2014-12-09 Planning & Organisation Committee Agenda

PLANNING & ORGANISATION COMMITTEE MEETING AGENDA                                   9 DECEMBER 2014


Council engaged an external hydrologist to conduct a peer review of the Flood Assessment. The
review confirmed the non-worsening to be accurate but raised concerns with the unconventional
flood strategy because approximately 50% of the flood storage is achieved by “roughness”
provided by flood plain vegetation of the western tributary. Notwithstanding Conventional flood
storage in the form of a bio retention basin and a restrictive footbridge across the eastern
tributary are sufficient to address flooding for development applications REC14/0008 and
REC14/0009. As is standard practice, a sensitivity test was provided that modelled uncontrolled
vegetation growth in the flood plain and a high blockage factor of the footbridge in a Q100 event,
which indicates that in this worst case scenario, there would be worsening at the Blue Wren
Place boundary. It is difficult to model and consider every possible flooding scenario, but the
Code seeks to ensure the development does not compromise the safety of people and property
from floods. Although the proposed lots are all above the worst case scenario flood levels, the
development has the potential to unreasonably impact on upstream residences.
It is not standard industry practice to use “roughness” of the flood plain for flood detention
storage and by doing so, poses a risk to Council in the long term to rely on riparian vegetation for
flood storage. Given the risk to surrounding residents, and to Council, the flood strategy is not
supported and should be amended to provide a conventional flood strategy.
4.     CONSULTATION
4.1. Referrals
The application was forwarded to Unitywater and the following internal Council specialists:
     Engineering Officer
     Ecologist
     Strategic Planning Officer
     Sport and Recreation Officer
     External peer review of flood the assessment by Hydrology & Water Management
       Consulting Pty Ltd.
Their assessment forms part of this report.
5.     CONCLUSION
The proposal complies with the provisions of the Planning Scheme in terms of layout, vegetation
rehabilitation and site works. However, the proposed unconventional flood detention strategy
raises concerns and poses unacceptable risks to surrounding residents and for Council in relying
upon vegetation for flood storage purposes. The Sustainable Planning Act 2009 permits the
assessment manager to issue a preliminary approval when an aspect of development does not
comply with the Planning Scheme and then to upgrade to a Development Permit as part of the
Negotiated Decision process. In this regard it is recommended a Preliminary Approval is granted
to allow the applicant to revise the flood strategy to meet the provisions of the Planning Scheme.
Departments/Sections Consulted:

     Community Services                        X   Planning & Infrastructure
     Disaster Management & Public Order            Building & Plumbing Services
     Waste & Environmental Health                  DA Planning
     Community Facilities                          Strategic Land Use Planning
     Cultural Facilities                           Asset Design & Investigations
                                                   Asset Planning
                                                   Civil Operations
                                                   Environment

     Executive Office                              Corporate Services
     Community Engagement                          Finance
     Customer Service                              ICT
     Executive Support                             Procurement & Fleet
     Governance                                    Property & Facilities
     Human Resources                               Revenue Services



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