2014-11-17 General Committee Agenda

GENERAL COMMITTEE MEETING AGENDA                                            17 NOVEMBER 2014


   Reduction in flood levels across the driveway in a 10 year ARI and 2 year ARI floods, with
     reduced inundation times.
   No increase in flood depth across the driveway within the site for the design case in a 100
     year ARI Flood and a 10 – 50mm increased depth within the road reserve. Inundation time
     is reduced and access and egress from the site is not currently available in an existing 100
     year ARI flood event.
   Up to 100mm increased depth within the site and up to 150mm within the road reserve over
     the access in the extreme 50% blockage case submitted for sensitivity analysis.
   No increased flood depth for a 500 year ARI flood.
The applicant’s response to outstanding issues in Attachment 1 also states that the access
arrangement for the site will be generally unaffected by the works. Overall, the proposed design
is considered to improve access to the residents’ property in more common flood events and no
unacceptable impacts are posed during larger events.
Flood Freeboard
The residents were concerned that adequate freeboard will be maintained to the floor level of
their house during extreme events. The applicant’s response in Attachment 1 confirms that
greater than 500mm freeboard will be maintained in the extreme 50% blockage case for the
modelled 100 year ARI flood event.
Impacts at Rear of Site
The residents were concerned structures at the rear of their house (studio outbuilding,
greenhouse, etc. near the southern boundary) had not been considered and may be impacted by
increased flooding. The previously submitted modelling shows no increased flood depths behind
the house and no increased flood impacts are posed to those structures.
Blockage Provision
The residents questioned whether the 20% design blockage provision represents industry best
practice and has considered the latest Australian Rainfall & Runoff 2014 methodology for
blockage assessment. The residents also requested engineering certification be provided
confirming the design blockage provision. The applicant’s response in Attachment 1 includes
certification provided by its hydrologist.
The peer review subsequently submitted by the residents included as Attachment 2 agrees with
20% design blockage provision to the pipes and culverts but suggests that a 100% blockage
should be assumed for solid guard rails and recommends that alternatives be considered. An
additional condition is included in the amended recommendation in this report to provide this at
Operational Works approval stage.
Screening to Pipework, Debris Deflectors and Traps
The peer review provided by the residents included in Attachment 2 raises some new issues
with respect to the design of the works. The review generally supports the approach Council has
taken in setting and reviewing the design standards and design of the Garnet Street upgrade
works but identifies pipe screens, debris deflectors/traps and, in particular, vehicle barriers as
aspects that should be further considered. These aspects have been considered in the
applicant’s design process to date, however, the finalised design for the works is yet to be
submitted to Council for operational works approval and opportunity exists to further review them.
An additional condition is included in the amended recommendation below for that purpose.
Vegetation
The residents raised concerns with the extent of vegetation removal within the road reserve that
may be required by the works. The applicant’s engineers explained the layout and footprint to the
residents on site and made an undertaking to minimise vegetation removal at the edge of the
works where possible. Minimisation of vegetation clearing will also be considered as part of the
operational works approval stage.



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