Brisbane River Catchment Flood Studies

The Queensland Government and local councils are working on a long-term plan to manage the impact of floods and improve community safety and resilience within the Brisbane River catchment.

This work supports recommendation 2.2 from the Queensland Floods Commission of Inquiry that a comprehensive flood study of the Brisbane River catchment be completed as soon as practicable, with the aim of identifying the probability and extent of various floods occurring.

Flood Study

The Brisbane River Catchment Flood Study is the most comprehensive study of its kind to be undertaken in Australia.

The Flood Study area includes parts of the Brisbane River catchment, with a focus on flooding events downstream of Wivenhoe Dam including the Brisbane River, Lockyer Creek and the Bremer River system.

Two major components of the Flood Study are the hydrologic and hydraulic assessments.

  • The hydrologic assessment investigated how combinations of rainfall, dam levels, ground conditions and tide influences could merge to create potential floods events within the floodplain. This assessment considered the entire Brisbane River catchment (including the Lockyer Valley and other regions outside of the Brisbane River floodplain).
  • The hydraulic assessment used the data inputs from the hydrology assessment to model how floodwaters progressed through the Brisbane River floodplain, taking into account terrain characteristics of rivers, creeks and floodplains, and infrastructure such as bridges, stormwater networks, dams and levees. The hydraulic assessment generated flood modelling for the lower Brisbane River downstream of Wivenhoe Dam.

The Flood Study provides a comprehensive analysis of a range of flood events that may occur within the Brisbane River catchment and is a critical first step toward developing a Strategic Floodplain Management Plan for the region.

The Flood Study overview is a guide to the work carried out in the Flood Study and how this information will be used.

Watch the Flood Study animation video to find out more about the purpose of the Flood Study and what it means for you.

  • A Flood Study overview has been developed to provide a non-technical summary of the processes undertaken to deliver the Flood Study and how this information will be used to inform a coordinated approach to flood risk management across the Brisbane River floodplain.

More information

The Flood Study is a regional study and property owners should contact their local council for more specific information relating to flood mapping for individual properties.  Current local flood mapping informaiton is available online at:

Councils will consider the Flood Study information to identify any necessary changes to flood products, tools and policies. Each council will apply the Flood Study to their planning schemes and current development applications according to their own internal policies and procedures, as appropriate. For further information on this, contact your local council.

A range of small and large flood events are modelled in the Flood Study that will increase our ability to plan for a wide variety of emergency responses and decisions about critical infrastructure which must consider larger, less frequent floods.

The purpose of the Strategic Floodplain Management Plan is to provide a coordinated and consistent approach throughout the Brisbane River floodplain for land-use planning, building controls, disaster management, community resilience and prioritisation of flood related infrastructure. This approach will then be used to inform the development of local floodplain management plans.

To register your interest in community consultation opportunities for the Strategic Floodplain Management Plan, please email BRCFS@qldra.qld.gov.au or freecall 1800 110 841

More information

Flood plain Management Fact Sheet

  • The Flood Study complements flood studies of nearby tributaries such as Lockyer Creek and the Bremer River as commissioned by Lockyer Valley Regional Council and Ipswich City Council.
  • Wivenhoe and Somerset Dams Optimisation Study – As the first output from the Brisbane River catchment studies, the Queensland Government completed the Wivenhoe and Somerset Dams Optimisation Study in 2014.  This study presented options for improving the use of existing dam infrastructure to deliver better flood mitigation outcomes ahead of the 2014-15 summer wet season, without putting future water supplies at risk. Under the adopted operational strategy, more flood water will be released earlier from Wivenhoe Dam to increase water storage space in case a large flood eventuates. While this may result in some crossings, like Colleges Crossing in Ipswich, being closed more regularly, it will mean that fewer buildings (around 500 to 1500) may be affected in Brisbane and Ipswich if a flood of a similar magnitude to 2011 was to occur.

How do I find out about the flood levels for my property under this study?

The Flood Study has been developed in consultation with Brisbane City, Ipswich City, Somerset Regional, and Lockyer Valley Regional Councils.

The Flood Study focusses on 'regional' scale flooding, rather than at an indivicual level.  

Residents and businesses seeking specific information about the flood levels for their property under the Flood Study should contact their local council for more information.

 

My property didn’t flood in 2011 or 1974, so does that mean I’m safe from future flood events?

No two flood events are exactly the same, and can involve minor localised flooding due to high rainfall over a short period in an isolated catchment or major flood events across the entire catchment due to extreme weather over an extended period.

The Flood Study considers Brisbane River based floods arising from a variety of events based on different rainfall patterns, dam levels, catchment conditions, tides and the probability of multiple floods occurring in the Brisbane River system at any one time.

The Flood Study provides detailed modelling of a range of different flood event scenarios ranging from likely rainfall events to extremely unlikely rainfall events and it is important that our community is informed about potential future events and how they may differ from major historic floods such as from 2011 and 1974.

 

Why can’t we stop flooding altogether?

It is not possible to prevent all flooding from occurring when living on a floodplain. However, we can reduce the risk and extent of flooding through a variety of measures such as land use planning, improved early warning systems, infrastructure, community education and emergency response plans.

 

Shouldn’t the dams be able to prevent future flooding?

Dams reduce the severity of flooding but cannot prevent all flooding from occurring. In a 1% AEP event (similar to the 2011 floods), the Flood Study shows that the existing dams provide a reduction in peak flow rates caused by rainfall upstream of the dams by approximately 30 per cent.

The Flood Study modelling shows that the existing dams reduce the peak flow rates across the full range of flood extents, however their impact diminishes for larger events. The dams also have no impact on the reduction of flooding caused by heavy rainfall occurring further downstream such as from the Lockyer Valley or Bremer River catchments.

 

Why has the Flood Study focused on areas downstream of Wivenhoe Dam?

The Queensland Floods Commission of Inquiry recommended a study be undertaken downstream of the Wivenhoe Dam to understand flooding in areas where people live. 

 

What is an AEP (Annual Exceedance Probability) event?

An Annual Exceedance Probability (AEP) event is the probability of a level of flooding being equalled or exceeded, at least once, in any given year. For example, a 1% AEP, is a flood level that has a one per cent chance of occurring in any given year.

 

How should I prepare for the possibility of floods in my area?

Residents in flood prone areas are encouraged to seek information and advice from their local council to help them plan in advance for how they will respond in the event of a flood. This includes how to access relevant flood warnings during a flood event, how to interpret flood warnings at their local level, the location of evacuation routes and its level of flood immunity, when to evacuate, what to take and whom to notify. You should then follow the advice of your local council and emergency services in implementing your plan during a major rainfall event.

The Queensland Government provides a range of information and tools to assist residents in preparing for a flood event via the Get Ready Queensland website. For comprehensive weather information and warnings for your area you can also visit the Bureau of Meteorology website at www.bom.gov.au.

 

What has happened since the 2011 floods?

The Queensland Government and local governments continue to work with their communities and emergency services to manage flood risk.

The four local governments involved in the Flood Study have all adopted planning scheme amendments that incorporate revised flood overlays and policies as recommended through the Queensland Flood Commission of Inquiry.

A Disaster Management Tool was developed to deliver a set of disaster management maps in time for the 2013/14 wet season. The Disaster Management Tool complements existing local government flood strategies and provides interim guidance for flood emergency management until the Brisbane River Catchment Floodplain Management Plan is developed in 2017.

The Wivenhoe and Somerset Dams Optimisation Study was completed in 2014 and examined existing dam flood operations to determine options for improved flood mitigation (whilst preserving water supply security). Seqwater has subsequently updated its flood operations manual for Wivenhoe and Somerset dams making changes to flood releases from Wivenhoe Dam that provide improved flood mitigation outcomes for urban areas without putting future water supply security at risk.