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Byron Shire
July 20, 2024

Lismore draft Flood Risk Management Plan out for feedback

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Flooding in Lismore, looking north. 30 March 2022. Photo David Lowe.

The Lismore City Council has released its draft Flood Risk Management Plan, with public submissions due by 23 June.

Councillors at the May ordinary meeting agreed to the draft document going on public exhibition in accordance with a recommendation from the Flood Risk Management Committee.

But the council was yet to publicly announce the draft document and submissions deadline in media outside the ‘Your Say’ section of its website at time of publishing.

Consultancy firm Engeny put together the plan as part of a broader report, with the committee noting it as opposed to formally endorsing it at their April meeting but recommending it go on public display for feedback.

Consultant issues disclaimer on flood risk management report for Lismore

Engeny says in a disclaimer to its flood risk management report for Lismore the content is ‘based on previous information and studies supplied by Lismore City Council’.

‘Engeny accepts no liability or responsibility whatsoever for it in respect of any use of or reliance upon this Report by any third party,’ the company says.

At nearly 90 pages long including six sections, appendices, a list of tables and another list of figures, it’s a lot of detail to deny responsibility for but it will ultimately be up to the council to decide on recommendations via vote.

Lismore’s Flood Risk Management Plan

Flood impacted house from the 2022 flood. Photo Aslan Shand

One of the most significant sections of the report is Part 4, a Flood Risk Management Implementation Plan.

Notes on the plan are brief but include: ‘flood behaviour modification measures have been combined where they concern the same structural location (such as a raise to the South Lismore levee to either a 5% or 1% Annual Exceedance Probability flood level) and are recommended for further hydraulic investigation and feasibility studies prior to implementation’.

The plan is then set out in a three-page table outlining ten recommended flood risk management measures, resources and responsibility required, timeframes and costs.

Measures include a community preparedness campaign, updating flood data for development control, and extending the NSW Reconstruction Authority’s Resilient Homes Program to cover more houses in the area.

Some measures are listed as dependent on unspecified grant funding to happen, including improved warnings, increased levees in Lismore and South Lismore, nature-based solutions and gathering flood level data on individual properties.

Only two of the measures stand out as relying on staff time alone to happen: zoning and development control, and a community flood awareness readiness program.

Higher Flood Planning Level recommended for Lismore

Flooding in South Lismore, 1 March 2022. Photo David Lowe.

Potential climate change impacts are also reviewed in the report, using ‘Representative Concentration Pathway 8.5 future climate conditions’.

‘This reflects an increase in rainfall intensity of 19.7%,’ the report says, ‘to account for a temperature increase of about 4.3 ̊C by 2090’.

The report says the figures are considered a ‘worst-case’ scenario by the Australian Rainfall and Runoff (ARR) 2019 Data Hub.

A 2024 NSW Government Update on Addressing Flood Risk in Planning Decisions Planning Circular is also referred to.

The circular reportedly recommends incorporation of climate change into land use planning.

In response, the report recommends updating Lismore’s official Flood Planning Level with potential climate change impacts taken into account.

‘A higher FPL could help to protect against possible increases in flood water depths as a result of climate change,’ the report says.

A higher FPL would also provide greater safety in case of a need for evacuation, the report says, ‘due to increased potential for shelter in place until extraction in the worst-case scenario where the evacuation window is missed’.

‘A number of localities in Lismore have evacuation constraints potentially resulting in people becoming trapped by roads being cut off early in a flood event,’ the report says.

Worst case scenario: flood hits previously unaffected areas

Worst case climate change scenario FML mapping in report for Lismore’s flood risk management PIC Lismore City Council

Consideration of a 1% Annual Exceedance Probability 2090 Climate Change level plus 500 mm freeboard, or the 0.2% AEP + 500 mm freeboard, for Lismore’s Flood Planning Level is then included in the report.

Subsequent mapping shows the estimated increase in rainfall intensity ‘will result in increases to design flood levels of approximately 350-600 mm across the Probable Maximum Flood (PMF) extent’.

The map shown in section 2.9 shows Lismore and vast surrounding areas in a deep red, coded for flood levels between 500 – 600 mm, under the worst case climate change scenario.

‘The extent of inundation was shown to be increased (indicated on flood impact map as “was dry now wet”),’ the report says, ‘particularly within South Lismore and the fringe areas of the floodplain’.

‘This is likely to result in impacts to currently unaffected properties,’ the report says.

‘In particular, impacts to multiple properties surrounding Wade Park and Nielson Park were observed due to backwater from the Wilsons River up the Gundurimba Canal.’

The report is available via the Lismore City Council’s website here, with submissions on the draft Lismore Flood Risk Management Plan able to be made here until 23 June.

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