Middleton Storm Event Update - Public Meeting on Middleton Flood Study

Dear Middleton resident

Re: Invitation to Public Meeting on Middleton Flood Study | Flood Mitigation Report – 13 March 2023 5:30pm – Middleton Pioneer Hall.

On 12 November 2022, South Australia experienced a major storm event, which included widespread damage across the greater Alexandrina Council area. Significant flooding occurred within the Middleton township causing a large number of private properties to be inundated, damage to a variety of public and privately owned infrastructure within the town and the closure of major roads. The event led to the displacement of residents from their homes, it affected businesses and livelihoods, and left a lasting impact on the community's well-being.

At the 21 February 2023 Community Meeting to discuss the event, it was agreed that Council and the Community needed to know what happened and what measures could be implemented to mitigate any future event.

Council engaged the engineering firm Tonkin to perform a Hydrologist Report. The purpose of the report was to summarise the flood modelling and assessments that were undertaken along the main watercourse that passes through Middleton. It covers the following aspects:

  • Details of the hydrological and hydraulic modelling process
  • The November 2022 flood investigations
  • Hydraulic modelling of the performance of the existing infrastructure and analysis of the results
  • Preparation of the 100-year, 50-year and 20-year average recurrence interval (ARI) flood maps for the existing infrastructure scenario
  • Identification of several potential flood mitigation options
  • Hydraulic modelling of these options and analysis of the results
  • Preparation of the 100-year ARI flood maps for the flood mitigation scenarios
  • Preliminary high-level cost estimates for each of the scenarios
  • Discussion of the above and recommendations for potential next steps.

Based on the results of the modelling for the existing infrastructure scenario, a shortlist of potential flood mitigation options to be investigated further was developed. These are as follows:

  • Creating levee banks on private land along the creek to prevent floodwaters from breaking out of the creek.
  • Widening the creek channel (on private land) to increase the creek flow capacity.
  • Increasing the culvert size under the State Government-owned Goolwa Road to increase the capacity under the road and reduce the likelihood of culvert blockage.
  • Reducing the amount of understory vegetation along the creek lines on private land to increase the creek’s capacity.
  • Providing flood detention storage upstream of Middleton on private land to reduce the peak flow rates that arrive at Middleton; and
  • Providing an early warning system to allow for early evacuations and flood response plans to be activated before the arrival of floodwaters.

Each of these options have their advantages and disadvantages and complications given that the solutions will need to be implemented on privately owned land or State Government infrastructure.

A full copy of the Middleton Flood Study | Flood Mitigation Report will be made available to view in hardcopy at the Council Office/Library, 11 Cadell Street, Goolwa, or it can be downloaded electronically from this My Say page under 'Key Documents'.

The Hydrology Report identified the flood as being primarily due to flows coming from the creek which passes through the centre of town. Therefore, the investigations undertaken have focused on the flood behaviour of the creek. The report also focused on future mitigations. It does not provide an exact map of what occurred on 12 November 2022.

I would like to invite you to a Community Meeting to discuss this report and raise any questions. Representatives from the Council will be present to listen to the Community and discuss options. We have asked the author of the report to attend to present the findings. They will also be available for questions.

Unfortunately, additional notice for the meeting could not be provided. March 13 was the only date where all the required resources could be available. I do hope that you or a representative can make it.

I invite you to attend:

Middleton Pioneer Hall

1 Walker Pl, Middleton

13 March 2024

Doors open at 5 pm for a 5:30 pm start.

I welcome your questions, input and feedback on the findings of this report either before or after the meeting via email at alex@alexandrina.sa.gov.au or via postal correspondence. If questions are raised before the meeting, we will attempt to answer them at the meeting.

At this stage, the Hydrologist Report will be presented to the 15 April 2024 Council Meeting with recommendations for next steps. Any feedback received will also be shared with Council Members.

I look forward to meeting those who attend on the 13 March 2024.


Yours sincerely

Nigel Morris

Chief Executive Officer

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