SC6.3.1 Purpose

The purpose of this planning scheme policy is to:

1. Provide advice about achieving outcomes in the Flood hazard overlay code.
2. Identify and provide guidance about information that may be required to support a development application where subject to the Flood hazard overlay code.
3. Identify guidelines that may be relevant to achieving outcomes in the Flood hazard overlay code.

SC6.3.2 Application

This planning scheme policy applies to development which requires assessment against the Flood hazard overlay code.

SC6.3.3 Background information—Flood mapping

Council's Flood hazard overlay maps are derived from:

1. Detailed flood modelling studies identified in Appendix 1 of this planning scheme policy.
2. Interim flood assessment overlay mapping completed by the Queensland Reconstruction Authority.

SC6.3.4 Guidelines for achieving Flood hazard overlay code outcomes

For the purposes of the performance outcomes and acceptable outcomes in the Flood hazard overlay code, the following are relevant guidelines:

1. Floodplain Management in Australia: Best Practice Principles and Guidelines SCARM Report 73 (CSIRO, 2000).
2. the relevant State Planning Policy (Department of State Development, Infrastructure and Planning) and State Planning Policy Guidelines.
3. Planning for stronger more resilient floodplains, Part 2, Measures to support floodplain management in future planning scheme (Queensland Reconstruction Authority, 2012).
4. Queensland Urban Drainage Manual (QUDM), Australian Rainfall and Runoff (IEAust, 1999).

SC6.3.5 Climate change/variability

Climate change/variability investigations must include tailwater increases that account for a projected sea level rise of 0.8m and must include the effects of an increase in 1% AEP rainfall intensity of 20%.

SC6.3.6 Guidelines for the preparation of a flood hazard assessment report and flood hazard mitigation report

1. Flood hazard assessment report
   1. A flood hazard assessment report is to be certified by a Registered Professional Engineer Queensland with demonstrated expertise in hydrology, hydraulic modelling and stormwater engineering and is to:
      1. Be prepared in accordance with the methodology prescribed in Queensland Reconstruction Authorities publication Planning for stronger more resilient floodplains Part 2.
      2. Include accurate hydrological and hydraulic modelling of the waterway network and assessment of existing flooding and flood levels of major water systems including accounting for climate change/variability.
      3. Include modelling of the 10%, 2% 1%, 0.5%, 0.2% and 0.1% AEP flood events and any other relevant AEPs based on development category and the PMF. This analysis is to include volumes, depths of flooding, and velocity.
      4. Include a qualitative assessment of the piped drainage and hydraulic analysis of the drainage network particularly in relation to the potential for a regional event to cause backflow flooding of the drainage network.
      5. Address the potential impacts of climate change.
2. Flood hazard mitigation report
   1. A flood hazard mitigation report is to:
      1. Assess the potential impacts of the development on flood hazard.
      2. Assess the potential impacts of flood hazard on the development.
      3. Recommend strategies to be incorporated into the proposed development to satisfy the outcomes of the Flood hazard overlay code.
      4. Describe and evaluate the impact of the proposed mitigation strategies on the existing and likely future use of land and buildings in proximity to the proposed development.
      5. Address the following:
         1. waterways, including bank stability
         2. impacts on adjacent properties both upstream and downstream
         3. preferred areas and non-preferred areas on site for various activities, based on the probability of inundation and the volume, depth, velocity and depth velocity products of flows. The preferred areas are also the be based on availability of evacuation routes
         4. the use of flood resistant materials and construction techniques able to withstand relevant hydraulic and debris loads where appropriate
         5. the location and height of means of ingress and egress, including possible flood-free escape routes which are to be passible by a two wheel drive sedan during the 1% AEP flood event.
         6. the location and height of buildings, particularly habitable floor areas
         7. structural design, including the design of footings and foundations to take account of static and dynamic loads (including debris loads and any reduced bearing capacity owing to submerged soils)
         8. the location and design of plant and equipment, including electrical fittings
         9. the storage of materials which are likely to cause environmental harm if released as a result of inundation or stormwater flows
         10. the appropriate treatment of water supply, sanitation systems and other relevant infrastructure
         11. relevant management practices, including flood warning and evacuation measures
         12. details of any easements or reserves required for stormwater design, and
         13. details of detention/retention storages to achieve non worsening and located above the 1% AEP flood level.
3. Flood risk management
   1. A flood risk assessment is:
      1. Only required to address a performance outcome of the Flood hazard overlay code where the proposed land use is not compatible with the acceptable outcomes of the code.
      2. To be carried out by a Registered Professional Engineer Queensland with demonstrated expertise in flood risk management and shall comply with the procedures outlined in AS/NZS ISO31000:2009 Risk Management.
      3. To ensure that risks are compatible with the flood hazard and level of flood immunity and the risks to people and property is minimised.
   2. A risk assessment process should include the following elements:
      1. The number of people likely to be at risk and may need to be evacuated.
      2. Hazards associated with floods larger than the DFE.
      3. Flood warning time.
      4. Evacuation routes and the safety thereof.
      5. The potential for isolation for extended periods.
      6. The impact to special needs groups (the publication Evacuation Planning by Emergency Management Australia lists special needs groups).
      7. Flood recovery times and economic impacts.
      8. Impacts of greater rainfall intensity.

SC6.3.7 Appendix 1

Calliope River Flood Risk Assessment Study, Sargent Consulting, April 2006.

Auckland Creek Flood Study Report, GHD, August 2006.

Report on Awoonga Dam, Boyne River Dam Break and Flood Modelling Study, Sunwater, October 2003.

SC6.3.8 Floodplain risk management

The flood management strategy used by the Council is based on the principles of floodplain risk management to ensure that development on a floodplain occurs having regard to:

1. The compatibility of the development type with the flood hazard to minimise the risk to people's safety or structural damage to buildings.
2. The social, economic and environmental costs and benefits of developing within a floodplain when balanced against the flood risks.
3. While development controls may apply to land affected by the defined flood events which is typically, but not always a 1% AEP flood event, significantly larger floods can occur up to a probable maximum flood. Some types of development that are more susceptible to flooding will need to consider, mitigate for or design to floods larger than the 1% AEP.
4. When considering the safety of people, a full range of flood probabilities up to the probable maximum flood need to be considered. Development should not wholly rely on Council's disaster management response for managing the risk with such rare floods, although it is a consideration in managing the risk.