Banana Shire Flood Study

THEODORE

Historic flooding

Flooding at Theodore is primarily controlled by Theodore Weir for flood events contained within the river’s banks. As floodplain flow is activated, flooding is controlled by the natural constriction point in the terrain approximately 1.5 km downstream of the weir. Theodore Township is vulnerable to flooding in large events as high flows struggle to pass the constriction, causing upstream areas to act as a flood basin. As flow increases, water levels upstream rise, flooding farmland and eventually properties in the main town.

 

Extent of flooding

The below table explains the multiple Annual Exceedance Probability (AEP) flood events analysed as part of the Study. AEP indicates the probability of a flood event occurring each year expressed as a percentage. Flood probability can also be expressed as an Annual Recurrence Interval (ARI).

Annual Exceedance Probability, AEP

Approximate Annual Recurrence Interval, ARI

Impact on Township

10% chance of occurring each year or 10% AEP

Approximately 1 in 10 year event

  • Inundation of Eidsvold-Theodore Road and Leichhardt Highway north
  • Isolation from Theodore Aerodrome

5% chance of occurring each year or 5% AEP

Approximately 1 in 20 year event

  • Lower areas surrounding Theodore inundated
  • Lower lying areas of township inundated around Eleventh Avenue

2% chance of occurring each year or 2% AEP

Approximately 1 in 50 year event

  • Most of Theodore up to Third Avenue inundated
  • RSL Hall and evacuation centre inundated
  • Isolated, flood free area at the southern end of The Boulevard
  • Complete isolation of Township due to inundation of Leichhardt Highway

1% chance of occurring each year or 1% AEP

Approximately 1 in 100 year event

  • Entire town is flooded
  • Similar magnitude to the 2010 flood event

1% AEP event Climate Change (CC) sensitivity simulation or 1% + CC AEP

Approximately 1 in 100 year event - adjusted for climate change sensitivity

  • Identified in image below

 

0.05% chance of occurring each year or 0.05% AEP

Approximately  1 in 2000 year event

  • Extreme inundation

 

A Probable Maximum Flood (PMF) event is the largest flood event that could occur at any given location. It is usually an estimated rainfall depth calculated using a range of methods and patterns.

  • Catastrophic inundation

 

 

Considering the information above, the proposed area of investigation to protect residents from the impact of flooding is shown below.

Image: Proposed area of investigation, potential road upgrade and potential upstream mitigation option with 1% + CC AEP flood inundation depths shown

*The Nathan Dam and Pipelines Project is considered to be one of the best long-term solutions for the provision of reliable water supplies to the Dawson-Callide and Surat Basin areas of Queensland. This project is a major initiative, however it does not yet have business case or funding approval. It has been included as a flood mitigation measure because it is a plausible long-term, regional scale option that could provide flood benefits to the town of Theodore.

 

Potential flood mitigation options

Flood mitigation strategies are aimed at reducing residual risk, improving safety, minimising damage by reducing peak flood levels and depths, improving warning times and reducing flow velocities. This can be achieved through both structural and non-structural measures.

Some non-structural measures already form part of Council’s current Local Disaster Management Plan and Planning Scheme. After the completion of the Floodplain Management Plan, additional measures and updates to Council’s plans and schemes may occur.

As flood inundation in Theodore is primarily governed by a natural constriction in the terrain downstream of the town, it is not feasible to completely remove the flood risk from Theodore.

Therefore, there are a limited number of feasible e structural measures that could be implemented to reduce the flood risk in the proposed area of investigation. This area is shown in the image above.

The structural measures identified that may reduce flood risk within the proposed area of investigation include:

  • Upgrading and improving flood immunity to Eidsvold-Theodore Road to Theodore Aerodrome to improve evacuation
  • Low levees, large levees or a combination of both to provide some level of flood protection to residents
  • Raising of existing stumped houses.

 

Submit your feedback

Community feedback is a vital tool when analysing the viability and acceptance of proposed areas of investigation. To submit your feedback, please fill out the survey by clicking on the link below.

When answering Question 4, please rate your most preferred option as 1, your second most preferred option as 2, your third option as 3, and least preferred option as 4.

Surveys can be downloaded and submitted by email at floodstudies@kbr.com or by mail at Reply Paid GPO BOX 633, Brisbane QLD 4001.

 

Survey for Theodore