues filling the building envelope to the
PMF is not necessary as an evacuation route off-site to Glenridge Dve is available from this Lot in
the PMF. This is flawed as the residents can not actually go anywhere from Glenridge Dve apart
from to higher ground within the street, as the road network will be cut.
The flooding for Lot 1 is caused by overland flow from a local catchment north of the site, rather
than from the main creek. The building envelope is partly inundated from this overland flow flooding
in even the 63%AEP (1:1yr ARI). In the 1%AEP (2100) event, flooding in this location would be
approximately 250mm deep.
While the impacts from filling the building envelope for Lot 1 can be managed, the question is
whether the inundation should be avoided as required by the Flood Hazard Overlay Code PO3 and
AO3. In this case, my view is that there is not sufficient justification for non-compliance with the
code. The reasons for the non-compliance being non-trivial are:
•    Over 0.5m of fill is proposed over ~1200m2, equating to around 600m3 of filling
•    The area has very low existing flood immunity (1:1yr)
•    The depth of flooding is not trivial (~250mm)
•    The building envelope will still have overland flow flooding directly adjacent for all flood
     events modelled even after filling
Whilst the proposal demonstrates that lots 2 to 8 comply with the Code, concerns are raised as to
the impacts of flooding on the greater road network and implications for safe evacuation of the site
and access to urban services. A limited theoretical review was conducted externally which
indicated that Mckinnon Drive was not expected to be cut off for extended periods during a defined
flood event (1%AEP), however for a 72 hour PMF event, Mckinnon Drive (at Wooroi Creek) may
be inundated for four and half days.
Due to the above concerns with inundation, Switchback Consulting provided a further preliminary
risk assessment based on the ‘Australian Disaster Resilience Handbook Collection Guideline 7-5
- Flood Information to Support Land Use Planning’ Guideline which details four Flood Planning
Constraint Categories (FPCC) from the most constrained land and least suitable for intensification,
(FPCC 1), to the least constrained land (FPCC 4). The Guideline details examples of land use
planning and options for development in the flood plain including the requirement for the
submission of a detailed risk assessment that demonstrates an appropriate mix of planning,
building and emergency management controls to mitigate risk Switchback Consulting has
indicated that the site would be classified as FPCC 2.
The Flood Hazard Overlay Code of the Noosa Plan 2020 includes the following outcomes for
Disaster Management:




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